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An electron spin resonance study of nitro-substituted naphthalene anion radicals and ion-pairs Nakano, Fumio 1966

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AN ELECTRON SPIN RESONANCE STUDY OF NITRO-SUBSTITUTED NAPHTHALENE ANION RADICALS AND ION-PAIRS BY FUMIO NAKANO B . S c , The U n i v e r s i t y of Tokyo, 1959 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF Master of Science i n the Department of Chemistry We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1966 In presenting t h i s t h e s i s 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 an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study, 1 f u r t h e r agree that permission-for extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s representatives. I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of Ch^ml st.-ry The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8 , Canada Date December 3<5 , 1 9 6 6 . ABSTRACT. The r a d i c a l anions and i o n - p a i r s of 1 , 8 - d i n i t r o -naphthalene and 1 , 4 , 5 , 8 - t e t r a n i t r o n a p h t h a l e n e have been perpared and the e l e c t r o n s p i n resonance spectra have been i n v e s t i g a t e d i n d e t a i l . The spectra were i n t e r p r e t e d completely i n terms of a set of two equivalent n i t r o g e n atoms and three sets of two equivalent hydrogen atoms f o r the 1 , 8 - d i n i t r o n a p h t h a l e n e r a d i c a l , four equivalent n i t r o -gen atoms and four equivalent hydrogen atoms f o r the 1 , 4 , 5 , 8 - t e t r a n i t r o n a p h t h a l e n e r a d i c a l , r e s p e c t i v e l y . The hyper-f i n e s p l i t t i n g constants obtained . are compared w i t h the values derived from molecular o r b i t a l c a l c u l a t i o n s . In the i o n - p a i r s of 1 , 8-dinitronaphthalene the d i s t i n c t a l k a l i metal hyperfine s p l i t t i n g have been observed The magnitude of the metal hyperfine s p l i t t i n g shows remark-able temperature dependency, and the temperature dependency i s i n t e r p r e t e d i n terms of the c a t i o n exchange mechanism b between two nitr.o. groups of 1 , 8 - d i n i t r o n a p h t h a l e n e . In the anion r a d i c a l of 1 , 8-dinitronaphthalene as w e l l as i n the corresponding i o n - p a i r s , anormalous l i n e width v a r i a t i o n has been.observed. This b e h a v i o r . i s i n t e r -preted i n terms of the c a t i o n exchange mechanism and sup-ports the hypothesis proposed f o r Hihe temperature dependency of a l k a l i metal s p l i t t i n g i n the i o n - p a i r s of the compound. I n the anion r a d i c a l of 1 , 4 , 5 , ' 8-tetranitronaphtha-lene the t w i s t i n g angle of the n i t r o group from the plane of aromatic r i n g i s estimated to be (35 t 10 )° from the observed s p l i t t i n g constants by employing the s p i n d e n s i t i e s obtained w i t h McLachlan method. The temperature dependency of the n i t r o g e n and hydrogen s p l i t t i n g s has been determined. The phenomenon i s explained i n terms of a hindered r o t a t i o n of.the n i t r o group .in 1 , 4 , 5 , 8-tetranitronaphthalene. From the asymmetry of the spectra i t i s p r e d i c t e d that the s p i n d e n s i t y on the n i t r o g e n nucleus i s p o s i t i v e . TABLE OF CONTENTS. page A b s t r a c t i Table of Contents i i i L i s t of Tables v i L i s t of Figures v i i Acknowledgement x Chapter I . Basic Theory of E l e c t r o n Spin-Resonance 1 A. I n t r o d u c t i o n 1 B. Some Concepts of E l e c t r o n Spin Resonance 2 C. T h e o r e t i c a l I n t e r p r e t a t i o n of the ;'HJfp'erfine S p l i t t i n g Constant 7 D . R e l a t i o n between the S p l i t t i n g Constant and Spin D e n s i t i e s 9 E. C a l c u l a t i o n of Spin D e n s i t i e s 11 (1) Huckel Molecular, O r b i t a l Method 12 ( 2 ) McLachlan SCF Method. . ' . . . 1 4 Chapter I I . . Experimental Procedures 17 A. I n t r o d u c t i o n 17 B. Reduction w i t h A l k a l i Metals 1$ C. El e c t r o c h e m i c a l Reduction 19 . D . ESR Spectrometer 21 E. V a r i a b l e Temperature Apparatus 22 F, . Chemicals 23 (1) Solvents 23 ( 2 ) Supporting E l e c t r o l y t e s 23 (3) Reagents (4) Compounds Investigated G . Computer . Calculations Chapter I I I . A n i o n . Radical Ion-Pairs of 1,8-. :Dinitronaphthalene Generated by Chemical 1 Reduction 26 . A. Introduction 26 (1) Ion-Pairs 26 (2) Causes of the Metal Hyperfine S p l i t t i n g 27 (3) Temperature Dependency of the Metal. Hyperf ine S p l i t t i n g '?29 a) O s c i l l a t i o n of the Cation 29 . . b) P u l l i n g - o f f Mechanism of Solvent 31 c) Equilibrium between Two Different. Ion-Pairs 32 (4):'- Line Width Variation, of Metal S p l i t t i n g . 33 B. . Electron Spin Resonance Spectra.of 1 , 8-Dinitronaphthalene Ion-Pair's 35 C. A l k a l i Metal Hyperfine S p l i t t i n g 46 D. Alternating Line Widths 49 Chapter IV. . Anion'Radical of 1 , 8-Dinitronaphthalene . Generated by Electrochemical Method 51 A. Introduction 51 B. Electron Spin Resonance Spectra 52 C. Hyperfine S p l i t t i n g Constants 68 D. - Alternating Line Width . 70 i v page 24 24 25 V •E. E f f e c t of Ion S i z e on S p l i t t i n g Constants 79 Chapter V. Anion R a d i c a l of 1 , 4 , 5 , 8 - T e t r a n i t r o -naphthalene 80 A. , I n t r o d u c t i o n 80 B. Hyperfine S p l i t t i n g Constants 110 C. Solvent E f f e c t 113 D. . Temperature Dependency of S p l i t t i n g Constants 118 . E. Asymmetry of the ESR Spectrum 120 B i b l i o g r a p h y 128 Appendix I . Atomic Numbering System . 133 Appendix.II. C o e f f i c i e n t s of the Lowest Unoccupied Molecular O r b i t a l of 1 , 8 - D i n i t r o -naphthalene (Huckel) 134 Appendix I I I . E f f e c t of t w i s t i n g Angle on Spin D e n s i t i e s of 1 , 4 , 5 , 8 - T e t r a n i t r o -naphthalene Anion R a d i c a l 135 Appendix IV. E f f e c t of Oxygen Coulomb I n t e g r a l Parameter on Spin D e n s i t i e s and . C a l c u l a t e d S p l i t t i n g Constants i n 1 , 4 , 5 > 8-Tetranitronaphthalene Anion R a d i c a l 137 v i LIST OF TABLES. page Table 1: Temperature Change of the Metal. Posi t i o n and S p l i t t i n g Constants 30 2: Radii of Cations of A l k a l i Metals 49 3: S p l i t t i n g Constants and g-values of the 1,8-Dinitronaphthalene Anion Radical 64 4: E f f e c t of Twisting Angle $ on Spin Densities and Calculated S p l i t t i n g Constants i n 138-Dinltronaphthalene Anion . 69 5:• Cation Dependency of Line Width Alternation i n ESR Spectra of l a8-Dinitronaphthalene Anion Radical 72 6: Spin Densities and S p l i t t i n g Constants for Anion Radical of I 34,5j8-Tetranitronaphtha-lene 110 LIST OF FIGURES. Figure 1: Glass Aparatus f o r Chemical Reduction 2: M^a Dependence of Line Width of Na-Naphthalene Ion- P a i r 3 : ( a ) ~ y ( h ) : ESR Spectra of 1 , 8 - D i n i t r o -naphthalene Ion-Pair In Li-DME 4 ( a ) ^ ( f : ) : ESR Spectra of 1,8-Dinitro-naphthalene I o n - P a i r i n Na-DME 5 ( a ) ^ ( e ) : ESR Spectra of 1 , 8 - D i n i t r o -naphthalene Ion- P a i r i n 3Ma-THF (72wt#)-DME (28wt#)' 6 ( a ) , ( b ) : ESR Spectra of 1 , 8 - D i n i t r o -naphthalene R a d i c a l i n K-DME System 7: S p l i t t i n g Constants i n Ion-Pairs and Anion R a d i c a l of m- and p - d i n i t r o -benzenes 8: Temperature Change of A l k a l i Metal S p l i t t i n g i n 1,8-Dinitronaphthalene Ion - P a i r s 9 ( a ) ~ ( d ) : ESR. Spectra of 1,8-Dinitro-naphthalene. Anion R a d i c a l i n LiClOi,-DMSO-DMF 10 ( a ) ~ ( d ) : ESR Spectra of 1 , 8 - D i n i t r o -naphthalene Anion R a d i c a l i n NaClOh-.DMSO-DMF 11 ( a ) — ( e ) : ESR Spectra of 1 , 8 - D i n i t r o -naphthalene Anion R a d i c a l i n KCIOj.-DMSO-DMF 12 ( a ) ~ ( c ) : ESR Spectra of 1,8-Dinitro-naphthalene Anion R a d i c a l i n CsClO/j.-•DMSO-DMF 13: ESR Spectrum of 1,8-Dinitronaphthalene Anion R a d i c a l i n KCIO4-DM.SO v i i i page Figure 14: • 15 : 16: . 17: 18 • 1 9 . 20 21 22 23 24 25 26 Temperature Change of S p l i t t i n g Constants of 1 , 8-Dinitronaphthalene Anion.Radical i n LiClO^-DMSO-DMF 67 Mi Dependency of Line Width Vari a t i o n 75 Mechanism of Cation Exchange for Interpretation of Line Width Va r i a t i o n 76 E f f e c t of Oxygen Coulomb Integral Parameter on Calculated S p l i t t i n g Constant 78 a ) ~ ( f ) : ESR Spectra of 1 , 4 , 5 , 8-Tetra-nitronaphthalene Radical i n Li-DME (Fast Scan) 8 l a ) ~ ( e ) : ESR Spectra of 1 , 4 , 5 , 8-Tetra-nitronaphthalene•Radical i n Li-DME (Slow Scan) 84 a)-^/(e): ESR Spectra of 1 , 4 , 5 , 8-Tetra-nitronaphthalene Radical i n Li-THF (Fast Scan) 89 a ) ~ ( e ) : ESR Spectra of 1 , 4 , 5 , 8-Tetra-nitronaphthalene Radical i n LI-THF (Slow Scan) 92 a ) ~ ( d ) : ESR. Spectra of 1 , 4 , 5 , 8-Tetra-nitronaphthalene Radical i n Na-DME (Fast Scan) 97 a ) ^ ( d ) : ESR Spectra of 1 , 4 , 5 , 8-Tetra-nitronaphthalene Radical i n Na-DME (Slow Scan) 99 a), (b): ESR Spectra of 1 , 4 , 5 , 8-Tetra-nitronaphthalene Radical i n Na-THF (Fast Scan) 103 a), (b): ESR Spectra of 1 , 4 , 5 , 8 - T e t r a -nitronaphthalene Radical i n Na-THF (Slow Scan) 104 a ) ~ ( c ) : ESR Spectra of 1 , 4 , 5 , 8-Tetra-nitronaphthalene Radical i n TPAP-DMF (Fast Scan) 107 i x page Figure 27 ( a ) ~ ( c ) : ESR Spectra of 1,4,5*8-Tetra-nitronaphthalene i n TPAP-DMF (Slow Scan) 108 28: Temperature Change of and C( T T i n 1,4,5 s8-Tetranitronaphthalene Anion R a d i c a l 109 29: E f f e c t of T w i s t i n g Angle Q on C a l c u l a t e d S p l i t t i n g Constants 112 30: E f f e c t of Oxygen Coulomb I n t e g r a l Parameter on C a l c u l a t e d S p l i t t i n g Constants of 1 .,4,53 8-Tetrani t r o -naphthalene Anion•Radical 117 31: O p t i c a l Spectrum of 134<,5 *8-Tetra-nitronaphthalene Na-DME System 123 ACKNOWLEDGEMENT I would l i k e to express my sincere appreciation to Professor "C.