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Addition mechanism of group V hydrides to hexafluorobutyne-2, and the electronic spectra of the resultant… Leeder, W. Ross 1969

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The A d d i t i o n Mechanism of Group V H y d r i d e s to H e x a f l u o r o b u t y n e - 2 , and the E l e c t r o n i c S p e c t r a of the R e s u l t a n t Adducts by W. Ross Leeder B.Sc. U n i v e r s i t y o f B r i t i s h Columbia, 1966 A T h e s i s Submitted i n P a r t i a l F u l f i l m e n t of the Requirements f o r the Degree o f Doctor of P h i l o s o p h y i n the Department o f Chemistry We a c c e p t t h i s t h e s i s as conforming to the r e q u i r e d s t a n d a r d The U n i v e r s i t y o f B r i t i s h December, 1969 Columbia In presenting t h i s thesis in p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library shall make i t f r e e l y available for reference and study. I further agree tha permission for extensive copying of th i s thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of t h i s thesis f o r f i n a n c i a l gain shall not be allowed without my written permission. Department The University of B r i t i s h Columbia Vancouver 8, Canada Date tvWcCL \ o q o ACKNOWLEDGEMENTS I wish to express my sincere gratitude to Dr. W. R. Cullen and Dr. D. C. Frost for t h e i r invaluable help and guidance throughout the course of t h i s i n v e s t i g a t i o n . I would also l i k e to thank Dr. D. McGreer for h i s many discussions, Mr. J . Ward f o r h i s kindness i n writing a program and Mr. A. Cornford for h i s assistance. I t i s with the greatest appreciation that I thank my wife L i l i , for her continuing encouragement throughout my work, and her help in a s s i s t i n g with the i n i t i a l typing and proof reading of t h i s t h e s i s . I would l i k e to thank Miss Donna Symons for typing the manuscript. I wish to express my gratitude to the University of B r i t i s h Columbia, Mr. H. R. McMillan (Queen E l i z a b e t h Scholarship) and the National Research Council for f i n a n c i a l support. ABSTRACT The addition of dimethylarsine to hexafluoro-butyne-2 has previously been shown to give the predominantly trans 1:1 adduct, Me2AsC(CF2)=C(CF.j)H. In t h i s work, a mechanistic study was made of the addition of dimethylarsine, as well as other Group V hydrides, to hexafluorobutyne-2. This was done to help shed l i g h t on the r e l a t i v e l y unknown area of noncatalyzed n u c l e o p h i l i c hydride additions to acetylenes. In the course of the mechanistic i n v e s t i g a t i o n , the e l e c t r o n i c properties of the product adducts became of i n t e r e s t , and consequently u l t r a v i o l e t and photoelectron spectroscopy were used to study the arsine adducts as well as s i m i l i a r Group V de r i v a t i v e s . The addition reaction was found to be k i n e t i c a l l y c o n t r o l l e d by the n u c l e o p h i l i c attack of the arsine molecule on the electron d e f i c i e n t carbon-carbon t r i p l e bond. A d e t a i l e d discussion of the addition stereochemistry i s necessary to explain many of the r e s u l t s found i n t h i s work, as well as those found by other i n v e s t i g a t o r s . Generally the noncatalyzed additions of Group V hydrides to acetylenes are predominantly, though not stereo-s p e c i f i c a l l y , trans additions. Cis k i n e t i c additions are possible under c e r t a i n circumstances. The u l t r a v i o l e t absorption found for the 1:1 i i i adducts of Group V hydrides and hexafluorobutyne-2, can be assigned to a n - i t * (or n-R) band. An unequivocal choice between the two p o s s i b i l i t i e s cannot be made from the r e s u l t s obtained i n t h i s work. These assignments are suggested from experimental data about the upper ground states using photoelectron spectroscopy, the excited state using u l t r a v i o l e t spectroscopy,and the i n t e n s i t i e s and solvent e f f e c t s of the u l t r a v i o l e t bands. TABLE OF CONTENTS ACKNOWLEDGEMENTS ABSTRACT CHAPTER 1 - GENERAL INTRODUCTION CHAPTER 2 - THE ADDITION REACTION 2.1 I n t r o d u c t i o n 2.1.1 E a r l y N u c l e o p h i l i c A d d i t i o n s 2.1.2 Amines and A l c o h o l s 2.1.3 R e c e n t S t u d i e s 2.1.3.1 T h i o l s , A l c o h o l s and Amines 2.1.3.2 T i n H y d r i d e s 2.2 E x p e r i m e n t a l 2.2.1 A r s i n e E x p e r i m e n t a l 2.2.1.1 S t a r t i n g M a t e r i a l s 2.2.1.1.1 D i r a e t h y l a r s i n e 2.2.1.1.2 D i m e t h y l a r s e n i c D e u t e r i d e 2.2.1.1.3 D i e t h y l a r s i n e 2.2.1.2 A r s i n e R e a c t i o n s w i t h H e x a f l u o r o b u t y n e 2.2.1.2.1 D i m e t h y l a r s e n i c D e u t e r i d e 2.2.1.2.2 D i e t h y l a r s i n e 2.2.1.2.3 D i m e t h y l a r s i n e i n the Gas Phase 2.2.1.2.4 D i m e t h y l a r s i n e i n M e t h a n o l a n c 3 d 4 M e t h a n o l S o l v e n t s page 2.2.1.3 K i n e t i c s o f A r s i n e A d d i t i o n s 22 2.2.1.3.1 D i m e t h y l a r s i n e A d d i t i o n t o H e x a f l u o r o b u t y n e - 2 2 2 2 . 2 . 1 . 3 . 2 D i e t h y l a r s i n e A d d i t i o n t o H e x a f l u o r o b u t y n e - 2 2 6 2.2.1.4 E q u i l i b r i u m o f A r s i n e s a n d A r s i n e A d d i t i o n P r o d u c t s 26 2.2.1.4.1 D i e t h y l a r s i n e a n d D i m e t h y l a r s e n i c D e u t e r i d e 2 9 2.2.1.4.2 D i e t h y l a r s i n e a n d 2 - d i m e t h y l -a r s i n o - 3 - d e u t e r o - l , 1 , 1 , 4 , 4 , 4 -h e x a f l u o r o b u t e n e - 2 2 9 2.2.1.4.3 d ^ - M e t h a n o l a n d t r a n s 2-d i m e t h y l a r s i n o - 1 , 1 , 1 , 4 , 4 , 4 -h e x a f l u o r o b u t e n e - 2 29 2.2.1.5 S t a b i l i t y o f t h e P r o d u c t s 30 2.2.1.6 C o m p e t i t i v e R e a c t i o n o f A r s i n e s R e a c t i n g w i t h H e x a f l u o r o b u t y n e - 2 30 2.2.1.7 S o l u b i l i t y o f H e x a f l u o r o b u t y n e - 2 i n D i e t h y l E t h e r ' 32 2.2.2 A m i n e E x p e r i m e n t a l 32 2.2.2.1 The A d d i t i o n o f D i e t h y l a m i n e t o H e x a f l u o r o b u t y n e - 2 32 2.2.2.2 K i n e t i c s o f t h e A d d i t i o n o f D i e t h y l a m i n e t o H e x a f l u o r o b u t y n e - 2 34 2.2.2.3 S t a b i l i t y o f t h e T r a n s P r o d u c t 35 v i P A ' J E 2.2.2.4 Soxvent and C o n c e n t r a t i o n E f f e c t s uu the A d d i t i o n 3 5 2.3 D i s c u s s i o n 38 2.3.1 A r s i n e s 38 2.3.1.1 K i n e t i c R e s u l t s 38 2.3.1.2 A r s i n e Isomer D i s t r i b u t i o n s and S t a b i l i t i e s 4 0 2.3.1.3 P o s s i b l e R e a c t i o n Mechanisms 41 2.3.1.4 D e t a i l s o f t h e N u c l e o p h i l i c A d d i t i o n s 4 7 2.3.2 Amines 48 2.3.2.1 K i n e t i c R e s u l t s 52 2.3.2.2 P r o d u c t Isomer D i s t r i b u t i o n 5 3 2.3.2.2.1 C o n c e n t r a t i o n o f R e a c t a n t s 5 4 2.3.2.2.2 S o l v e n t 55 2.3.2.2.3 S t e r i c E f f e c t s 58 2.3.2.2.4 I n t e r n a l Hydrogen B o n d i n g 58 2.3.3 Comparisons 60 2.3.3.1 K i n e t i c s and Rat e 60 2.3.3.2 S t e r e o c h e m i s t r y o f A d d i t i o n 65 2.3.4 S t e r e o s p e c i f i c i t y i n N u c l e o p h i l i c A d d i t i o n s ; A Comment 6 7 CHAPTER 3 3.1 I n t r o d u c t i o n 71 3.2 E x p e r i m e n t a l 75 3.2.1 S t a r t i n g M a t e r i a l s 75 3.2.1.1 B i s ( t r i f l u o r o m e t h y l ) a r s i n e 75 v i i P a t J e 3.2.1.2 3 i s ( t r ' i f l u o r o r a e t h y l ) a r s e n i c D e u t e r i d e 76 3.2.2 P r o t o n Exchange R e a c t i o n s and K i n e t i c s ^6 3.3 D i s c u s s i o n 8 ^ CHAPTER 4 - U l t r a v i o l e t and P h o t o e l e c t r o n S p e c t r o s c o p y S t u d i e s 4.1 I n t r o d u c t i o n 8 8 4.1.1 E l e c t r o n i c T r a n s i t i o n s and the Franck-Condon P r i n c i p l e 8 ^ 4.1.2 U l t r a v i o l e t S p e c t r o s c o p y 34 4.1.3 P h o t o e l e c t r o n S p e c t r o s c o p y 96 4.2 E x p e r i m e n t a l 99 4.2.1 U l t r a v i o l e t S p e c t r a and Sample P r e p a r a t i o n s 99 4.2.1.1 Sample P r e p a r a t i o n s 99 4.2.1.1.1 T r i s p r o p y n y l a r s i n e 99 4.2.1.1.2 T r i s p r o p y n y l s t i b i n e 101 4.2.1.1.3 T r i s p r o p y n y l p h o s p h i n e 101 4.2.1.1.4 1 , 1 , 1 - T r i f l u o r o p r o p y n e 102 4.2.1.2 U l t r a v i o l e t S p e c t r a 102 4.2.2 P h o t o e l e c t r o n S p e c t r o s c o p y 108 4.2.2.1 The S p h e r i c a l System _ 108 4.2.2.2 The 180° A n a l y z e r System 113 4.2.2.3 P h o t o e l e c t r o n S p e c t r a 115 4.3 D i s c u s s i o n 155 4.3.1 P h o t o e l e c t r o n S p e c t r o s c o p y 155 4.3.1.1 The S p h e r i c a l G r i d R e s u l t s 155 v i i i 4.3.1.2 Dirnethylamjne, d i m e t h y l a r s i n e and d i e t h y l p h o s p h i n e 159 4.3.1.2.1 Dimethylaroine 159 4.3.1.2.2 D i m e t h y l a r s i n e 161 4.3.1.2.3 D i e t h y l p h o s p h i n e 162 4.3.1.3 1 , 1 , 1 - t r i f l u o r o p r o p y n e and hexafluorobutyne-2 163 4.3.1.3.1 Hexafluorobutyne-2 163 4.3.1.3.2 1 , 1 , 1 - t r i f l u o r o p r o p y n e 166 4.3.1.4 The Group V Hydride - Hexafluorobutyne-2 Adducts 168 4.3.1.4.1 The Dimethylamine-Hexafluorobutyne-2 Adduct 170 4.3.1.4.2 The T r i m e t h y l s i l a n e - H e x a f l u o r o b u t y n e - 2 Adduct 170 4.3.1.4.3 The A r s i n e - H e x a f l u o r o b u t y n e - 2 A d d u c t s l 7 1 4.3.1.4.4 The D i e t h y l p h o s p h i n e -Hexafluorobutyne-2 Adduct 173 4.3.2 U l t r a v i o l e t S p e c t r o s c o p y 176 4.3.2.1 The Nature o f the T r a n s i t i o n s 176 4.3.2.2 D e l o c a l i z a t i o n and I n t e n s i t i e s 180 4.3.2.3 The U l t r a v i o l e t T r a n s i t i o n s 183 LIST OF TABLES I Rate Constants f o r E q u a t i o n 2.7 1 1 I I Rate Constants f o r E q u a t i o n 2.10 IS I I I K i n e t i c R e s u l t s f o r D i m e t h y l a r s i n e 2 7 IV C o n c e n t r a t i o n s o f the C o m p e t i t i v e R e a c t i o n s 31 V D i s t r i b u t i o n of Isomer Products from the C o m p e t i t i v e R e a c t i o n s 31 VI Rate R e s u l t s f o r D i e t h y l a m i n e 35 VII I s o m e r i z a t i o n of the t r a n s - D i e t h y l a m i n e -Hexafluorobutyne-2 adduct 36 V I I I S o l v e n t and C o n c e n t r a t i o n E f f e c t s on the D i e t h y l a m i n e A d d i t i o n 37 IX P o s s i b l e Mechanisms Based on the C o m p e t i t i v e R e a c t i o n 49 X Product D i s t r i b u t i o n f o r Hydride A d d i t i o n s to A c e t y l e n e s 55 XI Rate Data f o r Hydride A d d i t i o n s to A c e t y l e n e s 62 XII The Rate Constants and E q u i l i b r i u m Constants f o r the Proton Exchange between H y d r i d e s QI X I I I U l t r a v i o l e t A b s o r p t i o n s o f V a r i o u s Compounds J04 XIV A d i a b a t i c I o n i z a t i o n P o t e n t i a l s Obtained from the S p h e r i c a l P h o t o e l e c t r o n Spectrometer 117 XV The I o n i z a t i o n P o t e n t i a l s o f Me2NH H P XVI The I o n i z a t i o n P o t e n t i a l s of E t 2 P H 121 XVII The I o n i z a t i o n P o t e n t i a l s o f Me_AsH 123 P a 9 -XVIII The I o n i z a t i o n P o t e n t i a l s o f CF 3C=CCF 3 125, 126 XIX The I o n i z a t i o n P o t e n t i a l s of CF 3CSCH 131- 133 XX The I o n i z a t i o n P o t e n t i a l s of Me 2NC ( C F 3 ) =C ( C F 3 )II 139 XXI The I o n i z a t i o n P o t e n t i a l s of E t 2 P C ( C F 3 ) = C ( C F 3 ) H 141 XXII The Ioni z a t i o n P o t e n t i a l s o f Me „AsC ( C F ) =C (CF ) H 2 3 3 143 XXIII The I o n i z a t i o n P o t e n t i a l s of M e 2 A s C ( C F 3 ) = C ( C F 3 ) C l 147 XXIV The I o n i z a t i o n P o t e n t i a l s of E t 2 A s C ( C F 3 ) = C ( C F 3 ) H 151 XXV The I o n i z a t i o n P o t e n t i a l s o f M e 3 S i C ( C F 3 ) = C ( C F 3 ) H 153 XXVI The I o n i z a t i o n P o t e n t i a l s of E t h y l e n e s 157 XXVII The I o n i z a t i o n P o t e n t i a l s of Dimethylamine 160 XXVIII The I o n i z a t i o n P o t e n t i a l s of Some A r s i n e Adducts 172 XXIX A Comparison o f the Energy D i f f e r e n c e s f o r the F i r s t Two Ground L e v e l s of S e v e r a l Adducts 179 LIST OF FIGURES J2a_g_e 1. P l o t o f K i n e t i c Data f o r E q u a t i o n 2.12 2 5 2. A r h e n i u s P l o t f o r D i m e t h y l a r s i n e 28 3. S o l u b i l i t y o f Hexafluorobutyne-2 i n D i e t h y l e t h e r 33 4. *H n.m.r. Spectrum of the Methyl Peaks i n Me 2AsH and Me 2AsD 72 5. K i n e t i c P l o t f o r the Proton Exchange Between Me 2AsH and Me 2AsD 80 6. The Franck-Condon P r i n c i p l e 92 7. The S p h e r i c a l G r i d P h o t o e l e c t r o n Spectrometer 109 8a. The "Stopping Curve" f o r Ar 111 8b. The D i f f e r e n t i a l o f . F i g u r e 8a 112 9. The 180° A n a l y z e r P h o t o e l e c t r o n Spectrometer 114 10. The P h o t o e l e c t r o n Spectrum of Me 2NH 119,120 11. The P h o t o e l e c t r o n Spectrum of E t 2 P H 122 12. The P h o t o e l e c t r o n Spectrum o f Me 2AsH 124 13. The P h o t o e l e c t r o n Spectrum of CF 3C=CCF 3 127-130 14. The P h o t o e l e c t r o n Spectrum o f CF 3C=CH 134-138 15. The P h o t o e l e c t r o n Spectrum o f Me 2NC(CF 3)=C(CF 3 )H 140 16. The P h o t o e l e c t r o n Spectrum of E t 2 P C ( C F 3 ) = C ( C F 3 )H 142 17. The P h o t o e l e c t r o n Spectrum o f c i s - M e 2 A s C ( C F 3 ) = C ( C F 3 ) U 144 18. The Pho t o e l e c t r o n Spectrum of t r a n s - M e 2 A s C ( C F 3 )=C(CF 3)H 145,146 19. The P h o t o e l e c t r o n Spectrum o f Me 2AsC(CF 3)=C(CF .)C1 148-150 20. The P h o t o e l e c t r o n Spectrum o f E t 9 A s C ( C F 3 ) = C ( C F 3>H 15 2 x i i M i 21. The Fho t o e l e c t r o n Spectrum of MCgSiC (CF 3 ) =C (CF^ )H 154 22. The Superimposed P h o t o e l e c t r o n S p e c t r a of S e v e r a l Adducts 169 23. The Superimposed P h o t o e l e c t r o n S p e c t r a o f S e v e r a l D i e t h y l S u b s t i t u t e d Adducts 175 24. The U l t r a v i o l e t S p e c t r a o f S e v e r a l Adducts 177 25. The R e l a t i o n s h i p Between the U l t r a v i o l e t and P h o t o e l e c t r o n R e s u l t s 178 26. An Energy L e v e l Diagram o f S e v e r a l Adducts and T h e i r P r e c u r s o r H y d r i d e s 181 CHAPTER 1 GENERAL INTRODUCTION In 1965 C u l l e n e t a l (1) d i s c o v e r e d t h a t d i m e t h y l a r s i n e adds t o h e x a f l u o r o b u t y n e - 2 t o form b o t h i s o m e r s o f t h e 1:1 a d d u c t , 2 - d i m e t h y l a r s i n o - 1 , 1 , 1 , 4 , 4 , 4 -h e x a f l u o r o b u t e n e - 2 ( e g . 1.1, R=R'=Me). The r e a c t i o n i s r a p i d and e x o t h e r m i c . CF. H CF. CF-\ / 3 / 3 RR'AsH + CF C=CCF. > C=C + ^C=C RR'As/ V C F 3 RR«As / X H (*>90%) (A/10%) (1.1) A l i t e r a t u r e s u r v e y a t t h a t t i m e r e v e a l e d a l m o s t a t o t a l l a c k o f knowledge about t h e u n c a t a l y z e d a d d i t i o n o f n u c l e o p h i l i c h y d r i d e s t o a c e t y l e n e s , a l t h o u g h much was known i n t h e c a s e s o f e l e c t r o p h i l e s , and so i t was f e l t t h a t a d e t a i l e d s t u d y o f t h e above r e a c t i o n would be o f g r e a t i n t e r e s t . T h e r e f o r e , t h i s i n v e s t i g a t i o n was unde r -t a k e n t o s t u d y t h e mechanism o f e q u a t i o n 1.1, and t h e p r o p e r t i e s o f t h e s t a r t i n g m a t e r i a l s and p r o d u c t s . 2 The thesis i s divided into two sections. The f i r s t section describes the isotope exchange reactions between hydrides, k i n e t i c studies, s t a b i l i t y t e s t s , and competitive reactions that were done to help elucidate the mechanism of the addition r e a c t i o n . U l t r a v i o l e t spect-roscopy and low temperature n.m.r. techniques were chosen as two sui t a b l e means of studying the k i n e t i c s . The r e a c t i v i t y of the s t a r t i n g materials necessitated the use of low concentrations f o r rate determinations, and thus i n i t i a l l y the former technique seemed most appropriate f o r monitoring the r e a c t i o n . However, further studies showed n.m.r. methods to be more r e l i a b l e . The second section deals with the physical properties of the reactants and products. The addition products were found to have an u l t r a v i o l e t absorption at o about 2610 A. Since the arsine adduct i s s t r u c t u r a l l y r e l a t e d to an enamine molecule (a v i n y l amine), comparison of the u l t r a v i o l e t spectra of these compounds was of i n t e r e s t . Furthermore, since a knowledge of the e l e c t r o n i c influence of arsenic and other Group V atoms on the un-saturated carbon bonds could be h e l p f u l i n i n t e r p r e t i n g the u l t r a v i o l e t spectra, photoelectron spectroscopy was used to study the arsine adducts and other s i m i l a r molecules. One point should be noted regarding the convention used i n t h i s thesis for naming geometrical isomers; the mode 3 o f a d d i t i o n t o t h e a c e t y l e n e , and n o t t h e p r o d u c t c o n f i g u r a t i o n , i s t h e b a s i s f o r t h e assignment o f t h e d e s i g n a t i o n c i s and t r a n s t o t h e p r o d u c t i s o m e r s . CHAPTER 2 THE ADDITION REACTION 2.1 I n t r o d u c t i o n The t r i p l e bond of a c e t y l e n e s has been shown to r e a c t with many substances, both i n the presence and i n the absence o f c a t a l y s t s . In p a r t i c u l a r , t r i p l e bonds a c t i v a t e d by f u n c t i o n a l groups are o f t e n s u s c e p t i b l e t o the a d d i t i o n o f e l e c t r o p h i l e s ( 2 ) , f r e e r a d i c a l s (3) and n u c l e o p h i l e s . When the f u n c t i o n a l groups on the a c e t y l e n e are e l e c t r o -n e g a t i v e , n u c l e o p h i l i c a d d i t i o n t o the t r i p l e bond r e a d i l y t akes p l a c e . S i n c e the h y d r i d e s s t u d i e d i n the pr e s e n t i n v e s t i g a t i o n are n u c l e o p h i l e s , t h i s i n t r o d u c t i o n w i l l be r e s t r i c t e d m a i n l y t o a summary of n u c l e o p h i l i c h y d r i d e a d d i t i o n s to t r i p l e bonds. The i n t r o d u c t i o n w i l l be p r e s e n t e d i n t h r e e s e c t i o n s , f i r s t l y , e a r l y n u c l e o p h i l i c a d d i t i o n s to a c e t y l e n e s and f o r m u l a t i o n o f the " t r a n s a d d i t i o n " r u l e , s e c o n d l y , l a t e r amine and a l c o h o l a d d i t i o n s , and l a s t l y , r e c e n t d e t a i l e d s t u d i e s of h y d r i d e a d d i t i o n s t o t r i p l e bonds. I 5 2,1.1 Early Nucleophilie Additions and the  "Trans Addition" Rule Truce et a l (4) found i n a number of investigations that base catalyzed additions of t h i o l s to acetylenes, proceeded i n a trans manner (eq. 2.1, R=p-MeCgH^-). H H CCHCC=CH + RSNa ££22 > \ = c { (2.1) 6 5 C V H / NSR 6 5 M i l l e r and Krishnamurtly (5), M i l l e r and Shkapenko (6), Tsuruta et a l (7), and Rigamonti and Bernardi (8), studied the k i n e t i c s of base catalyzed t h i o l and alcohol additions to acetylenes, which s i m i l a r l y proceeded i n a trans manner. They found the reactions were f i r s t order i n acetylene, f i r s t order i n base, and zero order i n alcohol or t h i o l . M i l l e r and Shkapenko (6) suggested that the mechanism involved an i n i t i a l slow attack by alkoxide on the acetylene (eq. 2.2), followed by the rapid extraction of an alcohol proton' by the carbanion intermediate (eq. 2.3). XC=CY + MeO9 >MeOCX=CY (2.2) MeOCXSCY + MeOH >MeOCX=CYH + MeO® (2.3) On the basis of these and re l a t e d r e s u l t s , a r u l e of trans  addition of nucleophiles to acetylenes was postulated by Truce and Simms (9) and independently by M i l l e r (10). Since Jones and Whiting (11) had previously i s o l a t e d c i s 6 products from the addition of amines to acetylenes, Truce and Heine (12) subsequently q u a l i f i e d t h i s r u l e as being applicable only to those addition reactions where the intermediate (eq. 2.3) has a negative charge. In one t h i o l addition, c i s products were i s o l a t e d by Montanari and Negrini (13, 14) and Truce (12, 15). Truce and Goldhamer (15) suggested that t h i s r e s u l t was not a v i o l a t i o n of the trans addition r u l e , but was due to the isomerization of an i n i t i a l l y produced trans product (16). In 1964, Hendrickson et a l (17) extended the trans r u l e as follows: "whenever mobile protons are a v a i l a b l e , the f i r s t product of addition to acetylenedi-carboxylic esters i s the simple trans adduct". 2.1.2 Amines and Alcohols In 1949, Whiting and Jones (11) discovered that amines can add c i s to acetylenes, v i o l a t i n g the l a t e r postu-lated trans addition r u l e . It was only i n 1965 that further i n v e s t i g a t i o n s of uncatalyzed amine additions to acetylenes were continued by D o f i n i , Winterfeldt, Reimlinger, Huisgen and S t i r l i n g . D o f i n i (18) discovered that both c i s and trans addition of a z i r i d i n e to an activated t r i p l e bond was possible (eq. 2.4, X = MeG-C ). 7 X H X X (CH 2) 2NH + XC=CX H (2.4) The isomer d i s t r i b u t i o n was found to depend bn the solvent used. D o f i n i showed that c i s - t r a n s isomerization of the products did not occur under the experimental conditions. (22), and S t i r l i n g (23, 24) found that the uncatalyzed addition of primary and secondary amines to acetylenes gave predominantly c i s products. Although the proportion of c i s products was large from the addition of primary amines, i t was even greater from secondary amine additions. Also i t was found that the course of the r e a c t i o n was a function of the type of acetylene, amine, solvent, and the manner i n which the reactants were brought together. the addition of alcohols and phenols to acetylene dicarb-oxylate, methyl propiolate, dicyanoacetylene and phenyi-acetylene, to give trans products i n accordance with the trans addition r u l e . However, three cases of catalyzed c i s alcohol addition have appeared i n the l i t e r a t u r e (11, 26, 27). The uncatalyzed addition of alcohols r e s u l t i n the c i s product (19,20), and i t has been suggested (19) that these reactions, together with the uncatalyzed Winterfeldt (19, 20), Huisgen (21), Reimlinger Alkoxides (10) and t e r t i a r y amines (25) catalyze 8 addition of amines, may proceed by an intramolecular  proton s h i f t from the primary complex of the hydride and acetylene. X 2.1.3 Recent Detailed Studies of Hydride  Additions to Acetylenes U n t i l 1965, the mechanisms proposed for addition reactions were based on adduct configurations, which were determined by u l t r a v i o l e t and i n f r a r e d spectroscopy and other nonspectroscopic studies. The use of the recently a v a i l a b l e and more r e l i a b l e technique of nuclear magnetic resonance spectroscopy (n.m.r.),as outlined for hydride adducts by Truce et a l (16) and Stone et a l (28, 29), enabled a more d e t a i l e d i n v e s t i g a t i o n of the mechanism. It was p a r t i c u l a r l y important to use n.m.r. i n view of the frequent observation that the products could be isomerized by the precursor hydride. Thus Eisch and Kasha (30) discovered that the e l e c t r o p h i l i c aluminum hydrides i s o -merized t h e i r i n i t i a l c i s products to the trans products (eq. 2.5). Truce et a l (16) found a f t e r i s o l a t i n g a c i s addition product from a t h i o l r e a c t i o n , that the trans product isomerized to the c i s form i n the presence of the precursor t h i o l , suggesting that the mechanism was 9 Me (2.5) indeed a trans n u c l e o p h i l i c addition with a subsequent isomerization to c i s product. Fulton (31) also found that isomerization of t i n hydride-acetylene adducts, occurred i n the presence of t i n hydrides. In the l a s t few years, several groups have done more d e t a i l e d work on these and other important aspects of the hydride additions to acetylenes. 2.1.3.1 Addition of T h i o l s , Alcohols, and and trans /3-halocrotonates to base, Vessiere et a l found i t necessary to study both catalyzed and noncatalyzed (32, 33) additions of hydrides to acetylenes. In the base catalyzed additions of t h i o l s and alcohols to butyne-2 n i t r i l e and ethyl but-2-ynoate, a d i s t r i b u t i o n of reaction product isomers was found which depended on the concentration of base used. A 100% c i s addition i s possible using t h i o l s and alcohols at high concentrations of base. The n.m.r. monitored addition of primary amines to butyne-2 n i t r i l e and ethyl but-2-ynoate, proceeded n o n s t e r e o s p e c i f i c a l l y i n Amines to Acetylenes In the course of studying the s t a b i l i t y of c i s 10 both aprotic and p r o t i c solvents, though the amount of trans product increased i n the p r o t i c solvent. They found that by decreasing the concentration of a z i r i d i n e i n the addition to butyne-2 n i t r i l e , there was an increase i n the amount of c i s product formed. The configuration s t a b i l i t y (18, 20, 22, 23, 24, 34) and the k i n e t i c s of isomerization (34) of amine addition products, have been investigated by Huisgen, Reimlinger and S t i r l i n g . Huisgen (34) found the rate of isomerization of products, i n the cases where isomerization occurred at room temperature, was very slow. Traces of acid were found to increase the rate of isomerization. In the case of primary amines, i t was suggested that the trans product i s s t a b i l i z e d by intramolecular hydrogen bonding (eq. 2.6), and consequently the k i n e t i c a l l y c o n t r o l l e d c i s products often isomerize to the trans product. H—Q H C0 oR • . R'N^ \>0R \ / 2 k, v / yC=cC  L ^ XC=C( (2.6) R • k"! H / / H H c i s product trans product S t i r l i n g et a l (24) found the equilibrium isomer r a t i o changed with the solvent used and Truce (37) showed i t also depended upon the s t e r i c influences of the substituents on the acetylene. 11 The r a t e c o n s t a n t k^ f o r t h e e q u i l i b r a t i o n o f c i s m e t h y l 3 - c y c l o h e x y l a m i n o a c r y l a t e t o c i s and t r a n s —6 — 7 -1 i s o m e r s ( e q . 2.6) was o f t h e o r d e r o f 10 t o 10 sec a t 25° (A"0.05 m o l a r ) . Knowing t h a t t h e e q u i l i b r a t i o n r a t e was s l o w i n a c i d f r e e s o l v e n t , H u i s g e n and G e i s e (35) s t u d i e d t h e k i n e t i c s o f t h e a d d i t i o n o f amines t o c a r b o x y l i c a c e t y l e n e s i n a c e t o n i t r i l e a t 37° ( T a b l e I ) . The k i n e t i c s were found t o be second o r d e r , f i r s t o r d e r i n each o f t h e s t a r t i n g m a t e r i a l s , w i t h t h e f o r m a t i o n o f o n l y c i s p r o d u c t s i n t h e d i l u t e s o l u t i o n s used ( e q . 2 . 7 ) . , R„N H k„ 2 \ / R ?NH + XCECY > C=C (2.7) y/ Y T a b l e I Rate c o n s t a n t s , k^, ( l i t e r mole "" sec """) f o r e q u a t i o n 2 . 7 Amine A c e t y l e n e HC=CC0 2Me MeC0 2C=CC0 2Me a z i r i d i n e 0.024 5.67 p i p e r i d i n e e y e l o h e x y l a m i n e 2.25 0.020 445 17.7 1 2 The mechanism proposed by Huisgen et a l (36) has t h e same intermediate f o r both c i s and t r a n s a d d i t i o n ( e q . 2.8; see page 1 3 ) . C i s a d d i t i o n can occur by way of an i n t r a and/or i n t e r molecular process, and t r a n s a d d i t i o n by an i n t e r m o l e c u l a r p r o c e s s . T r u c e and Brady ( 3 7 ) r e a c t e d amines w i t h e t h y l p r o p i o l a t e and a c e t y l e n e s u l f o n e s . T h e i r r e s u l t s f o r t h e e t h y l p r o p i o l a t e a d d i t i o n s , c o r r e s p o n d e d w i t h t h e r e s u l t s o f H u i s g e n e t a l ( 3 6 ) , i n b e i n g n o n s t e r e o s p e c i f i c , w i t h c i s a d d i t i o n p l a y i n g a major r o l e . T r u c e and Brady ( 3 7 ) , and D o f i n i (18) f o u n d t h a t t h e a z i r i d i n e a d d i t i o n p r o d u c t s were s t a b l e t o i s o m e r i z a t i o n . T r u c e opened t h e a z i r i d i n e r i n g ( 3 7 ) i n a r e a c t i o n , and f o u n d immediate i s o m e r i z a t i o n t o t h e a n a l o g o u s c i s p r o d u c t . T r u c e argued t h a t t h e immonium i o n , w h i c h he p o s t u l a t e d n e c e s s a r y f o r i s o m e r i z a t i o n s e (CH 2) 2N=CH-CHS0 2C 7H 7-p was p a r t i c u l a r l y s t r a i n e d i n the case of a z i r i d i n e , and c o n s e q u e n t l y the isomer p r o d u c t s are s t a b l e . T r u c e a l s o i n v e s t i g a t e d t h e a d d i t i o n o f amines t o s u l f o n y l a c e t y l e n e s i n benzene a t -25°, and showed i n t h i s c a s e t h a t the k i n e t i c product was from t r a n s a d d i t i o n , f o l l o w e d by a f a s t i s o m e r i z a t i o n t o c i s p r o d u c t . A t room t e m p e r a t u r e t h e o n l y p r o d u c t o b s e r v e d i n t h e r e a c t i o n m i x t u r e by n.m.r., was t h e c i s p r o d u c t . He s u g g e s t e d t h a t OS X I 01 CM O u u III u x <u s CM o u V II OS 14 t h e t r a n s a d d i t i o n ( e q . 2 . 9 , R' = p-MeC^H^) was due t o t h e f a c t t h a t t h e t r a n s i t i o n s t a t e was i n t h e t r a n s c o n f i g u r a t i o n ( t h e s u l f o n y l group need n o t be p l a n a r f o r d e l o c a l i z e d s t a b i l i t y ) . ;low \ 0 R~NH + R'SO-CSCH > C-CK D 1 2 Vd*sb 4 - • H H , . H S 0 O R « f a s t \ / f a s t \ / 2 \ / f a s t \ / -> c=c{ > c=c; R 2 I x f / \ S 0 2 R ' R 2 N / ( t r a n s ) ( c i s ) ( 2 . 9 ) T r u c e s u g g e s t e d t h a t i n t h e c a s e s where immonium-type r e s o n a n c e o f t h e p r o d u c t i s p o s s i b l e , t h e r e i s r a p i d i s o m e r i z a t i o n t o t h e more s t a b l e c i s p r o d u c t . 2.1.3.2 A d d i t i o n o f T i n H y d r i d e s L e u s i n k e t a l ( 3 8 , 3 9 ) have made d e t a i l e d s t u d i e s o f t h e a d d i t i o n o f t i n h y d r i d e s t o a c e t y l e n e s . I t has been s u g g e s t e d t h a t an i o n i c mechanism c o u l d be o p e r a t i v e , i n what u n t i l t h e n had been o n l y c o n s i d e r e d as a f r e e r a d i c a l h y d r i d e a d d i t i o n ( 4 0 ) , so t h a t b o t h n u c l e o -p h i l i c ( 4 1 ) and e l e c t r o p h i l i c ( 4 2 ) r e a c t i o n s were p o s s i b l e . L e u s i n k p o s t u l a t e d t h a t t h e f o r m a t i o n o f t h e n o n - t e r m i n a l t r a n s p r o d u c t , i n t h e t i n h y d r i d e a d d i t i o n t o u n s y m m e t r i c a l 15 a c e t y l e n e : ; (X^Y) ( e q . 2.10), was due t o n u c l e o p h i l i c a t t a c k . The o v e r a l l k i n e t i c s o f t h i s p r o d u c t f o r m a t i o n i n b u t y r o -n i t r i l e s o l v e n t were second o r d e r , f i r s t o r d e r i n t h e h y d r i d e and a c e t y l e n e ( T a b l e I I ) . R 3SnX' + XCECY •> t r a n s - X 1 (X)C=C(SnR 3)Y (2.10) T a b l e I I Rate c o n s t a n t s ( l i t e r mole sec f o r e q u a t i o n 2.10 X Y R X« T(°C) k 2 ( l m * s< H C0 2Me Me H 49 1.15xl0"* 5 H CN Me H 20 1 . 1 8 x l O ~ 4 COgMe C0 2Me Me H 20 0.92x10 " 2 CN CN Me H 20 1 . 5 0 x l 0 _ 1 H C0 2Me E t H 50.3 3 . 8 0 x l 0 ~ 5 H 0 C0 2Me E t D 50.3 3 . 1 5 x l 0 ~ 5 H CN E t H 20.5 5 . 1 0 x l 0 ~ 4 H CN E t D 20.5 3 . 6 0 x l 0 - 4 C 0 2 E t C 0 2 E t E t H 0.0 C 0 2 E t C 0 2 E t E t D 0.0 a t 20' > > 1.4 1.3 16 L e u s i n k d i s c o v e r e d s o l v e n t p o l a r i t y a f f e c t e d t h e r a t e o f t h e r e a c t i o n s , b u t t h e r a t e was independent of t h e p r e s e n c e of a r a d i c a l i n h i b i t o r . The mechanism he p r o p o s e d as b e i n g most c o n s i s t e n t w i t h h i s r e s u l t s i s out-l i n e d below ( e q . 2.11). X X e slow \ ft \ R-SnH + XCHCY > .C=C\ > R ? S n w +• C=C\ If Y Uy Y \3nR 3 \ y f a s t \ / 3 R-Sn w + £=C\ > .C=CN d H Y H Y (2.11) 2.1.3.3 A d d i t i o n o f Group IV and V H y d r i d e s  t o F l u o r o c a r b o n A c e t y l e n e s C u l l e n e t a l ( 1 , 43, 44) i n a s e r i e s o f i n v e s t i g a t i o n s u s i n g f l u o r o c a r b o n a c e t y l e n e s , added E t P H 2 Me 2AsH, (CgH 5)(Me)AsH, ( C F 3 ) 2 A s H , MegSnH, 'EtgGeH, Me,SiH, (n-Bu)^SnH e t c . , t o h e x a f l u o r o b u t y n e - 2 , and some o f t h e s e t o 3 , 3 , 3 - t r i f l u o r o p r o p y n e . The i s o l a t e d p r o d u c t s were m a i n l y t h o s e which would be formed from t r a n s a d d i t i o n , o f t e n accompanied w i t h s m a l l amounts o f c i s p r o d u c t . The ease o f r e a c t i o n o f t h e a r s i n e s w i t h h e x a f l u o r o b u t y n e - 2 was i n t h e o r d e r PtegAsH >(CgHg)(Me)ASH> ( C F 3 ) 2 A s H w h i c h i s c o n s i s t e n t w i t h t h e i d e a o f a n u c l e o p h i l i c a t t a c k 17 by the a r s e n i c l o n e p a i r on the a c e t y l e n e . The r e a c t i o n o f d i m e t h y l a m i n e w i t h h e x a f l u o r o b u t y n e - 2 gave b o t h c i s and t r a n s p r o d u c t s ( t r a n s / c i s = 1 5 ) . S i n c e the a d d i t i o n s gave a h i g h p r o p o r t i o n o f t r a n s a d d u c t , and a s m a l l p r o p o r t i o n o f c i s a d d u c t , i t was o f i n t e r e s t t o c a r r y o u t a d e t a i l e d s t u d y o f mechanism(s) and p r o d u c t s t a b i l i t i e s . 18 2.2 E x p e r i m e n t a l V o l a t i l e r e agents and p r o d u c t s were manipulated i n a c o n v e n t i o n a l vacuum system. U n l e s s otherwise i n d i c a t e d r e a c t i o n s were c a r r i e d out i n s e a l e d P y r e x tubes. N.m.r. s p e c t r a were run on V a r i a n A-60 and HA-100 inst r u m e n t s and are r e p o r t e d i n ppm d o w n f i e l d from e x t e r n a l TMS. U l t r a -v i o l e t s p e c t r a were r e c o r d e d u s i n g Cary Model 11 and Cary Model 14 s p e c t r o m e t e r s . The Cary Model 14 was used f o r the k i n e t i c s t u d i e s . I n f r a r e d s p e c t r a were run on a Perkin-Elmer Model 457 i n s t r u m e n t . The e x p e r i m e n t a l s e c t i o n w i l l be d i v i d e d i n t o two p a r t s , the f i r s t p a r t concerns a r s i n e s and the second p a r t amines. 2.2.1 A r s i n e E x p e r i m e n t a l 2.2.1.1 S t a r t i n g M a t e r i a l s 19 2.2.1.1.1 Preparation of dimethylarsine The method used i s a modification of that of Dehn and Wilcox (45). A 1 - l i t r e 3-necked f l a s k was f i t t e d with dropping funnel, water-cooled condenser, s t i r r e r , nitrogen purge, and cold traps (-196°) to condense any v o l a t i l e products coming through the condenser. Mercuric chloride (30g) and zinc dust (290g) were placed i n the f l a s k and s t i r r e d vigorously with 100 ml of water. A solution of dimethylarsinic acid (50g) i n water (100 ml) was purged with nitrogen, transferred to the dropping funnel using a syringe, and combined with the s l u r r y i n the reaction f l a s k . In a s i m i l a r way 12N hydrochloric acid (250 ml) was slowly added to the vigorously s t i r r e d f l a s k . A f t e r six hours, the contents of the traps were taken i n t o the vacuum system and dried over P^^O* T n e y i e l d of dimethylarsine was 34.lg (89%). I t has a very strong As-H stretching frequency at 2085 cm"^ and the n.m.r. spectrum showed a doublet at 0.82 ppm (6H) and a septet at 2.82 ppm (IH) <J C H _ H = 7.0 Hz). 2.2.1.1.2 Preparation of dimethylarsenic deuteride Dimethylarsine (10.8g) was shaken with D 20 (30g) and a trace of hydrochloric acid (to speed exchange), f o r one week i n a sealed tube. The arsine was separated and r e - e q u i l i b r a t e d with fresh D 20. This y i e l d s a product which i s 100% dimethylarsenic deuteride as detected by 20 n.m.r. (1:1:1 t r i p l e t at 0.82 ppm (J-,„ „ = 1 Hz)). The CH3-D inf r a r e d spectrum showed a strong As-D stretching band at 1052 cm"1. 2.2.1.1.3 Preparation of d i e t h y l a r s i n e Chlorodiethylarsine was prepared from arsenic t r i c h l o r i d e and te t r a e t h y l l e a d (46). The chloroarsine was then reduced using lithiu m aluminium hydride (47). Diethylarsine has a very strong As-H stretching frequency at 2085 cm ^. The n.m.r. spectrum shows a quintet at 2.43 ppm (IH) (J = 6 Hz) and two mu l t i p l e t s (10H) at 1.42 and 1.15 ppm r e s p e c t i v e l y . 2.2.1.2 Reactions of Arsines with Hexafluorobutyne-2 2.2.1.2.1 Dimethylarsenic deuteride Dimethylarsenic deuteride (0.95g) and the acetylene (2.8g) were l e f t at 20° f o r one hour. The product, 2-dimethylarsino-3-deutero-l,1,1,4,4,4-hexa-fluorobutene-2, condensed i n a trap at -78°. The purity of the product was established by i t s n.m.r. spectrum which showed a quartet at 0.96 ppm ( 1 Hz). A small u p f i e l d quartet presumably corresponding with the c i s adduct was also present. Integration showed that t h i s was about 5% of the t o t a l product. 21. 2.2.1.2.2 D i e t h y l a r s i n e The a r s i n e (2.43g) and the a c e t y l e n e (3.68g) were l e f t f o r two days at 20°. The product, 2 - d i e t h y l a r s i n o - l , 1,1,4,4,4-hexafluorobutene-2, b.p. 146°, condensed i n a t r a p c o o l e d t o - 4 6 ° . The i d e n t i t y of the compound was e s t a b l i s h e d by i t s n.m.r. spectrum. T h i s showed i n the d o w n f i e l d r e g i o n a q u a r t e t o f q u a r t e t s c e n t e r e d at 6.58 ppm ( J = 8 and 2 Hz) and another q u a r t e t at 5.85 ppm ( J = 8.3 Hz). The r e l a t i v e i n t e n s i t y o f the two a b s o r p t i o n s , 22:1, i s the r a t i o of the t r a n s to c i s adducts ( 1 ) . U p f i e l d i s a t r i p l e t (CH^-CH^-) at 0 .94 ppm ( J = 7 Hz) and a complex m u l t i p l e t a t about 1.6 ppm (CH^-CH^-). The r e l a t i v e areas of a l l m u l t i p l e t s were as expected. 2.2.1.2.3 D i m e t h y l a r s i n e w i t h hexafluorobutyne-2 i n the gas phase Gaseous hexafluorobutyne-2 and d i m e t h y l a r s i n e were i s o l a t e d s e p a r a t e l y i n two evacuated b u l b s separated by a v a l v e . The v a l v e was opened and the gas allowed to mix a t room temperature. The e x t e n t o f r e a c t i o n c o u l d be f o l l o w e d by the p r e s s u r e decrease i n the system. In the absence o f l i g h t , complete r e a c t i o n r e q u i r e d t h r e e days. Under i d e n t i c a l i n i t i a l c o n d i t i o n s , but upon i r r a d i a t i o n w i t h u l t r a v i o l e t l i g h t (100 watt lamp, 20 cm from the a i r -stream c o o l e d b u l b s ) , the r e a c t i o n r e q u i r e d o n l y one day to go to c o m p l e t i o n . 22 The a n a l y s i s o f the pr o d u c t s from the two r e a c t i o n s showed 9 2 % t r a n s and 8% c i s adducts from the u l t r a v i o l e t i r r a d i a t e d experiment, and 9 4 % t r a n s and 6% c i s i n the absence of l i g h t . 2 . 2 . 1 . 2 . 4 D i m e t h y l a r s i n e with h e x a f l u o r o b u t y n e - 2 i n d^—methanol and methanol s o l v e n t D i m e t h y l a r s i n e , h e x a f l u o r o b u t y n e - 2 , and d^-methanol as a s o l v e n t , were s e a l e d i n l a y e r s i n a C a r i u s tube. The tube was q u i c k l y warmed and shaken v i g o u r o u s l y , and l e f t f o r t h r e e hours. The c o n t e n t s were then taken i n t o the vacuum system. T r a p - t o - t r a p d i s t i l l a t i o n gave a f r a c t i o n which condensed a t - 7 6 ° . The *H n.m.r. spectrum of t h i s f r a c t i o n had s i n g l e t s at 0 . 9 6 ppm, 4 . 3 5 ppm, and a q u a r t e t o f q u a r t e t s a t 6 . 4 5 ppm of r e l a t i v e areas ( 3 8 : 6 : 1 ) . No c i s product was i n d i c a t e d i n the n.m.r. A s i m i l a r experiment done i n methanol, y i e l d e d 100% t r a n s a d d i t i o n p r o d u c t . 2 . 2 . 1 . 3 K i n e t i c s o f A r s i n e A d d i t i o n s 2 . 2 . 1 . 3 . 1 K i n e t i c s o f the a d d i t i o n o f d i m e t h y l a r s i n e to h e x a f l u o r o b u t y n e - 2 The k i n e t i c s o f the a d d i t i o n r e a c t i o n s were determined by f o l l o w i n g the f o r m a t i o n o f pro d u c t , u s i n g 23 n.m.r. and u l t r a v i o l e t s p e c t r o s c o p y . I n a t y p i c a l n.m.r. m o n i t o r e d e x p e r i m e n t 0.1805g o f h e x a f l u o r o b u t y n e - 2 , d i m e t h y l a r s i n e (0.0554g), and d i e t h y l e t h e r were condensed i n t o an n.m.r. t u b e ( t o t a l volume a t 20° was 1.12 m l ) . The tub e was s e a l e d . The sample was warmed t o -35° and shaken j u s t b e f o r e p l a c i n g i t i n t o t h e c o o l e d probe (-30°) o f t h e s p e c t r o m e t e r i The r a t e o f f o r m a t i o n o f t h e p r o d u c t s was f o l l o w e d by i n t e g r a t i o n . The f o l l o w i n g r e s u l t s were f o u n d f o r t h e t r a n s a d d u c t : t ( s e c ) a c o n e , o f t r a n s p r o d u c t ( m o l e s / l l t r e - ) 260 0.120 344 0.147 830 0.237 780 0.246 1587 0.337 1620 0.340 2420 0.388 2445 0.394 OO ' 0.493 a t = 0 i s a r b i t r a r y same as t h e t r a n s . The r e l a t i v e amounts of t r a n s and c i s p r o d u c t s r e m a i n e d c o n s t a n t t h r o u g h o u t t h e e x p e r i m e n t . Assuming t h a t t h e r e a c t i o n i s b i m o l e c u l a r and 2 4 f i r s t order in each o f the s t a r t i n g materials, the following rate equation ( 2 . 1 2 ) can be derived: log f A o - U . k T ( A o - B o } t ( 2 . 1 2 ) B Q - I T " 2 . 3 0 3 t = time A » i n i t i a l concentration of acetylene, o J B q = i n i t i a l concentration of dimethylarsine. U = concentration of one product formed. k T = rate constant at temperature T. A o - U P l o t t i n g t against log (-^—E~Tj) gives a str a i g h t l i n e o (F i g . 1 ) . The experiments monitored by u l t r a v i o l e t absorption were followed by measuring the increase i n absorbance at o 2 6 1 0 A. The products but not the reactants absorb at t h i s wave length (see Chapter 4 ) . The reactants were condensed v i a a metal valve into a cold f i n g e r attached to a 1 or 0.1 mm path length s i l i c a c e l l . The arsine and ether ( 1 0 ml) were added f i r s t , mixed at room temperature, and then frozen. The hexafluorobutyne-2 was then condensed into the c o l d f i n g e r well above the arsine-ether mixture. The lower layer was quickly warmed and then vigorously shaken onto the s t i l l frozen acetylene. When the whole apparatus was at room temperature, i t was placed i n the adapted c a v i t y of the spectrometer. F i q u r e 1 26 Second order k i n e t i c s were observed f o r a l l r e a c t i o n s u n t i l a t l e a s t 50% c o m p l e t i o n . Allowance has been made f o r the s o l u b i l i t y of hexafluorobutyne-2 i n d i e t h y l e t h e r ( F i g . 3 ) . A summary of the exp e r i m e n t a l c o n d i t i o n s used f o r the k i n e t i c experiments i s g i v e n i n Tabl e I I I . The r a t e c o n s t a n t s o b t a i n e d from each run are a l s o l i s t e d . U s i n g the n.m.r. dat a , the a c t i v a t i o n energy of 6.54 _+ .20 kcal/mole, and a c t i v a t i o n entropy of -43.4 at 22° i s c a l c u l a t e d from the Ar h e n i u s p l o t shown i n F i g u r e 2 ( 4 8 ) . 2.2.1.3.2 K i n e t i c s of the a d d i t i o n of d i e t h y l a r s i n e  to h exafluorobutyne-2 T h i s r e a c t i o n was monitored by n.m.r. techniques as d e s c r i b e d above. D i e t h y l a r s i n e (0.052g), the a c e t y l e n e (0.1882g), and d i e t h y l e t h e r were s e a l e d i n an n.m.r. tube. A p l o t f o r second order k i n e t i c s , f i r s t o rder i n each of the s t a r t i n g m a t e r i a l s was l i n e a r . The r a t e was c a l c u l a t e d to be 1.528 x 10~ 3 l i t r e mole-"*" s e c " 1 a t -10° i n d i e t h y l e t h e r . 2.2.1.4 E q u i l i b r a t i o n o f A r s i n e and A r s i n e A d d i t i o n Products Table I I I Summary of R e s u l t s from D i m e t h y l a r s i n e A d d i t i o n S o l v e n t T(°C) Cone, o f C F 3 C E C C F 3 ( m o l e / l i t r e ) Cone, of A r s i n e ( m o l e / l i t r e ) Means of M o n i t o r i n g Jc T(xl0"-'lm~ E t 2 0 -30(_+3°C) 0.998 0.469 n.m.r. 0.78+0.01 E t 2 0 -30 1.588 1.568 n.m.r. 0.778 E t 2 0 -15 1.247 0.612 n.m.r. 1.69j_0.11 E t 2 0 -15 1.205 0.5665 n.m.r. 2.15+0.17 E t 2 0 -15 1.184 0.549 n.m.r. 3.15+0.5 a E t 2 0 -5 1.016 0.492 n.m.r. 2.70^0.4 E t 2 0 + 2 2 U 5 ° C ) 0. 376 0.0765 uv 5.26 E t 2 0 + 22 0.5 39 0.0671 uv 3.94 E t 2 0 +22 0.2325 0.1031 uv 7.12 E t 2 0 + 22 0.101 0.185 uv 3.33 E t 2 0 + 22 0.115 0.4298 uv 3.03 E t 2 0 +22 0.0892 0.2310 b uv 3.55 Me OH + 22 0.0093 0.0079 uv 560.00 a. I n i t i a t o r 2 , 2 • - a z o b i s ( 2 - m e t h y l p r o p i o n i t r i l e ) 0 b. D i m e t h y l a r s e n i c d e u t e r i d e used. .652 m o l e / l i t r e added. 29 2.2.1.4.1 D i m e t h y l a r s e n i c d e u t e r i d e and D i e t h y l a r s i n e Equal volumes o f d i e t h y l a r s i n e and d i m e t h y l a r s e n i c d e u t e r i d e were s e a l e d i n an n.m.r. tube. T h i s was q u i c k l y warmed to room temperature and the sample was p l a c e d i n a V a r i a n A-60 n.m.r. spectrometer. The i n c r e a s e i n the d i m e t h y l a r s i n e d o u b l e t c e n t e r e d a t 0.82 ppm ( J = 7.0 Hz) was observed f o r f o u r h o urs. The \ l i f e f o r the exchange was about t h i r t y minutes. 2.2.1.4.2 D i e t h y l a r s i n e and 2 - d i m e t h y l a r s i n o - 3 - d e u t e r o - l ,  1,1 14«4,4-hexafluorobutene-2 Equal volumes o f d i e t h y l a r s i n e and the a r s i n o -butene were s e a l e d i n an n.m.r. tube. The spectrum a f t e r t h r e e hours at 20° showed no d o w n f i e l d a b s o r p t i o n so t h a t no exchange of D and H o c c u r r e d . 2.2.1.4.3 d^-methanol and t r a n s 2 - d i m e t h y l a r s i n o - 1 ,  1,1,4,4,4-hexafluorobutene-2 Equal volumes o f d^-methanol and the adduct were mixed i n an n.m.r. tube. O b s e r v a t i o n o f the adduct by n.m.r. t e c h n i q u e i n d i c a t e d t h e r e was no d e t e c t a b l e exchange o f deuterium f o r hydrogen a f t e r 1% hours. A f t e r f o u r days exchange was found t o a sm a l l e x t e n t (< 5 % ) . 30 2.2.1.5 S t a b i l i t y of the Products of the Dimethylarsine- Hexafluorobutyne-2 Reaction The products from the r e a c t i o n of equation 1.1 (R=R»=Me) can be separated by v.p.c. ( s i l i c o n e o i l at 92°). When observed f o r extended periods of time, the trans product d i d not isomerize to the c i s product, when exposed to a i r , or dissolved i n d i e t h y l ether, dimethylarsine, and mixtures of dimethylarsine and d i e t h y l ether. S i m i l a r l y the c i s isomer was stable and d i d not isomerize under the same conditions. 2.2.1.6 Competitive Reaction of Diethylarsine and  Dimethylarsenic Deuteride with Hexafluorobutyne-2 Dimethylarsenic deuteride, d i e t h y l a r s i n e , and hexafluorobutyne-2 were frozen into a Carius tube. The tube was warmed under water (15°) and vigorously shaken. After f i v e minutes, the tube was frozen down, opened, and the contents taken into a vacuum system. The f r a c t i o n which condensed at -78° was separated by v.p.c. ( s i l i c o n e 128°). Four major f r a c t i o n s were found. These f r a c t i o n s were i d e n t i f i e d by n.m.r. to be c i s and trans isomers of the arsine-butyne adducts. The weight of the separated isomers indicated that the rea c t i o n went 93% trans, 7% c i s f o r adduct formations. The r a t i o of the products before and a f t e r separation was i d e n t i c a l proving that no 31 i s o m e r i z a t i o n o c c u r r e d w h i l e s e p a r a t i n g . From t h e i n t e g r a l s o f t h e n.m.r. s p e c t r a , t h e p e r c e n t a g e o f hydrogen c o u l d be c a l c u l a t e d f o r t h e s e p a r a t e d f r a c t i o n s and from t h i s t h e d e u t e r i u m p e r c e n t a g e c o u l d be f o u n d . The r e s u l t s o f two e x p e r i m e n t s a r e t a b u l a t e d i n T a b l e s IV and V. T a b l e IV E x p e r i m e n t M o l e s o f M o l e s o f Mole s o f Me 2AsD E t 2 A s H CF 3C=CCF 3 1 0.0113 0.0048 0.0225 ( e x c e s s ) 2 0.0059 0.0086 0.0586 ( e x c e s s ) T a b l e V >.c. F r a c t i o n E x p t . 1 Expt . 2 L C t i o n i d e n t i t y %D %H %D %H 7 0 a 3 0 a 4 0 a 6 0 a 1 t r a n s Me^As- 77 23 40 60 2 c i s Me 2As- 70 30 4 9 b 5 1 b 3 t r a n s E t ^ A s - 70 30 45 55 4 c i s E t 2 A s - _c _c 40 60 a I n i t i a l p e r c e n t a g e based on moles o f r e a c t a n t s ( T a b l e I V ) . b Poor s e p a r a t i o n , two u p f i e l d p r o t o n peaks o v e r l a p p e d r e s u l t i n g i n an i n c o n c l u s i v e i n t e g r a l , c I n s u f f i c i e n t p r o d u c t f o r an n.m.r. i n t e g r a l . 32 2.2.1.7 S o l u b i l i t y of Hexafluorobutyne-2 i n  D i e t h y l Ether Hexafluorobutyne-2 (0.02615g), t r i f l u o r o -acetophenone (0.1295g) and d i e t h y l e t h e r were s e a l e d i n an n.m.r. tube. The t o t a l volume was 1.0 ml and the c o n c e n t r a t i o n o f gas corresponded c l o s e l y w i t h t h a t o f the n.m.r. k i n e t i c s t u d i e s . The t r i f l u o r o a c e t o p h e n o n e was i n t r o d u c e d as an i n t e r n a l s t a n d a r d . The r a t i o o f the 19 i n t e g r a l s i n the F n.m.r. spectrum o f the sample was observed at v a r i o u s temperatures. At -76° two phases appeared. The percentage o f hexafluorobutyne-2 d i s s o l v e d i n the e t h e r i s p l o t t e d i n F i g u r e 3. In a separate experiment the vapor p r e s s u r e i n c r e a s e found on adding the a c e t y l e n e t o et h e r s o l u t i o n s of the a c e t y l e n e i n d i c a t e d t h a t at 24°, 12% of the a c e t y l e n e does not d i s s o l v e . T h i s corresponds w e l l with n.m.r. r e s u l t s . 2.2.2 Amine Ex p e r i m e n t a l 2.2.2.1 The r e a c t i o n o f d i e t h y l a m i n e with  hexafluorobutyne-2 The amine (0.22g) and the a c e t y l e n e (0.80g) were shaken t o g e t h e r . The r e a c t i o n was v i g o r o u s and a g r e a t d e a l o f polymer was formed. The pro d u c t , 2 - d i e t h y l a m i n o - l , 80 -1 1 1 1 1 i H -30 -20 -IO O +IO + 20 +30 T °C F i g u r e 3: A p l o t of the percentage of hexafluorobutyne-2 d i s s o l v e d i n d i e t h y l e t h e r , as a f u n c t i o n of temperature. 34 1 , 1 , 4 , 4 , 4 - h e x a f l u o r o b u t e n e - 2 , was t r a p p e d a t 76° i n 89% y i e l d . The n.m.r. s p e c t r a o f t h e f i r s t f r a c t i o n from t h e t r a p , which prove d t o be t h e t r a n s i s o m e r , had a d o w n f i e l d q u a r t e t c e n t e r e d a t 5.05 ppm ( J = 8.9 H z ) , a q u a r t e t c e n t e r e d a t 2.92 ppm ( J = 7.4 Hz) and a t r i p l e t a t 0.83 ppm ( J = 7.4 H z ) . The l e s s v o l a t i l e c i s i s o m e r ( 4 5 % o f t h e t o t a l p r o d u c t ) had a d o w n f i e l d q u a r t e t c e n t e r e d a t 4.46 ppm ( J = 9.5 H z ) , a q u a r t e t c e n t e r e d a t 2.89 ( J = 7.0 H z ) , and a t r i p l e t s uperimposed on t h e t r a n s t r i p l e t . I n t h i s m i x t u r e , t h e t r a n s d o w n f i e l d q u a r t e t s were s h i f t e d about 0.1 ppm d o w n f i e l d , due t o t h e s o l v e n t e f f e c t o f t h e c i s i s o m e r . The pure t r a n s i s o m e r , s e a l e d i n an a i r f r e e n.m.r. t u b e , g r a d u a l l y i s o m e r i z e d t o a m i x t u r e o f b o t h i s o m e r s . 