-A. McDowell for his guidance and encouragement i n the present work.• I would l i k e to thank Dr. J. B. Farmer for his kind advices. . I am grate f u l to Mr. J . S a l l o s and Mr. I. Murkus for their c a r e f u l maintenance of the spectrometer. I am indebted to Dr.. P. H.-H.. Fischer for introducing me to the technique of electro-l y t i c reduction, and.to Mr. D. Kennedy and Dr. P. J . Black for.. their kind supply of computer programs. I.also thank my wife for her help i n preparing the manuscript. CHAPTER I. BASIC THEORY OF ELECTRON SPIN RESONANCE. A. Introduction. Since the f i r s t a pplication of electron spin reso-nance to the t r a n s i t i o n metal ions was made by Zavoisky (1,2), extensive works have been carried out i n thi s f i e l d . The f i r s t a p p l i c a t i o n of the technique to the organic r a d i -cals with which the present thesis concerns was carried out on the o(, -diphenyl.picryl hydrazyl r a d i c a l by Yager (3) and Townes, Turkevich (4), followed by the application to the triphenyl-methyl r a d i c a l made by J a r r e t t and Sloan (5)-Many detailed reviews have been published on the theory or the applications of electron spin resonance (6-15). Some of the.concepts of electron spin resonance that are important i n the present investigation w i l l be b r i e f l y i l l u s t r a t e d i n section B. Since the quantity which can be observed experimentally i s the hyperfine s p l i t t i n g constant, the t h e o r e t i c a l meaning of the s p l i t t i n g constant and the to r e l a t i o n of the s p l i t t i n g .the spin densities w i l l be mentioned In section C .and .D .respectively, followed by a. b r i e f summary of the two methods for the c a l c u l a t i o n of spin densities which were employed i n this t h e s i s . - 2 -B. Some Concepts i n Electron Spin Resonance. A free electron has two kinds of magnetic moments. One i s due to the o r b i t a l motion of the electron and ex-pressed as ^ ' = • - £ 6 ( 1 . 1 ) where i s e ^ /2mc ( m: mass of the electron, c: the v e l o c i t y of l i g h t , e: electronic charge, -/L-: /L/27T , Planck's constant) and i s c a l l e d Bohr magneton, and i s the angular momentum. Another kind of magnetic moment i s caused by the spinning motion of the electron and i s respresented as - U 5 = - ( e f c /Wc )l = ~ 2 / ? s ( 1 . 2 ) where jS i s the spin angular momentum. With the correction from the r e l a t i v i s t i c theory (1.2) i s rewritten as /Us= ( 1 . 3 ) where ^ = 2 . o o 2 3 Therefore the t o t a l magnetic moment of a free electron, When the o r b i t a l angular momentum i s quenched as i n organic free r a d i c a l s solution (8, 16, 17) or i n the cases of some - 3 -t r a n s i t i o n m e t a l i o n s i n c r y s t a l s w h e r e t h e d e g e n e r a c y o f e n e r g y l e v e l s o f d - e l e c t r o n i s l i f t e d b y t h e c r y s t a l f i e l d , we h a v e , = (1 .5) When t h e m a g n e t i c moment o f a n e l e c t r o n e x p r e s s e d b y t h e e q u a t i o n (1 . 5 ) i s s u b j e c t t o a s u f f i c i e n t l y s t r o n g m a g n e t i c f i e l d a l o n g t h e z - a x i s , t h e H a m i l t o n i a n i s w r i t t e n a s ^ = -^Li ^-(-^/3S)H = %fSzN0 (1.6) w h i c h h a s e i g e n v a l u e s r e p r e s e n t e d a s B = %(B^-s Ho ( 1 . 7 ) w h e r e /M<3 i s t h e m a g n e t i c quantum number w h i c h c a n t a k e o n l y t h e v a l u e o f \ o r -\ f o r a n e l e c t r o n s p i n . Thus two e n e r g y l e v e l s e x i s t h a v i n g a s e p a r a t i o n o f • When a n e l e c t r o m a g n e t i c f i e l d o f f r e q u e n c y \J i s a p p l i e d t o t h e e l e c t r o n s y s t e m i n t h e d i r e c t i o n p e r p e n d i -c u l a r t o t h e s t a t i c m a g n e t i c f i e l d , and t h e f o l l o w i n g e q u a t i o n i s s a t i s f i e d b y t h e v a l u e o f ] ^ AY = up Ho a-8) t h e t r a n s i t i o n b e t w e e n two l e v e l s o c c u r s a c c o r d i n g t o t h e s e l e c t i o n r u l e 1 ^ = + ! . Thus e q u a t i o n (1.8) g i v e s t h e - 4 -resonance condition. The nucleus also has a magnetic moment due to the spin angular momentum. The nuclear magnetic moment,ju^ > i s expressed = I (1-9) where nuclear g-factor nucl ear magneton I :nuclear spin angular momentum. The magnetic moment of the electron i s influenced by the magnetic moment of the nucleus, and the hyperfine s p l i t t i n g appears on the electron resonance spectra owing to t h i s e f f e c t . The eff e c t of the nuclear spin appears i n three d i f f e r e n t ways as follows; 1) dipolar i n t e r a c t i o n between the electron spin and nuclear spin 2 ) i n t e r a c t i o n between the nuclear spin and the magnetic f i e l d due to th e . o r b i t a l motion of the electron 3) so-called Fermi contact term. The energy of the f i r s t e f f e c t , E ^ p , i s according to the c l a s s i c a l electromagnetic theory, E ^ p = {gf ^ - ' t)riAi-  l ) V ^  (1-10) where r i s the radius vector between the nucleus and the e l e c t r o n . The equation (1.10) i s r e w i t t e n i n the operator form as Assuming the Aji s and AL T are o r i e n t e d along the z- a x i s , the equation ( 1 : 1 1 ) turns out to be X>4^ = - frp$«p* -yi ( I ~ SCC^O ) S i l z (1-12) where # i s the angle between the rad i u s vector r and the As e x t e r n a l magnetic f i e l d vector H. Since the e l e c t r o n s i n the molecule have d i s t r i b u t i o n s determined by the o r b i t a l wave f u n c t i o n , the vector r^ and Q must be averaged over the d i s t r i b u t i o n . Thus the eigenvalue of the equation (1.12) i s £<ty =-hpfrfr <V 1-^(1- ^A-B)\^>,^I (1.13) Since the s e l e c t i o n r u l e f o r m-j- Is A m]-=0, the c o e f f i c i e n t of m m-j- gives the magnitude of hyperf ine sp-l i t t i n g due to the d i p o l a r i n t e r a c t i o n . From the equation (1.13) , the magnitude i s dependent upon the angle Q , namely, shows anisotropy. Since the equation contains — i-j i n the term to be averaged and i s an odd f u n c t i o n of r , Yr must be an odd f u n c t i o n such as f o r p or d o r b i t a l s to o b t a i n the non-zero value of E d i p . Thus i f the e l e c t r o n - 6 -i s i n an s - o r b i t a l which i s t o t a l l y symmetric, no dipole i n t e r a c t i o n e x i s t s . . I f the r a d i c a l has a tumble motion as In solution, the E ^ p can be p a r t i a l l y or completely averaged out to be zero (18,19), and i t i s usually not necessary to., take this dipolar i n t e r a c t i o n into account i n the study of electron spin resonance i n solution. ...The'second e f f e c t i s expressed, as When the o r b i t a l angular momentum.is quenched, the ef f e c t can be neglected. The t h i r d e f f e c t i s represented as where A~(r) i s DIrac delta function and r i s the radius vector between the nucleus and the electron. The equation (1.15) was. o r i g i n a l l y derived by Fermi (20), and i s sometimes ca l l e d as the Fermi contact'term. As i s evident from the equation., the e f f e c t has no d i r e c t i o n a l property, namely, is, i s o t r o p i c . . For the. electron i n a p- or d- o r b i t a l the iso is. zero, and.the electron i n an s - o r b i t a l only gives the non-zero eigenvalue of the ^ > l g o I t i s this term that mainly contributes to the hyperfine s p l i t t i n g of the electron spin resonance spectra i n solution. - 7 -Summarizing a l l the three types of e f f e c t the Hamiltonian f o r the hyperfine s p l i t t i n g i n t e r a c t i o n , hfs l s r e P r e s e n t e d as r-3 3 - ~ J (1.16) C. T h e o r e t i c a l I n t e r p r e t a t i o n of the Hyperfine S p l i t t i n g  Constant. In t h i s s e c t i o n we w i l l see how the s p l i t t i n g cons-t a n t : w h i c h : i s observed' experimentally i s defined i n . t h e theory of e l e c t r o n s p i n resonance. In general, as was shown by Abragam.and Pryce (21), the i n f l u e n c e * on the s p i n angular, momentum under, the ex-t e r n a l magnetic.field' i s w r i t t e n i n an abbreviated Hamil-tonian form ( s p i n H a m i l t o n i a n , ' ^ s) as The f i r s t term represents the e l e c t r o n i c s p i n - s p i n i n t e r a -c t i o n . This i n t e r a c t i o n does not e x i s t i n f r e e r a d i c a l s which-have.one unpaired e l e c t r o n , and can be neglected. The second term i s due to the Zeeman e f f e c t and more gene r a l i z e d expression of the equation (1.6). The g i s - 8 -the t e n s o r i a l q u a n t i t y and i s simply c a l l e d as g-tensor. The t h i r d term express the hyperfine i n t e r a c t i o n , and i s more, ge n e r a l i z e d r e p r e s e n t a t i o n of the equation(l.16),< A i s a l s o a . t e n s o r i a l q u a n t i t y and i s c a l l e d as the hyperfine s p l i t t i n g tensor. The f o u r t h term represents the quadrupole i n t e r a c t i o n . ' The f i f t h term i s due to the i n t e r a c t i o n of the n u c l e a r : s p i n . w i t h t h e e x t e r n a l magnetic f i e l d . The l a t t e r two.terms are. very small and can be u s u a l l y neglected. .:."'.:rrThus:;' the. ^ spin'iHamiltonian. i s r e w r i t t e n as & S = ? £ + IAS (1.18) For most-free r a d i c a l s i n s o l u t i o n , g and-A.are i s o t r o p i c >1. • ... due to the rapid-tumbling motion of. the r a d i c a l s , and can be regarded- as s c a l a r ..quantities. V-In a. s u f f i c i e n t l y strong magnetic f i e l d the component of a sp i n i s sharp along the .d i r e c t i o n of the f i e l d . When t h e . d i r e c t i o n . o f the f i e l d I s regarded as the z - a x i s , t h e ;Hamiltonian of (1.18) i s w r i t t e n as 'Hi = 9/SWSf - j - !n0S"H- £ S ^ r - O (1.19) Appying the sp i n Hamiltonian to the wave f u n c t i o n of p o l y e l e c t r o n i c system ( r a d i c a l ) , l p , represented as - 9 -= ^TM^t ( 1 . 