2.2.2.2 K i n e t i c s o f t h e d i e t h y l a m i n e a d d i t i o n t o  h e x a f l u o r o b u t y n e - 2 '••Diethylamine, h e x a f l u o r o b u t y n e - 2 , and s o l v e n t were mixed as d e s c r i b e d f o r t h e a r s i n e k i n e t i c s t u d i e s , i n t h e 0.1 mm c e l l a d a p t e d f o r t h e u.v. s p e c t r o m e t e r . The r a t e s o f r e a c t i o n were c o n s i s t e n t w i t h second o r d e r k i n e t i c s , f i r s t o r d e r i n d i e t h y l a m i n e and h e x a f l u o r o b u t y n e - 2 . The r a t e c o n s t a n t s k 2 , c a l c u l a t e d from e q u a t i o n 2 . 1 2 ( a r e o u t l i n e d i n T a b l e V I . 35 Table VI Solvent T(°C) E t 2 0 E t 2 0 Et 2Q MeOH 2 2± 3 21^3 16. 5^2 20 + 1 Cone, of Cone, of CF C3CCF 3 Et 2NH (moles/ ^ (moles/ -l i t e r ) X 1 0 ~ J l i t e r ) X 1 0 ~ J k 2 ( 1 mole "'"sec 3.55 1.52 1.45 1.45 1.39 3.71 3.49 1.45 1.23 ± 0.02 1.16 +_ 0.02 1.20 ± 0.06 too f a s t to measure 2.2.2.3 S t a b i l i t y of trans 2-diethylamino-l,  1,1,4,4,4-hexafluorobutene-2 The more v o l a t i l e trans isomer was separated from the c i s / t r a n s mixture i n a vacuum system. I t was sealed a i r fre e i n an n.m.r. tube,and i t s isomerization to the c i s product was followed as a function of time (Table V I I ) . In another experiment a mixture of adducts, 36% c i s and 64% trans, was sealed, a i r f r e e , with diethylamine i n an n.m.r. tube and heated to 120°. After 18 hours the c l e a r mixture had become dark and n.m.r. ana l y s i s indicated 32% c i s and 68% trans. A f t e r 32 hours no trace of the isomers was found, and the tube was f i l l e d with a black sludge. Table VII time (days) 0 12 17 % c i s 0 22 35 % trans 100 78 65 2.2.2.4 Solvent and concentration e f f e c t s on the addition of diethylamine to hexafluorobutyne-2 Diethylamine, hexafluorobutyne-2 and solvent i n some cases, were sealed i n an n.m.r. tube. The reaction was completed on warming to room temperature. No change i n product d i s t r i b u t i o n was found f o r two hours a f t e r r e a c t i o n . The r e s u l t s are tabulated i n Table VIII. T a b l e V I I I Reactant s l i g h t l y R a t i o i n excess, u n l e s s s o l v e n t / done neat. S o l v e n t r e a c t a n t ( s ) % t r a n s % c i s Et 2NH E t 2 0 1 54 46 Et 2NH E t 2 0 10 38.5 61.5 C F 3 C E C C F 3 MeOH 3 100 0 Et 2NH Et 2NH (neat) 2 6 3 37 if it Et 2NH Et 2NH (neat) 2 66 34 C F 3 C E C C F 3 CF 3CECCF 3 (neat) 5 51 49 C F 3 C E C C F 3 CF 3CECCF 3 (neat) 1 67 33 * Remained approximately c o n s t a n t a f t e r IS hours a t 120° i n a s e a l e d , a i r f r e e n.m.r. tube. u> 38 2.3 D i s c u s s i o n In t h i s c h apter the d i s c u s s i o n w i l l be broken i n t o t h r e e s e c t i o n s , the f i r s t one w i l l be concerned with the a r s i n e r e a c t i o n s , the second w i t h amine r e a c t i o n s , and the l a s t with a comparison o f the a r s i n e and amine a d d i t i o n s 2.3.1 A r s i n e s 2.3.1.1 K i n e t i c R e s u l t s The a d d i t i o n o f d i m e t h y l a r s i n e to h e x a f l u o r o b u t y n e i n e t h e r s o l u t i o n i s f i r s t o r d e r i n both a r s i n e and a c e t y l e n e (Table I I I and F i g . 1 ) . The r a t e c o n s t a n t s determined from the n.m.r. monitored experiments are r e p r o d u c i b l e and an a c t i v a t i o n energy o f 6.52 _£ .20 k c a l / mole f o r the r e a c t i o n can be o b t a i n e d from the v a r i a t i o n of k T with temperature. The a c t i v a t i o n entropy i s -43.4 +. 1 e.u. a t 22° ( 4 8 ) . Although the u l t r a v i o l e t monitored experiments g i v e good second o r d e r p l o t s , the r a t e c o n s t a n t s are i n c o n s i s t e n t ( T a b l e I I I ) . T h i s p r o b a b l y i s due t o the f o r m a t i o n o f v a r i a b l e amounts o f p o l y m e r i c (CF_C) , 39 v i s i b l e i n some c a s e s . A smal l a c c e l e r a t i n g e f f e c t due to the u l t r a v i o l e t r a d i a t i o n might a l s o be expected s i n c e the slow gas phase a d d i t i o n r a t e i s about t h r e e times f a s t e r when the r e a c t a n t s a re i r r a d i a t e d w i t h u l t r a v i o l e t l i g h t . Good temperature c o n t r o l was not p o s s i b l e i n the u l t r a v i o l e t monitored experiment, so the r a t e s would be expected to be n o n - r e p r o d u c i b l e on t h i s account a l s o . However, the g r e a t l y i n c r e a s e d r a t e found when methanol i s used as s o l v e n t i s a r e a l e f f e c t . In an attempt to determine i f the As-H bond i s i n v o l v e d i n the r a t e d e t e r m i n i n g s t e p o f the r e a c t i o n , the r a t e o f the a d d i t i o n o f d i m e t h y l a r s e n i c d e u t e r i d e t o the butyne was measured. However, t h i s experiment, n e c e s s a r i l y monitored by u l t r a v i o l e t a b s o r p t i o n , was i n c o n -c l u s i v e . The r a t e i s s i m i l a r t o t h a t found f o r the m a j o r i t y o f the u l t r a v i o l e t monitored experiments, (Table I I I ) . The r a t e o f a d d i t i o n o f d i e t h y l a r s i n e t o the butyne i s s i m i l a r though s l i g h t l y slower than the r a t e o f the a d d i t i o n o f d i m e t h y l a r s i n e . T h i s can be deduced from the r e s u l t t h a t the d i e t h y l a r s i n e r a t e a t -10° almost l i e s on the l i n e a r p l o t o f l o g k T a g a i n s t 1/T ( F i g . 2) used t o o b t a i n the a c t i v a t i o n energy f o r t h e d i m e t h y l a r s i n e a d d i t i o n . 40 2.3.1.2 Isomer A r s i n e D i s t r i b u t i o n s and S t a b i l i t i e s  and Products When d i m e t h y l a r s i n e i s added t o hexafluorobutyne-2, the d i s t r i b u t i o n o f isomer p r o d u c t s i s the same i n d i e t h y l e t h e r s o l v e n t , as when the r e a c t a n t s a re mixed neat, or r e a c t e d i n the gas phase, and i s unchanged when the r e a c t i o n i s done a t lower temperatures or under the i n f l u e n c e o f u l t r a v i o l e t r a d i a t i o n . At -30°C, the r a t e o f f o r m a t i o n o f the c i s product always p a r a l l e l s t h a t o f the t r a n s product. In methanol s o l v e n t 100% t r a n s product i s found. The isomer p r o d u c t s o f the a d d i t i o n o f a r s i n e s to hexafluorobutyne-2 can be se p a r a t e d by v.p.c. When the separ a t e d isomers were exposed to a i r , d i s s o l v e d i n d i e t h y l e t h e r , d i m e t h y l a r s i n e , and mi x t u r e s o f d i m e t h y l a r s i n e and d i e t h y l e t h e r f o r f o u r weeks, no i n d i c a t i o n o f i s o m e r i z a t i o n was observed f o r e i t h e r c i s or t r a n s p r o d u c t . C u l l e n e t a l (1) showed the t r a n s isomer was the thermodynamically s t a b l e p r o d u c t . The s t a b i l i t y o f the c i s and t r a n s isomers e l i m i n a t e s the p o s s i b i l i t y o f f o r m a t i o n o f 100% c i s product which subsequently i s o m e r i z e d to the thermodynamically s t a b l e t r a n s p r o d u c t . Thus the s t a b l e p r o d u c t s r e c o v e r e d from the a d d i t i o n b e i n g i n v e s t i g a t e d are both k i n e t i c a l l y c o n t r o l l e d , even though the t r a n s isomer i s the thermodynamically s t a b l e isomer. 41 2.3.1.3 P o s s i b l e R e a c t i o n Mechanisms Four g e n e r a l r e a c t i o n paths are c o n c e i v a b l e f o r the a d d i t i o n of a r s i n e to h e x a f l u o r o b u t y n e - 2 . These f o u r , the f r e e r a d i c a l , p r e - i o n i z a t i o n , e l e c t r o p h i l i c and n u c l e o p h i l i c mechanisms, w i l l now be c o n s i d e r e d s e p a r a t e l y t o determine which one i s most c o n s i s t e n t with the e x p e r i m e n t a l f i n d i n g s . The f i r s t , i n v o l v i n g f r e e r a d i c a l s , can be e l i m i n a t e d mainly on the b a s i s t h a t the r a t e of a d d i t i o n o f d i m e t h y l a r s i n e to the a c e t y l e n e i s s i g n i f i c a n t l y i n c r e a s e d i n methanol as compared to d i e t h y l e t h e r s o l v e n t (Table I I I ) . Other c o r r o b o r a t i n g e v i d e n c e comes from the f a c t t h a t the r e a c t i o n , i n the presence of an i n i t i a t o r i n s o l u t i o n , or under i n t e n s e u.v. r a d i a t i o n i n the gas phase, shows o n l y a s l i g h t i n c r e a s e i n r a t e . T h i s s l i g h t i n c r e a s e i n r a t e c o u l d v e r y w e l l be due to the u.v. r a d i a t i o n or the r a d i c a l i n i t i a t o r i n i t i a t i n g a r a d i c a l mechanism independent o f the main a d d i t i o n mechanism. The e f f e c t o f the i n t e n s e u l t r a v i o l e t r a d i a t i o n on a f r e e r a d i c a l a d d i t i o n mechanism should have been enormously i n c r e a s e d from t h a t o b s e r v e d . Truce e t a l (49) observed t h a t the f r e e r a d i c a l a d d i t i o n o f t h i o l s , induced by u l t r a v i o l e t l i g h t or azo-b i s i s o b u t y r o n i t r i l e , to a c e t y l e n e s was f a s t e r than the base c a t a l y z e d a d d i t i o n o f the t h i o l . The f r e e r a d i c a l r e a c t i o n was over i n about one minute, whereas the base c a t a l y z e d 4 2 a d d i t i o n , done i n r e f l u x i n g e t h a n o l , was o n l y 32% complete a f t e r n i n e h ours. Whatever s i g n i f i c a n t e f f e c t the u.v. l i g h t had on the a r s i n e r e a c t i o n was sm a l l as the product isomer d i s t r i b u t i o n was c o n s t a n t w i t h i n the e r r o r o f i n t e -g r a t i o n . The s l i g h t i n c r e a s e i n r a t e w i t h s t r o n g u.v. i r r a d i a t i o n may w e l l have been due to a temperature e f f e c t , though measures were taken t o t r y and remove t h i s with an a i r stream a c r o s s the v e s s e l . i o n i z a t i o n o f the a r s i n e p r e s u r s o r . Two p o s s i b l e modes of i o n i z a t i o n with t h e i r r e s p e c t i v e r a t e laws w i l l now be o u t l i n e d . A simple p r e - i o n i z a t i o n c o u l d be e n v i s i o n e d as i n e q u a t i o n 2.13. A second p o s s i b l e mechanism i n v o l v e s p r e -Me„AsH ; ~ Me.9As (2.13) The p o s s i b l e s t e p s are Me„AsH -> Me-As + H r© Me~As P + H® ->Me„AsH k i o n + a c e t y l e n e -> product i n t e r m e d i a t e i o n © + i n t e r m e d i a t e product 43 The r a t e law, assuming i s the r a t e c o n t r o l l i n g step i s 4? = k,(Me 0AsH) at 1 2 which does not corr e s p o n d with the ex p e r i m e n t a l r e s u l t s . I f the r a t e c o n t r o l l i n g s t e p i s k 2 the r a t e law becomes ^ £ = k 2 ( M e 2 A s H ) ^ ( a c e t y l e n e ) where k 2 = k^-fk U i s the product adduct c o n c e n t r a t i o n K i s the e q u i l i b r i u m c o n s t a n t f o r equa t i o n 2.13. T h i s r a t e law a l s o does not co r r e s p o n d to the experimental r e s u l t s . The more l i k e l y p r e - i o n i z a t i o n step o f equ a t i o n 2.14 c o u l d r e s u l t i n second o r d e r a d d i t i o n k i n e t i c s , f i r s t o r der i n h y d r i d e and a c e t y l e n e , i f a d d i t i o n of the a r s i n e anion t o the butyne i s slower than the r e v e r s e step of e q u a t i o n 2.14 2 Me 2AsH r ^ 1 " ^ M e 2 A s e + M e ^ s H ^ (2.14) P o s s i b l e s t e p s f o r t h i s a d d i t i o n are k. e 2 Me 2AsH ± _ > M e 2 A s + Me 2AsH, 44 M e 2 A s 6 + Me 2AsH 2^ ^->2 Me 2AsH i o n + a c e t y l e n e — k ^ — > i n t e r m e d i a t e 0 i o n + i n t e r m e d i a t e — k ^ - — > p r o d u c t s + Me 2 AsH I f k 2 i s the r a t e c o n t r o l l i n g s t e p and k 2 « k ^ » then the r a t e law, assuming a steady s t a t e approximation f o r Me 2As , i s o u t l i n e d below, dU 1 = k 2 ( a c e t y l e n e ) (Me 2AsH) where k 2 = k ^ K K = k 1 / k _ 1 However, t h i s p r e - i o n i z a t i o n a d d i t i o n i s not l i k e l y to c o n t r i b u t e s i g n i f i c a n t l y to the o v e r a l l mechanism of the a d d i t i o n r e a c t i o n s i n c e the maximum r a t e o f exchange o f the l a b e l o f d i e t h y l a r s i n e with d i m e t h y l a r s e n i c d e u t e r i d e , 2 r e g a r d l e s s of mechanism, i s 5 x 10 times slower than the r a t e o f the a d d i t i o n r e a c t i o n . The r a t e o f exchange o f the l a b e l s i n equ a t i o n 2.14, whether by an i o n i c or f o u r - c e n t e r e d p r o c e s s , where K = k^/k_^ - 1, i s c o n s i d e r e d i n g r e a t e r d e t a i l i n Chapter 3. k l E t 2 A s H + Me 2AsD " Et,-,AsD + Me 2AsH (2.14) 45 The r a t e c o n s t a n t , ^ 5 x 10 5 f o r e q u a t i o n 2.14, should not be too d i s s i m i l i a r from t h a t o f a h o m o l y t i c exchange as o u t l i n e d i n e q u a t i o n s 2.15. k l Me 0As H + Me~AsH ' Me„As H + Me„AsH 2 2 -1 k 1 (2.15) Et^As H' + E t 2 A s H v Et^As'H + E t 2 A s H ' I f the exchange r a t e s i n e q u a t i o n s 2.15 were the same order of magnitude as the a d d i t i o n r a t e of the h y d r i d e s to h e x a f l u o r o b u t y n e - 2 , the k i n e t i c s o f the a r s i n e a d d i t i o n s would have been complex and not simple second o r d e r . To get simple second order a d d i t i o n k i n e t i c s , the r a t e s of 2 exchange i n e q u a t i o n 2.15 would have to be about 10 f a s t e r than the r a t e s of a d d i t i o n , whose r a t e s are about -3 -1 -1 10 l i t e r mole sec . T h i s would r e q u i r e the exchanges 4 i n e q u a t i o n 2.15 to be about 5 x 10^ f a s t e r . t h a n the exchange i n e q u a t i o n 2.14, which seems very u n l i k e l y . Consequently any mechanism i n v o l v i n g p r e - i o n i z a t i o n seems most improbable. The t h i r d p o s s i b l e mechanism i n v o l v i n g e l e c t r o p h i l i c a t t a c k by the a r s i n e seems u n l i k e l y on c h e m i c a l e v i d e n c e . H a s z e l d i n e (50) has shown t h a t e l e c t r o p h i l i c a d d i t i o n t o hexafluorobutyne-2 i s d i f f i c u l t and o f t e n needs a c a t a l y s t . The a t t a c k of e l e c t r o p h i l e s on h exafluorobutyne-2 can be expected t o be d i f f i c u l t as 4 6 t h i s a c e t y l e n e ' s t r i p l e bond i s e l e c t r o n d e f i c i e n t and cannot form such i n t e r m e d i a t e s as proposed by E i s c h and Kaska (30), f o r the a d d i t i o n of Group I I I h y d r i d e s t o a c e t y l e n e s . X-CEC-Y I A l R C o n s i d e r a b l e c h e m i c a l evidence supports the f o u r t h p o s s i b l e mechanism, n u c l e o p h i l i c a t t a c k by the a r s i n e . Thus hexafluorobutyne-2 r e a c t s e a s i l y with a l k o x i d e s and oth e r n u c l e o p h i l e s (50, 51) and the ease of n u c l e o p h i l i c attack- on hexafluorobutyne-2 i s g r e a t e r than 3 , 3 , 3 - t r i f l u o r o p r o p y n e , CFgC^CH ( 5 0 ) . I t has a l r e a d y been shown t h a t d i m e t h y l a r s i n e r e a c t s f a s t e r with the butyne than the propyne ( 1 ) . Another p i e c e o f evidence p o i n t i n g t o n u c l e o p h i l i c a t t a c k i s the r e s u l t t h a t as the groups R on the secondary a r s i n e R 2AsH become more e l e c t r o n e g a t i v e the r e a c t i o n becomes more d i f f i c u l t . Thus the r e a c t i o n r a t e d e c r e a s e s i n the order (1) Me 0AsH> (CrHc)(Me)AsH> 2 6 5 ( C F 3 ) 2 A s H » a s e r i e s which r e f l e c t s the d e c r e a s i n g a v a i l a b i l i t y o f the a r s e n i c l o n e p a i r f o r n u c l e o p h i l i c a t t a c k , because o f the e l e c t r o n withdrawing e f f e c t o f the groups a t t a c h e d t o i t ( 5 2 ) . 4 7 2.3.1.4 D e t a i l s of the N u c l e o p h i l l e A d d i t i o n s In many amine a d d i t i o n s t o a c e t y l e n e s the p o s t u l a t e d mechanism i n v o l v e s an i n t r a m o l e c u l a r proton t r a n s f e r . T h i s p o s s i b i l i t y (eq. 2.16) R 2AsH + CP3C=CCF,-CF CF U 3 \ / 3 —> C=C^ — R 2 A £ -H CF CF„ C=C X ' R 2As H (2.16) must be c o n s i d e r e d f o r the a r s i n e a d d i t i o n s , e s p e c i a l l y f o r the f o r m a t i o n of the c i s adduct. To check on t h i s , the c o m p e t i t i v e experiment o f e q u a t i o n 2.17 was c a r r i e d out on a p r e p a r a t i v e s c a l e so t h a t the c i s and t r a n s isomers of the p r o d u c t s c o u l d be s e p a r a t e d . E t 2 A s H Me 2AsD CF 3C3ZCF -H E t 2 A s C ( C F 3 ) = C ( D ) C F 3 H M e 2 A s C ( C F 3 ) = C ( D ) C F 3 (2.17) The r e s u l t s are l i s t e d i n T a b l e s IV and V. The hydrogen-deuterium exchange e q u i l i b r a t i o n o f the a r s i n e s i s slow enough t o be i g n o r e d . Moreover, t h e r e i s no exchange of the deuterium l a b e l on the p r o d u c t s , with another product, A3 or w i t h a r e a c t a n t , and there i s no i s o m e r i z a t i o n of the r e a c t i o n p r o d u c t s once they are formed, even i n the presence of u n r e a c t e d a r s i n e . T h i s l a s t r e s u l t i s most important i n the l i g h t o f the d i s c o v e r y t h a t p r e c u r s o r h y d r i d e s can i o s m e r i z e product iosmers as o u t l i n e d i n the i n t r o d u c t i o n . S i n c e no i s o m e r i z a t i o n o f the a r s i n e h e x a f l u o r o -butyne-2 adduct was found and the e q u i l i b r a t i o n of the a r s i n e p r e c u r s o r protons i s slow compared to the a d d i t i o n r a t e , the d i s t r i b u t i o n of the deuterium l a b e l i s s i g n i f i c a n t and can be used as an a i d to e s t a b l i s h a mechanism f o r the r e a c t i o n . Assuming there i s no exchange of deuterium and hydrogen b e f o r e the f o r m a t i o n of the product, a t a b l e can be drawn up showing the e x p e r i m e n t a l l y found deuterium percentages and those percentages which can be c a l c u l a t e d from v a r i o u s t h e o r e t i c a l mechanisms, to determine which mechanism f i t s the d i s t r i b u t i o n b e s t . I t should be noted t h a t the l a b e l s i n the product adducts r e p r e s e n t complete s t a t i s t i c a l s c r a m b l i n g of the deuterium. The f o l l o w i n g t a b l e o u t l i n e s p o s s i b l e mechanisms f o r the f o r m a t i o n o f the t r a n s adduct of d i m e t h y l and d i e t h y l a r s i n e s . A s i m i l a r t a b l e can be drawn up f o r the c i s adducts. The r e s u l t s show t h a t an i n t r a m o l e c u l a r process i s most u n l i k e l y f o r the f o r m a t i o n of both isomers. The i n t e g r a t i o n e r r o r i n the e s t i m a t i o n of the c i s product, which i s a t most 1 0 % o f the t o t a l p r o d u c t s , i s g r e a t Table IX Trans Product E %D expt Me 2As 77 E t 2 A s 70 Me 2As 77 E t 2 A s 70 Me 2As 77 E t 2 A s 70 Me 2As 77 Et~As 70 t . 1 Expt. 2 %D %D %D c a l c . expt. c a l c . 100 40 100 0 45 0 95-100 40 95-100 <5 45 <5 70 40 40 70 45 40 65-70 40 35-40 65-70 45 35-40 Mechanism I n t r a m o l e c u l a r p r o t o n t r a n s f e r ( c i s a d d i t i o n i s a l s o i n t r a ) I n t r a m o l e c u l a r p r o t o n t r a n s f e r ( c i s a d d i t i o n i s i n t e r ) I n t e r m o l e c u l a r p r o t o n t r a n s f e r ( c i s a d d i t i o n i s i n t e r ) I n t e r m o l e c u l a r p r o t o n t r a n s f e r ( c i s a d d i t i o n i s i n t r a ) 50 enough to warrent q u e s t i o n i n g the e x c l u s i o n of an i n t r a -m o l e c u l a r p r o c e s s i n the c i s f o r m a t i o n . A mechanism can be p o s t u l a t e d from i n f o r m a t i o n about the k i n e t i c s of a d d i t i o n and the d i s t r i b u t i o n and s t a b i l i t y o f the product isomers under v a r y i n g e x p e r i m e n t a l c o n d i t i o n s . The i n i t i a l s t e p i n the mechanism c o u l d be the f a s t a t t a c k of the h y d r i d e n u c l e o p h i l e ' s l o n e p a i r of e l e c t r o n s on the a c e t y l e n e t r i p l e bond, to form a charge-t r a n s f e r complex. T h i s s u g g e s t i o n has been put forward by Dubois and G a r n i e r (53) f o r the a d d i t i o n of bromine to o l e f i n s , and a s i m i l a r type of complex i s e n v i s i o n e d by Dvorko and Travchuk (54) i n the n u c l e o p h i l i c h y d r o c h l o r o -i n a t i o n o f a c e t y l e n e s . F u r t h e r evidence o f a charge-t r a n s f e r complex i s suggested by the f a c t t h a t C u l l e n and Dawson (44) found a s o l u t i o n o f t r i m e t h y l a m i n e and hexafluorobutyne-2 was p a l e b l u e . The concept o f a charge t r a n s f e r complex c o u l d h e l p to e x p l a i n a number of the s t e r e o s p e c i f i c r e s u l t s and w i l l be d i s c u s s e d i n more d e t a i l l a t e r . The second slow s t e p (the k i n e t i c a l l y measured one) c o u l d be e x c i t a t i o n of the c h a r g e - t r a n s f e r complex, which undergoes f a s t p r o t o n a t i o n , or the f o r m a t i o n o f an i n t e r m e d i a t e a n i o n which then becomes pro t o n a t e d ( e q u a t i o n 2.19). Such a mechanism i s c o n s i s t e n t with a l l the i n f o r m a t i o n a v a i l a b l e and i s shown i n the m e c h a n i s t i c scheme below. 51 (2.18) CT a b s t r a c t i o n Xs^ of > C=CHY prot o n R 2 A s / (2.19) The s t e r e o c h e m i s t r y of the products depends on many f a c t o r s , as w i l l be shown i n d e t a i l f o r the amine a d d i t i o n s d i s c u s s e d i n the next s e c t i o n . The means o f fo r m a t i o n of the major t r a n s product of d i m e t h y l a r s i n e and hex a f l u o r o b u t y n e - 2 , i n v o l v e s an i n t e r m o l e c u l a r p r o t o n t r a n s f e r i n the f i n a l step ( e q u a t i o n 2.19). I t may be p o s s i b l e a t extremely low c o n c e n t r a t i o n s t h a t a l l a d d i t i o n goes by a predominantly i n t r a m o l e c u l a r p r o c e s s , but at the d i f f e r e n t c o n c e n t r a t i o n s used i n the experj.ments (0.009 t o 1.5 molar) no d i f f e r e n c e s i n the isomer d i s t r i b u t i o n were found. The low a c t i v a t i o n energy (6.52 kcal/rnole) f o r the f o r m a t i o n o f the t r a n s (and p o s s i b l y c i s ) adduct f i t s i n w e l l with the i d e a o f the a r s e n i c atom e a s i l y donating i t s lone p a i r t o the ve r y e l e c t r o n d e f i c i e n t carbon-carbon bond. The a c t i v a t i o n entropy, which i s v e r y n e g a t i v e , c o u l d r u s t R 2AsH + XC=CY — X-C = C-Y t R p A s H 52 be c o n s i s t e n t w i t h a h i g h l y a s s o c i a t e d t r a n s i t i o n s t a t e . The l a t t e r would a c c o u n t f o r t h e l a r g e i n c r e a s e i n the r a t e o f a d d i t i o n f o u n d when methanol i s t h e s o l v e n t . 2.3.2 Amines 2.3.2.1 K i n e t i c s o f Amine A d d i t i o n s The r a t e d a t a f o r t h e a d d i t i o n o f diethylamine'. t o h e x a f l u o r o b u t y n e - 2 i n d i e t h y l e t h e r i s c o n s i s t e n t w i t h a second o r d e r r a t e l a w , f i r s t o r d e r i n each of the s t a r t i n g m a t e r i a l s . The .amine a d d i t i o n k i n e t i c s a r e s i m i l a r t o t h e a r s i n e s , i n t h a t t h e y f o l l o w t h e same r a t e law. The a b s o l u t e v a l u e o f the r a t e c o n s t a n t \^ i s g r e a t e r f o r t h e amines and i n c r e a s e s i n p o l a r s o l v e n t s . The amine and a r s i n e r e s u l t s t o g e t h e r w i t h t h o s e on t h e k i n e t i c s o f a l k o x i d e ( 5 , 6, 7) and t h i o l (4) a d d i t i o n s t o a c e t y l e n e s , s u g gest t h e f o l l o w i n g r a t e c o n t r o l l i n g s t e p ; ( e q . 2.20, 2.21a; Nu = n u c l e o p h i l e ) slow Y x 6 Nu + YC = CX > C-C-X (2.20) Nu slow Yv e or R~MH * YC=CX > 9 ^OC-X (2.21a) * R2MH A d e t a i l e d d i s c u s s i o n o f the r e l a t i v e r a t e s w i l l be l e f t u n t i l t h e t h i r d s e c t i o n o f t h e d i s c u s s i o n . 53 2.3.2.2 P r o d u c t Isomer D i s t r i b u t i o n The a d d i t i o n o f d i e t h y l a m i n e t o h e x a f l u o r o b u t y n e - 2 g i v e s a v a r y i n g d i s t r i b u t i o n o f isomer p r o d u c t s , depending on t h e s o l v e n t used and t h e c o n c e n t r a t i o n o f r e a c t a n t s . I n methanol s o l v e n t 1 0 0 % t r a n s p r o d u c t i s o b t a i n e d , w h i l e in. d i e t h y l e t h e r s o l v e n t , d i f f e r e n t m i x t u r e s o f t h e i s o m e r s can be o b t a i n e d by c h a n g i n g t h e c o n c e n t r a t i o n s o f t h e r e a c t a n t s . The d i s t r i b u t i o n o f t h e i s o m e r s from t h e a d d i t i o n o f d i e t h y l a m i n e t o h e x a f l u o r o b u t y n e - 2 , agree q u i t e w e l l w i t h t h e r e s u l t s found f o r n o n - t e r m i n a l , n o n - c a r b o x y l i c s u b s t i t u t e d a c e t y l e n e s . The t r a n s amine isomer i n t h i s i n v e s t i g a t i o n , was s t a b l e f o r r e l a t i v e l y l o n g p e r i o d s o f t i m e , neat o r i n methanol s o l v e n t , when s e a l e d i n an a i r f r e e n.m.r. t u b e . C u l l e n e t a l ( 1 ) found t h a t t h e t r a n s d i m e t h y l a m i n e - h e x a f l u o r o b u t y n e - 2 adduct i o s m e r i z e d t o a m i x t u r e o f t h e c i s and t r a n s i s o m e r s upon exposure t o a i r , and c o n s e q u e n t l y a l l e x p e r i m e n t s were done i n s e a l e d n.m.r. t u b e s ( see e x p e r i m e n t a l s e c t i o n ) . The s t a b i l i t y o f t h e t r a n s p r o d u c t under t h e c o n d i t i o n s m e ntioned above, suggest t h a t a t l e a s t i n methanol i t i s t h e k i n e t i c a l l y c o n t r o l l e d p r o d u c t . Care must be t a k e n though, because as n o t e d by S t i r l i n g e t a l ( 2 4 ) , when one isomer was d i s s o l v e d i n a s o l v e n t , i t i s o m e r i z e d t o a m i x t u r e o f c i s and t r a n s p r o d u c t s , where the r e l a t i v e abundance o f t h e i s o m e r s 54 changed i n d i f f e r e n t s o l v e n t s . The l a t t e r o b s e r v a t i o n may w e l l e x p l a i n why the d i s t r i b u t i o n o f c i s and t r a n s amine adduct remained c o n s t a n t when they were heoted i n d i e t h y l a m i n e s o l v e n t , though the t o t a l amount of adduct g r a d u a l l y d e c r e a s e d . T a b l e X c o n t a i n s data f o r some of the more p e r t i n e n t non c a t a l y z e d a d d i t i o n s of n u c l e o p h i l e s to a c e t y l e n e s t h a t r e a c t as o u t l i n e d i n e q u a t i o n 2.21b. X. H Xv Y \ / \ / RR'NH + XCECY > O C s + C=C( ( t r a n s ) ( c i s ) (2.21b) The r e s u l t s of T a b l e X, and those o f the d i e t h y l a m i n e - h e x a f l u o r o b u t y n e - 2 adducts i n d i c a t e t h a t a number of* p o s s i b l e ' c o n c l u s i o n s can'be made r e g a r d i n g the e f f e c t o f the r e a c t i o n v a r i a b l e s , such as c o n c e n t r a t i o n , s u b s t i t u e n t s e f f e c t s , and s o l v e n t e f f e c t s , on the s t e r e o c h e m i s t r y of amine a d d i t i o n s to a c e t y l e n e s . 2.3.2.2.1 C o n c e n t r a t i o n of R eactants t The r a t i o of c i s to t r a n s isomers i n the p r o d u c t s of an amine a d d i t i o n i s dependent on the c o n c e n t r a t i o n of the r e a c t a n t s . Thus V e s s i e r e (#11, 12) found t h a t when he i n c r e a s e d the c o n c e n t r a t i o n o f a z i r i d i n e t o butyne-2 Table X R R 1 X Y Cone. I Cone.II (m/1) (m/1) 1 n-Bu H Me C 0 2 E t 0.05 0.05 2 c g H 1 1 H M e C 0 2 E t , 0.05 0.05 3 n-Bu H Me CN " 4 ^ " l l 5 E t E t Me C 0 2 E t " '« 6 " " " CN " " 7 ( C H 2 ) 2 Me C 0 2 E t " " 8 ( C H 2 ) 2 " C N 9 ( C H 2 * 2 " C 0 2 E t 10 " Me " " " 11 ( C H 2 } 2 " C N 1 1 12 . . . . ! 4 13 ( C H 2 ) 2 H C ° 2 M e ° » 5 ° * 5 1 ^  it H it II M 16 C 6 H n H H C0 2Me " " 17 C.H,, H C0 oMe CO_Me 6 11 2 2 T(°C) S o l v e n t 3 Product A Product B Ref. %t %c %t %c 20 EtOH 50 50 88 12 33 20 EtOH 100 0 33 50 50 2 98 " 0 100 " 8 92 " 94 6 0 100 40 50 40 60 95 5 9 3 7 B 14 86 " z DMF 6 94 " B 75 25 z 6 B 14 86 14 66 36 z EtOH 47 5 3 4 7 5 3 MeSH 76 24 76 24 B 25 75 88 12 34 z B 30 70 0 100 z 18 E t E t C0 2Me CC 2Me I I i t H d i o x a n e 7 93 36 19 If I I M I I I I •I B z 11 89 II 20 i t I I II n n I I H Me OH 62 38 II 21 t-Bu H H C o 2 E t 5.0 5.0 35 EtOH 65 35 68 32 37 22 I I I I n II II H It B z 26 74 67 33 1! 23 E t E t H C 0 2 E t It I I II EtOH 14 86 0 100 II 24 25 E t I I E t I I H II S0 2R II II II M I I I i -25 B z H 0 80 100 20 0 0 100 100 It II 26 n-Fr H H S0 2R II I I 25 B z 80 20 0 100 II a B i s ; z benzene s o l v e n t , DMF i s d ime thy1formamide P r o d u c t A i s the p r o d u c t o b s e r v e d d u r i n g the r e a c t i o n by n.m.r. i n the c a s e o f r e f . 34 and 36 i t was i n i t i a l l y o b t a i n e d . P r o d u c t B i s the p r o d u c t r e c o v e r e d from the r e a c t i o n , u s u a l l y found on workup. 01 57 n i t r i l e , i n benzene s o l u t i o n , the percentage of t r a n s product i n c r e a s e d . W i n t e r f e l d t et a l (20) found 100% c i s product when amines were s l o w l y added to a c e t y l e n e . Huisgen and Giese (35) found 100% c i s p r o d u c t s a t the low c o n c e n t r a t i o n s used i n t h e i r k i n e t i c s t u d i e s of amines a c e t y l e n e s , whereas both isomers were p r e s e n t when h i g h e r c o n c e n t r a t i o n s were used. So a t low c o n c e n t r a t i o n s of h y d r i d e these r e s u l t s i n d i c a t e the main mode of proton a d d i t i o n i s the i n t r a m o l e c u l a r p r o c e s s , to g i v e c i s p r o d u c t . In the p r e s e n t i n v e s t i g a t i o n i t was found q u a l i t a t i v e l y t h a t the a d d i t i o n o f d i e t h y l a m i n e to hexafluorobutyne-2 y i e l d s d i f f e r e n t " d i s t r i b u t i o n s of p r o d u c t s , when the c o n c e n t r a t i o n of the r e a c t a n t s and the amount of s o l v e n t i s v a r i e d . T h i s t r e n d corresponds with those d e s c r i b e d above. 2.3.2.2.2 S o l v e n t The source o f p r o t o n i n the f i n a l f a s t step (eq. 2.19) i n the f o r m a t i o n of product i s from a competing i n t e r n a l and e x t e r n a l p r o t o n source (#13-15 and 18-22). In a p r o t i c medium th e r e i s an i n c r e a s e i n the amount of t r a n s adduct formed. The d i e t h y l a m i n e - h e x a f l u o r o b u t y n e - 2 adduct formed 100% t r a n s i n methanol s o l v e n t , whereas the percentage of the t r a n s isomer was much lower i n d i e t h y l e t h e r s o l v e n t . T h i s e f f e c t i s s i m i l i a r t o t h a t observed by o t h e r i n v e s t i g a t o r s such as Vessie\re e t a l (33) who found t h a t the r e a c t i o n o f d i e t h y l a m i n e with butyne-2 58 n i t r i l e i n e t h a n o l s o l v e n t , y i e l d s almost 100% t r a n s p r o d u c t . At low c o n c e n t r a t i o n s i n p r o t i c s o l v e n t , i t i s to be expected t h a t the a d d i t i o n product would be 100% t r a n s , as t h e r e i s a ready supply of e x t e r n a l p r o t o n s . Undoubtedly, the s o l v e n t i s i n v o l v e d i n the t r a n s i t i o n s t a t e and thus e x t e r n a l p r o t o n a t i o n i s s t r a i g h t forward. However, comments on t h i s a s p e c t are d i f f i c u l t to make with c e r t a i n t y . 2.3.2.2.3 S t e r i c I n f l u e n c e s No n o n c a t a l y z e d s t u d i e s on the a f f e c t o f s t e r i c i n f l u e n c e s on t h e a d d i t i o n r e a c t i o n have been c a r r i e d out. In base c a t a l y z e d a d d i t i o n , Truce et a l (16, 49) attempted, without s u c c e s s , to v i o l a t e h i s p o s t u l a t e d t r a n s a d d i t i o n r u l e with s t e r i c a l l y h i n d e r e d t h i o l s , and r e c e n t l y Landesberg and K e l l n e r (27) have suggested thab s t e r i c i n f l u e n c e s o c c u r r i n g i n the f a s t p r o t o n e x t r a c t i o n step, r a t h e r than the i n i t i a l r a t e c o n t r o l l i n g s t e p , c o n t r o l t h e i r p r o d u c t c o n f i g u r a t i o n . 2.3.2.2.4 I n t e r n a l Hydrogen Bonding T h i s i n f l u e n c e may have a l a r g e i n f l u e n c e on both the mode o f a d d i t i o n and product s t a b i l i t y . I f we c o n s i d e r the complex formed i n e q u a t i o n 2.18, t h e r e c o u l d be a p r e f e r r e d o r i e n t a t i o n o f the N-H bond, when hydrogen bonding t o a group (X^Y) on the a c e t y l e n e i s p o s s i b l e . 59 X-C='C-C-OF.t II 0 / R-N-H / R Complex When the c h a r g e - t r a n s f e r complex goes to the e x c i t e d s t a t e , t h e r e may be a g r e a t e r p r o b a b i l i t y o f c i s a d d i t i o n t o the above complex i f f o r m a t i o n of an i n t e r m e d i a t e c a r b a n i o n w i l l o r i e n t a t e the N-H bond s t e r e o s p e c i f i c a l l y to the t r i p l e carbon bond (Table X ) . Thus c i s a d d i t i o n c o u l d be p r e f e r r e d ( e x c e p t i n g s o l v e n t e f f e c t s , e t c . ) as seen i n e q u a t i o n 2.22. Truce and Brady (37) and Cram e t a l (55), suggested t h a t the s u l f o n y l group i n eq u a t i o n 2.23, does not have to be l i n e a r t o p r o v i d e s t a b i l i t y , whereas the c a r b o x y l group i n e q u a t i o n 2.22, i n p r o v i d i n g s t a b i l i t y by resonance, must be l i n e a r . The N-H bond becomes a s s o c i a t e d to the s u l f o n y l oxygen atoms and t r a n s a d d i t i o n becomes p r e f e r r e d , as shown i n eq u a t i o n 2.2 3 (see Table X, #21-26). / OEt X - C = C - C / II x -> c = c R-N»«"H C - OEt II X^ C 0 2 E t R_N / \ ( c i s ) H 0 X - c — c - s * II A\ . 0 / XH-- R R R R' \ 0 ^ C = C. — 9/ \ N .S = 0 '| NH...C^k R (2.22) R 2N^ \o2R ( t r a n s ) (2.23) 60 2.3.3 Comparisons In the p r e v i o u s s e c t i o n s o f t h e d i s c u s s i o n , i t has been suggested t h a t the h y d r i d e a d d i t i o n s t o hex a f l u o r o b u t y n e - 2 , take p l a c e i n a number of s t e p s . I t seems p o s s i b l e t h a t two of these steps can be s t u d i e d . One s t e p i s the r a t e c o n t r o l l i n g s t e p , f o r which k i n e t i c s t u d i e s can g i v e i n f o r m a t i o n . A second s t e p , which seems to l e n d i t s e l f t o study, i s the one i n v o l v e d i n the p r o t o n a t i o n o f the i n t e r m e d i a t e which determines the adduct s t e r e o c h e m i s t r y . The a d d i t i o n s o f d i e t h y l a m i n e , d i m e t h y l a r s i n e , and d i e t h y l a r s i n e , to hexafluorobutyne-2 are v e r y s i m i l a r i n t h e i r k i n e t i c s , but ve r y d i f f e r e n t i n the d i s t r i b u t i o n o f t h e i r isomer p r o d u c t s . The k i n e t i c s and r a t e of a d d i t i o n o f d i e t h y l a m i n e and the a r s i n e s w i l l be compared wit h one another, and with o t h e r p e r t i n e n t r a t e d a t a . The d i s t r i b u t i o n o f the isomer a d d i t i o n products v / i l l be d i s c u s s e d and p o s s i b l e e x p l a n a t i o n s w i l l be noted to r a t i o n a l i z e the d i f f e r e n c e s . 2.3.3.1 K i n e t i c and Rate comparisons The k i n e t i c s of t h e a d d i t i o n o f d i e t h y l a m i n e , d i m e t h y l a r s i n e , and d i e t h y l a r s i n e t o hexafluorobutyne-2 have been shown t o be second order o v e r a l l , f i r s t o r d e r i n h y d r i d e and a c e t y l e n e . The r a t e c o n s t a n t s f o r these 61 and s i m i l a r r e a c t i o n s which have the same r a t e law (eq. 2.24) are o u t l i n e d i n Tab l e XI. RR'MH + XCECY (or R'• SnH) In d i e t h y l e t h e r s o l v e n t , the d i e t h y l a m i n e 2 a d d i t i o n t o hexafluorobutyne-2 i s about 1.5 x 10 times f a s t e r than the a r s i n e a d d i t i o n s . Both h y d r i d e r e a c t i o n s have an i n c r e a s e d r a t e i n methanol s o l v e n t . The r a t e of a d d i t i o n of d i e t h y l a m i n e t o hexafluorobutyne-2 i s ap p r o x i m a t e l y the same as those of the oth e r amines to other a c t i v a t e d a c e t y l e n e s (Table X I ) , though a c l o s e comparison i s not p o s s i b l e due t o the d i f f e r e n c e s i n the a c e t y l e n e s and s o l v e n t s used. The examples c i t e d i n Table XI demonstrate some i n t e r e s t i n g r e s u l t s which l i n k the r a t e of r e a c t i o n to the e l e c t r o n withdrawing a b i l i t y o f the s u b s t i t u e n t s on the a c e t y l e n e . As the number of e l e c t r o n e g a t i v e groups on the a c e t y l e n e i s i n c r e a s e d from one to two, the r e a c t i o n r a t e 2 4 i n c r e a s e s about 10 f o r the amine a d d i t i o n s (35), and 10 f o r the t i n h y d r i d e a d d i t i o n s ( 38). S i m i l a r s u b s t i t u e n t e f f e c t s have been noted by C u l l e n e t a l who found c n l o r c -d i m e t h y l a r s i n e added t o hexafluorobutyne-2 (56) but not to butyne-2 (57), and H a z e l d i n e (50) who showed t h a t n u c l e o p h i l i c \ / X \ —Vc=c\ RR 'M Y / C=C (2.24) RR' M H (or R«' Sn) (or R''^SnH) 62 Table X I h y d r i d e X Y T(°C) S o l v e n t k,; ( 1 in~^ sec"' Me 2AsH C F 3 C F 3 20 E t ? 0 2 x l O ~ 3 * Me 2AsH C F 3 C F 3 20 MeOH 4 x l 0 _ i * E t ? N H C F ? C F 3 15-25 s t 2 o 1.16+.04 * E t 2 N H CF C F 3 20+1 MeOH a * ( C H 2 ) 2 N H II CC>2Me 37 MeCN 0.024 35 ( C H 2 ) 2 N H CO^Me CO ?Me 3 7 MeCN 5.67 3 5 p i p e r d i n e H CO^Me 37 MeCN 2 ,25 35 p i p e r d i n e C0 2Me C0 2Me 37 MeCN 445.0 35 c y c l o h e x y 1 amine - H CC 2Me 37 MeCN 0.02 3 5 II C0 2Me CO-Me 37 MeCN 17.7 3 5 Me 3SnH C0 2Me H 20 n-BuCN 3 . 0 x l 0 " 5 38 Me^SnH CN II 20 n-BuCN l . l O x l O " 4 38 Me 3SnH C 0 2 E t C 0 2 E t 20 n-BuCN 0„92xl0~ 2 38 Me^SnH CN CN 20 n-DuCN 1.5X10" 1 38 E t 3 S n H CN II 20 n-BuCN 5 . 1 x l 0 ~ 4 38 * t h i s work a too f a s t t o measure a d d i t i o n to hexafluorobutyne-2 was e a s i e r than to 1,1,1-t r i f l u o r o p r o p y n e . Other examples a r i s e i n d i c a t i n g a s i m i l a r t r e n d ( 5 7 ) . Thus n u c l e o p h i l e s r e a c t f a s t e r and e a s i e r w i t h a c e t y l e n e s whose t r i p l e bond have been a c t i v a t e d by e l e c t r o n e g a t i v e s u b s t i t u e n t s . C u l l e n et a l (1) have a l s o s t u d i e d the e f f e c t of e l e c t r o n e g a t i v e s u b s t i t u e n t s on the p r e c u s s o r h y d r i d e s and found the ease of a d d i t i o n of a r s e n i c h y d r i d e s to hexafluorobutyne-2 d e c r e a s e s as the groups on the a r s i n e become more e l e c t r o -n e g a t i v e . Thus the r a t e and ease o f a d d i t i o n i s f i r m l y l i n k e d with the e l e c t r o n withdrawing a b i l i t y of the s u b s t i t u e n t s on. the r e a c t a n t a c e t y l e n e and h y d r i d e . S o l v e n t a f f e c t s the h y d r i d e a d d i t i o n r a t e s as demonstrated i n T a b l e X I . The a d d i t i o n r a t e of a r s i n e s and d i e t h y l a m i n e i n c r e a s e s i n methanol, compared with d i e t h y l e t h e r as s o l v e n t . A s i m i l a r s o l v e n t e f f e c t was observed i n the n u c l e o p h i l i c t i n h y d r i d e a d d i t i o n s s t u d i e d by Leusink (38), and i n amine a d d i t i o n s by Truce ( 3 7 ) . Huisgen (35), i n a more d e t a i l e d study, found t h a t there was a l i n e a r c o r r e l a t i o n between the r a t e c o n s t a n t s f o r an amine with a p a r t i c u l a r a c e t y l e n e ( l n k^) and the Brownstein s o l v e n t parameter 3 (58). The s o l v e n t and s u b s t i t u e n t e f f e c t s on the r e a c t i v i t y of the h y d r i d e a d d i t i o n s to an a c e t y l e n e , seem most c o n s i s t e n t with a n u c l e o p h i l i c a t t a c k of the h y d r i d e p r e c u r s o r on the e l e c t r o n d e f i c i e n t a c e t y l e n e bond. The complex p o s t u l a t e d i n t h i s t h e s i s as forming b e f o r e the r a t e c o n t r o l l i n g s t e p i s a l s o c o n s i s t e n t with these r e s u l t s (eq. 2.25). R2MH + XCECY f a s t X-CEC-Y e x c i t e d complex Complex + R2MH - k ^ X-CEC-Y R ^ H Complex e x c i t e d complex R 2M / H (2.25) (2.26) X v H \ / R 2M / C-C\ (2.27) I t has been suggested i n e l e c t r o p h i l i c a d d i t i o n t h a t t h i r d o r d e r k i n e t i c s may be important where k 0 / v k 2 , or when t h e r e i s a c o n s e c u t i v e r e a c t i o n o f two h y d r i d e molecules w i t h the a c e t y l e n e ( 5 9 ) . T h i s has been e x p e r i m e n t a l l y shown f o r e l e c t r o p h i l i c a d d i t i o n s t o a c e t y l e n e s ( 60). However, under the ex p e r i m e n t a l c o n d i t i o n s used f o r the n u c l e o p h i l i c a d d i t i o n s i n t h i s t h e s i s , where r e a c t a n t c o n c e n t r a t i o n s v a r i e d from 0.009 t o 1.5 moles/1, o n l y second order k i n e t i c s were ob s e r v e d . 65 2.3.3.2 The S t e r e o c h e m i s t r y of A d d i t i o n The s t e r e o c h e m i s t r y of the a d d i t i o n of h y d r i d e s to a c e t y l e n e s seems to be d i f f e r e n t f o r d i e t h y l a m i n e than f o r secondary a r s i n e s . Under a l l experimental c o n d i t i o n s attempted, the d i m e t h y l a r s i n e a d d i t i o n t o hexafluorobutyne-2 gave 90% t r a n s product by a k i n e t i c a l l y c o n t r o l l e d mechanism. In methanol s o l v e n t t h i s reached 100% t r a n s . On the o t h e r hand, the d i e t h y l a m i n e a d d i t i o n done neat or i n d i e t h y l e t h e r , gave m i x t u r e s o f the c i s and t r a n s isomers, w h i l e the a d d i t i o n done i n methanol gave 100% t r a n s isomer. I t has been noted by many o t h e r authors t h a t amines can add c i s o r t r a n s , depending on the c o n d i t i o n o f the r e a c t i o n , a c e t y l e n e used, e t c . In almost every c a s e , however, the isomer s t a b i l i t i e s were not s t u d i e d , so i t i s d i f f i c u l t t o draw many v a l i d c o n c l u s i o n s , from these s t u d i e s . In c a r e f u l l y s t u d i e d c a s e s , the amines g e n e r a l l y add c i s through a p o s t u l a t e d i n t r a m o l e c u l a r p r o c e s s (19). However, i n the case of the d i e t h y l a m i n e a d d i t i o n t o h e x a f l u o r o b u t y n e - 2 , where m i x t u r e s o f p r o d u c t s were o b t a i n e d , i f i t i s assumed t h a t the p r o d u c t s are k i n e t i c a l l y c o n t r o l l e d , and not a e q u i l i b r i u m m i x t u r e c h a r a c t e r i s t i c o f the s o l v e n t medium as found by S t i r l i n g e t a l (24), then i t seems p o s s i b l e the r e a s o n f o r the d i f f e r e n c e i n the a d d i t i o n s t e r e o -c h e m i s t r y l i e s i n the n a t u r e o f the e x c i t e d complex (eq. 2.26). I t has been suggested (5^9) t h a t i n e l e c t r o p h i l i c a d d i t i o n s t o a c e t y l e n e s , t h a t the s t e r e o c h e m i s t r y i s governed by 6 6 i n t e r m e d i a t e s such as those below: X \ c=c -/ (I) ( I I ) - c = c • X ( I I I ) (I) c o u l d g i v e a mixture o f c i s and t r a n s products upon p r o t o n a t i o n , w h i l e ( I I ) and ( I I I ) would g i v e e n t i r e l y t r a n s p r o d u c t s with the a p p r o p r i a t e a c e t y l e n e s and s o l v e n t . In the case o f the n u c l e o p h i l e s being s t u d i e d , i t c o u l d then be suggested t h a t the d i s t r i b u t i o n o f the a d d i t i o n isomers, c o r r esponds w i t h the a b i l i t y o f the r e a c t a n t s t o form such i n t e r m e d i a t e s . Some of these p o s s i b i l i t i e s are o u t l i n e d below. R2MH + XC=CY -> X-C = C-Y M R ' H (2.28) R X-C==C-Y R ' .L H \ e c=c -x K Ry2 \H -> t r a n s c i s and t r a n s (2.29) (2.30) 67 The a r s i n e a d d i t i o n s c o u l d go predominantly through e q u a t i o n 2.29 to g i v e n e a r l y a l l t r a n s product, w h i l e the amine a d d i t i o n s may r e a c t e i t h e r way, depending on the amine and a c e t y l e n e . The d i f f e r e n c e i n the s t a b i l i t i e s of the a r s i n e and amine i n t e r m e d i a t e s may l i e i n the ex t e n t o f the o v e r -l a p o f the h y d r i d e and the a c e t y l e n e o r b i t a l s : the a r s i n e p r e f e r e n t i a l l y forms the c y c l i c i n t e r m e d i a t e , r a t h e r than the p o s s i b l e open amine i n t e r m e d i a t e (eq. 2.30). The p o s s i b i l i t y t h a t d i e t h y l a m i n e adds t r a n s to hexafluorobutyne-2 and then i s o m e r i z e s t o the c i s and t r a n s adducts cannot be d i s c o u n t e d c o m p l e t e l y . Truce and Brady (37) d i s c o v e r e d amines add t r a n s t o s u l f o n e a c e t y l e n e s when observed by low temperature n.m.r., but t h e r e was o n l y c i s product i d e n t i f i e d and observed a t room temperature A l s o t o be c o n s i d e r e d , i s S t i r l i n g | s f i n d i n g (24), t h a t an • isomer d i s s o l v e d i n d i f f e r e n t s o l v e n t s o f t e n forms a mix t u r e o f c i s and t r a n s isomers, with a d i f f e r e n t d i s t r i b u t i o n f o r each s o l v e n t . 2.3.4 S t e r e o s p e c i f i c i t y i n N u c l e o p h i l i c A d d i t i o n s ;  A Comment From the f o r e g o i n g s e c t i o n s , i t has been shown t h a t the r a t e s and the s t e r e o c h e m i s t r y o f the a d d i t i o n of n u c l e o p h i l i c h y d r i d e s t o a c e t y l e n e s , i s i n f l u e n c e d by a number o f f a c t o r s , such as the r e a c t a n t s used and the c o n d i t i o n s the r e a c t i o n s a re done under. In these a d d i t i o n s , 6 8 the s t a b i l i t y o f the products i s a most important f a c t o r , and must be c a r e f u l l y s t u d i e d . Often a k i n e t i c a l l y c o n t r o l l e d isomer i s not the thermodynamically s t a b l e isomer, and i s o m e r i z a t i o n o c c u r s a t v a r y i n g r a t e s , f r e q u e n t l y c a t a l y z e d by a c i d s , bases or p r e c u r s o r h y d r i d e s . A f u r t h e r c o m p l i c a t i o n was observed by S t i r l i n g e t a l (24) who found t h a t when a p a r t i c u l a r isomer was d i s s o l v e d i n a s o l v e n t , o f t e n a mixture of t h e isomers r e s u l t e d , where the r a t i o o f the c i s and t r a n s p r o d u c t s v a r i e d with the s o l v e n t . Thus statements about n u c l e o p h i l i c a d d i t i o n mechanisms, based on the study of a product c o n f i g u r a t i o n a l o n e , w i l l o f t e n be i n c o r r e c t , and are c e r t a i n l y open to q u e s t i o n . The s t r o n g base c a t a l y z e d a d d i t i o n s of n u c l e o -p h i l e s have corresponded q u i t e w e l l w i t h the r e v i s e d " t r a n s " a d d i t i o n ru.le p o s t u l a t e d by Truce e t a l (9, 12). However V e s s i e r e and Theron (32) have r e c e n t l y shown t h e i r isomer p r o d u c t s can v a r y d r a s t i c a l l y with d i f f e r e n c e s i n c o n c e n t r a t i o n of the base c a t a l y s t , w h i l e Landesberg and K e l l e r (27), Eaton and Stubbs (26), and Whiting and Jones (11) have i n d i c a t e d p r o b a b l e base c a t a l y z e d c i s a d d i t i o n . Whether or not a l l these c a s e s are a c t u a l l y c i s a d d i t i o n , but r a t h e r f a s t i s o m e r i z a t i o n t o the thermodynamically f a v o u r e d c i s product, caused by base c a t a l y s i s , awaits f u r t h e r work. 6 9 In the case o f the n o n c a t a l y z e d n u c l e o p h i l i c h y d r i d e a d d i t i o n , t h e r e seems t o be no s t e r e o s p e c i f i c a d d i t i o n r u l e . U n f o r t u n a t e l y , i n many i n s t a n c e s , c i s a d d i t i o n o f amines i s p o s t u l a t e d from the c o n f i g u r a t i o n of the i s o l a t e d p r o d u c t . Recent s t u d i e s u s i n g n.m.r. te c h n i q u e s have i n d i c a t e d t r a n s amine a d d i t i o n s at some time d u r i n g the a d d i t i o n , but with e v e n t u a l i s o l a t i o n of the c i s isomer, or m i x t u r e s of both isomers, from the r e a c t i o n m i x t u r e . I t i s p o s s i b l e i n many cases t h a t i s o m e r i z a t i o n o f the k i n e t i c a l l y formed product i s too f a s t t o observe a t room temperature. The low temperature n.m.r, s t u d i e s t h a t c o u l d be used t o study many o f these mechanisms i n d e t a i l , have o n l y been conducted f o r a few amines by Truce and Brady (37), and f o r d i m e t h y l - and d i e t h y l a r s i n e i n t h i s i n v e s t i g a t i o n . Truce found the amines added t r a n s a t low temperatures, and then i s o m e r i z e d t o the c i s p r o d u c t , whereas a t room temperature o n l y f o r m a t i o n o f the c i s was observed by n.m.r. The a r s i n e s s t u d i e d i n t h i s i n v e s t i g a t i o n , added t r a n s a t room temperature o r a t -30°, t o g i v e m a i n l y the k i n e t i c a l l y and thermodynamically c o n t r o l l e d t r a n s product, but a l s o the k i n e t i c a l l y c o n t r o l l e d c i s p r o d u c t . I t seems p o s s i b l e then t h a t the major k i n e t i c a l l y c o n t r o l l e d mode o f a d d i t i o n f o r a l l Group V h y d r i d e s c o u l d be through t r a n s a d d i t i o n as o u t l i n e d i n e q u a t i o n 2.29. However, d i f f e r e n t r e a c t i o n c o n d i t i o n s , and s u b s t i t u t i o n o f c a r b o x y l i c groups on the a c e t y l e n e and the h y d r i d e , may l e a d to k i n e t i c a l l y c o n t r o l l e d c i s a d d i t i o n s , such as those found by Huisgen e t a l (21, 34, 35, 36). Thus the p o s t u l a t i o n o f a s t e r e o s e l e c t i v e r u l e f o r the n o n c a t a l y z e d a d d i t i o n of n u c l e o p h i l i c h y d r i d e s t o a c e t y l e n e s does not seem p o s s i b l e CHAPTER 3 3.1 I n t r o d u c t i o n The r a t e o f exchange o f secondary a r s i n e protons, as i n e q u a t i o n 3.1, was important i n d e t e r m i n i n g the mechanism of the a d d i t i o n o f secondary a r s i n e s t o hex a f l u o r o b u t y n e - 2 , as d i s c u s s e d i n Chapter 2. Me 0AsD + E t 0 A s H , i f f Me„AsH + Et~AsD (3.1) Proton t r a n s f e r r e a c t i o n s such as e q u a t i o n 3.1, have been s t u d i e d u s i n g such t e c h n i q u e s (61) as d e n s i t y measurements, i n f r a r e d s p e c t r a , r e f r a c t i v e index, thermal c o n d u c t i v i t y and mass s p e c t r a of samples c o n v e r t e d t o hydrogen and ethane. S p e c i a l i z e d f a s t r e a c t i o n t e c h n i q u e s (62), such as temperature-jump, pressure-jump, e l e c t r i c -impulse and p u l s e n.m.r. s p e c t r o s c o p y , have a l s o been used t o study some o f the many f a s t p r o t o n t r a n s f e r r e a c t i o n s . P r e l i m i n a r y work (63) on the r e a c t i o n o f e q u a t i o n 3.1 i n d i c a t e d the exchange was slow. The methyl s p l i t t i n g s (see F i g u r e 4) of d i m e t h y l a r s i n e and d i m e t h y l a r s i n e d e u t e r i d e i n t h e i r "^H n.m.r. s p e c t r a were separated w e l l enough t o be i n d i v i d u a l l y measured, and the exchange slow enough so i n t e g r a t i o n o f the r e s p e c t i v e h y d r i d e and Leaf 72 omitted i n page numbering. 