2 0 ) the equation ( 1 . 2 1 ) i s obtained E f^H'tytl = ^  M 5 H ^ | 3 f t Mx Ms ( i . 2 1 ) where Mg and M-j- are given ;as • Sj 4MJ = , Vftl*-- Ml "f"-i ' ( 1 . 2 2 ) Since the e l e c t i o n rule i s M'=1 and M T = 0 , the resonance s J- ' condition i s - ^ L J = %PH -T- {^B*-Mr ( 1 . 2 3 ) As i s evident from ( 1 . 2 3 ) , i t i s the value of OL that one observes experimentally'in unit of gauss as the hyperfine s p l i t t i n g constant. D. Relation between the S p l i t t i n g Constant and Spin. Densities. • A b r i e f comment w i l l be made on the. hyperf ine i n t e r a c t i o n of an aromatic C-H' proton and the one of nitrogen nuclei.which were investigated i n the present thesis. In case of . the aromatic C-F; proton, the unpaired electron i s in the p_ o r b i t a l . a t the ground state. Since the p o r b i t a l - 10 -has a node on the aromatic plane, the contact term i s zero. The dipolar i n t e r a c t i o n i s averaged out to be zero i n solu-t i o n . Therefore no proton hyperfine s p l i t t i n g should appear i n t h i s case. However the s p l i t t i n g of the order of ^ 25 gauss has been observed i n experiment. The interpretation of t h i s dilemma was attempted i n various ways (3, 2 2 , 23) without any success except for the one hypothesis which involves the 0" - 71 i n t e r a c t i o n for the excited state. In the (T -7T i n t e r a c t i o n theory McConnell ( 2 4 ) , Bersohn (25), J a r r e t t (26) and Weissman (27) showed the s l i g h t mixing of the ground state of the r a d i c a l with the excited state of the r a d i c a l i n which electrons i n 0~-o r b i t a l s are unpaired provides a reasonable picture for the inte r p r e t a t i o n of the hyperfine s p l i t t i n g of the aromatic C-H proton. McConnell (28) proposed the r e l a t i o n for the proton s p l i t t i n g ; a H = o H f I ( i . 2 4 ) where Q,JJ i s a constant and have a value of -25 ~ _ 3 5 gauss, depending upon the aromatic system. ^ i s the proton s p l i t t i n g constant. f>ltc Is the 7t -electron spin density on the carbon atom adjacent to the proton. In general the TC -spin density on r th atomic o r b i t a l , T> i s defined as = (f^s ( i ^ l ^ J | ^ > ( 1 . 2 5 ) - 11 -/\ r ( i ) i s defined so that A r ( i ) = l only when i t h e l e c t r o n i s oh-the r t h atomic o r b i t a l and ^ r ( i ) = 0 elsewhere. With regard to the N]_^ hyperfine s p l i t t i n g , a s i m i l a r expression to the equation (1.24) namely, was found to give good agreements i n c e r t a i n r a d i c a l s (29, 30, 31)' The equation suggested by Rieger and Fraenttel(32) i s more complicated and i s w r i t t e n as O/=(0*f;+ 2.fc- 2 Q J J (1-26> and the. values of Q c and.Q Q were determined experimentally to be ± (99.O ± 10.2), 0 and • + (35.8 ± 5-9), r e s p e c t i v e l y when the McLachlan s p i n d e n s i t i e s are used as the values of Pr's • E. C a l c u l a t i o n of S p i n . D e n s i t i e s . In the preceding s e c t i o n i t has been shown that the s p i n d e n s i t y i s c l o s e l y r e l a t e d to the hyperfine s p l i t t i n g constant. Therefore i f i t i s p o s s i b l e to c a l c u l a t e the s p i n d e n s i t y t h e o r e t i c a l l y , one can p r e d i c t the magnitude of the hyperfine s p l i t t i n g constant. T h e o r e t i c a l c a l c u l a t i o n s of s p i n d e n s i t i e s have been- performed w i t h valence-bond method by•McConnell (24) a n d . J a r r e t t (26), w i t h the u n r e s t r i c t e d Hartree-Foek. method by McConnell and Chesnut (33) 3 w i t h - 12 -the simple Huckel molecular o r b i t a l by Weissman (27) and with the simple SCF method by McLachlan (34). Because of the s i m p l i c i t y of the c a l c u l a t i o n proce-dures the l a t t e r two methods were used i n the present thesis, and w i l l be i l l u s t r a t e d i n the following paragraphs. (1) Huckel Molecular O r b i t a l Method (^5, l6): The theory employs the.following assumptions; a) (J* o r b i t a l s and 7L - o r b i t a l s are completely separated so that one can leave the o~ o r b i t a l s completely out of conside-r a t i o n for aromatic "JT-radicals b) The t o t a l Hamiltonian 3£ i s . the sum of the e f f e c t i v e Hamiltonian h for each -fly-atomic o r b i t a l . c) The t o t a l molecular o r b i t a l Is described as <i%=OL( homnt^pci) 7 ^(2i- I ) & (2*) ) Where 0l»is the antisymmetrizer operator and (£> j_ i s the l i n e a r combination .of the atomic o r b i t a l s r , namely 4 = ix,c,^ (i.28) As the consequences of the assumptions b) and c ) , the many-electron problem " x 3 " i s reduced to the one-electron problem. Now the problem i s to solve the equation. 4o></V') = </; ( 1 . 2 9 ) on b a s i s set of • By using the v a r i a t i o n a l p r i n c i p l e the c o e f f i c i e n t of the % r i n each molecular o r b i t a l i s the s o l u t i o n of the. secular equations; i f H « - ^ S h s ) C K = 0 ( 1 > 3 0 ) where £ j_ can be obtained by s o l v i n g the secular determinant d e t | J H r * - £ S r s f r ? = o . ( 1 . 3 1 ) d) In the simple Huckel method f u r t h e r assumptions are made as f o l l o w s ; s f o r a l l r i f s = r t 1 i f s * r ± 1 The s l i g h t m o d i f i c a t i o n of the parameters i s necessary f o r heteroatoms such as the oxygen and ni t r o g e n atoms of the n i t r o group as f o l l o w s ; Srs H r r = * H r s H r s = 0 - 14 -H H-r r •rs ~ i f s = r + 1 H. r s = 0 i f s ^ r I 1 where and r are d etermined s e m i e m p i r i c a l l y (36, 37) Applying the s p i n d e n s i t y operater defined i n the equation (1.25) to the molecular o r b i t a l thus c a l c u l a t e d , one can o b t a i n the TC-spin d e n s i t y , o n ^ n e r "^ h a t ° m i n the f o l l o w i n g manner. o r b i t a l i n the h a l f occupied molecular o r b i t a l . (2) McLachlan SCF Method; The s e l f - c o n s i s t e n t f i e l d method (SCF) o r i g i n a l l y employed to o b t a i n the b e t t e r approximation of atomic o r b i t a l s (38, 39) can be a l s o a p p l i e d to the molecular o r b i t a l (40). The complete set of simultaneous equations to give the SCF molecular o r b i t a l s and the energy of them have been worked out f o r a r a d i c a l (40). However the c a l c u -l a t i o n procedure i s too l a b o r i o u s to be p r a c t i c a l as i t stands, and some s i m p l i f y i n g assumptions are required to perform a c t u a l c a l c u l a t i o n s ( 4 l ) . The simplest SCF method i s due to McLachlan (3^), and i t i s most f r e q u e n t l y used i n fir = ( C r h a l f occ\2 (1-32) where C^  h a l f occ i s the c o e f f i c i e n t of r t h atomic 7C -- 15 -the study of e l e c t r o n s p i n resonance. I n the s e l f - c o n s i s t a n t f i e l d (SCF) method of mole-c u l a r o r b i t a l s , the t o t a l T C-electron Hamiltonian f o r a r a d i c a l i s given ( 3 9 ) as & = ( - 4 r V - i w ) + i £.£L ( 1 - 3 3 ) where V r i s the p o t e n t i a l due to the nucleus r screend by i t s <T - e l e c t r o n . The i n t e r a c t i o n between TC-electrons i s e x p l i c i t l y taken i n t o account i n t h i s Hamiltonian. According to t h i s i n t e r a c t i o n , i t was shown by McLachlan ( 3 ^ ) , the e n e r g e t i c a l l y lower e l e c t r o n s of c/ -and. ^ff-spin move i n t o the s p a l i a l l y different o r b i t a l s although the e l e c t r o n o r b i t a l i s not a f f e c t e d . Thus the t o t a l 1Z - e l e c t r o n wave f u n c t i o n \p_can be w r i t t e n i n a TC manner of u n r e s t r i c t e d SCF wave f u n c t i o n ( 4 l ) . ^ = <rL(4>?o)<x«)<Tf(i.){$(i) ) ( i - 3 4 ) The p e r t u r b a t i o n on the s p i n d e n s i t i e s due to the e l e c t r o n i n t e r a c t i o n has been c a l c u l a t e d by McLachlan ( 3 ^ ) using s e v e r a l s i m p l i f y i n g assumptions and-employing • the ••Huefee 1 molecular o r b i t a l s as the s t a r t i n g o r b i t a l to be t (Cf.l - C r , £ ) 1 - 16 -where i s the c o e f f i c i e n t of ordi n a r y Huckel o r b i t a l s and C r i are the c o e f f i c i e n t of Huckel o r b i t a l obtained by changing the coulomb i n t e g r a l b ( r to tf / s <*y l*Cr,/>m ' ^ (1-35) where C r, n+1 are the c o e f f i c i e n t of r t h atomic o r b i t a l of.the h a l f f i l l e d molecular o r b i t a l obtained by the ordi n a r y Huckel method. X i s u s u a l l y taken as 1 .2. Thus the s p i n d e n s i t y on r t h atom i s w r i t t e n i n McLachlan method as Although the McLachlan SCF method was o r i g i n a l l y derived f o r a l t e r n a n t hydrocarbon r a d i c a l s , the method has been proved to be a l s o u s e f u l f o r the n i t r o - (37) and cyano-aromatic r a d i c a l anions ( 3 2 ) , The occurrence of negative s p i n d e n s i t i e s can be explained by t h i s method. - 17 -CHAPTER I I . EXPERIMENTAL PROCEDURES. A. I n t r o d u c t i o n . Several methods have been used f o r p r e p a r a t i o n of r a d i c a l anions -. They are a l k a l i metal r e d u c t i o n (42), e l e c t r o l y s i s (43, 44), i r r a d i a t i o n (45, 46) or combination of a l k a l i metal r e d u c t i o n and i r r a d i a t i o n (47). The f i r s t two methods were used i n the present work. B. Reduction w i t h A l k a l i Metals. Chemical r e d u c t i o n was performed i n 1,2-dimethoxyethane (DME), tetrahydrofuram (THF) or mixture of the two, using l i t h i u m , sodium, potassium and cesium. To keep the anion r a d i c a l s t a b l e and e l i m i n a t e the broadening of the s p e c t r a l l i n e s caused by the s p i n - s p i n I n t e r a c t i o n w i t h para-magnetic oxygen (48), a l l the prepa-r a t i o n s were performed under vacuum w i t h the s t r i c t e x c l u s i o n of oxygen. The g l a s s apparatus used i s shown i n f i g u r e 1. The p o r t i o n , marked as F, i s i n s e r t e d i n the c a v i t y and i s made of s i l i c a to decrease the absorption of microwave energy. A f t e r baking out the g l a s s apparatus completely, a small amount of the compound to be reduced i s placed i n F, and the apparatus was connected to vacuum system. A small piece of a l k a l i metal was placed In B, and the part A was sealed. - 1 9 -During evacuation of the apparatus, the metal was sublimed along the side arm to ob t a i n the clean f i l m of the metal on the w a l l i n s i d e the v e s s e l D. A f t e r s e a l i n g o f f at C, solvent was d i s t i l l e d i n t o D from.solvent r e s e r v o i r by c o o l i n g D w i t h l i q u i d nitrogen-Using s e v e r a l cyeles of f r e e z i n g - m e l t i n g procedures, the solvent i n D was completely degassed. A f t e r s e a l i n g o f f at E, solvent was mixed- w i t h the compound at F to o b t a i n r a d i c a l anions. For unstable r a d i c a l s the mixing was per-formed at -95°C i n a 5 {L dewar f i l l e d w i t h methanol cooled to i t s f r e e z i n g temperature (-95°C). Cesium was put i n t o the g l a s s apparatus i n a dry box. Li t h i u m i s d i f f i c u l t to handle, and when t h i s metal i s used, great care should be paid to avoid small e x p l o s i o n of the glass apparatus. The solvents i n the r e s e r v o i r s were kept under vacuum w i t h sodium and anthracene. The s o l u t i o n e x h i b i t e d the greenish blue colour of anthracene r a d i c a l . The con c e n t r a t i o n of compounds reduced i n the solvent was about 10~* M. The mixing r a t i o of the solvent mixture was determined by gas-chromatography. C. Electrochemical' Reduction. The e l e c t r o l y s i s , c e l l designed by Dr.P.H.H.Fischer was used f o r the present work. The d e t a i l s of the e l e c t r o -- 20 --chemical r e d u c t i o n have been given by F i s c h e r (49). N, N'-dimethylformamide (DMF), dimethyl s u l f o x i d e (DMSO) or mixture of both were used as sol v e n t s . Dimethylformamide was chosen because r e l a t i v e l y many works on the study of n i t r o aromatics i n t h i s solvent have been published. D i -meth y l s u l f o x i d e was used because i t was the best solvent f o r a l k a l i metal p e r c h l o r a t e s . D i m e t h y l s u l f o x i d e freezes out at r e l a t i v e l y high temperature and does not have a s u f f i c i e n t l y wide solvent range f o r adequate measurement of the e f f e c t of temperature on the r a d i c a l species. By mixing dimethyIformamide w i t h the solvent the measurable temperature range was extended. The mixture (2DMS0:1DMF) was used i n a l l cases. L i t h i u m p e r c h l o r a t e , sodium perchlo-r a t e , potassium p e r c h l o r a t e , cesium p e r c h l o r a t e and t e t r a - n -propylammonium p e r c h l o r a t e were used as supporting e l e c t r o -l y t e s . The co n c e n t r a t i o n of the supporting e l e c t r o l y t e s was about 0.05 M i n a l l cases and the con c e n t r a t i o n of the compound to be reduced was about 10~*M or l e s s . The weighed compound and e l e c t r o l y t e were d i s s o l v e d i n an erlenmeyer f l a s k and t r a n s f e r r e d i n t o the e l e c t r o l y s i s c e l l . By connecting the c e l l to the vacuum system, the s o l u t i o n was degassed at l e a s t f o r 1 hour at room temperature. The p o t e n t i a l a p p l i e d to the c e l l f o r e l e c t r o l y s i s was measured w i t h respect to the mercury pool e l e c t r o d e . - 21 -D. ESR Spectrometer. The spectrometer used i n the present work i s almost i n d e n t i c a l w i t h the V a r i a n V-k^OO 100 Kc ESR spectrometer. The frequency of X-hand was about 9200 Mc. The microwave power was supplied by a V a r i a n V-153 K l y s t r o n , the fil a m e n t voltage of which was s t a b i l i z e d w i t h a Kepco t r a n s i s t o r i z e d DC power supply. The magnetic f i e l d was supplied by a V a r i a n # V 4012 A 12" magnet which has a 2.5" pole gap, and the magnetic f i e l d was modulated at 100 Kcs. The f i e l d was measured w i t h a proton resonance magnetometer which has a probe w i t h p l a s t i c cap surrounded by a c o i l and f i l l e d w i t h g l y c e r o l . The probe was i n s e r t e d i n t o the magnetic f i e l d as c l o s e l y as p o s s i b l e to the c a v i t y and connected to the magnetometer o s c i l l a t o r FM-modulated at 20 cps. The o s c i l l a t o r supplied a v a r i a b l e frequency around lk Mcs to the g l y c e r o l probe, and the frequency was made to beat w i t h a s i g n a l generator (General Radio Co. Model 1001-A). The frequency of the generator was read d i r e c t l y w i t h a Hewlet Packard 5^25 L E l e c t r o n i c Counter. The 100 Kcs d e t e c t i o n system i s e s s e n t i a l l y the same as the V a r i a n V-4-500 system except that the t r a n s m i t t e r and receiver were separated and shielded by a copper p l a t e to achieve about 15 times of s i g n a l - n o i s e r a t i o . - 22 -Since the s a t u r a t i o n of e l e c t r o n i c l e v e l s of the anion r a d i c a l e a s i l y occurred even at a very low power i n the present work, the microwave power was monitored using a Hewlett Packard microwave power meter (Model 430C). S e n s i t i v i t y of the d e t e c t i o n system and the modulation am-p l i t u d e below,25 m i l l i g a u s s were used to achieve enough r e -s o l u t i o n of the spectra to allow p r e c i s e measurement of the temperature change of s p l i t t i n g s . E. V a r i a b l e Temperature Apparatus. A V a r i a n V-4547 V a r i a b l e Temperature Accessary was used to vary the temperature of the sample. Dry n i t r o g e n gas was precooled by passing i t through.a c o i l e d s t a i n l e s s s t e e l tube immersed i n a 5 JL dewar f i l l e d . w i t h l i q u i d n i t r o gen or d r y - i c e acetone, and was allowed to pass through a c y l i n d r i c a l dewar made of quartz i n the ESR c a v i t y where the sample tube was placed. Temperature was c o n t r o l l e d a c c u r a t e l y by r e g u l a t i n g the flow r a t e using a p r e c i s i o n needle valve i n a d d i t i o n to the ord i n a r y r e g u l a t o r f o r gas c y l i n d e r s . To o b t a i n higher temperature than the ambient one, the dry n i t r o g e n was allowed to flow along a s t i c k heater mounted i n s i d e the v a r i a b l e temperature apparatus. The temperature was measured w i t h a copper-constantan thermo-couple and a Rhodes potentiometer. - 2 3 -F. Chemicals. ( 1 ) Solvents: 1,2-Dimethoxyethane, EK # 4639, was p u r i f i e d by f r a c t i o n a l d i s t i l l a t i o n (b.p. 84 - 8 5°C), refluxed ort sodium metal for several hours, d i s t i l l e d onto fresh sodium pieces, and degassed by using four to f i v e cycles of freezing-pumping procedures. I t was stored with anthracene and sodium on a vacuum system. Tetrahydrofuran, Anachemia Ac 8 9 1 4 , was percolated through alumina column to remove peroxide which might be formed aft e r a long period of storage, treated s i m i l a r l y to DME, and stored on sodium with anthracene. N, N'-Dimethylformamide, Eastman.Spectro Grade, was used without further p u r i f i c a t i o n . Dimethylsulfoxide, Baker Analyzed, was dried i n contact with Molecular Sieve 5A, and used without further treatment. (2) Supporting E l e c t r o l y t e s : Lithium perchlorate, sodium perchlorate, potassium perchlorate and cesium perchlorate were obtained from G.F. Smith Chemical Co. - 24 -These p e r c h l o r a t e s , except potassium p e r c h l o r a t e which was used as supplied were evacuated f o r s e v e r a l hours before use. Tetra-n- p r o p y l ammonium per c h l o r a t e was prepared by t r e a t i n g a 1 0 $ aqueous s o l u t i o n of t e t r a - n - p r o p y l ammonium hydroxide (EK) w i t h an equivalent amount of p e r c h l o r i c a c i d . The p r e c i p i t a t e formed was washed w i t h c o l d water, r e c r y s -t a l l i z e d i n an a c e t o n i t r i l e B w a t e r mixture, and d r i e d w i t h evacuation f o r s e v e r a l hours. White needles were obtained. (3) Reagents: L i t h i u m (B.D.H.), sodium ( F i s c h e r S - 2 0 6 ) , potassium (B and A 2 0 8 0 ) , cesium (Alpha, 99.4$+) were used. (4) Compounds I n v e s t i g a t e d : 1 , 8-Dinitronaphthalene already p u r i f i e d by F i s c h e r (49) was r e c r y s t a l l i z e d from chloroform. Y e l l o w i s h p l a t e s of m.p. 173°C were obtained. 1 , 4 , 5 , 8 - T e t r a n i t r o n a p h t h a l e n e was synthesized by d i n i t r a t i n g 1 , 5-dinitronaphthalene according to the Whitehurst's method (50) as f o l l o w s . 1 , 5-dinitronaphthalene (2g) was d i s s o l v e d i n n i t r i c a c i d (20 cc, d 1 . 