73 d e u t e r i d e peaks was p o s s i b l e . Thus, u n l i k e many of the co m p l i c a t e d a f o r e mentioned t e c h n i q u e s , n e c e s s a r y to study p r o t o n t r a n s f e r r e a c t i o n s , simple n.m.r. i n t e g r a t i o n c o u l d be used t o f o l l o w the r e a c t i o n o f e q u a t i o n 3.1. In e a r l y work on e q u i l i b r a t i o n o f h y d r i d e s , most of the p r o t o n t r a n s f e r r e a c t i o n s were too f a s t to study k i n e t i c a l l y (64, 65, 66), so t h a t o n l y the e q u i l i b r i u m c o n s t a n t s c o u l d be determined, such as f o r the exchange between a r s i n e (67) or phosphine (68) gas and water. The e q u i l i b r i u m c o n s t a n t s t h a t were e x p e r i m e n t a l l y found, c o r r e l a t e d w e l l with those t h e o r e t i c a l l y d e r i v e d from s p e c t r o s c o p i c d a t a ( 6 9 ) . R e c e n t l y t e c h n i q u e s have been p e r f e c t e d f o r s t u d y i n g these f a s t p r o t o n t r a n s f e r r e a c t i o n s , so d e t e r m i n a t i o n o f t h e i r k i n e t i c s and r a t e s (62) i s p o s s i b l e . A number of r e a c t i o n s w i t h exchanges s i m i l a r t o e q u a t i o n 3.1 have been s u c c e s s f u l l y s t u d i e d , such as the exchange o f o - n i t r o p h e n o l w i t h v a r i o u s amines by Jannakoudakis and Moumtzis (70), i s o b u t y r i c a c i d with i s o -b u t y lmercaptan by Denisov and S m o l y a n s k i i (71), and t r i e t h y l t i n d e u t e r i d e w i t h t r i - i s o b u t y l t i n h y d r i d e by Newmann and Sommer (72) . These authors a l l suggested a f o u r - c e n t e r e d mechanism f o r the p r o t o n t r a n s f e r r e a c t i o n , s i m i l a r t o the one proposed by Gold and S a t c h e l l (61), f o r the exchange between d e u t e r a t e d ethylamine and n-heptylamine. 74 The n o n - i o n i c proton t r a n s f e r between a l c o h o l s and water (64, 65) i n e q u a t i o n 3.2, has been s t u d i e d by Meiboom e t a l (73, 74) u s i n g f a s t r e a c t i o n t e c h n i q u e s . H 1OH + ROH ^ HOH + ROH 1 (3.2) For methanol (R = Me) and e t h a n o l (R = E t ) , the r a t e of pr o t o n exchange i s A/3 and 0.8 1 mole 1 sec 1 r e s p e c t i v e l y a t 22 _+ 2 ° . When a c i d or base i s added, an i o n i c mechanism 6 —1 r e s u l t s i n an i n c r e a s e d exchange r a t e of ™ 10 1 mole sec 1 . 75 3.2 E x p e r i m e n t a l 3.2.1 S t a r t i n g M a t e r i a l s d 4-methanol (99.9%) and d ^ - d i e t h y l e t h e r were purchased from Merck, Sharp and Dohme of Canada L t d . S p e c t r o s c o p i c grade methanol, and d r y d i e t h y l e t h e r were used f o r s o l v e n t s . 3.2.1.1 P r e p a r a t i o n o f b i s ( t r i f l u o r o m e t h y l ) a r s i n e The p r e p a r a t i o n i s based on the methods d e s c r i b e d by C u l l e n (75) and Emeleus e t a l ( 7 6 ) . Four C a r i u s tubes c o n t a i n i n g 52.07 g of t r i f l u o r o m e t h y l i o d i d e {ro 12 g per tube) and 48.6 g o f a r s e n i c metal {ro 12 g. per tube) were heated a t 190° f o r 65 hours. The v o l a t i l e l i q u i d was taken i n t o a vacuum system, where t r a p t o t r a p d i s t i l l a t i o n gave 6 g o f i o d o - b i s ( t r i f l u o r o m e t h y l ) a r s i n e which condensed i n a t r a p at-64°. The i o d o a r s i n e was then s e a l e d i n a C a r i u s tube w i t h 14.2 g of mercury, and was v i g o r o u s l y shaken f o r 18 hours. The c o n t e n t s were pumped i n t o the vacuum system and 3.55 g o f t e t r a k i s ( t r i f l u o r o m e t h y l ) -d i a r s i n e were o b t a i n e d . The d i a r s i n e was s e a l e d i n a C a r i u s tube w i t h 27.6 g of mercury and 1.0 g o f anhydrous hydrogen c h l o r i d e . A f t e r shaking v i g o r o u s l y f o r f o u r days, 76 the v o l a t i l e p r o d u c t s were taken i n t o a vacuum system and 1.5 g of b i s ( t r i f l u o r o m e t h y l ) a r s i n e was r e c o v e r e d from a t r a p at 125°. I n f r a r e d spectrum (gas, main bands): 2150 w, 2040 s, 1220 m, 1190 s, 1170 s, 1122 s, 1115 s, 730 m cm" 1. N.m.r. s p e c t r a : the spectrum showed a s e p t e t c e n t e r e d 19 a t 5.08 ppm (JQF _ h = 9.2 Hz); the F spectrum ( r e l a t i v e to i n t e r n a l CFCL^) showed a d o u b l e t c e n t e r e d a t 42.3 ppm ( J C F _ H = 8.85 H z ) . 3.2.1.2 P r e p a r a t i o n of b i s ( t r i f l u o r o m e t h y l ) a r s i n e d e u t e r i d e The p r e p a r a t i o n of the a r s i n e was the same as j u s t o u t l i n e d above, f o r b i s ( t r i f l u o r o m e t h y l ) a r s i n e , except t h a t anhydrous DC1 was s u b s t i t u t e d f o r HC1 i n the l a s t s t e p . The "'"H n.m.r.- spectrum of the a r s i n e product i n d i c a t e d t h a t t h e r e were pro t o n s s t i l l p r e s e n t i n the a r s i n e . The p a r t i a l l y d e u t e r a t e d a r s i n e was then shaken with a g r e a t excess o f D^O f o r two weeks to y i e l d pure b i s ( t r i f l u o r o m e t h y l ) a r s e n i c d e u t e r i d e . I n f r a r e d spectrum: (gas phase) (main abands): 1548 m, 1190 s, 1168 s, 1120 s, 734 m cm" 1. 3.2.2 P r o t o n Exchange R e a c t i o n s and K i n e t i c s Weighed p o r t i o n s o f m a t e r i a l s whose exchange was to be f o l l o w e d , p l u s a measured amount of s o l v e n t 77 when used, were s e a l e d i n n.m.r. tubes and kept, f r o z e n u n t i l they were to be s t u d i e d . The tubes were q u i c k l y warmed to room temperature and p l a c e d immediately i n a V a r i a n A-60 n.m.r. spe c t r o m e t e r . Care was taken t o i s o l a t e the s t a r t i n g m a t e r i a l s w i t h a l a y e r o f s o l v e n t , t o t r y and prevent any unnecessary exchange b e f o r e the mixing was complete. In a t y p i c a l experiment, 0.118 g. of d i e t h y l -a r s i n e , then d ^ Q - d i e t h y l e t h e r , and f i n a l l y 0.036 g. of d i m e t h y l a r s e n i c d e u t e r i d e were s e a l e d i n an n.m.r. tube. Upon q u i c k l y warming the tube t o 35°, the exchange was f o l l o w e d by i n t e g r a t i n g over the methyl peaks o f d i m e t h y l -a r s i n e and d i m e t h y l a r s e n i c d e u t e r i d e . F i g u r e IV shows the peaks of these separated and mixed d i m e t h y l a r s i n e s a t a 50 c.p.s. sweep w i d t h . The f o l l o w i n g r e s u l t s were found. t ( s e c ) a C o n c e n t r a t i o n (moles/1) of Me2AsD 3600 b 0.458 3765 0.459 3870 0.452 7935 0.337 8100 0.341 8220 0.331 10080 0.303 10260 0.301 10425 0.306 78 11940 0.271 12030 0.280 12120 0.278 a - t = 0 i s a r b i t r a r y b - p r e v i o u s t o t h i s time the methyl peaks of the h y d r i d e and d e u t e r i d e c o u l d not be separ a t e d very w e l l . The f o l l o w i n g r e a c t i o n scheme y i e l d s a k i n e t i c r a t e law which corresponds w i t h the ex p e r i m e n t a l r e s u l t s . AD + BH -1 > AH + BD (3.3) AD + BD k ^ > AD + BH (3.4) The f o l l o w i n g ^ a b b r e v i a t i o n s o f c o n c e n t r a t i o n s w i l l be made: . at t = a, (AD) = a a t t = t (AH) = x = (BD) (BH) = b (AD) = a - x The r a t e law from e q u a t i o n s 3.3 and 3.4 i s 4$ = k ^ ( a - x ) ( b - x) - k . x 2 (3.5) dt 1 —1 S o l v i n g e q u a t i o n 3.5 and n o t i n g the e q u i l i b r i u m c o n s t a n t , K = k 1 / k _ 1 , g i v e s the s o l u t i o n 7 9 k nt= i m ( * c x + d. ~s/l3) (3.6) where q = 4Kab(K-l) + K 2 ( a + b ) 2 c = ( K - l ) d = -K(a+b) P l o t t i n g t a g a i n s t l n ^ 2 c x + d '+ NT^O^ g i v e s a s t r a i g h t l i n e as seen i n F i g u r e V. From the s l o p e , k_ 1 and thus k^, can be determined from a knowledge of the v a l u e of K. A number of exchange r e a c t i o n s of d i m e t h y l -a r s i n e or d i m e t h y l a r s e n i c d e u t e r i d e were monitored by n.m.r., as d e s c r i b e d above, and the r e s u l t s are summarized i n T a b l e X I I . K = 1.3S5 = k 1/k_ 1 '-1 3.8 x 10 ^ m o l e 1 s e c 1 k^ = 5.2 x 10 ^ m o l e 1 s e c 1 — L _ 1 1 1 I i i 1 t 4000 60*00 8000 10000 12000 t ( s e e s ) F i q u r e 5 The e x c h a n g e o f Me,AsD a nd Me^AsK i n d i r. - E t - O ^ 2 <L 10 <L 81 __V._L'- ]:\ .'he Rata and ,iI i . br i urn ;~~b>n:~i: a n i . l : c r She P r o t o n 'J;-: change Roach i o n s React, ant "one. .1 React.art one. V/ So]venL K in {mole/1) (mole/1 ) Me ?AsD - t'l 7AcTl - neat Me^AsD 4. 3 2 £t ?AsH 5,95 neat 1. 3 J. J Me 0 A s i ) 3. 74 Kt u '•->, 24 nea L l . 3 5 3 Me^AaD 1. 1 2 i;:t ,,AsH 2.43 d10~ L : t2° T i . 10 Me,AsD 0,8 = 2 2.1'j *10- E t2° l . 3f>5 Me.,A3l) 0,275 ..As:* 2.71 d 1 0 ^ 2 ° b Me,, As D 0 . 3 0 VeOi; 24. a MeOH 0 11 Me., AsH 1.75* CD 3OD 2 3 . 3 ° CF.^OD • 10° Me., AsH 2.40 r 30. 0 f CD.. OD J k 151 Me ->Ar>H 2 . A G ) 2AsD 1,7 6 d l ( T E t 2 0 28 Me 7A«H 0.107 (CF . . ) -,A-n . 4:,0 d, 0~: ;:t. 9o 3C b a - I- L i f e i s about .3 0 rninut.es b - due to the s m a l l amount of d i m e t h y l a r s e n i c d e u t e r i d e used, the d i e t h y l a r s i n e peaks o v e r l a p p e d s e r i o u s l y i n t h e n.m.r. sp e c t r u m c - too f a - i t t o measure d - 2. G m i .111 mo I e s e - 34.2 l i i i l l i m o l e s i: - m i l l i m o l e s 82 3.3 Discussion Of the d i f f e r e n t proton exchanges of hydrides with dimethylarsine investigated (Table XII), only the reaction i n equation 3.1 could be studied k i n e t i c a l l y . Me2AsD + Et 2AsH k ^ = ± : MSgAsH + Et-^AsD (3.1) The other proton transfers were too fast to monitor using n.m.r. i n t e g r a t i o n , and thus only the equilibrium constants could be determined for these f a s t e r reactions. The proton exchange of the arsines i n equation 3.1 was found to correspond with a rate law (eq. 3.5) based on the mechanism outlined i n equations 3.3 and 3.4, whose so l u t i o n i s equation 3.6. A plot of t against l n ( n C X ' + , "" J^S) gave a st r a i g h t l i n e (Figure V) for the 2cx + d + v^ q ^ ^ ^ three experiments that could be analyzed. The rate constants (k^) f o r the exchanges done neat and i n d^Q -d i e t h y l ether solvent, are 5.9 x 10 ^ and 4.95_+0.25 x 10 ^ 1. mole 1 sec 1 at 35°. The equilibrium constants are 1.335_+ 0.020 and 1.2 + 0.1 r e s p e c t i v e l y . ) 83 The range of c o n c e n t r a t i o n s t h a t c o u l d be s a t i s f a c t o r i l y used f o r these r a t e s t u d i e s was very s m a l l , as w i l l now be e x p l a i n e d . S i n c e the e q u i l i b r i u m i n e q u a t i o n 3.1 was t o the r i g h t , i t was d e s i r a b l e to study the exchange from the l e f t s i d e , t o i n c r e a s e the r e l a t i v e d i f f e r e n c e i n c o n c e n t r a t i o n s between the d i m e t h y l a r s i n e d e u t e r i d e and h y d r i d e , monitored d u r i n g the r e a c t i o n . At high d i m e t h y l a r s e n i c d e u t e r i d e c o n c e n t r a t i o n s , r e l a t i v e to d i e t h y l a r s i n e , t h e r e were too few protons exchanged at e q u i l i b r i u m t o make i n t e g r a t i o n p r a c t i c a l . Consequently, the d i e t h y l a r s i n e c o n c e n t r a t i o n had to be the g r e a t e r of the two to g i v e s a t i s f a c t o r y r e s u l t s . Due to the o v e r l a p of s m a l l d i e t h y l a r s i n e peaks i n the n.m.r., with the methyl peaks f o r d i m e t h y l a r s i n e , d i m e t h y l a r s e n i c d e u t e r i d e c o u l d not be l e s s than 1/3 the c o n c e n t r a t i o n o f d i e t h y l a r s i n e . I f i t were l e s s than t h i s , a n a l y s i s would be i m p o s s i b l e as i s seen i n the l a s t d i e t h y l a r s i n e example i n T a b l e X I I . The o p t i m a l r e l a t i v e c o n c e n t r a t i o n s were used f o r the r a t e s t u d i e s i n the t h r e e s u c c e s s f u l l y a n a l y z e d experiments. I t was found when the c o n c e n t r a t i o n s were changed a b s o l u t e l y and not r e l a t i v e l y , these exchanges obeyed t h e A same r a t e law and had s i m i l i a r r a t e c o n s t a n t s . The exchange of these h y d r i d e s was s l i g h t l y f a s t e r when done neat, than when done i n d^g"" d i e t h y l e t h e r . The exchange r a t e o f b i s ( t r i f l u o r o m e t h y l ) a r s e n i c 84 d e u t e r i d e with d i m e t h y l a r s i n e was s t u d i e d i n the hope of f i n d i n g another slow exchange system t h a t c o u l d be used i n the c o m p e t i t i v e a d d i t i o n t o hexafluorobutyno-2, d i s c u s s e d i n Chapter 2. The r a t e o f exchange i n eq u a t i o n 3.7 was found t o be too f a s t t o measure by n.m.r. i n t e g r a t i o n t e c h n i q u e s . C a l c u l a t i o n o f the e q u i l i b r i u m c o n s t a n t , 0.32+0.06 i n d^Q- d i e t h y l e t h e r a t 35° was p o s s i b l e however. ( C F 3 ) 2 A s D + Me 2AsH ^ ^ ( C F - ^ A s H + Me 2AsD (3.7) Consequently these h y d r i d e s were u n s u i t a b l e f o r the c o m p e t i t i v e a d d i t i o n r e a c t i o n , as they would exchange protons t o a s i g n i f i c a n t e x t e n t b e f o r e a d d i t i o n to the a c e t y l e n e o c c u r r e d . D i m e t h y l a r s i n e was r e a c t e d with hexafluorobutyne-2 i n d^-methanol, as d e s c r i b e d i n Chapter 2, to form the 100% t r a n s 1:1. a r s i n e aclduct, which was 85% d e u t e r a t e d . Any f a s t and s i g n i f i c a n t exchange of protons between d i m e t h y l a r s i n e and d^-methanol b e f o r e the a r s i n e a d d i t i o n t o the a c e t y l e n e was completed, would make an i n t e r p r e -t a t i o n of the deuterium p r o t o n c o n t e n t o f the adduct product i m p o s s i b l e . When d i m e t h y l a r s i n e and d^-methanol were mixed (eq. 3.8), an exchange was found t o have o c c u r r e d which was too f a s t t o measure. The e q u i l i b r i u m c o n s t a n t was 0.175+ 0.025. 85 Me 2AsH + CD3OD ^ = ± : Me 2AsD + CD 3OH (3.8) ( s o l v e n t ) A s l i g h t exchange was observed immediately upon mixing d i m e t h y l a r s e n i c d e u t e r i d e and methanol (eq. 3.9). The e q u i l i b r i u m c o n s t a n t was 0.011. Me 2AsD + MeOH ~ ± Me 2AsH + MeOD (3.9) Thus the pro t o n and deuterium d i s t r i b u t i o n i n the t r a n s a d d i t i o n product o f d i m e t h y l a r s i n e and hexafluorobutyne-2 (d^-methanol s o l v e n t ) was not mean i n g f u l , as the a r s i n e and a l c o h o l undergo an immediate and s i g n i f i c a n t p roton exchange (eq. 3.8), which i s much f a s t e r than the a r s i n e a d d i t i o n r a t e . The mechanism i n v o l v e d i n these exchanges i s open to s p e c u l a t i o n . An i o n i c or f o u r - c e n t e r e d mechanism can meet the k i n e t i c r e q u i r e m e n t s . Meiboom e t a l (73, 74) have i n d i c a t e d t h a t the water-methanol proton t r a n s f e r i s n o n - i o n i c i n a n e u t r a l s o l u t i o n , but i o n i c when t r a c e s o f bases o r a c i d s are p r e s e n t . The r a t e o f the n o n i o n i c p r o c e s s (k^ 10® 1 mole 1 sec "*") i s much slower than the t r a c e a c i d or base induced i o n i c p r o c e s s (k^ — 10^ 1 mole 1 sec 1 ) . I t i s p o s s i b l e t h a t the a r s i n e s are s t r o n g enough bases t o promote an i o n i c exchange between themselves and methanol. However, the slow r a t e f o r the d i m e t h y l a r s e n i c 86 -3 -1 -1 d e u t e r i d e - d i e t h y l a r s i n e exchange (WlO 1 mole sec ) i s a g a i n s t an i o n i c mechanism i n t h i s c a s e . The r a t e of e q u i l i b r a t i o n of d i m e t h y l a r s i n e with d^-methanol and b i s ( t r i f l u o r o m e t h y l ) a r s e n i c d e u t e r i d e are f a s t e r than with d i e t h y l a r s i n e and t h e i r k i n e t i c s c o u l d not be s t u d i e d by n.m.r. However, these f a s t exchange r a t e s c o u l d be 10^ f a s t e r 1 mole 1 sec 1 ) than f o r d i e t h y l a r s i n e and d i m e t h y l a r s e n i c d e u t e r i d e , and s t i l l be the same order o f magnitude as the n o n i o n i c methanol-water exchange r a t e . Thus a f o u r - c e n t e r e d mechanism c o u l d very w e l l be the main path f o r the a r s i n e exchange mechanisms as d e p i c t e d i n e q u a t i o n 3.10, because of the slow r a t e s of exchange found between d i m e t h y l a r s e n i c d e u t e r i d e and d i e t h y l a r s i n e . However, an i o n i c mechanism cannot be d i s m i s s e d f o r the a r s i n e s and p a r t i c u l a r l y f o r the a r s i n e -methanol exchange. Even i f e q u a t i o n 3.10 i s the main r e a c t i o n path, an i o n i c mechanism may c o n t r i b u t e to the exchange. E t 2 A s . . H Me 2AsD + E t 2 A s H H AsMe, Et 2 A s D + Me 2AsH (3.10) T h i s mechanism i s favo u r e d by Gold and S a t c h e l l (61) f o r amine p r o t o n t r a n s f e r s , as w e l l as by oth e r authors f o r v a r i o u s r e l a t e d p r o t o n exchanges (71, 72). 87 C a l c u l a t i o n o f the e q u i l i b r i u m c o n s t a n t s from s p e c t r o s c o p i c d a t a , which e x i s t f o r some, but not a l l of the m o l e c u l e s , was not attempted s i n c e the i n f o r m a t i o n t h a t c o u l d be o b t a i n e d , was o u t s i d e the scope of t h i s t h e s i s . Chapter 4 U l t r a v i o l e t and P h o t o e l e c t r o n Spectroscopy S t u d i e s 4.1 I n t r o d u c t i o n In a search f o r a means to study the a d d i t i o n k i n e t i c s d i s c u s s e d i n Chapter 2, i t was d i s c o v e r e d t h a t the isomer p r o d u c t s had an a b s o r p t i o n i n the near u l t r a -v i o l e t r e g i o n . More than one s u g g e s t i o n (77, 78, 79, 80) has been put forward t o e x p l a i n the low energy e l e c t r o n i c t r a n s i t i o n s t h a t are found i n molecules where Group V atoms are bonded t o u n s a t u r a t e d systems. Consequently i t was d e c i d e d to study the u l t r a v i o l e t a b s o r p t i o n of the 1:1 adducts d i s c u s s e d - i n Chapter 2, as .well as* s i m i l a r d e r i v a t i v e s of the type R 2MC(CF 3) = C(CF,)X a) M = N, R = Me, X = 'H, C l b) JM = N, R = E t , x = H c) M = P, R = E t , X = H d) M = As, R = Me, X = H, C l e) M = As, R = E t , X = H. I t was f e l t t h a t the d e t e r m i n a t i o n o f the b i n d i n g 89 e n e r g i e s o f the m o l e c u l a r o r b i t a l s of these compounds c o u l d a s s i s t i n the assignment of the e l e c t r o n i c t r a n s i t i o n s , and so p h o t o e l e c t r o n s p e c t r o s c o p y was used t o o b t a i n the i o n i z a t i o n p o t e n t i a l s o f many o f the compounds. Of T h e ^ f i r s t d i s c u s s e s e l e c t r o n i c s t a t e s and the Franck-Condon p r i n c i p l e , the second u l t r a v i o l e t s p e c t r o s c o p y and the l a s t p h o t o e l e c t r o n s p e c t r o s c o p y . 4.1.1 E l e c t r o n i c T r a n s i t i o n s and the Franck-Condon  P r i n c i p i e I t has been found e x p e r i m e n t a l l y t h a t the energy i n atoms and m o l e c u l e s i s of a d i s c r e t e n a t u r e ( q u a n t i z e d ) . The S c h r o e d i n g e r e q u a t i o n i n t e r p r e t s these r e s u l t s , and g i v e s the exact energy l e v e l s . However, the e q u a t i o n can o n l y be s o l v e d e x p l i c i t l y f o r one e l e c t r o n system, and v a r i o u s a p p r o x i m a t i o n s have been made so t h a t c a l c u l a t i o n s f o r more c o m p l i c a t e d systems are p o s s i b l e . The S c h r o e d i n g e r e q u a t i o n can be s o l v e d u s i n g the Born-Oppenheimer ap p r o x i m a t i o n t h a t the t o t a l wave f u n c t i o n i s s e p a r a b l e into t r a n s l a t i o n a l , electronic, v i b r a t i o n a l and ro t a t i o n a l wave functions n e c e s s i t y t h i s i n t r o d u c t i o n i s broken i n t o t h r e e s e c t i o n s . t r a n s e l (4.1) So f o r ( 4 . 2 ) H T V ( E t r a n s + E e l + E v i b + ( 4 ' 3 ) In g e n e r a l c a l c u l a t i o n s o f the e l e c t r o n i c l e v e l s of atoms and molecules are i n a c c u r a t e and the e n e r g i e s must be o b t a i n e d e x p e r i m e n t a l l y . S i n c e the energy s e p a r a t i o n of the d i f f e r e n t k i n d s : of energy s t a t e s ( i n the Born-Oppenheimer approximation) are an o r d e r of magnitude d i f f e r e n t , one would expect t o see, i n a g i v e n e l e c t r o n i c t r a n s i t i o n , the v i b r a t i o n a l s t a t e s r e v e a l e d as f i n e s t r u c t u r e , and the r o t a t i o n a l s t a t e s as f i n e r s t r u c t u r e on the v i b r a t i o n a l s t a t e s . The r o t a t i o n a l s t r u c t u r e can be r e s o l v e d o n l y i n small m o l e c u l e s . s t a t e d i f f e r e n c e i n energy (cm 1 ) e l e c t r o n i c 10,000. v i b r a t i o n a l 1,000 r o t a t i o n a l 10-100 The d i s t r i b u t i o n o f molecules i n a s t a t e of energy E n i n an e q u i l i b r i u m system, i s g i v e n by the Boltzmann f a c t o r N = N exp(-E /kT) ( 4 . 4 ) n o 1 n where N i s the number i n the energy s t a t e E n n N i s the number i n the energy s t a t e E o ^ 1 • o -1 S i n c e kT i s a p p r o x i m a t e l y 200 cm a t room temperature, i t i s expected t h a t e x c i t e d e l e c t r o n i c l e v e l s are never 91 t h e r m a l l y p o p u l a t e d . The lowest e x c i t e d v i b r a t i o n a l ..level i s p o p u l a t e d to a s m a l l e x t e n t , and many of the r o t a t i o n a l l e v e l s o f the aero t h v i b r a t i o n a l l e v e l are popu l a t e d . The Franck-Condon p r i n c i p l e a f f e c t s the i n t e n s i t i e s o f a b s o r p t i o n bands. T h i s p r i n c i p l e s t a t e s t h a t s i n c e n u c l e a r motion , where a p p r e c i a b l e d i s p l a c e -ment of atoms does not occur i n l e s s than about 10 to -12 10 sec, i s much slower than e l e c t r o n i c phenomena, which take as l i t t l e as 10 s e c , the geometry of a molecule a f t e r a b s o r p t i o n must be almost i d e n t i c a l with i t s geometry b e f o r e a b s o r p t i o n . The e x c i t a t i o n o f the ground e l e c t r o n i c s t a t e , predominantly i n i t s z e r o t h v i b r a t i o n a l l e v e l , may p o s s i b l y be t o the h i g h e r v i b r a t i o n a l l e v e l s i n a h i g h e r e l e c t r o n i c s t a t e . F o r a d i a t o m i c m o l e c u l e , F i g u r e 6 (a) p i c t o r i a l l y r e p r e s e n t s the e l e c t r o n i c t r a n s i t i o n between two s t a t e s whose e q u i l i b r i u m i n t e r n u c l e a r d i s t a n c e s (r ) are s i m i l a r . The most prob a b l e t r a n s i t i o n i s from v = 0 (lowest v i b r a t i o n a l l e v e l ) o f the ground e l e c t r o n i c s t a t e , t o v' = 0 o f the e x c i t e d s t a t e . T h i s i s c a l l e d an " a d i a b a t i c " t r a n s i t i o n . F i g u r e 6 (b) cor r e s p o n d s w i t h a moderate change i n r i n the e x c i t e d s t a t e , and g i v e s a d i s t r i b u t i o n o f e e n e r g i e s as t h e maximum t r a n s i t i o n p r o b a b i l i t y would occur t o a h i g h e r v i b r a t i o n a l l e v e l (v' > 0 ) . T h i s i s c a l l e d a F i g u r e s 6 ( a ) , ( b ) , (c) and (d) 9 3 " v e r t i c a l " t r a n s i t i o n . The a d i a b a t i c p rocess r e q u i r e s the l e s s e r energy t o re a c h the a p p r o p r i a t e e l e c t r o n i c l e v e l . In F i g u r e 6 (c) i t can be seen t h a t i f r £ changes g r e a t l y i n the e x c i t e d s t a t e , the v e r t i c a l t r a n s i t i o n i n t e r s e c t s the e x c i t e d s t a t e energy curve a t an energy above the d i s s o c i a t i o n l i m i t , and the molecule can d i s s o c i a t e . F i g u r e 6 (d) r e p r e s e n t s the e x c i t a t i o n to a r e p u l s i v e e l e c t r o n i c s t a t e which w i l l l e a d t o d i s s o c i a t i o n . The i n t e n s i t y o f t r a n s i t i o n s are p r o p o r t i o n a l t o the d i p o l e s t r e n g t h and can be w r i t t e n V i OC R = J ^ . M ^ l d ^ ( 4 . 