5 2 ) , and fuming s u l f u r i c a c i d (20 cc, d 1.84) was added slowly at about 80°C. A f t e r 30 minutes, - 25 -ice was added to the solution u n t i l a c r y s t a l l i n e p r e c i p i -tate appeared, which was collected on a sintered glass c r u i c i b l e , washed, and extracted with a small amount of cold acetone. The residue was c r y s t a l l i z e d from n i t r o -benzene, .pale fine needles were obtained. No trace of l , 5 -dinitronaphthalene was found i n thin layer chromatography of s i l i c a gel using benzene-petroleum ether as eluent. Elemental analysis; found C=39.35, H=1.23, N=17.9^ calculated C=39.0, H=1.3, N=l8.2 . G. Computer Calculations. Molecular o r b i t a l calculations were performed using the computer program supplied by.D. Kennedy (named as HMO-DK-22). Computer p l o t t i n g of ESR spectra were done employing the program supplied by P. J . Black (named as^ESR-PLOT). - 2 6 -CHAPTER I I I . ANION RADICAL ION-PAIRS OF 1,8-DINITRONAPHTHALENE  GENERATED BY CHEMICAL REDUCTION. A. Introduction. (I) Ion-Pairs: When the anion r a d i c a l i s generated with a l k a l i metals i n solvents of low d i e l e c t r i c constant, the hyperfine s p l i -t t i n g (h.f.s.) due to nuclei of the a l k a l i metals appears i n several cases, and the h.f.s. indicates the presence of some kind of ion associations (ion pair),between the anion and the metal. The phenomenon was f i r s t discovered by Adam and Weissman i n the sodium ketyl of benzophenone system (51)' Since that time, the a l k a l i metal s p l i t t i n g s have been observed i n various aromatic molecules such as naph-thalene (52,53), anthracene (53), biphenyl (53), pyrene (53), pyracene (54), m-xylene (55); heteroaromatic molecules such as p h t h a l o n i t r i l e (56), pyrazlne (31,57) 2, 2 ' - d i p y r i d ^ l (58, 59)» nitrosubtituted benzenes (60), tetracyanoethylene (62); ketyls such as benzophenone (51,63), d i - t - b u t y l k e t y l ( 2 4 ) . . The observed behavior of ion-pair suggests that there i s a continuous gradation i n the degree of association, ranging from loosely bound ion-pairs to strongly associated ion-pairs. - 2 7 -An example of the former type i s the naphthalene-sodium system, where the a l k a l i metal h . f . s . i s h i g h l y dependent on temperature and solvent ( 5 2 ) . The c a t i o n does not have much e f f e c t on the s p i n d i s t r i b u t i o n i n the anion i n t h i s system. An example of the s t r o n g l y bound i o n - p a i r i s the m-dinitrobenzene-sodium system, i n which the sodium i o n i s f i x e d i n the v i c i n i t y of one of the n i t r o groups, and s p i n d i s t r i b u t i o n on the i o n - p a i r i s e n t i r e l y d i f f e r e n t from that of the f r e e anion r a d i c a l . The s p l i t t i n g constants are a f f e c t e d very l i t t l e w i t h v a r i a t i o n of the temperature o r , s o l v e n t , so long as the l a t t e r i s of low d i e l e c t r i c constant. (2) Causes of the Metal Hyperfine S p l i t t i n g : A t h e o r e t i c a l treatment of.naphthalene-sodium i o n -p a i r s suggests -i that a charge-transfer mechanism produces the sodium h.f.s.(66). A small amount of the e x c i t e d charge t r a n s f e r s t a t e i n which the outer s - o r b i t a l of the c a t i o n i s d i r e c t l y occupied by the unpaired e l e c t r o n of anion i s mixed w i t h the ground s t a t e . Thus i f the s t a t e i n which unpaired e l e c t r o n i s comp-l e t e l y t r a n s f e r r e d i n t o the lowest unoccupied molecular o r b i t a l of naphthalene i s expressed as '^ r 0 (Ar~, N a + ) , and - 28 -the non-bonding s t a t e which a r i s e s from the mi g r a t i o n of the unpaired e l e c t r o n from the negative i o n i n t o the outer s-o r b i t a l of sodium metal, i s expressed as ijf ^  (Ar, Na), then the wave f u n c t i o n , f o r the ground s t a t e of the i o n - p a i r i s approximated as 1j/- 0(Ar", Na +) + 7 ^ ^ , Na) (3-1) The mixing parameter 7v i s determined from the f i r s t order p e r t u r b a t i o n theory as 7v= - H 1 0 / A E 1 0 (3.2) ' A E 1 0 = E 1 1 L - H 0 0 + e 2 / r = A - I + e 2 / r H i j - < ^ i | 3 i l Y j > where Is the e l e c t r o n i c Hamiltonian of t h i s system, A and I are the e l e c t r o n a f f i n i t y of the aromatic molecule and the i o n i z a t i o n p o t e n t i c a l of the sodium atom, r e s p e c t i -v e l y , and r ' i s the distance between /Mth carbon and the sodium atom. Using Huckel molecular o r b i t a l s f o r naphtha-lene, and a SCF atomic o r b i t a l f o r the sodium atom, Hj_j, e-/r and then A. were c a l c u l a t e d . The metal s p l i t t i n g was given as: Q - M = * f i \ f I Jr(<miV/&>+2\(tl W+ A^Wt>) 0.3) - 29 -The f i r s t term i n the equation (3.3) i s n e g l t p l y s m a l l , the second term contributed to the r e s u l t at most one tenth compared w i t h the t h i r d term. Thus only the where JX^ and I are the magnetic moment: and the t o t a l s p i n angula-r momentum of the Na nucleus i n u n i t of fi , r e s p e c t i v e l y . The c a l c u l a t e d value of (fa was ^ / 0 . 8 gauss, which agrees w e l l w i t h the experimentally observed value. Recently de Boer and Mackor have found i n the Cs-pyracene system that the temperature change of a l k a l i metal hyperfine s p l i t t i n g has a minimum, and the behavior was thought to be caused by the negative s p i n d e n s i t y on the nucleus of the cesium due to spi n p o l a r i z a t i o n (67)• (3) Temperature Dependency of the Metal Hyperfine S p l i t t i n g : The magnitude of metal h . f . s . i s , i n the case of loose i o n - p a i r s , dependent upon the temperature. Three mechanisms have been proposed to i n t e r p r e t the phenomenon. a) O s c i l l a t i o n of the Cation: Here i t i s assumed that the metal i s o s c i l l a t i n g over the node of the 7C*-molecular o r b i t a l , the decrease t h i r d term was r e t a i n d to c a l c u l a t e (Xv\ as - 30 -of temperature makes the amplitude of the o s c i l l a t i o n s m a l l e r , and the overlap between the outer s - o r b i t a l of the c a t i o n and the TL o r b i t a l of anion, so that the s p l i t t i n g becomes smaller. .Aono and Oohashi made a t h e o r e t i c a l c a l c u l a t i o n on naphthalene-sodium system based upon the model mentioned above, and regarding the i o n - p a i r s as a charge t r a n s f e r complex, they i n t e r p r e t e d q u a n t i t a t i v e l y the temperature dependency of the sodium h . f . s . i n the system (66). Assuming the motion of the sodium i o n as a one dimensional harmonic along the x-a x i s and i n t r o d u c i n g the de n s i t y matrix, they c a l c u l a t e d Q . M ' s a s s n o w n in.Table 1. Table 1. Temperature Change of the Metal P o s i t i o n and S p l i t t i n g Constants. ,T(°K) 77 100 150 200 250 300 V < £ **$>(£) ^ & M ^ > (gauss) 0.618 0.40 0.704 0.49 0.861 0.67 0-995 0.79 1Y111. 0.90 11233 0.98 Here^pc*.^is the mean square amplitude of o s c i l l a t i o n of Na+, given as « X i » = j x 2 p ( O d x ^ / j f>Mix (3-5) - 31 -a n d c o r r e l a t e d w i t h A? i .n (3-^) a s A 2 » = A 7 " « * l » I f we a s s u m e j - ^ i n (3.2 i n t e g r a l ( S ) b e t w e e n X - o r b i t a l o f t h e a r o m a t i c m o l e c u l e a n d N a , A - i s p r o p o r t i o n a l t o S a n d t h u s i s d e p e n d e n t o n t h e s y m m e t r y o f t h e l o w e s t u n o c c u p i e d m o l e c u l a r -7c - o r b i t a l t h e c e n t e r o f o s c i l l a t i o n f r o m t h e t r e n d o f t h e t e m p e r a t u r e d e p e n d e n c y . T h u s t h e m e t a l h . f . s . o f N a - b i p h e n y l i o n - p a i r h a s n e g a t i v e t e m p e r a t u r e d e p e n d e n c y , a n d i t i s i n t e r p r e t e d (68,53) a s b e i n g d u e t o t h e s y m m e t r i c d i s t r i b u t i o n o f 7£ m + 1 w i t h r e s p e c t t o t h e p l a n e t h a t i s p e r p e n d i c u l a r t o a n d b i s e c t s t h e 1-1' b o n d a l o n g w h i c h t h e o s c i l l a t i o n o f t h e N a + c a t i o n i s s u p p o s e d t o o c c u r . t o i n t e r p r e t t h e t e m p e r a t u r e d e p e n d e n c y o f a l k a l i m e t a l h . f . s . i n p y r a z i n e - a l k a l i m e t a l i o n - p a i r (31,69). b ) P u l l i n g - o f f M e c h a n i s m o f S o l v e n t ( 4 7 ) : O n c o o l i n g , t h e . d e g r e e o f d i s s c c i a t i o n i n t o s o l v a t e d i o n s i n c r e a s e d , a n d s o l v a t i o n b e c o m e s m o r e e f f e c t i v e a n d t h i s m u s t a p p l y a l s o t o t h e i o n - p a i r . I n t h i s p u l l i n g - o f f m e c h a n i s m t h e s o l v e n t i s b o u n d m o r e t i g h t l y t o t h e i o n s a n d s o t h e m o r e c o m p l e t e i s t h e d i s s o c i a t i o n t h e g r e a t e r i s o f t h e a n i o n (fC m + j-) • H e n c e i t i s p o s s i b l e t o d e t e r m i n e T h i s m e c h a n l i s m h a s a l s o b e e n s u c c e s s f u l l y a p p l i e d - 32 -the decrease i n the h . f . s . coupling of the anion to the c a t i o n . Although t h i s mechanism i s u s e f u l i n some cases i t cannot e x p l a i n the negative temperature dependency as was observed i n Na-biphenyl i o n - p a i r s ( 5 3 ) * c) E q u i l i b r i u m between Two D i f f e r e n t I o n - P a i r s (70,71): The temperature dependency of the sodium s p l i t t i n g i n Na-naphthalene i o n - p a i r s was i n t e r p r e t e d on the bases of r a p i d e q u i l i b r i a o c c u r r i n g between two d i f f e r e n t i o n - p a i r s , ;A and B.: Let A and B have d i f f e r e n t sodium h . f . s p l i t t i n g s Aa and Ab^and the p r o b a b i l i t y of f i n d i n g form A and form B be given Pa and Pb r e s p e c t i v e l y . The e q u i l i b r i u m constant K i s given by K = Pb T b where " Z a and T b a r e the l i f e times of the A and the B ; forms r e s p e c t i v e l y . In the l i m i t of r a p i d exchange the observed sodium hyperf ine ' s p l i t t i n g cZjja i s given by, & N a = P a A a + P b A b = Pa(Aa + KAb) = — -A a + KAb I f a reasonable range of values of Aa and Ab i s experimentally a v a i l a b l e , i t i s p o s s i b l e to determine the - 33 ~ equilibrium constant, K, through the use of equation (3-8) and then by p l o t t i n g log K vs.1/T, one can obtain ther-modynamic quantities for these ion-pairs. (k) Line Width- Va r i a t i o n of Metal S p l i t t i n g : The l i n e width of the h.f.s. of the Na-naphthalene ion-pair varies with the temperature. This behavior has been also interpreted by the rapid interconversion of two d i f f e r e n t ion-pairs (33). The contribution of exchange to the l i n e width i s given i n the l i m i t of rapid .exchange (3^), by the following equation H p 2 W = P a 2 P b 2 ( W a _ w b ) 2 T a ( 1 + K ) ( 3 ' 9 ) where Wa and Wb are the resonance frequencies of the ion-pairs, A and B, and -|- (Aa -Ab) for M^a = t -|- l i n e s " Wa - Wb = • M , o (Aa -Ab) for M^a = t -2— l i n e s Therefore broadening due to the interconversion processes' depends on the magnetic quantum state of the sodium nucleus, M7^a. Thus as shown i n figure 2, the 3 —1_ l i n e s are much broader than the 3 — i _ l i n e s . 