5 ) where R i s the t r a n s i t i o n moment M i s the e l e c t r i c d i p o l e moment o p e r a t o r summed over a l l e l e c t r o n s I i s the wave f u n c t i o n of the e x c i t e d s t a t e 2 Vj^  i s the wave f u n c t i o n o f the ground s t a t e d t i s the volume element N e g l e c t i n g r o t a t i o n and u s i n g the Born Oppenheimer appr o x i m a t i o n , the t o t a l wave f u n c t i o n s can be f a c t o r e d i n t o e l e c t r o n i c ' ^ ^ e ^ ^ a n d v i b r a t i o n a l p a r t s . U s i n g the assumption t h e r e i s no displacement o f n u c l e a r 94 c o o r d i n a t e s d u r i n g the time r e q u i r e d f o r e x c i t a t i o n , the f i r s t term i n e q u a t i o n 4.6 can be s e t to a c o n s t a n t R e, IOC ( 1 2 e l M LP l e i LP IP 2 v i b l v i b dr)' R ' j ^ v i b ^ I v i b (4.6) (4.7) where dr i n d i c a t e s i n t e g r a t i o n over the n u c l e a r c o 6 r d i n a t e s r . The Franck-Condon f a c t o r q i s p r o p o r t i o n a l to the t r a n s i t i o n p r o b a b i l i t y ( 2 v i b T: l v i b d r ) ' (4.8) 4.1.2 U l t r a v i o l e t S pectroscopy As p r e v i o u s l y mentioned, e l e c t r o n i c t r a n s i t i o n s a r i s e from the molecule a b s o r b i n g energy and b e i n g e x c i t e d from i t s ground, room temperature s t a t e , to a h i g h e r e l e c t r o n i c s t a t e , p o s s i b l y accompanied by the simultaneous changes i n the v i b r a t i o n a l and r o t a t i o n a l s t a t e s . The u l t r a v i o l e t and v i s i b l e r e g i o n of the energy spectrum c o r r e s p o n d s t o the energy d i f f e r e n c e s between two e l e c t r o n i c s t a t e s . The Franck-Condon p r i n c i p l e r e s u l t s i n a wide a b s o r p t i o n peak, whose maximum corresponds with " v e r t i c a l " e x c i t a t i o n . The i n t e n s i t y o f the t r a n s i t i o n can be c a l c u l a t e d by two methods. The f i r s t method a l l o w s 9 5 i n t e n s i t i e s t o b e s t u d i e d b y a p p l y i n g t h e B e e r - L a m b e r t l a w , t o o b t a i n " a " , t h e m o l a r e x t i n c t i o n c o e f f i c i e n t . A = l o g ( I / I ) = abc (4.9) w h e r e A i s t h e a b s o r b a n c e a t t h e p e a k m a x i m u m a i s t h e m o l a r e x t i n c t i o n c o e f f i c i e n t ( 1 m o l e 1 c m I i s t h e i n t e n s i t y o f t h e l i g h t t r a n s m i t t e d I i s t h e i n t e n s i t y o f t h e i n c i d e n t l i g h t b i s t h e t h i c k n e s s o f t h e l a y e r ( c m ) c i s t h e c o n c e n t r a t i o n ( m o l e 1 " * " ) . T h e s e c o n d m e t h o d o f s t u d y i n g i n t e n s i t i e s i s t h e c a l c u l a t i o n o f t h e o s c i l l a t o r s t r e n g t h s , f , d e f i n e d i n e q u a t i o n 4 . 1 0 , w h i c h i s m o r e p r e c i s e a n d f u n d a m e n t a l q u a n t i t y t h a n a . f = 4 . 3 1 9 x 1 0 9 | a d V ( 4 . 1 0 ) w h e r e d~i> i s t h e d i f f e r e n c e i n e n e r g y ( c m ) T h e o s c i l l a t o r s t r e n g t h i s r e l a t e d t o t h e t h e o r e t i c a l d e t e r m i n a b l e t r a n s i t i o n m o m e n t , R, d e f i n e d i n e q u a t i o n 4.5 b y t h e f o l l o w i n g e q u a t i o n . f = 4 . 7 0 3 x 1 0 2 9 V k n | R | 2 ( 4 . 1 1 ) w h e r e ~^ yn i s t h e a v e r a g e w a v e n u m b e r o f t h e a b s o r p t i o n b a n d i n c m \ 96 4.13 P h o t o e l e c t r o n Spectroscopy P h o t o e l e c t r o n s p e c t r o s c o p y , a new technique f o r the d e t e r m i n a t i o n of out e r as w e l l as i n n e r (.5 21.22 eV) i o n i z a t i o n p o t e n t i a l s , was used to o b t a i n the e n e r g i e s o f the m o l e c u l a r o r b i t a l s i n the adducts mentioned i n the b e g i n n i n g of the i n t r o d u c t i o n . T h i s t e c h n i q u e was f i r s t a p p l i e d by V i l e s s o v et a l (81, 82). Many i n s t r u m e n t a l v a r i a t i o n s have been used s i n c e then, such as the s p h e r i c a l g r i d p h o t o e l e c t r o n spectrometer used by F r o s t e t a l (83, 84) and the 127° s e l e c t o r and magnetic d e f l e c t o r of Turner and h i s co-workers (85, 86). R e c e n t l y , Branton e t a l (87) have used a 180° e l e c t r o s t a t i c h e m i s p h e r i c a l energy a n a l y z e r , which g i v e s an energy r e s o l u t i o n o f about 20 mV FWHM ( F u l l width a t h a l f maximum). I o n i z a t i o n ' p o t e n t i a l s can be used t o e s t a b l i s h the b i n d i n g e n e r g i e s i n n e u t r a l m o l e c u l e s , because the energy r e q u i r e d f o r removal of an e l e c t r o n i s equal to the b i n d i n g energy o f the o r b i t a l from which i t was removed. P h o t o e l e c t r o n s p e c t r o s c o p y circumvents many of the d i f f i c u l t i e s found i n o t h e r i o n i z a t i o n methods, and a l l o w s the d e t e r m i n a t i o n o f the i n n e r i o n i z a t i o n p o t e n t i a l s . The p r i n c i p l e o f the method i s t h a t a photon of energy, h"v , i n t e r a c t s w i t h a molecule and causes the e m i s s i o n o f a p h o t o e l e c t r o n . In the case of molecules, the major p r o c e s s e s r e s u l t i n g from t h e i r p h o t o i o n i z a t i o n 97 can be summarized as f o l l o w s ; a) A3 •+ hD >AB f + e b) > AB + + e > A + + B + e c) >A + + B f e d) > AB* >A + + B~ However i n each of the cases a) and b ) , the primary step i s the e j e c t i o n of a p h o t o e l e c t r o n t o form AB +. The photo-e l e c t r o n e m i t t e d c a r r i e s w i t h i t v i r t u a l l y a l l the excess k i n e t i c energy, g i v e n by hV (energy of the photon) l e s s the a p p r o p r i a t e i o n i z a t i o n p o t e n t i a l f o r the s p e c i e s , I. The k i n e t i c energy of the p h o t o e l e c t r o n i s measured, and then the i o n i z a t i o n p o t e n t i a l i s determined u s i n g e q u a t i o n 4.12. K.E. = hv -'.'.I (4.12) where K.E. i s the measured energy of the p h o t o e l e c t r o n hV i s the energy o f the photons; f o r the helium source used, i t i s 21.22 eV I i s the i o n i z a t i o n p o t e n t i a l of the s p e c i e s . In p h o t o e l e c t r o n s p e c t r o s c o p y , the Franck-Condon p r i n c i p l e i s important and l e a d s t o both q u a l i t a t i v e and q u a n t i t a t i v e r e s u l t s . The number and the energy d i f f e r e n c e s of the v i b r a t i o n a l l e v e l s , upon the f o r m a t i o n o f a p a r t i c u l a r i o n i c s t a t e , i s an i n d i c a t i o n of a change 98 i n r on i o n i z a t i o n . e The shape of the peak o f t e n a s s i s t s i n a s s i g n i n g the i o n i c s t a t e s formed. The removal of a non-bonding e l e c t r o n g i v e s a sharp peak because t h e r e i s no d i m e n s i o n a l change on i o n i z a t i o n , and no v i b r a t i o n a l e x c i t a t i o n . The removal o f a bonding o r a n t i b o n d i n g e l e c t r o n r e s u l t s i n an i n c r e a s e or decrease i n the i o n i c s t a t e e q u i l i b r i u m d i s t a n c e r^, c a u s i n g v i b r a t i o n a l broadening such as i s found i n u l t r a v i o l e t s p e c t r a (see F i g u r e 6 (a) and 6 ( b ) , n o t i n g t h a t the e x c i t e d s t a t e i s an i o n i c s t a t e ) . I f they can be r e s o l v e d , a measurement o f the v i b r a t i o n a l s e p a r a t i o n i n some cases can make the assignment o f the m o l e c u l a r o r b i t a l s p o s s i b l e . 99 4.2 Experimental The experimental s e c t i o n w i l l be d i v i d e d i n t o two p a r t s . The f i r s t summarizes the u l t r a v i o l e t s p e c t r o s c o p i c i n v e s t i g c i t i o n s and the p r e p a r a t i o n of s t a r t i n g m a t e r i a l s used. The second p a r t d e s c r i b e d the apparatus and the te c h n i q u e s used t o determine i o n i z a t i o n p o t e n t i a l s from p h o t o e l e c t r o n s p e c t r o s c o p y . 4.2.1 U l t r a v i o l e t S p e c t r a and Sample P r e p a r a t i o n s U l t r a v i o l e t s p e c t r a o f v a r i o u s compounds were r e c o r d e d on the Cary Model 11 and Model 14 sp e c t r o m e t e r s . Of the compounds s t u d i e d , one, hexafluorobutyne-2 was o b t a i n e d from P e n i n s u l a r Chem. Research Inc., some were s y n t h e s i z e d f o r the purpose of o b t a i n i n g s p e c t r a , and the remainder were the k i n d g i f t s o f Drs. Dawson, Styan and C u l l e n . 4.2.1.1 Sample P r e p a r a t i o n s 4.2.1.1.1 T r i s p r o p y n y l a r s i n e The method used f o r the p r e p a r a t i o n of t h i s compound was s i m i l a r t o t h a t used by Benaim (88), Whiting 100 e t a l (89), Arens and V o s k u i l (90), and M i l l e r and Lemmon (91). E t h y l magnesium bromide was p r e p a r e d from l l g of e t h y l bromide and 2.5g o f magnesium m e t a l i n a minimum o f d r y t e t r a h y d r o f u r a n . The G r i g n a r d s o l u t i o n was s y r i n g e d i n t o a d r y , n i t r o g e n f l u s h e d v e s s e l , and propyne was bubbled through i t f o r one hour. The prop y n y l G r i g n a r d s o l u t i o n was s y r i n g e d i n t o the dropping f u n n e l o f a n i t r o g e n purged v e s s e l and d r i p p e d f o r one hour onto a s o l u t i o n o f 6g of t r i c h l o r o a r s i n e d i s s o l v e d i n 50ml of t e t r a h y d r o f u r a n a t - 3 0 ° . The s o l u t i o n was allowed to warm to room temperature, then i t was c o o l e d to -20" and 50ml of 10% aqueous ammonium c h l o r i d e was s t i r r e d i n . The t e t r a h y d r o f u r a n l a y e r was d r i e d over anhydrous c a l c i u m c h l o r i d e f o r a day, and then f i l t e r e d . The t e t r a h y d r o f u r a n was then removed by f l a s h e v a p o r a t i o n . The s o l i d product was sublimed and r e c r y s t a l l i z e d t o a c o n s t a n t m e l t i n g p o i n t o f 127° ( l i t . m.p., 131° (88)) from 30-60° petroleum e t h e r / c a r b o n t e t r a c h l o r i d e s o l v e n t . A n a l , found: C, 56.15; H, 4.90%. C a l c . f o r As(C=CMe) 3: C, 56.25; H, 4.69%. N.m.r. spectrum: a s i n g l e t a t 2.00 ppm i n C C l ^ s o l v e n t . I n f r a r e d s p e c t r a : ( C C l ^ s o l u t i o n ) , 2965 vw, 2917 m, 2850 w, 2193 s, 1430 w, 1009 s; (KBr p e l l e t ) , 2949 vw, 2909 w, 2936 vw, 2172 s, 2120 m(sh), 2035 vw, 1999 vw, 1430 m, 1361 w, 1258 vw, 1080 vw, 1003 v s , 798 w, 523 w, 458 v s , 434 v s , 383 m, 342 m, 255 s. U l t r a v i o l e t s p e c t r a : see T a b l e X I I I . 101. 4.2.1.1.2 T r i s p r o p y n y 1 s t i b i n o The s t i b e n e p r e p a r a t i o n was t h e same as d e s c r i b e d f o r t h e a r s i n e above. A f t e r two s u b l i m a t i o n s of t h e p r o d u c t , 2g o f t h e s t i b e n e were r e c o v e r e d ( 2 5 % y i e l d ) , w h i c h was r e c r y s t a l l i z e d from 30-60° p e t r o l e u m e t h e r . A n a l , f o u n d : C, 45.6; H, 3.99%. C a l c . f o r Sb (C=CMe): C, 45.2; H, 3.80%. N.m.r. spec t r u m : a s i n g l e t a t 1.98 ppm i n C C l ^ s o l v e n t . I n f r a r e d s p e c t r a : ( C C L 4 s o l u t i o n ) , 2958 w, 2916 m, 2880 w, 2845 w, 2167 s, 1435 w, 1362 vw, 1035 w, 994 s; (KBr p e l l e t ) , 2963 vw, 2911 w, 2840 vw, 2160 v s , 2120 w ( s h ) , 1430 w, 1382 vw, 992 v s , 740 w, 400 v s . 358 m, 330 s. U l t r a v i o l e t s p e c t r u m : see T a b l e X I I I . 4.2.1.1.3 T r i s p r o p y n y l p h o s p h i n e The p h o s p h i n e p r e p a r a t i o n was t h e same as d e s c r i b e d f o r t h e a r s i n e and s t i b e n e p r e p a r a t i o n s . A f t e r t h r e e s u b l i m a t i o n s 0.08g o f p r o d u c t was r e c o v e r e d ( 1 5 % y i e l d ) , w h i c h was r e c r y s t a l l i z e d from 30-60° p e t r o l e u m e t h e r . - E l e m e n t a l a n a l y s i s was made d i f f i c u l t by t h e e x p l o s i v e n e s s o f t h e sample upon h e a t i n g . A n a l . Found: C, 71.84; H, 5.96%. C a l c . f o r P(C=CMe) 3: C, 72.9; H, 6.0%. N.m.r. s p e c t r a : t h e "^ H n.m.r. s p e c t r u m i n CC1. s o l v e n t gave a d o u b l e t a t 1 0 2 1.98 ppm = 2.2 Hz). I n f r a r e d spectrum: (KBr p e l l e t ) , 2980 w, 2915 m, 2848 w, 2912 vs, 2150 w(sh), 2075 w, 2036 vw, 1429 m, 1368 w, 1263 m, 1223 m, 10£9 m, 1060 s, 1040 vs, 1025 s ( s h ) , 821 w(sh), 804 m, G46 w, 569 s, 531 s, 4 3 4 w, 323 w, 2S5 s ( s h ) , 274 s. U l t r a v i o l e t spectrum: see T a b l e X I I I . 4.2.1.1.4 1 , 1 , 1 - t r i f l u o r o p r o p y n e The method used f o r the p r e p a r a t i o n o f t h i s gas was s i m i l i a r t o t h a t used by Finnegan and N o r r i s (92). Z i n c dust (72g), f u s e d z i n c c h l o r i d e (80g), and 100ml of d r y N,N-dimethy l a cetamide were p l a c e d i n a 500 ml f l a s k . The v e s s e l was heated to 140-160° and 100ml of 1,1,2-t r i c h l o r o - 3 , 3 , 3 - t r i f l u o r o p r o p e n e was s l o w l y added over 1% hours. A f t e r s t i r r i n g f o r a f u r t h e r % hour, the mixture was c o o l e d t o 55° and about 100 ml o f water was s l o w l y added. The e v o l v e d 1 , 1 , 1 - t r i f l u o r o p r o p y n e was c o l l e c t e d i n t r a p s at -76° and -124°. A f t e r d r y i n g over P^OJQJ 25.5g o f product was o b t a i n e d (54% y i e l d ) , whose p u r i t y was checked u s i n g i n f r a r e d and n.m.r. s p e c t r o s c o p y . 4.2.1.2 U l t r a v i o l e t S p e c t r a The s o l u t i o n , and/or gas u l t r a v i o l e t s p e c t r a of some u n s a t u r a t e d f l u o r o c a r b o n adducts o f Group IV and V, were s t u d i e d on the Cary Model 11 and Model 14 103 s p e c t r o m e t e r s . The r a n g e s t h a t were s u i t a b l e f o r s t u d y were s l i g h t l y d i f f e r e n t d e p e nding on the s o l v e n t and o i n s t r u m e n t u s e d . The g e n e r a l r e g i o n s t u d i e d was 3500 A t o 2050 A (30,000 cm to 49,000 cm K 0.1 mm, 1.0 mm and 1.0 cm path l e n g t h q u a r t z c e l l s were used f o r the s o l u t i o n s p e c t r a , and a 10 cm p a t h l e n g t h s i l i c a c e l l f o r the gas phase measurements. The samples s t u d i e d a r e l i s t e d o i n T a b l e X I I I , w i t h t h e i r a b s o r p t i o n maxima ( A ) , e x t i n c t i o n c o e f f i c i e n t s (1 mole 1 cm - 1) and i n some c a s e s t h e i r o s c i l l a t o r s t r e n g t h s . The o s c i l l a t o r s t r e n g t h s were c a l c u l a t e d from the a p p r o x i m a t i o n f = (4.6 x 10~ 9) a AS)3 (4.13) max % f i s the o s c i l l a t o r s t r e n g t h a „ i s the molar e x t i n c t i o n c o e f f i c i e n t max a t the peak maximum A^ i i s the h a l f i n t e n s i t y band w i d t h i n cm" 1. '1 To a t t a i n r e l i a b l e maxima and i n t e n s i t i e s , s p e c t r a were t a k e n on two i n s t r u m e n t s from d i f f e r e n t s o l u t i o n . To o b t a i n c o n s i s t e n t v a l u e s f o r the e x t i n c t i o n c o e f f i c i e n t s and o s c i l l a t o r s t r e n g t h s , samples were weighed i n a v o l u m e t r i c f l a s k and i m m e d i a t e l y mixed with' s o l v e n t . These p r e c a u t i o n s gave an a c c u r a c y o f _+ 5% on the o i n t e n s i t i e s and _+ 3 A on the peak maxima o f w e l l s e p a r a t e d s i n g l e p e a ks. Because many o f t h e peaks o v e r l a p p e d one a n o t h e r , and were found by s u b t r a c t i o n , t h e s e peak maxima Compound S o l v . a C F 3 C = C C F 3 g a s E t 2 A s H E M e 2 N ( C F 3 ) C = C ( C F 3 ) H g a s n E f . g E f E t 2 N ( C F 3 ) C = C ( C F 3 ) H E M M e 2 N ( C F 3 ) C = C ( C F 3 ) C l E M E t 2 P \ / C F 3 h \>c( E b ' h C F ^ H M b , h A b s o r p t i o n #2 maxima (A) max 3 . 3 x l C ~ 3 0.256 2100 2 0 0 0 0.045 0.159 2160 1970 0.043 0.260 2150 2 0 0 0 0.046 0.271 2125 1-DC 0.045 0.117 e "*e e 0.169 e e e 0.150 c c c 0.130 c c c 0.018 c c c - c c c — c c c r—1 o Compound Me-As CF / c = c \ C F 3 H Me 0As H 2 \ / O C C F 3 / ^ 3 E t 2 A s ( C F 3)C=C(CF )H (90% t r a n s ) M e 2 A s ( C F 3 ) C = C ( C F 3 ) C l A b s o r p t i o n #1 Lv. a maxima o (A) a max f n 261C+2 1520_+20 0 .041 E 2614+1 1335_+55 -K 2614_+1 1370_+ -C 262 7+3 1345^35 -n 2535+1 2.700+100 0 .068 E 2G12 2705 -M 2662 2730 -C 2630 2-764 -gas 2608 '- -E 2692 1000+70 0 .032 M 2698 1062 -gas 2500 - -n 2620 1 1080 0 .045 E 2630 940 0 .041 A b s o r p t i o n #2 maxima (A) max f c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c 2070 2100 9650 0.243 2150 6700 0.156 A b s o r p t i o n #1 Compound S o l v . maxima o (A) max MeBrAs(CF 3)C=C(CF ) C l n E 2900 h'J 2940 816 Me^S - S i H c=c x / \ C F 3 C F 3 E t 3 S n CF. x c = c ( CF. H Bu 0 S n ( C ( C F 0 ) = C ( C F 0 ) H ) . Me 0As-C=C-CF_ 2 1/ 3 CF„ As(CH = C H 2 ) 3 As(CF = C F 2 ) 3 Me 3SiC=CCF 3 Me-AS(CECCF 3) 2 E E M gas gas gas gas M 1 2506 2518 2350 1 2350 4500 4950 850 A b s o r p t i o n #2 maxima o (A) max 0.037 2160 10150 2192 8600 0.326 0.318 2250 2000 0.097 0.113 2125 d d 2247 b 2025+10 2140 1 2150 3000 d d 4500+450 d d o A b s o r p t i o n #1 A b s o r p t i o n #2 Compound P(C=CMe) 3 As (CECMe) Sb(CECMe) S o l v . d n d n M n maxima o (A) 2 4 6 0 1 2 3 4 5 1 2 3 5 5 1 2432 max 1400 3520 9100 0.047 0.061 0.140 maxima o (A) 2 2 0 0 1 2 1 9 9 1 2 1 9 0 1 2290 max 1650 3610 9100 0.022 0.056 0.140 a) S o l v . i s t h e s o l v e n t u s e d , where M i s MeOH, E i s E t 2 0 , n i s n-heptane, and C i s C H 2 C 1 2 . "gas" r e f e r s t o a gas phase s p e c t r u m . b) + 15 A o c ) a s t r o n g end a b s o r p t i o n a t £ 2000 A o d) a medium s t r e n g t h end a b s o r p t i o n a t m 2 0 0 0 A o e) a weak end a b s o r p t i o n a t 2000 A f ) no end a b s o r p t i o n a t d 2000 A g) exposed t o a i r h) v e r y b r o a d \-> ° o i ) peaks o v e r l a p so +_ 15 A j ) t h e c o n c e n t r a t i o n was t o o low t o o b s e r v e t h e peak p r o p e r l y . 108 were o n l y a c c u r a t e t o + 15 A f o r the most f a v o u r a b l e c a s e s , w h i l e the e x t i n c t i o n c o e f f i c i e n t s and o s c i l l a t o r s t r e n g t h s were o n l y a c c u r a t e t o _f 20%. The experimental accuracy was l i m i t e d by the d i f f e r e n c e s i n volume o f the s o l v e n t f o r s l i g h t temperature changes, by the e r r o r i n weighing of the samples ( u s u a l l y ^ 0.05 t o 0.005 g) and by the accuracy of the v o l u m e t r i c f l a s k s (50 and 100 ml s i z e s ) . 4.2.2 P h o t o e l e c t r o n Spectroscopy The i o n i z a t i o n p o t e n t i a l s o b t a i n e d i n t h i s study were determined on two p h o t o e l e c t r o n s p e c t r o m e t e r s . The f i r s t was a s p h e r i c a l g r i d spectrometer used by F r o s t e t a l (83, 84) on which m o d i f i c a t i o n s , t o be d e s c r i b e d , were made f o r some o f the r u n s . The second instrument used a 180° h e m i s p h e r i c a l a n a l y z e r (Branton e t a l (87)) at a 90° i n c i d e n t angle t o the photon beam, t o a n a l y z e the e l e c t r o n e n e r g i e s . 4.2.2.1 The s p h e r i c a l system The s p h e r i c a l p h o t o e l e c t r o n spectrometer i s shown i n F i g u r e 7. I o n i z a t i o n takes p l a c e i n the c e n t e r o f the two g r i d s . The p h o t o e l e c t r o n measurements were made by a p p l y i n g a g r a d u a l l y i n c r e a s i n g p o s i t i v e r e t a r d i n g p o t e n t i a l t o the i n n e r g r i d with r e s p e c t t o the grounded c o l l e c t o r . A c o n s t a n t p o t e n t i a l ( u s u a l l y 1-3 v o l t s ) 109 PHOTOELECTRON SPECTROMETER / helium F i g u r e 7: The s p h e r i c a l g r i d p h o t o e l e c t r o n spectrometer. between the i n n e r a n d o u t e r g r i d s served t o t u r n back any e n e r g e t i c p o s i t i v e i o n s . The r e s u l t a n t spectrum i s the " s t o p p i n g c u r v e " i n F i g u r e 8a ( i t should be noted t h a t th a b s o l u t e energy s c a l e i n F i g u r e 8a a n d 8b i s a r b i t r a r y ) . The a d i a b a t i c i o n i s a t i o n p o t e n t i a l corresponds to the i n i t i a l r i s e i n the cu r v e , and the v e r t i c a l i o n i z a t i o n p o t e n t i a l t o the p o i n t o f maximum s l o p e . A m o d i f i c a t i o n i n the apparatus was made by scanning both g r i d s t o g e t h e r T h i s gave more s h a r p l y d e f i n e d s t o p p i n g c u r v e s . The s t o p p i n g c u r v e s were time averaged on a Nuc l e a r - C h i c a g o ( 4 0 0 word memory) Instrument Computor and t r a n s f e r r e d to punch tape, which was f e d to an IBM/360 Model 67 computor. A program, k i n d l y w r i t t e n by Mr. J . Ward, was used t o p l o t and d i f f e r e n t i a t e the stopping c u r ves ( F i g u r e 8 a ) . The d i f f e r e n t i a l o f Ar shown i n F i g u r e 8b gave s a t i s f a c t o r y r e s u l t s . However, with s m a l l amounts of n o i s e , the d i f f e r e n t i a l procedure became unworkable, p a r t i c u l a r l y when any " s t e p " (peak) i n the spectrum was too i n t e n s e . T h i s made c a l i b r a t i o n with Ar d i f f i c u l t i f a d i f f e r e n t i a l was d e s i r e d . O f t e n the cu r v e s were u n r e l i a b l e because of d i f f i c u l t t o d e t e c t , low c r o s s s e c t i o n t r a n s i t i o n s , or because s l i g h t changes i n s l o p e due to i o n i z a t i o n near the He l i g h t source t h r e s h o l d , were not e a s i l y d i s c e r n a b l e . I t was thus most d i f f i c u l t t o determine I l l CO (..._.. I - ••! cr t- -,• (X) cr cr U J or a: 1 0 o o r i__ C J UJ 1 •LU 15 8 16.0 16.2 ELECTRON ENERGY 16.4 VOL v.; F i g u r e 8a: The " s t o p p i n g c u r v e " f o r Ar u s i n g the He 584 A l i n e . ELECTRON ENERGY. VOLTS F i g u r e 8b: The d i f f e r e n t i a l of the Ar " s t o p p i n g c u r v e " shown i n F i g u r e 8a. 113 from a s t o p p i n g curve where a l l the i o n i z a t i o n p o t e n t i a l s were. Consequently s p e c t r a o b t a i n e d from the 180° h e m i s p h e r i c a l a n a l y z e d p h o t o e l e c t r o n spectrometer, to be d e s c r i b e d next, gave more s a t i s f a c t o r y r e s u l t s . However, the s p h e r i c a l spectrometer has the advantage that i t c o l l e c t s i o n s i n almost a l l of t h e d i r e c t i o n s from the i o n i z a t i o n r e g i o n . In the 180° and 127° a n a l y z e r s p e c t r o m e t e r s , o n l y e l e c t r o n s e m i t t e d a t approximately r i g h t angles to the i o n i z a t i o n r e g i o n are a n a l y z e d , and i f i n c e r t a i n cases t h e r e i s a marked dependence of i o n i z a t i o n c r o s s s e c t i o n s upon the angle of e l e c t r o n e j e c t i o n , then t h e r e i s a danger of m i s s i n g d a t a , or o b t a i n i n g a f a l s e i n d i c a t i o n o f the r e l a t i v e i n t e n s i t i e s . 4.2.2.2 The 180° A n a l y z e r System A diagram o f t h i s p h o t o e l e c t r o n spectrometer i s shown i n F i g u r e 9. I o n i z a t i o n takes p l a c e i n the c o l l i s i o n chamber, and the p h o t o e l e c t r o n s which are e j e c t e d at a pproximately r i g h t angles t o the i n c i d e n t photon beam, e n t e r the 180° e l e c t r o s t a t i c h e m i s p h e r i c a l a n a l y z e r . The spectrum i s scanned by v a r y i n g the p o t e n t i a l a p p l i e d between the c o l l i s i o n chamber and the c e n t r e tap of the a n a l y z e r (ground p o t e n t i a l ) . The a n a l y z e r i s p r e s e n t t o g i v e the maximum f o c u s of e l e c t r o n s with a p p r o x i m a t e l y 2 eV energy, which g i v e s a c o n s t a n t r e s o l u t i o n throughout the s c a n . The e l e c t r o n s are MAGNETIC TAPE RAMP TO ENERGY ANALYZER FABRITEK IOOO CHAN ANALYZER DISCRIM PULSE AMP X-Y PLOTTER CHANNEL MULTIPLIER ISOLATION VALVES SAMPLE MOLECULES LIQUID NITROGEN TRAP DIFFUSION PUMPS FORE PUMP FORE PUMP MICROWAVE DISCHARGE POWER SUPPLY <3> NEEDLE VALVE I CONTROLS CONTROLS SCANNING FOR FOR POTENTIAL ENERGY ELECTRON FOR COLLISION ANALYZER LENS SYSTEM CHAMBER J He CYLINDER HIGH SPEED FORE PUMP Schematic Diagram of Photo-Electron Spectrometer F i g u r e 9: The 180° h e m i s p h e r i c a l a n a l y z e r p h o t o e l e c t r o n s p e c t r o m e t e r . 1 1 5 d e t e c t e d i n a M u l l a r d channel m u l t i p l i e r , and a f t e r a m p l i f i c a t i o n the s i g n a l i s f e d to a r a t e meter. The s i g n a l i s then f e d to a F a b r i t e k 1 0 2 4 m u l t i c h a n n e l a n a l y z e r and the r e s u l t s p l o t t e d on a Moseley XY p l o t t e r . Both the peaks and t h e i r t o t a l i n t r e g a l , where the i n t e g r a l i s e q u i v a l e n t t o the s t o p p i n g c u r v e f o r the s p h e r i c a l spectrometer, can be o b t a i n e d from the F a b r i t e k a n a l y z e r . The poor r e s o l u t i o n and the l a c k of v i s u a l c l a r i t y o f the i o n i z a t i o n p o t e n t i a l on t h e i n t e g r a l s o b t a i n e d t h i s way, demonstrated the s u p e r i o r i t y o f the r a t e meter monitored experiment. A l l compounds, which were of low c r o s s s e c t i o n compared t o Ar, were run with Ar mixed w i t h them to energy c a l i b r a t e the s p e c t r a . A comphrehensive study was made o f the d i m e t h y l a r s i n e and dimethylamlne adducts. The o t h e r samples were not done i n as much d e t a i l . In some cases where no more than 2 or 3 drops o f sample e x i s t e d , the s p e c t r a were not extremely s a t i s f a c t o r y . However, s i n c e the t r e n d s o f the f i r s t few i o n i z a t i o n p o t e n t i a l were o f primary importance, t h i s l i m i t a t i o n was not s e r i o u s . 4.2.2.3 P h o t o e l e c t r o n s p e c t r a The p h o t o e l e c t r o n s p e c t r a o f the compounds d i s c u s s e d i n the i n t r o d u c t i o n t o t h i s c h a p t e r , as w e l l as those o f some r e l a t e d m a t e r i a l s are t a b u l a t e d i n the 1 1 6 f o l l o w i n g pages. The r e s u l t s were o b t a i n e d from the s p h e r i c a l g r i d ( Table XIV), and the 1 8 0 ° a n a l y z e r ( T a b l e s XV t o XXV) i n s t r u m e n t s , u s i n g the He 584 A resonance l i n e . Only t a b u l a t e d r e s u l t s are i n c l u d e d f o r the s p h e r i c a l g r i d because o n l y the f i r s t i o n i z a t i o n p o t e n t i a l s are r e l i a b l e f o r the l a r g e m o lecules s t u d i e d ( T a b l e XIV) on t h i s i n s t r u m e n t . A l l i o n i z a t i o n p o t e n t i a l s t a b u l a t e d i n the f o l l o w i n g t a b l e s a re i n e l e c t r o n v o l t u n i t s . In the f i g u r e s , the base l i n e s are i n e l e c t r o n v o l t energy u n i t s and the v e r t i c a l axes are a r b i t r a r y i n t e n s i t y u n i t s . The a b s o l u t e s c a l e on the base l i n e s may not e x a c t l y c orrespond w i t h the r e a l s c a l e ( v a l u e s r e p o r t e d ) . When a group of i o n i z a t i o n p o t e n t i a l s a re formed t o g e t h e r , a b r a c k e t e n c l o s e s a l l the t a b u l a t e d v a l u e s from the group. Q u e s t i o n a b l e v a l u e s of i o n i z a t i o n p o t e n t i a l s are i n d i c a t e d by a q u e s t i o n mark. The a c c u r a c y of measuring the i o n i z a t i o n p o t e n t i a l s i s g e n e r a l l y about +_ 0 . 