2 M HQ Z Ion Dependence of -Pair ( reference /z '2. (4) ( l . ) V-V [Q ) (4) V-X (6) 14) it— Line Width of Na-Naphtha lene 71 ) - 35 -B. Electron Spin Resonance Spectra of 1,8-Dinitronaphthalene  Ion-Pairs. 1,8-dinitronaphthalene showed sharp a l k a l i metal h.f.s. when, i t w®s. treated with lithium or sodium i n DME or mixture of DME and THF. The r a d i c a l was also produced with potassium i n DME without the metal s p l i t t i n g being detectable. Treatment with cesium at -95°C did not give any r a d i c a l species. Radicals were not produced i n THF ~ only, possibly due to the i n s u f f i c i e n t s o l u b i l i t y of the compound i n that solvent. Since the l i n e s were r e l a t i v e l y broad and the spectra were complicated owing to the super-po s i t i o n of the metal s p l i t t i n g , the accurate determination of s p l i t t i n g constants of protons and nitrogen nucleus was u not possible. Therefore no attempt was made to psrsue ; : studies of the temperature change of these s p l i t t i n g s . In the Li-DME system, the r a d i c a l solution was colored f a i n t brown. The spectra were obtained for the range from -38°C to 50°C. The spectra are shown i n figures 3 (a) to 3 (h). The metal s p l i t t i n g was too small to be resolved when the temperature was below 0°C. In the Na-DME system the colour was pale brown and gradually darkened. The spectra were obtained for the tempera-ture range from -51°C to +50°C. The a l k a l i metal could not Figures 3 ( a ) ~ ( h ) ESR Spectra of I, 8-Dinitronaphihalene Ion Pair in Li-DME I I (b) -M°C 3 2 5 0 . 4 6 3 2 5 1 . 2 4 3252.53 3257.13 3361.15 3 2 6 5 . 3 0 tort*A/VV\ ( c ) » B ° C 3251.31 3 256.52 3261.15 3265.49 3 2 5 0 . 4 6 | 3 2 4 9 . 8 5 3250 .95 ( d ) - 9 a C 3251.85 3255.79 3254.10 3 2 5 1 5 7 3252.13 3252.53 3251.54 3252.27 3251.94 3252. - 4o -be resolved when the temperature was below 0°C. The spectra are shown i n f i g u r e s 4(a) to 4 ( f ) . In the Na-DME-THF system the r a d i c a l s o l u t i o n was colored pale brown. However the c o l o r g r a d u a l l y darkened. In s e v e r a l hours a f t e r p r e p a r a t i o n a pale v i o l e t c o l o r appeared i n the s o l u t i o n without changing the c h a r a c t e r i s t i c s of the spectra. When the solvent mixture c o n s i s t i n g of THF (72 wt$) and DME (28 wt$) was used, the spectra were very s i m i l a r to those obtained i n the system p r e v i o u s l y mentioned. Therefore only t y p i c a l examples are shown i n f i g u r e 5-In K-DME the s o l u t i o n was greysh-blue. Since the spectra d i d not e x h i b i t any detectable metal s p l i t t i n g , no temperature study was performed. A t y p i c a l spectrum i s shown i n f i g u r e 6. Although a few previous works on n i t r o a r o m a t i c s have been published (60,61), they were only concerned w i t h n i t r o -s u b s t i t u t e d benzenes. Moreover the a l k a l i metal s p l i t t i n g s found i n these system were temperature independent and the spi n d i s t r i b u t i o n was found to be s t r o n g l y perturbed as exem p l i f i e d i n ..figure 1. Figures 4 ( c. ),~^, ( f ) ESR Spccira of 1,8-QJ nifronaphf haiene Ion Pc i r in No-DME 3260.56 3265.12 (c ) 9 ° C 3270.52 3254.31 ( d ) 2 0 ° C 3265.02 3270.75 Figures 5 ( a ) ~ ( o ) ESR Spectra of 1, 8-Din itronaphf halene ( c ) 2 0 ° C - 5^ -Figures e { G ),( b ) E S R Spectra of 1,8- Dinitro---naphfhalene Radical in K-DME System { Q ) I 4 ° C 2 0 °--.C"> Anion R a d i c a l Ion P a i r s Figure 7. S p l i t t i n g Constants (gauss) i n Ion - P a i r s and  Anion R a d i c a l of m- and p-Dinitrobenzenes (60, 6 l , 73). Thus these i o n - p a i r s ' can be described a s . s t r o n g l y a s s o c i a t e d i o r v p a i r s . The metal h . f . s . of 1,8-dinitronaphthalene was found to be temperature dependent and the s p i n d i s t r i b u t i o n was not perturbed much by the a s s o c i a t i o n . o f c a t i o n s as w i l l be described l a t e r . Thus the i o n - p a i r s can be regarded as a l o o s e l y bound i o n - p a i r s , and t h i s i s the only case where the n i t r o s u b s t i -tuted compound forms l o o s e l y bound i o n - p a i r s . C. A l k a l i Metal Hyperfine S p l i t t i n g . Since the metal s p l i t t i n g was a qua r t e t , only one c a t i o n was a s s o c i a t e d with-the anion r a d i c a l . The metal h . f . s . increased w i t h temper a t}vre as shown i n f i g u r e 8. ° L i in DUE o Na in THF - DME A HQ in DME Figure 8 o © A © - 3 0 - 2 0 -10 Temperature in 1,8-Dini o A o © A A Temperature ( 0 10 2 0 3 0 Change of Alkali Metal S tronaphf halene Ion-Pairs 4 0 - 48 -The temperature dependency would be i n t e r p r e t e d i n terms of e q u i l i b r i u m of two d i f f e r e n t i o n - p a i r s ' . However, i f two d i f f e r e n t i o n - p a i r s are present, the h . f . s . should show the s p e c i f i c broadening as mentioned i n s e c t i o n A-(4) of t h i s chapter. One might o b t a i n the c o n d i t i o n f o r the s p e c i f i c l i n e broadening by lowering the temperature of the s o l u t i o n . However no such behavior was a c t u a l l y observed. Therefore the temperature dependency may be caused by the o s c i l l a t i o n mechanism. As shown i n Appendix I I , the lowest unoccupied Huckel molecular o r b i t a l of 1,8-dinitronaphthalene i s antisymmetric, and has a node on a symmetry plane passing through 9 and 10 p o s i t i o n s and perpendicular to the aromatic plane. The o s c i l l a t i o n probably occurred v e r t i c a l l y and w i t h respect to the plane, and p o s s i b l y . i n the v i c i n i t y of n i t r o groups which have the highest negative charge d e n s i t i e s . With the temperature the c a t i o n t r a v e l s away from the plane so that the overlapping w i t h TL-electron increases. There may be a shallow p o t e n t i a l minimum between two.nitro groups which can i n f l u e n c e only small c a t i o n s such as l i t h i u m and sodium. Cs+ and K+ may be too l a r g e to be s t a b i l i z e d at the p o t e n t i a l minimum, and that may be the reason why Cs+ and K+ d i d not produce s t a b l e i o n - p a i r s w i t h the compound. - 49 -This p o s t u l a t e may be r a t i o n a l i z e d , i f one considers i o n r a d i i of a l k a l i metal c a t i o n s shown i n t a b l e 2, and the distance between two n i t r o groups of 1,8-dinitronaphthalene ( ~ 2.4 £ ) . Table 2. R a d i i of Cations of A l k a l i Metals. r(A) Li+ 0.60 Na+ 0.90 K+ 1.33 Cs+ 1.66 (NBu 4)+ 3.5 The presence of the shallow p o t e n t i a l minimum between the two n i t r o groups may be the main reason why t h i s substance i s the only n i t r o compound that can form a l o o s e l y bound i o n -p a i r . D. A l t e r n a t i n g Line Widths. Although the metal s p l i t t i n g d i d not e x h i b i t any s p e c i f i c l i n e , broadening, the l i n e s due to. the n i t r o g e n atoms and hydrogen atoms showed a pronounced behavior of a l t e r n a t i n g l i n e width as shown, say, i n f i g u r e 3. The second outermost t r i p l e t disappeared below 0°C. The l i n e width became g r a d u a l l y sharpened and the i n t e n s i t y of the t r i p l e t increased w i t h temperature. - 50 -As the phenomenon a l s o appeared i n case of the anion r a d i c a l produced by e l e c t r o l y s i s , and there i s l i t t l e d i f f e r e n c e between the behavior of i o n - p a i r s and the anion radmcalj the phenomenon w i l l be discussed i n chapter IV. - 51 -CHAPTER-IV. ANION 1 RADICAL OF 1,8-DINITRONAPHTHALENE  GENERATED BY ELECTROCHEMICAL METHOD. A. I n t r o d u c t i o n . E x t e n s i v e s t u d i e s h a v e b e e n c a r r i e d o u t w i t h a n i o n r a d i c a l s o f n i t r o a r o m a t i c s g e n e r a t e d b y t h e e l e c t r o c h e m i c a l m e t h o d . M a k i and Geske m e a s u r e d t h e s p l i t t i n g c o n s t a n t s o f n i t r o - a nd d i n i t r o b e n z e n e s (44, 74). R i e g e r and F r a e n k e l • (37) f o u n d t h a t t h e s u i t a b l e MO p a r a m e t e r s f o r t h e s e n i t r o a r o m a t i c s a r e ; « N = <* + 2.2^ , 0(Q = o<+ 1.4£ ; a n d t h e n i t r o g e n s p l i t t i n g c o n s t a n t o f n i t r o g r o u p , c a n be c a l c u l a t e d a s Q N = +(99.otL0.2) f> N + ( 3 5 . 8 t 5 . 