0 5 eV. However, i n cases w i t h no v i b r a t i o n a l s t r u c t u r e , the p o s i t i o n o f assignment t o an a d i a b a t i c o r v e r t i c a l i o n i z a t i o n p o t e n t i a l , i s o f t e n o n l y a c c u r a t e to 0.1—0.2 eV where wide peaks are found. 117 The a d i a b a t i c i o n i z a t i o n p o t e n t i a l s o b t a i n e d u s i n g the s p h e r i c a l g r i d p h o t o e l e c t r o n spectrometer. M o l e c u l e The f i r s t a d i a b a t i c i o n i z a t i o n p o t e n t i a l Me 2AsH 8.92 E t 2 A s H 8.57 CF 2=CF 2 10.32 CF 2=CFCF 3 10.62 CF 2=CFC1 9.82 CF 2=CC1 2 9.62 CF 2=CFBr 9.67 118 T a b l e XV The i o n i z a t i o n p o t e n t i a l s o f f ^ N H ( F i g u r e 10 (a) and ( b ) ) . A l l i o n i z a t i o n p o t e n t i a l s i n the next t a b l e s are o b t a i n e d on the 180° i n s t r u m e n t . A d i a b a t i c V e r t i c a l F i g u r e 10a F i g u r e 10b 8.07+0.2 8.96_+0.15 11.70_+0.3 12.74 12.73 13.32 13.87 13.88 15.26 15.09 16.77 16.69 19.30 ? F i q u r e 1 0 a : Complete p h o t o e l e c t r o n spectrum of Me_,NH. F i q u r e 10b: D e t a i l e d study of the 12-13 eV range of Me?MH 121 Tab l e XVI The i o n i z a t i o n p o t e n t i a l s of E t 2 P H ( F i g u r e 11) A d i a b a t i c (±.0.1 eV) V e r t i c a l (± 0.1 eV) 8.69 9.64 11.52 12.13 13.34 14.12 15.54 16.78 18.82 123 T a b l e XV1T The i o n i z a t i o n p o t e n t i a l s of Me^AsH ( F i g u r e 12) A d i a b a t i c 8.55 10.23 12.68 V e r t i c a l 9.12 11.12 11.71 c e n t e r e d at 11.44 13.71 14.71 c e n t e r e d at 14.20 17.8+0.1 (not i n c l u d e d i n F i g u r e 12) 20.0+0.2 (not i n c l u d e d i n F i g u r e 12) a . v . n , • 1 i " i ~ T ' 1 1 • • * 9.0 11.0 13-0 15-Q ! I F i g u r e 12: The f i r s t i o n i z a t i o n p o t e n t i a l s of Me^AsH. 12 5 T a b l e XVIII The i o n i z a t i o n p o t e n t i a l s of CF^C-CCF^ ( F i q u r e 13 ( a ) , ( b ) , (c) and (d) a d i a b a t i c v e r t i c a l 12.31 14.88 12.83 1 15.48 15.7+.1 16.42 i i 17.49 i n the v i b r a t i o n a l s t r u c t u r e has the s e p a r a t i o n o u t l i n e d (page 126). 126 i o n i z a t i o n  p o t e n t i a l v i b r a t i o n a l d i f f e r e n c e s eV era ^( + 50 cm ^) i ) 12.33 ( F i g u r e 13b) 0,0 0,1 0,0 1,0 1,1 0,1 0,2 1,0 1,1 1,2 0.264 0.261 0.133 0.258 0.258 2129 2105 1073 2081 2081 i i ) 15.7jf.l ( F i g u r e 13c) 0- 1 1- 2 2- 3 3- 4 0.123 0.123 0.123 0.123 992 992 992 992 i i i ) 17.49 ( F i g u r e 13d) 0,0 - 0,1 0,0 - 1,0 1,0 - 1,1 0.157 0.091 0.154 1266 733 1244 12.0 14-0 15.0 \ Si 'HA 18.0 5.0 F i g u r e 13a: The complete p h o t o e l e c t r o n spectrum of CF^C=CCF^ ' ' ' ' C-0 0-2 0-4 0-6 E V F i g u r e 13c: A d e t a i l e d spectrum o f the second group of i o n i z a t i o n p o t e n t i a l s W 1 5 - 1 7 eV) of CF.CECCF.. 0 1 2 3 -V i 1 "1 ! i \m.i i f ' " l t* if' ft' / / A \. 7,, •:» % \^ "!\ / 1 / 0-0 0.1 0-2 0-3 eV F i g u r e 13d: A d e t a i l e d spectrum of the l a s t i o n i z a t i o n p o t e n t i a l ("17-18 eV). 131 Tabl e XIX The i o n i z a t i o n p o t e n t i a l s o f CF^CSCH ( F i g u r e 14 ( a ) , ( b ) , ( c ) , (d) and (e) a d i a b a t i c 11.83 13.76 14.67 17.13 18.07 v e r t i c a l " 12.12 1 1 3 . 7 6 1 1 15.22 15.62 15.96+0*1 17.13 : 17.13 : 18.07 18.28 a - the v i b r a t i o n a l s t r u c t u r e has the s e p a r a t i o n s o u t l i n e d (page 132). 132 i o n i z a t i o n  p o t e n t i a l v i b r a t i o n a l d i f f erences ev- ent ^(+50 cm 1 ) i ) 12.12 0,0 - 0,1 0.250 2016 ( F i g u r e 14b) 0,1 - 0,2 0.250 2016 0 , 0 - 1 , 0 0.134 1081 1.0 - 1,1 0.236 1904 1.1 - 1,2 0.236 1904 1,0 - 2,0 0.134 1081 2,0 - 2,1 0.226 1823 2,0 - 3,0 0.131 1057 i i ) 13.76 0-1 0.135 1088 1-2 ; 0.200 1613 i i i ) 17.13 ( F i g u r e 14d) i v ) 17.13 ( F i g u r e 14e) 0- 1 1- 2 2- 3 3- 4 4- 5 5- 6 6- 7 7- 8 0-1 0.155 0.100 0.082 0.093 0.075 0.087 0.101 0.148 0.143 1250 806 661 750 605 702 814 1194 1150 133 i o n i z a t i o n v i b r a t i o n a l p o t e n t i a l d i f f e r e n c e s eV cm ^(+50 cm 1) 1- 2 0.133 1073 2- 3 0.133 1073 3- 4 0.133 1073 F i q u r e 14a: A f u l l p h o t o e l e c t r o n spectrum o f CF^C=CH. F i q u r e 14b: A d e t a i l e d spectrum of the f i r s t i o n i z a t i o n p o t e n t i a l (^11-13 eV) of CF,C=CH. — ' — l _ 1 5-0 16.0 F i g u r e 14c: A d e t a i l e d spectrum o f . t h e second group o f i o n i z a i o n p o t e n t i a l s (^14-17 eV) of CF^CECH. 1 ' ' 0.0 0-1 0.2 0-3 0-4 sV F i g u r e 14d: A d e t a i l e d spectrum of the f i r s t i o n i z a t i o n p o t e n t i a l at 17.12 eV, of- CF,C=CH. F i q u r e 14e: A d e t a i l e d spectrum of the l a s t group of i o n i z a t i o n p o t e n t i a l s ("16-20 eV) of CF C-CH. 139 T a b l e XX  The i o n i s a t i o n p o t e n t i a l s a d i a b a t i c 8.22 10.79 12.43 of Me 0NC(CF.)=C(CF.)H ( F i g u r e 15) v e r t i c a l ( c i s and t r a n s isomers) 8.78 11.42 12.92 13.40 +. 0.3 14.48 15.76 16.98 18.80 19.80 141 T a b l e X X I The . i o n i z a t i o n p o t e n t i a l s o f E t ^  PC (CP n ) =C (CP -) H , , _ : . j „ : j ( F i g u r e 16) a d i a b a t i c v e r t i c a l ( t r a n s i s o m e r ) 8.34 10.19 8.94 10.86 11.68 12.74 13.83 14.99 15.80 16.96 19.13 20.13 10.0 14.0 18.0 Figure 16: The complete photoelectron spectrum of Et~PC(CF_)=C(CF_)H 143 T a b l e X X I I The i o n i z a t i o n p o t e n t i a l s of Me-AsC(CP)-C(CF) H _______________________ —Z""" • •"' 1 • ~ j 3 The values for both the c i s (Figure 17) and trans (Figure 18 (a) and (b)) are included, the trans being i n brackets. The trans values are not as r e l i a b l e as there was no i n t e r n a l Ar standard and an external Ar standard was attempted. adiabatic v e r t i c a l 8.61 _ .1 (8.71) 10.31 (10.59) 12.77 (13.10) 9 .42 (9.47) 10 .96 (11.04) 11 .98 (12.00) 13 .70 (^14.00) 14 .96 (^15.00) 15 .60 (^15.72) 16 .72 (17.09) 18 .84 (19.16) 20 .15 (20.49) f 0- It 10.0 14.0 18.0 F i g u r e 17: The complete p h o t o e l e c t r o n spectrum of c i s - M e 2 A s C ( C F )=C(CF .)H, 145 F i g u r e 18a: The complete p h o t o e l e c t r o n spectrum of t r a n s - M e 2 A s C ( C F 3 ) = C ( C F 3 ) H . F i g u r e 18b: The d e t a i l e d p h o t o e l e c t r o n s p e c t r a o f F i g u r e 18a: ( i ) - the f i r s t 3 i o n i z a t i o n p o t e n t i a l s ; ( i i ) - the second s e t o t i o n i z a t i o n p o t e n t i a l s (14-18 eV) ;. ( i i i ) the l a s t i o n i z a t i o n p o t e n t i a l s (18-21 eV) cn 14 7 T a b l e XXIII The i o n i z a t i o n p o t e n t i a l s o f Me2AsC(CF 3)=C(CF 3)Cl (see F i g u r e 19 ( a ) , (b) and ( c ) ) a d i a b a t i c v e r t i c a l F i g u r e 19a F i g u r e s 19b, 19c 8.81 + 0.2 9.43 10.36 11.50 12.28 13.82 14.95 15.66 16.88 19.17 20.24 11.96 9.31 10.43 11.76 12.34 13.72 14.79 16.95 12.03 F i g u r e 19a: The complete p h o t o e l e c t r o n spectrum c f Ma^AsC(CF^)=C(CF_)Cl. oo — ' — ~« -<--—. 1 . ^ £ ,,„_.„_. l „ 9-0 il.O 13.0 F i q u r e 19b: A d e t a i l e d spectrum o f the f i r s t i o n i z a t i o n p o t e n t i a l s of F i g u r e 19a. !_ 14.0 » 1 6 . 0 F i g u r e 19c: A d e t a i l e d spectrum of the second group of i o n i z a t i o n p o t e n t i a l s of F i g u r e 19a. 151 T a b l e XXIV The i o n i z a t i o n a l p o t e n t i a l s o f E t 2 A s C ( C P 3 ) = C ( C F 3 ) H a d i a b a t i c v e r t i c a l (90% t r a n s isomer) 8.44 +_ .1 9.00 9.85 _+ .15 10.44 11.55 12.68 13.58 14.2 14.94 15.72 17.00 (2?) 19.10 20.03 T a b l e XXV The i o n i z a t i o n p o t e n t i a l s o f Me-SiC(CF_)=C(CF_)H 3 • — 3 J — — -a d i a b a t i c v e r t i c a l ( c i s isomer) 9.86 10.91 11.74 11.74 12.53 _+ 0.2 13.63 14.79 15.89 16.99 19.50-20.64 154 15 5 4 , 3 D i s c i ; a s i on The d i s c u s s i o n w i l l be considered i n two s e c t i o n s . The f i r s t i s concerned with the r e s u l t s obtained from photo-e l e c t r o n spectroscopy, and how these r e s u l t s c o r r e l a t e with other i n v e s t i g a t i o n s dene on i o n i z a t i o n p o t e n t i a l s . The second section presents the r e s u l t s of the u l t r a v i o l e t absorption experiments, and shows how these findings correspond with the i o n i z a t i o n p o t e n t i a l s determined, to make i t possible to assign the u l t r a v i o l e t bands observed. 4.3.1 Photoelectron Spectroscopy 4.3.1.1 The spherical g r i d r e s u l t s The f i r s t i o n i z a t i o n potentials of dimethyl-and d i e t h y l a r s i n e , and a number of fluorocarbon ethylenes, are l i s t e d i n Table XIV. The value of these i o n i z a t i o n p o t e n t i a l s may not be accurate to more than _ 0.3 eV, as external and not i n t e r n a l Ar was used to c a l i b r a t e the spectra. However, the difference between two v e r t i c a l i o n i z a t i o n p o t e n t i a l s i n the same spectra should be accurate to at l e a s t _ 0.1 eV. The adiabatic i o n i z a t i o n p o t e n t i a l s of 8.92 and 8.57 eV were determined for dimethyl- and d i e t h y l a r s i n e r e s p e c t i v e l y . These i o n i z a t i o n p o t e n t i a l s are probably associated with the removal of a nonbonding electron from the arsenic atom, as has previously been suggested for the 136 f i r s t i o n i z a t i o n p o t e n t i a l a of a r s i n e (5?) and amines (9 3 ) . U s i n g e l e c t r o n impact, .Frost and C u l l e n (52) determined t h e i o n i z a t i o n p o t e n t i a l of d i m e t h y l a r s i n e t o be 9.0 _+ 0.1 eV. They suggested t h i s v a l u e was s l i g h t l y l a r g e r than t h e a d i a b a t i c i o n i z a t i o n p o t e n t i a l . The lower i o n i z a t i o n p o t e n t i a l determined f o r d i e t h y l a r s i n e (8.57 eV) as compared to d i m e t h y l a r s i n e (.8.92 eV) , was found i n the analogous amine d e r i v a t i v e , d i e t h y l a m i n e (8.44 eV) and dimethyl amine (8.93 eV) , by C o l l i n ( 9 4 ) , u s i n g the e l e c t r o n impact method. The f i r s t i o n i z a t i o n p o t e n t i a l s of a number of s u b s t i t u t e d f l u o r o e t h y l e n e s were o b t a i n e d ( T a b l e XIV), to determine i f the e f f e c t o f a t r i f l u o r o m e t h y l or c h l o r i n e s u b s t i t u e n t on t e t r a f l u o r o e t h y l e n e , was s i m i l a r to t h e i r e f f e c t on e t h y l e n e , and to e s t i m a t e the v a l u e o f the f i r s t i o n i z a t i o n p o t e n t i a l f o r o t h e r f l u o r o e t h y l e n e s . The f i r s t i o n i z a t i o n p o t e n t i a l s o f e t h y l e n e s have been a s s i g n e d to the removal of a TT bonding e l e c t r o n (95, and r e f e r e n c e s t h e r e i n ) . These f i r s t a d i a b a t i c i o n i z -a t i o n p o t e n t i a l s , determined i n t h i s work as w e l l as by o t h e r workers, v a r y i n the range of 9.5 to 10.5 eV, as shown i n T a b l e XXVI. The e f f e c t of the s u b s t i t u e n t s on the f i r s t i o n i z a t i o n p o t e n t i a l ( p i e l e c t r o n ) i s r e a d i l y o b s erved. S u b s t i t u t i o n o f a t r i f l u o r o m e t h y l group on the e t h y l e n e r a i s e s the i o n i z a t i o n p o t e n t i a l about 0.3 - 0.4 eV. The T a b l e XXVI The f i r s t i o n i z a t i o n p o t e n t i a l s o f v a r i o u s e t h y l e n e s e t h y l e n i o n i z a t i o n p o t e n t i a l (e' f l u c r o e t h y l e n e H 2C = OH- IO.56 (95) 10.43 (96) 10.50 (97) 10.48 (98) C F 2 - CF, 10.32 (*) 10.12 (99) CH- = CHC1 10.06 (95) 9.99 (99) 10.00 (101) CF_ = CFC1 9.82 (*) CH 2 = CHBr 9.80 (99) C F 2 = CFBr 9.67 (*) CH. - CC1 2 9.83 (95) 9.79 (99) 9.49 (102) CF., = CC1- 9.62 (*) rr 1 = CC1. 9.40 (95) 9.55 (100) CH 2 = CHCF- 10.9 (99) CF- = CfCF 10.6 2 (*) * t h i s work 158 r a i s i n g of the i o n i z a t i o n p o t e n t i a l can probably be a s s o c i a t e d with the inductive e f f e c t of the t r i f l uoromethyl group. This e f f e c t i s additive for a second t r i f l u o r o m e t h y l group substituted c i s or trans on the ethylene. h similar e f f e c t has been observed for the methyl and c h l o r i n e s u b s t i t u t e d e t h y l e n e s ( 9 5 ) . The l o w e r i n g o f the i o n i z a t i o n p o t e n t i a l observed from s u b s t i t u t i o n , on the same carbon atom, of the f i r s t W O . 4 - 0 . 5 eV) and second ( ^ 0 . 2 eV) c h l o r i n e , i s about the same f o r e t h y l e n e and t e t r a f l u o r o e t h y l e n e . The i n c r e a s e d ease o f removal of the TT e l e c t r o n , upon s u b s t i t u t i o n of c h l o r i n e i n e t h y l e n e , was observed by F r o s t and Sandhu ( 9 5 ) u s i n g p h o t o e l e c t r o n s p e c t r o s c o p y . T h i s l o w e r i n g o f the i o n i z a t i o n p o t e n t i a l has been p o s t u l a t e d ( 9 9 ) as being due to the i n c r e a s e d s i g n i f i c a n c e o f resonance s t r u c t u r e s , + such as C=C-C1, as compared to the i n d u c t i v e e f f e c t o f the c h l o r i n e . The s i m i l i a r i t y o f the i o n i z a t i o n o f et h y l e n e and t h e i r analogous f l u o r o e t h y l e n e , suggests the i n d u c t i v e and resonance e f f e c t s o f the f l u o r i n e atom on the o r b i t a l s o f the e t h y l e n e s , are about e q u a l . T h i s r e s u l t has been a l s o observed by B r a l s f o r d e t a l ( 9 9 ) . A l s o o f i n t e r e s t i s the f a c t t h a t both the et h y l e n e and t e t r a f l u o r o e t h y l e n e halogen d e r i v a t i v e s have lower i o n i z a t i o n p o t e n t i a l s as a halogen atom i s r e p l a c e d by the one below i t i n the P e r i o d i c T a b l e . T h i s i n d i c a t e s 159 t h a t t h e i m p o r t a n c e of r e s o n a n c e , v/ith r e s p e c t t o t h e i n d u c t i v e e f f e c t s , i n c r e a s e s as one g o e s down t h e P e r i o d i c T a b l e . 4 . 3 . 1 . 2 D i m e t h y l a m i n e , d i m e t h y l a r s i n e and d i e t h y l p h o s p h i n e The v e r t i c a l i o n i z a t i o n p o t e n t i a l s of the cbove Group V h y d r i d e s were determined on the 180° a n a l y z e r p h o t o e l e c t r o n i n s t r u m e n t (87) u s i n g the He 584 A5 resonance l i n e , and the r e s u l t s summarized i n T a b l e s XV to XVII ( F i g u r e s 10 to 12) . 4.3.1.2.1 Dimethylamine The v e r t i c a l (and some a d i a b a t i c ) i o n i z a t i o n p o t e n t i a l s o f dimethylamine are l i s t e d i n Tab l e XV, and the p h o t o e l e c t r o n spectrum shown i n F i g u r e 10. The f i r s t v e r t i c a l i o n i z a t i o n p o t e n t i a l i s 8.96 eV ( a d i a b a t i c ; 8.07 _ 0.2 eV), and has been a s s i g n e d to the removal of a nonbondirig e l e c t r o n from n i t r o g e n ( 93). The f i r s t i o n i z a t i o n p o t e n t i a l o f dimethylamine has been determined by many workers (94, 96, 103, 104, 105), but i t has v a r i e d somewhat w i t h the i n d i v i d u a l . The i n n e r a d i a b a t i c i o n i z a t i o n p o t e n t i a l s have been r e p o r t e d by Turner and A l - J o b o u r y (96), u s i n g a c y l i n d r i c a l a n a l y z e r p h o t o e l e c t r o n i n s t r u m e n t . Some of the f i r s t i o n i z a t i o n p o t e n t i a l s found f o r dimethylamine are l i s t e d i n T a b l e XXVII. 160 Table XXVII The F i r s t I o n i z a t i o n P o t e n t i a l of Dimethylamine I. P. (eV) ine thud r e f e r e n c e 8.9o _r 0.15 ( a d i a b a t i c , p n o t o e l e c t r o n * 0 . 0 7 + 0 , 2 ) 8.93 + 0.03 R.P.D.-electron 94 impact 8.24 p h o t o i o n i z a t i o n 105 8.36 ( a d i a b a t i c ) p h o t o e l e c t r o n 96 * t h i s work There i s a good correspondence between the f i r s t v e r t i c a l i o n i z a t i o n p o t e n t i a l determined i n t h i s work, and the one o b t a i n e d by C o l l i n (94), u s i n g e l e c t r o n impact. The a d i a b a t i c i o n i z a t i o n p o t e n t i a l determined i n t h i s i n v e s t i g a t i o n i s s l i g h t l y lower than the p r e v i o u s l y determined a d i a b a t i c v a l u e s , but there i s almost agreement w i t h i n the e x p e r i m e n t a l e r r o r . The second a d i a b a t i c i o n i z a t i o n p o t e n t i a l determined i n t h i s work was 11.70 _+ 0.3 eV which i s very d i f f e r e n t from the p h o t o e l e c t r o n r e s u l t o f Turner and A l - J o b o u r y ( 9 6 ) , who r e p o r t e d i t as b e i n g 12.88 eV. The remaining i n n e r i o n i z a t i o n p o t e n t i a l s l i s t e d i n T a b l e XV do not correspond w i t h Turner and A l - J o b o u r y 1 s 161 a d i a b a t i c v a l u e s of 14.63, 16.35 and perhaps 19.62 eV. T h e i r i o n i z a t i o n p o t e n t i a l s f a l l i n the peak d e p r e s s i o n s seen i n F i g u r e 10a and 1 0 b . No i n d i c a t i o n i s g i v e n by T u r n e r t h a t p o s s i b l y 2 or 3 i o n i z a t i o n p o t e n t i a l s a r e found between 11 . 0 and 14.5 eV. The v e r t i c a l i o n i z a t i o n p o t e n t i a l a t 15.09 eV may be the removal o f an e l e c t r o n from the N-H bond, because t h i s i o n i z a t i o n p o t e n t i a l i n ammonia comes at 15.5 eV (106). 4.3.1.2.2 D i m e t h y l a r s i n e The v e r t i c a l (and some a d i a b a t i c ) i o n i z a t i o n p o t e n t i a l s found f o r d i m e t h y l a r s i n e are l i s t e d i n Table XVII and the p h o t o e l e c t r o n spectrum shown i n F i g u r e 12. The f i r s t i o n i z a t i o n p o t e n t i a l , determined to be 9.12 eV, ( a d i a b a t i c ; 8.58) i s a s s o c i a t e d w i t h the removal of the nonbonding e l e c t r o n (93). F r o s t and C u l l e n (52), u s i n g the e l e c t r o n impact method, determined a v a l u e of 9.0 _+ 0.1 eV f o r the f i r s t i o n i z a t i o n p o t e n t i a l of d i m e t h y l a r s i n e . The v e r t i c a l i o n i z a t i o n p o t e n t i a l f o r d i m e t h y l a r s i n e (9.12 eV) i s lower than the f i r s t i o n i z a t i o n p o t e n t i a l determined f o r a r s i n e (10.58 eV) by Branton e t a l (107). The l o w e r i n g of the i o n i z a t i o n p o t e n t i a l found i n a r s i n e s upon the replacement o f hydrogen w i t h a methyl group, has a l s o been demonstrated f o r amines and a r s i n e s u s i n g e l e c t r o n impact (52, 94). 162 One o f the two i o n i s a t i o n p o t e n t i a l s o f d i m e t h y l a r s i n e a t 11 012 and 11.71 may be a s s o c i a t e d w i t h the r e m o v a l o f an e l e c t r o n from an o r b i t a l , p r i m a r i l y l o c a l i z e d on the A s — H bond, as the i o n i z a t i o n p o t e n t i a l o f the A s— H bond i n a r s i n e ( 1 0 7 ) i s 11.44 eV ( a d i a b a t i c ) . T h i s assignment i s g i v e n f u r t h e r w e i g h t by the f a c t t h a t a s t r o n g i o n i z a t i o n p o t e n t i a l i n dimethylamine i s found near the i o n i z a t i o n p o t e n t i a l a s s i g n e d to the N—H bond i n ammonia. 4.3.1.2.3 D i e t h y l p h o s p h i n e The i o n i z a t i o n p o t e n t i a l s found f o r d i e t h y l -phosphine are l i s t e d i n T a b l e XVI and the p h o t o e l e c t r o n spectrum i s o u t l i n e d i n F i g u r e 11. The f i r s t i o n i z a t i o n p o t e n t i a l a t 9.64 eV can be a s s o c i a t e d with the removal o f a nonbonding e l e c t r o n (52, 93) from the phosphorus atom, by analogy w i t h the amines and a r s i n e s . The spectrum ( F i g u r e 11) i s more c o m p l i c a t e d than f o r dimethylamine or d i m e t h y l a r s i n e , which i s undoubtedly due to the a d d i t i o n a l o r b i t a l s a s s o c i a t e d w i t h the e t h y l g r o u p . The determined f i r s t i o n i z a t i o n p o t e n t i a l (9.64 eV) seems somewhat l a r g e r than would be expected ( 8.3 eV). T h i s value i s chosen because the f i r s t i o n i z a t i o n p o t e n t i a l s of ammonia, phosphine and a r s i n e , and a l s o dimethylamine and d i m e t h y l a r s i n e , are s i m i l a r ; and because there i s a l o w e r i n g o f t h i s 1 6 3 i o n i z a t i o n p o t e n t i a l w h e n a m e t h y l g r o u p i s r e p l a c e d w i t h e t h y l g r o u p i n a m i n e a n d a r s i n e d e r i v a t i v e s . T h e d i s c r e p a n c y b e t w e e n t h e d e t e r m i n e d a n d e x p e c t e d v a l u e o f t h e i o n i z a t i o n p o t e n t i a l , c o u l d - be d u e t o an i n c o r r e c t , a s s i g n m e n t o f t h e s c a n n e d s p e c t r u m w i d t h , o r i t c o u l d be t h a t t h e r e a l i o n i z a t i o n p o t e n t i a l i s a n o m a l o u s . S i n c e o n l y a s m a l l amount o f t h e sample was a v a i l a b l e , a r e p e a t r u n was n o t p o s s i b l e . 4.3.1.3 1 , 1 , 1 - t r i f l u o r o p r o p y n e and h e x a f l u o r o b u t y n e - 2 The v e r t i c a l i o n i z a t i o n p o t e n t i a l s o f the above a c e t y l e n e s have been d e t e r m i n e d on the 180° a n a l y z e r p h o t o e l e c t r o n i n s t r u m e n t (87) u s i n g t h e He 584 A l i n e , and the r e s u l t s a r e summarized i n T a b l e s X V I I I and XIX ( F i g u r e s 13 and 1 4 ) . 4.3.1.3.1 H e x a f l u o r o b u t y n e - 2 The v e r t i c a l (and some a d i a b a t i c ) i o n i z a t i o n p o t e n t i a l s d e t e r m i n e d f o r h e x a f l u o r o b u t y n e - 2 a r e l i s t e d i n T a b l e X V I I I and the p h o t o e l e c t r o n s p e c t r a a r e o u t l i n e d i n F i g u r e s 1 3 ( a ) , ( b ) , (c) and ( d ) . The f i r s t i o n i z a t i o n p o t e n t i a l a t 12.83 eV ( a d i a b a t i c ; 12.31 eV) i s p r o b a b l y a s s o c i a t e d w i t h the r e m o v a l o f a TC o r b i t a l e l e c t r o n . U n l i k e t e t r a f l u o r o e t h y l e n e , whose f i r s t i o n i z a t i o n p o t e n t i a l i s v e r y s i m i l a r t o 164 e t h y l e n e , i t might be e x p e c t e d t h a t h e x a f l u o r o b u t y n e - 2 has a lower f i r s t i o n i z a t i o n p o t e n t i a l than b u t y n e - 2 . T h i s i s because t h e r e i s a d e c r e a s e i n the i m p o r t a n c e o f the r e s o n a n c e e f f e c t as compared to the i n d u c t i v e e f f e c t i n the t r i f l u o r o m e t h y 1 g r o u p o f h e x a f l u o r o b u t y n e - 2 , whereas t h e s e e f f e c t s may be b a l a n c e d i n the f l u o r i n e s u b s t i t u t e d e t h y l e n e s . The magnitude o f the f i r s t i o n i z a t i o n p o t e n t i a l o f h e x a f l u o r o b u t y n e - 2 i s about what would be e x p e c t e d . U s i n g the l o w e r i n g o f the i o n i z a t i o n p o t e n t i a l i n e t h y l e n e (10.50 eV) as compared t o a c e t y l e n e (11.4 eV (109, 110)) of (11.4-10.5 = 0.9) 0.9 eV, one ~ o u l d e s t i m a t e the i o n i z a t i o n p o t e n t i a l o f h e x a f l u o r o b u t y n e - 2 (see s e c t i o n 4.3.1.1) to be about 12.1 t o 12.2 eV. The e x p e r i m e n t a l l y d e t e r m i n e d v a l u e i s 12.3 eV. T h i s r e s i i l t , as w e l l as t h o s e noted p r e v i o u s l y i n the d i s c u s s i o n (see s e c t i o n 4.3.1.1), suggest t h a t t h e e f f e c t o f s u b s t i t u e n t s , on o p p o s i t e carbons o f an u n s a t u r a t e d s y s t e m , a r e a d d i t i v e when c o n s i d e r i n g i o n i z a t i o n p o t e n t i a l s . The v i b r a t i o n a l s t r u c t u r e on the f i r s t i o n i z a t i o n p o t e n t i a l ( F i g u r e 13b) can be a s s i g n e d t o the CSC s t r e t c h i n g and C-F ("v^ s t r e t c h i n g f r e q u e n c i e s . The values d e t e r m i n e d by Berney e t a l (108) f o r t h i s m o l e c u l e a r e 2300 (^) and 1248 (^2^ c m _ 1 r e s p e c t i v e l y , w h i l e t h o s e a s s i g n e d t o the f i r s t i o n i z a t i o n p o t e n t i a l a r e 2129 and 1073 c i n " \ T h i s r e s u l t s u g g e s t s r e s o n a n c e e f f e c t s have a 165 s i g n i f i c a n t importance i n the bonding, as C-F s t r e t c h i n g v i b r a t i o n a l s t r u c t u r e i s found on the YC e l e c t r o n i o n i z a t i o n potential„ The group o f i o n i z a t i o n potential.:.