9 ) f 0 ( ^ 2 ) w h e r e f^ and ^ a r e s p i n d e n s i t i e s c a l c u l a t e d b y M c L a c h l a n m e t h o d . The p a r a m e t e r s a n d t h e e q u a t i o n f o r w e r e u s e d f o r 1 , 8 - d i n i t r o n a p h t h a l e n e i n t h e p r e s e n t i n v e s t i g a t i o n . No o t h e r w o r k ha^e b e e n p u b l i s h e d a b o u t ESR o f n i t r o s u b s t i -t u t e d n a p h t h a l e n e e x c e p t t h e one b y F i s c h e r and M c D o w e l l (75). F i s c h e r and M c D o w e l l r e p o r t e d t h e • E S R s p e c t r a o f 1,8-d i n i t r o n a p h t h a l e n e a n i o n r a d i c a l p r o d u c e d b y e l e c t r o l y s i s u s i n g t e t r a - n - p r o p y l ammonium p e r c h l o r a t e t o p r o v i d e t h e - 52 -b counter i o n , but d i d not f i n d any anosmalous l i n e broadening which was observed w i t h sodium p e r c h l o r a t e i n the present work. B. E l e c t r o n Spin Resonance Spectra. E l e c t r o l y s i s of 1 , 8-dinitronaphthalene i n each s o l u t i o n r e s u l t e d i n the f o l l o w i n g colour being produced; system Colour of the R a d i c a l S o l u t i o n E l e c t r o l y s i s Voltage (vs. Hg-pool) Figures LiClOjj-DMSO-SMF g r e y i s h brown 1.10 9 NaC10^-DMS0-DMF g r e y i s h brown 1.25 10 KCIO^-DMSC-DMF greenish yellow 1.20 11 CsC10^-DMS0-DMF greenish yellow 1.15 12 NaClO^-DMF pale grey 1.20 — KCIO^-DMF brown 1.20 — KCIO^-DMSO greenish yellow 1.20 13 T y p i c a l examples of the spectra obtained are shown i n the f i g u r e s i n d i c a t e d i n the above t a b l e . S p l i t t i n g constants obtained are tabulated i n t a b l e 3, which was f i n a l l y checked by s y n t h e s i z i n g the spectra using a computer program ESR-PLOT. Some of the computed spectra are shown along w i t h the a c t u a l spectra. Figures 10 ( a ) M d ) ESR Spectra of 1,8 - Dinitronaphthale Radical in Na CI04 - DMSO-DMF 3265.89 (d) 22 ° C Figures II ( a ) ~ ( e ) ESR Spectra of 1,8-Dinitronaphthalene Anion Radical in KCIO 4 -DMF -DMSO o o ID ro (e ) Computed Spectrum (for 35°c ) Figures 12 ( a ) ~ (c) ESR Spectra of 1,8-Dinitronaphthalene Anion Radical in Cs Cl O4 - DMSO - DMF 3255.18 3260.18 ( a ) 2 3 ° C 1 O N 3270.17 3256.66 ( b) Figure 13 ESR Spectrum of 1 , 8 - Dinitronaphthalene Anion •KC!0 4~DMS0 ( S3 c C ) - 64 -In the system c o n t a i n i n g NaClO^ the l i n e s were r e l a t i v e l y broad and overlapped e x t e n s i v e l y , which made i t d i f f i c u l t to measure the s p l i t t i n g constants a c c u r a t e l y . Table 3. S p l i t t i n g Constants and g-values of the 1 , 8-Dinitronaphthalene Anion R a d i c a l . system . LiC10^-DMS0-DMF temperature (°C) -17 -5 +6 +23 ft(N) ft(H2)and£l(H4) Q(H3) g-value 3.23 3.20 3.22 3.20 3.65 3 .80 3-7g 3.80 3.62 3.70 3-76 3.85 0 . 9 8 0 . 9 2 1 .05' 1 .03 2 .oo4l 2.0042 system NaClO^-DMSO-DMF ^ 3.97 — 3-^5 a(H 3) ~ 1.05 g-value - 65 -system KC10 4-DMSC-DMF KClO^-DMSO temperature (°C) -9 +23 +35 +23 d(N) 3.^0 :3;.^0 3.29 3.30 d(H 2)and 3-75 3-70 3.67 3.67 3-70 3-75 3.76 3.60 tt(H3) 0.98 1.03 1.03 I.03 g-value 2 . o o 4 l 7 2.004lg 2 . 0 0 4 l 3 2.0043 system KG10^-DMF C S C I O 4 --DMSO-DMF TPAP-DMF (F i s c h e r ) temperature ( UC) +23 +23 +36 +23 ff(N) 3.82 3.23 3.26 3.03 (2(H2)and (2(Ei;)' 3.52 3.70 3.70 3.73 3.^6 3-68 3.70 3.63 (2(H 3) 1.03 1.10 1.03 0.95 g-value 2.0042 2.0041 2.0070 - 66 -S p l i t t i n g constant e v i d e n t l y changed w i t h temperature. For example i n the LiC10^-DMSO-DMF system the cross-marked l i n e s of the spectrum at -17°C emerged i n t o the cross-marked s i n g l e l i n e i n the spectra at +6°C owing to the s l i g h t decrease og the n i t r o g e n s p l i t t i n g . :. The behavior was i l l u s t r a t e d i n f i g u r e 14 u s i n g s t i c k diagrams. The l i n e p o s i t i o n s move i n the d i r e c t i o n i n d i c a t e d by arrows w i t h decrease of the n i t r o g e n s p l i t t i n g constant. However the temperature v a r i a t i o n of the s p l i t t i n g was too small to be measured w i t h s u f f i c i e n t accuracy, and ther e f o r e no i n t e r p r e -t a t i o n on the temperature change w i l l be attempted i n the present work. - 4 ° C J..— 1 1 I 1J_ x . J L ± - 17 ° C Q N =3.30 Q H 2 = Q H 4 =3.65 Q H 3 =1.00 Theoretical Spectrum ( for - I7 °C ) gauss ^ H 2 •aN Figure 14 Temperature Change of Splitting Constants of 1,8-DNN Anion Radical in L 1 C I O 4 - D M S O - D M F - 68 -C. Hyperfine S p l i t t i n g Constants. F i s c h e r and McDowell pointed out that there e x i s t e d a l a r g e d i s c r e p a n c y . i n s p l i t t i n g constants of 1 , 8 - d i n i t r o -naphthalene between molecular o r b i t a l c a l c u l a t i o n s and experimental r e s u l t s , and that the discrepancy might be due to the s t e r i c i n t e r a c t i o n between two n i t r o groups (75). One of the simplest methods which can be used to t r e a t t h i s . i n t e r a c t i o n q u a n t i t a t i v e l y , i s to assume that the plane of n i t r o group i s twi s t e d from the plane of aromatic r i n g by an angle 9 . Since a c t u a l spectra showed a outer-most 1:2:1 t r i p l e t c l e a r l y and the spectra can be i n t e r p r e t e d completely i n terms of a set two equivalent n i t r o g e n s , the $ should be the same f o r both n i t r o groups of the molecule. Thus assuming the resonance i n t e g r a l between the carbon atom on the aromatic r i n g and the n i t r o g e n atom, ^ Q ^ , to be; ^ C N = f °CN 6 o § ^ * 1 , 2 •§ c o s &  3 ( 4 ' 3 ) molecular o r b i t a l c a l c u l a t i o n s using both the.Huckel and the McLachlan method were performed. The r e s u l t s are shown i n t a b l e 4-. - 69 -Table 4. E f f e c t of Tw i s t i n g Angle & on Spin' D e n s i t i e s and  Ca l c u l a t e d S p l i t t i n g Constants i n 1 ,8-Dinitronaphthalene Anion. f.OFl.2f( £=0°) ^=1 .04^(^=30° ) p o s i t i o n HMO McL IO.I HMO McL 1 0.0356 0.0028 o.o4i4 0. 0129 • ' . . 2 • 0.1228 0.1763 4.18 0.1109 0.1563 3.70 • • . 3 :{(;• 0.0095 -0.0455 1.08 0.0113 -O.O386 0.91 4 0.l4l2 0.2152 5.10 0.1325 0. 1994 4.73 9 0 -0.0095 0 -0. 0103 10 0 -0.0430 0 -0. o4o4 11(N) O.O63I 0.0617 1.97 0.0692 0.0692 2.34 13(0) 0.0639 0.0579 0.0674 O . 0 6 3 O Experimental |<3.l p o s i t i o n HMO McL TPAP-DMF . KCIO^-DMSO 1 0.0489 0.0290 2 0.0960 0.1299 3.08 3.63 3 .60 3 0.0137 -0.0299 0.71 0.95 1.03 4 0.1220 0.1792 4.25 3.73 3.67 9 0 -0.0115 10 0 -0.0359 11(N) 0.0769 0.0774 2.73 3.03 3.30 13(0) 0.0712 0.0688 - 70 -Although the agreement i s s t i l l not so impressive, i t i s surely.improved. Therefore one can reasonably assume the n i t r o group i s tw i s t e d from the plane of the aromatic r i n g system. In f a c t , r e c e n t l y , Kojima and Nagakura have reported as the r e s u l t of vacuum u l t r a v i o l e t spectroscopic studies that the t w i s t i n g angle of the n i t r o group i n the 1,8-d i n i t r o n a p h t h a l e n e molecule i s about 60° (76). I t i s qu i t e p o s s i b l e t h a t the n i t r o groups are a l s o twisted.mn anion r r a d i c a l although the t w i s t i n g angle may be smaller than i n n e u t r a l molecule owing to the greater e l e c t r o n d e l o c a l i z a t i o n caused by the e x t r a odd electeon i n anion r a d i c a l . D. A l t e r n a t i n g Line Width. Line width a l t e r n a t i o n was c l e a r l y observed f o r the .. anion r a d i c a l of 1,8-dinitronaphthalene i n the ..NaClO^-DMSO system as shown.in f i g u r e 10. This behavior* was a l s o observed i n i o n - p a i r s of the compound w i t h l i t h i u m and sodium in- DME or mixture of DME and THP. Lines f o r which Mz(£.Ni)=0, t2 are sharp; and l i n e s f o r which M z ( ^ N ^ ) = t l are broadened. Lines f o r which M z(22H i)=ll are sharp and l i n e s f o r which Mz(2Hj_)=0 are broadened. The e f f e c t i s more pronounced f o r the hydrogen s p l i t t i n g s than f o r the n i t r o g e n s p l i t t i n g , and the l i n e s of Mz(y )=0 do hot appear when the temperature i s below 0°C. - 71 -The a l t e r n a t i v e l i n e width e f f e c t decreases w i t h v: temperature as a l s o shown i n f i g u r e 10. . I t appears that the l i n e w idth a l t e r n a t i o n of the n i t r o g e n s p l i t t i n g s does not vary much w i t h temperature. The phenomenon of a l t e r n a t i n g l i n e widths have been i n v e s t i g a t e d on s e v e r a l cases. For durosemiquinone, the e f f e c t was a s c r i b e d to the c i s - t r a n s isomerism (77),and f o r m-dinitrobenzene (78), i t was. a t t r i b u t e d to the fact, t h a t the plane of n i t r o group are enforced to be out of the plane of the aromatic r i n g due to i n t e r a c t i o n w i t h the so l v e n t . In case of the potassium pyracene i o n - p a i r i n t e t r a -hydrofuran c a t i o n exchange between two equivalent s i t e s were proposed as a mechanism of l i n e width a l t e r n a t i o n (79)» The migrant species which o s c i l l a t e s between two equ i v a l e n t s i t e s i s not n e c e s s a r i l y a c a t i o n , and can be a solvent molecule.: (80). In case of the present r a d i c a l , the l i n e width a l t e r n a t i o n was observed only when l i t h i u m and sodium ions are present, was not observed f o r any other c a t i o n s , and was independent of solvent as shown i n ta b l e 5. - 72 -Table 5. Cation Dependency of Line Width A l t e r n a t i o n i n ESR Spectra of 1,8-Dinitronaphthalene Anion R a d i c a l . system Metal h . f . s . Line Width A l t e r n a t i o n Li-THF-DME . observed a l t e r n a t i o n Na-THF-DME observed a l t e r n a t i o n Li-DME observed a l t e r n a t i o n ; Na-DME observed a l t e r n a t i o n : K-DME .ntofeeobseriyed no a l t e r n a t i o n LiClO^-DMSO-DMF not observed no a l t e r n a t i o n NaC10^-DMS0-DMF . not observed a l t e r n a t i o n KClOj,.