-, between 15 and 17 eV ( F i g u r e 13c) may be a s s o c i a t e d with the C-F b o n d i n g , and f l u o r i n e nonbonding e l e c t r o n s . B a s s e t t and L l o y d (111) observed there were three i o n i z a t i o n p o t e n t i a l s f o r CF^, where they a s s i g n e d the f i r s t to the C-F bonding o r b i t a l , and the h i g h e r tv/o to the f l u o r i n e l o n e - p a i r s of e l e c t r o n s . I t i s p o s s i b l e the t h r e e i o n i z a t i o n p o t e n t i a l s i n h e x a f l u o r o -butyne-2 between 15 and 17 eV, though s l i g h t l y lower i n energy than those i n CF., are due to the C-F bonding and f l u o r i n e non-bonding e l e c t r o n s . The middle i o n i z a t i o n p o t e n t i a l i n t h i s group (15.7 +• 0.1 eV) has v i b r a t i o n a l s t r u c t u r e which cannot be a s s i g n e d . I t i s u n l i k e l y t h i s i o n i z a t i o n p o t e n t i a l i s due to an i m p u r i t y , as a s i m i l a r i o n i z a t i o n p o t e n t i a l i s found i n 1 , 1 , 1 - t r i f l u o r o p r o p y n e . I f the i o n i z a t i o n p o t e n t i a l i s r e a l , the v i b r a t i o n a l s e p a r a t i o n of 990 _+ 50 c m - 1 suggests t h a t the i n f r a r e d assignments of Berney et a l (108), and M i l l e r and Bauman (112) may be i n c o r r e c t . The l a s t v e r t i c a l i o n i z a t i o n p o t e n t i a l of h e x a f l u o r o b u t y n e - 2 i s at 17.49 eV. I t i s a s s i g n e d to the p r edominantly C— CF^ bonding o r b i t a l . The v i b r a t i o n a l s t r u c t u r e ( F i g u r e 13d) can be a s s i g n e d to the C-F t ^ ) and C-C ("v^ ) s t r e t c h i n g f r e q u e n c i e s . The v i b r a t i o n a l s e p a r a t i o n s are 1266 +_ 50 and 733 + 50 cm" 1, whereas the 166 v a l u e s a s s i g n e d to t h e m o l e c u l e by Berney e t a l (108) are 1245 N ) and 771 (-y^ c m - 1 . T h i s would s u g g e s t t h a t the e l e c t r o n was removed from e i t h e r a C-F o r C—CF..^ bond i n g o r b i t a l . S i n c e the i o n i z a t i o n p o t e n t i a l a s s i g n e d ho the removal o f an e l e c t r o n from the C-F bonding o r b i t a l was determined to be 16.30 eV (111), i t seems u n l i k e l y i t i s r a i s e d to 17.49 ev" by the e t h y l e n e system. Consequently t h i s i o n i z a t i o n p o t e n t i a l (17.49 eV) i s a s s i g n e d to the o r b i t a l t h a t i s mainly l o c a t e d i n the C-CF-j bond. 4.3.1.3.2 1 . 1 . 1 - t r i f l u o r o p r o p y n e The v e r t i c a l (and some a d i a b a t i c ) i o n i z a t i o n p o t e n t i a l s determined f o r 1 , 1 , 1 - t r i f l u o r o p r o p y n e are l i s t e d i n T a b l e XIX from F i g u r e s 14(a), ( b ) , ( c ) , (d) and ( e ) . The f i r s t i o n i z a t i o n p o t e n t i a l a t 12.12 eV ( a d i a b a t i c ; 11.83 eV) i s p r o b a b l y a s s o c i a t e d with the removal o f a bonding TT o r b i t a l e l e c t r o n . T h i s i o n i z a t i o n p o t e n t i a l i s s i m i l i a r to, though l e s s than the f i r s t i o n i z a t i o n p o t e n t i a l of hexafluorobutyne-2 (12.83 eV). The v i b r a t i o n a l s t r u c t u r e on the f i r s t i o n i z a t i o n p o t e n t i a l ( F i g u r e 14b) can be a s s i g n e d to the C=C (V^) s t r e t c h i n g and C-F ("v^ s t r e t c h i n g f r e q u e n c i e s . The v a l u e s determined by Berney e t a l (108) f o r the molecule are 2165 (V^) and 1254 (i^ ) cm" 1, w h i l e those a s s i g n e d from the f i r s t i o n i z a t i o n p o t e n t i a l are 2016 and 1081 cm 1 r e s p e c t i v e l y . T h i s r e s u l t i s s i m i l i a r to the v i b r a t i o n s found on the f i r s t i o n i z a t i o n p o t e n t i a l of 16 7 hexafluorobutyne-2» T h i s s u g g e s t s t h a t i n b o t h c a s e s t h e resonance e f f e c t b e t w e e n t h e t r i f l u o r o n i e t h y 1 group and t h e carbon-carbon TT o r b i t a l s i s i m p o r t a n t , a l t h o u g h t h e i n d u c t i v e e f f ec t i s dorair>.an t . The remaining i o n i z a t i o n p o t e n t i a l s c a n n o t be w e l l a s s i g n e d , i f a t a l l . T h e r e are more i o n i z a t i o n s p o t e n t i a l s i n 1 , 1 , 1 - t r i f l u o r o p r o p y n e than would be expected, p a r t i c u l a r l y when they are compared to those of h e x a f l u o r o -butyne-2. The correspondence was e x c e l l e n t when an i n f r a -r e d o f the gas was compared to t h a t o f Berney et a l (108), a l t h o u g h the same i m p u r i t i e s may have been found i n both. The i o n i z a t i o n p o t e n t i a l at 13.76 eV may correspond to the removal o f an e l e c t r o n from the C-H o r b i t a l . However, the v i b r a t i o n a l s e p a r a t i o n on t h i s u n u s u a l l y low i o n i z a t i o n p o t e n t i a l , suggests t h i s assignment i s not a good one. The i o n i z a t i o n p o t e n t i a l s ( F i g u r e 14c) a t 15.22, 15.62 and 15.96 eV, may be a s s o c i a t e d w i t h the CF^- group. The i n t e n s i t y of these peaks, w i t h r e s p e c t to the i o n i z a t i o n p o t e n t i a l o f the TT bonds, i s o n l y h a l f o f that, of the comparable i o n i z a t i o n p o t e n t i a l s i n h e x a f l u o r o b u t y n e - 2 , w h i l e the p a t t e r n remained c o n s t a n t . The remaining i o n i z a t i o n p o t e n t i a l s are unassigned a l t h o u g h there i s v i b r a t i o n a l s t r u c t u r e t h a t c o u l d be a s s o c i a t e d w i t h the C-F s t r e t c h i n g f r e q u e n c i e s . The f i r s t i o n i z a t i o n p o t e n t i a l at 17.13 eV c o u l d be the bond which i s m ainly F-C-C, as both v i b r a t i o n a l p a t t e r n s c o u l d f i t i t . 168 F u r t h e r c a r e f u l s t u d i e s are nece s s a r y on t h i s molecule to h e l p a s s i g n these i o n i z a t i o n p o t e n t i a l s . 4.3.1.4 The Group V Hydride - Hexafluorobutyne-2 Adducts The i o n i z a t i o n p o t e n t i a l s o f the ? r-ducts l i s t e d below, were determined on the 180° a n a l y z e r p h o t o e l e c t r o n o instrument, u s i n g the He 584 A resonance l i n e , and the r e s u l t s summarized i n T a b l e s XX to XXV from the s p e c t r a i n F i g u r e s 15 to 21. R MC(CF 0) = C(CF_)X n j 3 f o r : n=2 M - N R=Me X=H M=As R=Me X=H, C l R=Et X=H M=P R=E t X=H n=3 M=Si R=Me X=H The s p e c t r a o f a number of the adducts are compared wi t h one another i n F i g u r e 22. An attempt at a s s i g n i n g a l l the peaks was u n s u c c e s s f u l due to the g r e a t number of them which o v e r l a p p e d . Only the f i r s t two or three i o n i z a t i o n p o t e n t i a l s c o u l d be as s i g n e d w i t h success, although they l a c k e d v i b r a t i o n a l s t r u c t u r e . The group o f i o n i z a t i o n p o t e n t i a l s from ^ 1 2 . 0 0 to 18.00 eV have a s i m i l i a r p a t t e r n i n a l l the adducts, and are prob a b l y due to the removal o f e l e c t r o n s from o r b i t a l s a s s o c i a t e d with 170 the f l u o r o e t h y l e n e p a r t of the molecule. 4.3.1.4.1 The Dimathylamine - Hexafluorobutyne-2 Adduct The i o n i z a t i o n p o t e n t i a l s determined f o r t h i s adduct are l i s t e d i n Ta b l e XX, from the spectrum shown i n F i g u r e s 15 and 22a. The f i r s t i o n i z a t i o n p o t e n t i a l at 8.78 eV i s a s s i g n e d to the removal o f a nonbonding e l e c t r o n on the n i t r o g e n atom. T h i s i o n i z a t i o n p o t e n t i a l (8.78 eV) i s s i m i l i a r , though lower than the i o n i z a t i o n p o t e n t i a l determined f o r dimethylamine (8.96 _+ 0.15 eV) . The second i o n i z a t i o n p o t e n t i a l at 11.42 eV i s a s s i g n e d to the removal of a TT bonding e l e c t r o n from the molecu l e . T h i s i s l e s s than the f i r s t i o n i z a t i o n p o t e n t i a l of h e ^ a f l u o r o b u t y n e (12.83 eV). I t i s b e l i e v e d that there i s s t a b i l i z a t i o n due to the o v e r l a p o f the n i t r o g e n non-bonding o r b i t a l w i t h a TT o r b i t a l on the e t h y l e n e p a r t of the m o l e c u l e . A f u r t h e r d i s c u s s i o n o f t h i s w i l l be made l a t e r , when the u l t r a v i o l e t r e s u l t s are c o n s i d e r e d . 4.3.1.4 2 The T r i m e t h y l s i l a n e - H e x a f l u o r o b u t y n e - 2 Adduct The i o n i z a t i o n p o t e n t i a l s determined f o r t h i s adduct are l i s t e d i n Ta b l e XXV, from the spectrum shown i n F i g u r e s 21 and 22c. One of the f i r s t i o n i z a t i o n p o t e n t i a l s at 10.91 171 and 11.74 eV can be a s s i g n e d to the r e m o v a l o f a TT e l e c t r o n . A c o m p a r i s o n o f t h i s adduct w i t h t h a t o f d i m e t h y l a r s i n e ( t o be d i s c u s s e d n e x t ) , s u g g e s t s t h a t the i o n i z a t i o n p o t e n t i a l a t 10.91 eV i s t h e one a s s o c i a t e d w i t h the e l e c t r o n . 4.3.1.4.3 The A r s i n e - H e x a f l u o r o b u t y n e - 2 A d d u c t s The i o n i z a t i o n p o t e n t i a l s d e t e r m i n e d f o r the i s o m e r s o f the d i m e t h y l a r s i n e adduct a r e l i s t e d i n T a b l e X X I I from the s p e c t r a i n F i g u r e s 17, 18 and 22c. Most o f the v a l u e s d e t e r m i n e d f o r the c i s and t r a n s i s o m e r s were the same. However, a number o f d i f f e r e n c e s were fo u n d . The i o n i z a t i o n p o t e n t i a l a t 16.72 eV i n the c i s i s o m e r , was l o w e r t h a n i n the t r a n s i s o m e r (17.09 e V ) . The t r a n s i somer has a s t r o n g i o n i z a t i o n p o t e n t i a l a t 19.16 eV w h i l e the c i s isomer has o n l y a s l i g h t i n f l e c t i o n a t 18.84 eV. The f i r s t i o n i z a t i o n p o t e n t i a l s f o r the c i s -d i m e t h y l a r s i n e - , d i e t h y l a r s i n e - and c h l o r o d i m e t h y l a r s i n e -h e x a f l u o r o b u t y n e - 2 a d d u c t s are l i s t e d i n T a b l e X X V I I I . The f i r s t i o n i z a t i o n p o t e n t i a l o f t h e c h l o r o d i m e t h y l - , d i m e t h y l - and d i e t h y l a r s i n e a d d u c t s , b e i n g 9.39, 9.42 and 9.00 eV r e s p e c t i v e l y , a r e a s s i g n e d to the rem o v a l o f a nonbonding e l e c t r o n from t h e a r s e n i c atom. The i o n i z a t i o n p o t e n t i a l s a r e h i g h e r i n the a d d u c t s t h a n i n t h e i r p r e c u r s o r h y d r i d e s , d i m e t h y l a r s i n e (9.12 eV) and d i e t h y l a r s i n e ( a d i a b a t i c ; 8.57 e V ) . The d i f f e r e n c e i n the a d i a b a t i c 172 T a b l e X X V I I I The f i r s t I o n i z a t i o n P o t e n t i a l s (-^12.50 eV) f o r Some A r s i n e - H e x a f l u o r o b u t y n e - 2 A d d u c t s I .P. 2 3 4 10.44 11.55 12.68 10.96 11.98 10.43 11.76 12.34 i o n i z a t i o n p o t e n t i a l s o f the a d d u c t s i s 0.42 eV, whereas the d i f f e r e n c e i n the p r e c u r s o r h y d r i d e s i s 0.45 eV. T h i s s u g g e s t s t h a t the e t h y l e n e p o r t i o n o f the m o l e c u l e has the same e f f e c t on the i o n i z a t i o n p o t e n t i a l o f e i t h e r the d i m e t h y l a r i n e o r d i e t h y l a r s i n e p a r t of the m o l e c u l e . The second i o n i z a t i o n p o t e n t i a l i n the a r s i n e a d d u c t s i s a s s i g n e d t o the removal o f a TT e l e c t r o n . The e f f e c t o f s u b s t i t u t i n g e t h y l groups f o r m e t h y l s on the a r s i n e p a r t o f the m o l e c u l e , i s to l o w e r the i o n i z a t i o n p o t e n t i a l o f the e t h y l e n e e l e c t r o n . Other w o r k e r s have found t h a t t h e i o n i z a t i o n p o t e n t i a l o f e t h y l e n e i s l o w e r e d as m e t h y l - , e t h y l - and n - b u t y l groups a r e s u b s t i t u t e d on t h e e t h y l e n e ( 9 9 ) . The e f f e c t o f t h e c h l o r i n e atom on the i o n i z a t i o n p o t e n t i a l o f the e t h y l e n e a d d u c t s i s s i m i l i a r t o the r e s u l t s f o u n d by o t h e r w o r k e r s . The i o n i z a t i o n p o t e n t i a l M o l e c u l e E t _ A s C ( C F 3 ) = C ( C F 3 ) H 9.00 Me-AsC(CF 3) = C(CF 3>II 9.42 K e 2 A s C ( C F 3 ) = C ( C F 3 ) C 1 9.39 1 7 3 o f the c h l o r o adduct ( T a b l e X X V I I I ) was l o w e r e d to 10.36 eV. T h i s i s p r o b a b l y due to the g r e a t e r i n f l u e n c e o f the r e s o n a n c e e f f e c t s as compared to the i n d u c t i v e e f f e c t s , from the c h l o r i n e atom on the e t h y l e n e p o r t i o n o f the m o l e c u l e . The l o w e r i n g o f i o n i z a t i o n p o t e n t i a l due to the c h l o r i n e atom i n the c h l o r o d i m e t h y l a r s i n e - h e x a f l u o r o -b utyne-2 a d d u c t i s 0.53 eV, whereas th e e f f e c t o f the f i r s t c h l o r i n e s u b s t i t u t e d i n e t h y l e n e or t e t r a f l u o r o e t h y l e n e i s 0.5 eV. 4.3.1.4.4 The D i e t h y l p h o s p h i n e - H e x a f l u o r o b u t y n e - 2  A dduct The i o n i z a t i o n p o t e n t i a l s d e t e r m i n e d f o r the d i e t h y l p h o s p h i n e adduct a r e l i s t e d i n T a b l e XXI from the s p e c t r u m shown i n F i g u r e 16. The s pectrum i s most c o m p l i c a t e d due t o the e t h y l g r o u p s , b u t i s v e r y s i m i l i a r t o t h a t o f d i e t h y l a r s i n e , as i s shown i n F i g u r e 23. The f i r s t i o n i z a t i o n p o t e n t i a l a t 8.94 eV i s a s s i g n e d to the r e m o v a l o f a nonbonding e l e c t r o n from the phosphorus atom. Assuming t h e r e i s a l o w e r i n g o f t h i s i o n i z a t i o n p o t e n t i a l compared t o d i e t h y l p h o s p h i n e , s i m i l i a r t o t h a t f o u n d f o r d i m e t h y l a r s i n e i n i t s a d d u c t (^0.4 e V ) , one v.ould e x p e c t to f i n d the d i e t h y l p h o s p h i n e i o n i z a t i o n p o t e n t i a l a bout 8.54 eV. E x p e r i m e n t a l l y i t was f o u n d t o be 9.64 eV, and a comment has p r e v i o u s l y been made ( s e c t i o n 4.3.1.2.3) about t h i s a n o m a l o u s l y h i g h v a l u e . 174 The second i o n i z a t i o n p o t e n t i a l a t 10.86 eV i s a s s i g n e d ro the removal of a TT bonding e l e c t r o n . T h i s v a l u e compares f a v o u r a b l y v i th the TT e l e c t r o n i o n i z a t i o n o o t e n t i a l s of th _. other adducts. 10.0 14.0 _ i 18.0 1 7 6 4.3.2 U l t r a v i o l e t S p e c t r o s c o p y The u l t r a v i o l e t s p e c t r a o f the compounds s t u d i e d are l i s t e d i n T a b l e X I I I . In F i g u r e 24, compounds o f the type R_,MC(CF-,) = C(CF-JH, where M i s a Group V atom, have an a b s o r p t i o n i n the near u l t r a v i o l e t , as w e l l as an end a b s o r p t i o n . The t r a n s i t i o n s can be a s s i g n e d to e i t h e r a * * n-TC (or n-R) band, and TT — TT (or .Tf-R) band r e s p e c t i v e l y . These assignments are made on the b a s i s o f p h o t o e l e c t r o n and u l t r a v i o l e t e v i d e n c e . 4.3.2.1 The Nature o f the T r a n s i t i o n The r e s u l t s from the p h o t o e l e c t r o n study g i v e e x a c t v a l u e s f o r the ground s t a t e e l e c t r o n i c l e v e l s (see F i g u r e 25). The u l t r a v i o l e t r e s u l t s c o r r e s p o n d to the d i f f e r e n c e i n energy between the ground s t a t e e l e c t r o n i c l e v e l s , and one or more of the e x c i t e d ( h i g h e r nonoccupied) e l e c t r o n i c l e v e l s (see F i g u r e 25). The energy of the f i r s t two ground l e v e l s were determined f o r the above mentioned adducts, and they were a s s i g n e d to a nonbonding and T T o r b i t a l r e s p e c t i v e l y . I t i s p o s s i b l e t h a t the e l e c t r o n i c t r a n s i t i o n s from these l e v e l s both go to the same e x c i t e d s t a t e as seen i n F i g u r e 25. I f t h i s i s t r u e , then the d i f f e r e n c e i n energy between the u l t r a v i o l e t t r a n s i t i o n s , E . - E „ , s h o u l d e q u a l "The U l t r a v i o l e t S p e c t r a of S e v e r a l A d d u c t s Me-NCfCF-) = C(CF-.)H ( c i s and tra n s ) F t - N C ( C F - ) - C ( C F 2. 5 ( c i s a n d t r a n s ) E t 2 P C ( C F 3 ) --• C ( C F ; 3 ) H ( t r a n s ) E t . A s C t C F g ) = C ( C F 3 ) H ( t r a n s ) M e 2 A s C ( C F 3 ) = C ( C F 3 ) H ( c i s a n d t r a n s ) M e - A s C ( C F - ) = C ( C F , ) C 1 ( c i s a n d t r a n s ) M e 3 S i C ( C F 3 ) - C ( C F 3 ) H ( t r a n s ) A \ \ 1 y 4 , , 1 1 h A 1 1 -" 1 1 r H 1 1 1 1 1 y •\ 1 1 1 1 1 r i 1 1 1 1 r 3300 ' 2900 ' 2500 ' 2100 o A 178 u l t r a v i o l e t t r a n s i t i o n s / d e termined from p h o t o e l e c t r o n 2> s p e c t r o s c o p y . F i g u r e 25 the d i f f e r e n c e i n energy between the p h o t o e l e c t r o n r e s u l t s p2 * " p i * T a b l e XXIX p r e s e n t s the d i f f e r e n c e s , E^-E^ and P2~P1 t a b u l a t e d form, f o r the a d i a b a t i c and some v e r t i c a l d i f f e r e n c e s . The v e r t i c a l t r a n s i t i o n d i f f e r e n c e between the two u l t r a v i o l e t bands can be measured i n o n l y one adduct, Me 2AsC(CF 3) = C ( C F 3 ) C 1 (Table X I I I ; F i g u r e 24). With the e x c e p t i o n o f the amine adducts who have j u s t one a b s o r p t i o n i n the near u l t r a v i o l e t , o n l y the a d i a b a t i c d i f f e r e n c e s can be o b t a i n e d from the u l t r a v i o l e t s p e c t r a o f the rema i n i n g adducts whose second t r a n s i t i o n i s an end o a b s o r p t i o n (^2000 A ) . The v e r t i c a l and a d i a b a t i c d i f f e r e n c e s o f Me 2AsC(CF 3) = C ( C F 3 ) C 1 are eq u a l w i t h i n e x p e r i m e n t a l e r r o r , which i n d i c a t e s t h a t the d i f f e r e n c e i n the band shapes o f the e l e c t r o n i c l e v e l s b e i n g s t u d i e d , are the same i n e i t h e r of the s p e c t r o s c o p i c t e c h n i q u e s T a b l e XXIX A Comparison of the Energy D i f f e r e n c e s f o r the F i r s t Two Ground L e v e l s o f S e v e r a l Adducts M o l e c u l e *P 2-P 1(cm 1 ) £ 1 - E 2 ( c m ~ 1 ) Gaseous Gaseous S o l u t i o n A d i a b a t i c V e r t i c a l A d i a b a t i c V e r t i c a l A d i a b a t i c V e r t i c a l M e 2 A s C ( C F 3 ) = C ( C F 3 ) C l 10,200+1000 8243+1000 9800+1300 8247+100 10,966+2000 8892+100 Me 2 A s C ( C F 3 ) = C ( C F 3 ) H 13,600+1000 12,420+1000 11.200+1000 E t 2 A s C ( C F 3 ) = C ( C F 3 ) H 10,772+2000 11,615+1000 11,760+1000 E t 2 P C ( C F 3 ) = C ( C F 3 ) H 14,922+1000 14,700+1000 10,500+1000 13,400+1000 * These d i f f e r e n c e s were measured d i r e c t l y from the s p e c t r a . 180 b e i n g used. The e r r o r i n energy i n v o l v e d i n these measurements (+ 0.2 eV) i s p r o b a b l y much l e s s than the d i f f e r e n c e between two e x c i t e d l e v e l s . In the compounds where no v e r t i c a l d i f f e r e n c e s can be o b t a i n e d , the a d i a b a t i c d i f f e r e n c e s f o r the gas phase are not a l l a v a i l a b l e . E x t r a p o l a t i o n from the s o l u t i o n to the gas phase t r a n s i t i o n s , by adding r o u g h l y 1000 c m - 1 to the s o l u t i o n d i f f e r e n c e s , b r i n g s the a d i a b a t i c d i f f e r e n c e s w e l l w i t h i n e x p e r i m e n t a l e r r o r . T h i s evidence s t r o n g l y suggests t h a t both the n» and TT ground s t a t e o r b i t a l e l e c t r o n s are b e i n g e x c i t e d to the same upper l e v e l . The e x c i t e d l e v e l cannot be a s s i g n e d with o n l y the e x p e r i m e n t a l r e s u l t s o b t a i n e d i n t h i s i n v e s t i g a t i o n . The upper l e v e l c o u l d be e i t h e r an a n t i b o n d i n g s t a t e , or a Rydberg s t a t e . The s m a l l r e d s o l v e n t s h i f t s of the near u l t r a v i o l e t band, t h a t were found when the s o l v e n t p o l a r i t y was i n c r e a s e d , i s a g a i n s t a n-TT* t r a n s i t i o n (113), as a b l u e s h i f t i s expected. However, the e f f e c t s o f the p o s s i b l e d e l o c a l i z a t i o n on the i n t e n s i t y o f the t r a n s i t i o n s , suggests t h a t t h i s i s a n-TT* t r a n s i t i o n . 4.3.2.2 D e l o c a l i z a t i o n and I n t e n s i t i e s F i g u r e 26 c o n t a i n s the energy l e v e l s of the n and Tf o r b i t a l s o f a number o f adducts, as w e l l as t h e i r p r e c u r s o r h y d r i d e s . The TT energy l e v e l o f the amine adduct seem s t a b i l i z e d compared to the analogous a r s i n e 8.00 9.00 10.00 .. 11.00 12.00 _ (n) (n) (n) (TT) (vO M e 2 A s C ( C F 3 ) - C ( C F 3 ) H M e „ N C ( C F _ ) = C ( C F . ) H / J J M e 2 A s H M e 3 S i C ( C F 3 ) = C ( C F 3 ) H F i g u r e 26 The L o w e r G r o u n d S t a t e s o f S e v e r a l A d d u c t s and t h e i : P r e c u r s o r H y d r i d e . 03 182 adduct, which has almost the same Tt e l e c t r o n i o n i z a t i o n p o t e n t i a l as the t r i m e t h y l s i l a n e adduct. S t a b i l i z a t i o n o f the TV o r b i t a l may occur from o v e r l a p of the nonbonding o r b i t a l s on the n i t r o g e n atom, with the TT o r b i t a l . From F i g u r e 26 t h i s can be seen to be A/0.45 eV, i f the t r i m e t h y l -s i l a n e and d i m e t h y l a r s i n e adducts have no d e l o c a l i z a t i o n s t a b i l i t y . The reason t h a t d e l o c a l i z a t i o n does not seem to be found i n the a r s i n e or phosphine adducts, may be because the energy r e q u i r e d to make the molecule p l a n a r (eg. the a r s i n e i s p l a n a r so that the maximum o r b i t a l o v e r l a p i s p o s s i b l e ) i s l a r g e r than the energy i n c r e a s e from the g r e a t e r o r b i t a l o v e r l a p . Weston (114) found t h a t i t r e q u i r e s a g r e a t d e a l more energy to make phosphine (1.3 eV) or a r s i n e (1.5 eV) p l a n a r , than i t does f o r ammonia (0.26 e V ) . The t o t a l d e l o c a l i z a t i o n s t a b i l i t y t h a t would be expected from the amine adduct i s 0.71 eV (0.45 + 0.26 = 0.71). I f the a r s i n e or phosphine adducts become p l a n a r , the t o t a l d e l o c a l i z a t i o n energy (^0.7 eV) i s l e s s than the b a r r i e r to p l a n a r i t y (^1.4 eV), and c o n s e q u e n t l y a l a r g e o v e r l a p o f the nonbonding and o r b i t a l s does not seem p r o b a b l e . The i n t e n s i t y o f the n-Tf* u l t r a v i o l e t t r a n s i t i o n i n these adducts, s h o u l d i n c r e a s e w i t h i n c r e a s e d d e l o c a l i z a t i o n . Thus the amine adduct would have a f a r l a r g e r o s c i l l a t o r s t r e n g t h (or e x t i n c t i o n c o e f f i c i e n t ) than the a r s i n e or phosphine adducts. T h i s corresponds w i t h the e x p e r i m e n t a l r e s u l t s 16 3 found i n the u l t r a v i o l e t s t u d i e s . I t i s presumed t h a t a t r a n s i t i o n to an e x c i t e d R y d b e r g l e v e l would not have t h i s i n t e n s i t y change from the amines to the a r s i n e s and phosphines ( 1 1 5 ) , a l t h o u g h the t r a n s i t i o n c o u l d be o f s i m i l i a r e n e r g y . 4.3.2.3 The U l t r a v i o l e t T r a n s i t i o n s The p h o t o e l e c t r o n t e c h n i q u e i d e n t i f i e d the n and Tt ground s t a t e energy l e v e l s . The e x c i t a t i o n of an e l e c t r o n from b o t h o f these l e v e l s to an f f * or R e x c i t e d s t a t e i s o b s e r v e d i n the near u l t r a v i o l e t . The s o l v e n t e f f e c t ( r e d s h i f t ) o f the u l t r a v i o l e t band s u g g e s t s i t i s not a n-Tf* s t a t e . However, the i n t e n s i t y o f the t r a n s i t i o n f o r the amine, p h o s p h i n e and a r s i n e a d d u c t s , f a v o u r s the n-Tf* and n o t the n-R t r a n s i t i o n . The e x p e r i m e n t s done i n t h i s i n v e s t i g a t i o n cannot d i s t i n g u i s h between the two • p o s s i b l e (TT* c r U) e x c i t e d s t a t e s . R e c e n t l y Weiner and P a s t e r n a l e ( 7 9 , 00) have p u b l i s h e d the u l t r a v i o l e t y p e c t r a o f iniiny a r s i n e ;.md p h o s p h i n e au!)3 h i t u t o d e t h y l e n e s . T h e i r a s s i g n m e n t o f the near u l t r a v i o l e t t r a n s i t i o n s t o a c h a r g e - t r a n s f e r n-Tf* type o f band, was based on the e a r l i e r work o f C u l l e n and H o c h s t r a s s e r (77, 7 8 ) . The n e a r u l t r a v i o l e t t r a n s i t i o n i n v e s t i g a t e d i n t h i s work does not seem to be a pure c h a r g e - t r a n s f e r band, because the e x p e c t e d l i n e a r p l o t o f the i o n i z a t i o n p o t e n t i a l (n o r b i t a l ) f o r the a d d u c t s a g a i n s t t h e i r u l t r a v i o l e t a b s o r p t i o n s , was n o t f o u n d . 184 However, i t i s p o s s i b l e t h a t the u l t r a v i o l e t bands have c h a r g e - t r a n s f e r c h a r a c t e r . The compounds i n T a b l e X I I I , o t h e r t h a n the a d d u c t s d i s c u s s e d so e x t e n s i v e l y i n t h i s c h a p t e r , have near u l t r a v i o l e t a b s o r p t i o n s which a r e b e l i e v e d t o be n-Tf* ( o r n-R) t r a n s i t i o n s . These t r a n s i t i o n s may have c h a r g e - t r a n s f e r c h a r a c t e r . The s o l v e n t e f f e c t i s a r e d s h i f t i n the more p o l a r s o l v e n t s , which i s the same as i s found f o r the a d d u c t s . I t i s b e l i e v e d t h a t the n-TT* a s s i g n m e n t , p o s s i b l y w i t h some c h a r g e - t r a n s f e r c h a r a c t e r , i s the more l i k e l y o f t h e p o s s i b l e a s s i g n m e n t s f o r a l l the e t h y l e n e s s t u d i e d . The s o l v e n t e f f e c t i s the o p p o s i t e o f what would be e x p e c t e d , b u t the c o n t r i b u t i o n o f the c h a r g e - t r a n s f e r c h a r a c t e r to the t r a n s i t i o n , c o u l d e x p l a i n t h i s anomaly. I t i s p o s s i b l e t h a t the e x c i t e d s t a t e , w i t h more c h a r g e -t r a n s f e r c h a r a c t e r than the ground s t a t e , i s s t a b i l i z e d i n p o l a r s o l v e n t s more than the ground s t a t e . 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