-DMSO-DMF not observed no a l t e r n a t i o n CsClO^-DMSO-DMF not observed no a l t e r n a t i o n KCIO^-DMSO not observed no a l t e r n a t i o n TPAP-DMF(r e f.8) not observed no a l t e r n a t i o n THF: Tetrahydrofuran, DME: 1,2-Dimethoxyethane DMSO: . D i m e t h y l s u l f o x i d e , DMF: N,N'-Dimethylformamide TPAP: Tetra-(n-propyl)-ammonium p e r c h l o r a t e - 73 -The c a t i o n dependency and the solvent independency of the phenomenon i n d i c a t e that the behavior i s probably due to the c a t i o n exchange mechanism. Therefore the phenomenon.will be discussed i n d e t a i l assuming the c a t i o n exchange mechanism. Let us consider the e q u i l i b r i u m (4.4). MA j"* M+ + A" (4.4) whEEe M + and A" are r e s p e c t i v e l y a c a t i o n and a r a d i c a l anion. I f the v e l o c i t i e s of forward and backward r e a c t i o n s are s u f f i c i e n t l y l a r g e , and the l i f e t i m e s of the r a d i c a l species become s u f f i c i e n t l y s h o r t , then as a consequence of the un-c e r t a i n t y p r i n c i p l e , the energy l e v e l s of the various s p i n s t a t e s of the r a d i c a l cannot be sharp. Because of this un-c e r t a i n t y i n energy l e v e l s , e.s.r. t r a n s i t i o n s between them w i l l be broadened. This broadening i s expressed i n terms of the mean l i f e - t i m e of the r a d i c a l , t , as f o l l o w s ( 4 7 ) where t : the mean l i f e - t i m e (sec) AY •• h a l f - h e i g h t l i n e width (c y c l e / s e c ) I f the r a d i c a l possesses two equivalent s i t e s w i t h which the counter i o n may i n t e r a c t , then t h i s l a t t e r i o n can migrate between the two s i t e s . The process may be w r i t t e n as - 74 -NA <• >AM (4.6) k b Line-width a l t e r n a t i o n w i l l occur when the l i f e - t i m e of each c o n f i g u r a t i o n i s comparable w i t h the r e c i p r o c a l of the d i f f e r e n c e s between the hyperfine c o u p l i n g constants. Consider the case where a c a t i o n i s m i g r a t i n g between p o s i t i o n 1 and 2 of r a d i c a l , and assume the only one nucleus i s a t each p o s i t i o n . When the l i f e - t i m e of each c o n f i g u -r a t i o n i s s u f f i c i e n t l y short to cause l i n e width a l t e r n a -t i o n , the width of any component of the e.s.r. spectrum i s given by where y i s the gyromagnetic r a t i o of the e l e c t r o n , t i s the mean l i f e - t i m e of the r a d i c a l i n a p a r t i c u l a r con-f i g u r a t i o n , •]_ and (X^ are the s p l i t t i n g constants of the two p o s i t i o n s i n that c o n f i g u r a t i o n , and M^, and M 2 are the appropriate magnetic quantum numbers. I f CLand d 2 are not equal, then only those components f o r which M^_ =M2 w i l l remain sharp. The behavior i s i l l u s t r a t e d f o r two equivalent n i t r o g e n n u c l e i and f o r two equivalent hydrogen n u c l e i ( f i g u r e 1 5 ) . I -I I o / X -2 0 0 0 I -I 4 $ pn \B|7 p7 N \ / I (o ) TWO Nitrogen Nuclei ( Reference 81 ) I 0 l i I N M| S low Exchange Intermediate Exchange Fast Exchange JL 2 j . 2 1 i N 2 x 2 2 Y^//////\ \ B \ \ i l I i l l 2 0 N (b) Two Hydrogen Nuclei Figure 15 M- Dependency of Line Width Var iat ion N; Narrow Line B', Broad Line - 76 -In the l i m i t of extreme broadening, only the hyper-f i n e s p l i t t i n g l i n e s f o r which M1=M2 w i l l remain, and thus i t w i l l appear as i f the s p l i t t i n g were due to only one of the two s i t e s . However the apparent hyperfine s p l i t t i n g w i l l be twice as much as the true value and the i n t e n s i t y d i s t r i b u t i o n w i l l be obtained by squaring the expected d i s t r i b u t i o n f o r one p o s i t i o n . I f 67. i and CL 2 a r e known, t may be estimated from the l i n e width of the broad components of the spectrum u s i n g the equation (4.4). Thus, app l y i n g the theory so f a r atated to the present r a d i c a l , the procass can be represented as i n f i g u r e 16. Figure 16. Mechanism of Cation'Exchange f o r I n t e r p r e t a t i o n  of Line Width V a r i a t i o n . ( I ) ( I I ) There e x i s t a set of two equivalent n i t r o g e n n u c l e i and three sets of two equivalent hydrogen n u c l e i . - 77 -According to the theory, the l i n e s of M 7 (II t 2 w i l l be sharp, the l i n e s of M z ( H N ^ ) = t l w i l l be broad. The l i n e s of Mz(ZHj_)=±l w i l l be sharp and l i n e s of MZ(T1E±)=0 w i l l be broad. These types of behavior were a c t u a l l y observed. Assuming f o r s i m p l i c i t y that the e f f e c t of c a t i o n coordina-tioncon-one n i t r o group i s represented by the increase of oxygen coulomb i n t e g r a l of the n i t r o group, then change of s p l i t t i n g constant on the n u c l e i concerned can be c a l c u l a t e d u s i n g molecular o r b i t a l treatment. Shown i n f i g u r e 17 are the r e s u l t s obtained by McLachlan method us i n g the parameters represented by equations (4.1) and usi n g the equation \M = 23.7 ( 4- 8) where ^ i s McLachlan s p i n d e n s i t y of the carbon atom adjacent to the hydrogen nucleus concerned. For the sets of H 2 and Hy, and H , the d i f f e r e n c e s between the s p l i t t i n g constants on the two c o n f i g u r a t i o n s , Cb\~ &2> are l a r g e , and according to the equation (4.7)s the l i n e width broadening are expected to be l a r g e . The d i f f e r e n c e i s very l i t t l e f o r the set of H3 and Hg, and hence l i t t l e a l t e r n a t i o n w i l l be expected f o r these n u c l e i . Again these d i f f e r e n t behaviors were c l e a r l y observed i n our experiments. S.4 Figure 17 .6 Oxygen Couterafo Integral Coefficient, £. E ^ : G € " J ©I? Oxygen Coul< Pares mete?1 on Calculated Splotting Constant ~ 79 -E. E f f e c t of Ion S i z e on S p l i t t i n g Constants. The n i t r o g e n s p l i t t i n g changes d r a s t i c a l l y w i t h the s i z e of the c a t i o n . The hyperfine s p l i t t i n g constants C t N t s i n the system of DMSO-DMF at 23°C are; E l e c t r o l y t e LiClO]. NaCIO,, KCIO^ CsClO^ & N (gauss) 3 - 2 0 4 . 0 0 3 . 4 0 3 - 2 3 This tendency i s the same as that .observed i n the trinitrobenzene-DMSO system ( 8 2 ) . The r e s u l t s a l s o i n d i c a t e that the c a t i o n i s i n v o l v e d in- the r a d i c a l system, and support the c a t i o n exchange mechanism proposed to i n t e r -p r e t the l i n e w idth a l t e r n a t i o n . I t appears unusual that &^ i s the smallest f o r ' L i C l O ^ . The r e s u l t together w i t h the f a c t that no l i n e .Width a l t e r -n a t i o n was observed i n LiClOj,-DMSO-DMF system may be inter?? preted i n the f o l l o w i n g way. Hogen-Esch and-Smid reported i n t h e i r i n v e s t i g a t i o n of f l u o r e n y l - a l k a l i metal i o n - p a i r s that the a l k a l i metal i o n can be s t r o n g l y solvated by the solvent molecules and the tendency of s o l v a t i o n increases w i t h the decrease of i o n s i z e of a l k a l i m e t a l s ( 8 3 ) . In the present case the L i i o n i n LIC'IO^-DMSO-DMF system .may be s t r o n g l y s o l v a t e d , and the strength, of i n t e r a c t i o n between the c a t i o n and anion r a d i c a l may be c o n s i d e r a b l y decreased so that i t i s comparable to that of the Cs i o n . - 8o -CHAPTER V. ANION RADICAL OF 1,4.5,8-TETRANTTRONAPHTHALENE. A. I n t r o d u c t i o n . The anion r a d i c a l , off 1,4,5,8-tetranitronaphthalene (TNN) was produced 'both c h e m i c a l l y and e l e c t r o l y t i c a l l y . The anion r a d i c a l produced w i t h sodium or l i t h i u m was comparatively unstable and was prepared at -95°C A small s i g n a l was observed when TNN was tr e a t e d w i t h Na-K a l l o y . However the s i g n a l degraded very r a p i d l y even at -95°C, and could not be measured. Each s o l u t i o n e x h i b i t s the f o l l o w i n g c o l o u r : ' System .Colour Figures •TNN-(DME or THF) pale yellow . Ll-DME-TM reddish brown 18, 19 •Li-THF-TNN reddish brown 20, 21 Na-DME-TNN reddish brown 22, 23 Na-THF-TNN reddish brown ' 24, 25 NaK-DME-TM blue Cs-DME-TNN . blue T y p i c a l spectra i n each system are shown i n the f i g u r e s i n d i -cated above. Treatment of the compound w i t h cesium metal d i d not produce any paramagnetic species although a d e f i n i t e c o l o r change from pale yellow to dense blue was observed. The blue c o l o u r of the s o l u t i o n e x h i b i t e d when tr e a t e d w i t h Na-K a l l o y or cesium may be due to diamagnetic d i n e g a t i v e ions. Figures 13 ( a ) ( f ) ESR fSpectra of 1 ,4 ,5 ,8 -Tetra nitro naphthalene Radical in Li -( Fast Scan ) ( a ) - 9 5 ° C ( d ) 2 ° C (e) 2 0 ° C ( f ) 3 5 ° C Figures 19 ( a ) ~ (e) ESR Spectra of 1 , 4 , 5 , 8 - Tetrcinitron Radical , in- Li - D M E (S low Scan) aphthalene ( c ) - 3 0 ° C o o CM ro 00 CVJ IO ( b ) - 8 0 °C ( d) - 3 8 ° C Figures 21 (a)~(e) ESR Spectra of 1,4,5,8-Tetranitronaphthalene Radical in Li-THF ( S l o w S can ) ( c ) - 6 0 ° C ( d ) -38°C Fi gu res 23 (qI) ^ (d) ESR Spectra of I, 4 , 5 , 8 - Tetranitronaphthalene Radical in Na-DME ( S l o w Scan) ( a ) - 9 7 @C (b) -76 °C Figures 2 4 ( a ) , ( b) E S R S p e c t r a o f 1,4,5,8-•Tetranitronaphthalene Rad i ca l in Na -THF ( Fast Scan ) (a )-l 0 0 ° C u ' e s 25 (a) , (b) ESR Spectra of I 4 5 a vi or «, o, 8 - Tetranttronaphthal Radical in N Q - T H F ( S l ow S c a n ) 3265.33 ene ( a ) - IOO °C 3267.70 - io6 -The compound was a l s o e i e c t r o l y z e d i n N 5N'-dimethyl-formamide u s i n g t e t r a - n - p r o p y l ammonium pe r c h l o r a t e as a s u p p o E t i n g e l e c t r o l y t e . When the e l e c t r o l y t e was added to the s o l u t i o n of l,4,5 38-tetranitronaphthalene i n DMF on exposure to a i r , a b r i g h t r e d d i s h brown colour appeared. The colour d i d not change w i t h temperature or e l e c t r o l y s i s a f t e r degassing. The spectra i n t h i s system are shown i n figure. 26 and 27. The spectra of a l l the systems i n v e s t i -gated were w e l l r e s o l v e d and were i n t e r p r e t e d i n terms of 4 e q u i v a l e n t hydrogen n u c l e i and 4 equivalent n i t r o g e n n u c l e i . The spectra d i d not e x h i b i t metal hyperfine s p l i t t i n g s or a l t e r n a t i n g l i n e widths over the temperature range i n v e s -t i g a t e d , and l i t t l e d i f f e r e n c e was observed between the che m i c a l l y produced r a d i c a l and the e l e c t r o l y t i c a l l y gener-ated r a d i c a l s except i n the magnitude of s p l i t t i n g constants. S p l i t t i n g constants obtained are shown i n f i g u r e 28 and w i l l be compared with the values'•calculated w i t h MO treatment i n s e c t i o n B. 0 An evident solvent e f f e c t on the s p l i t t i n g - c o n s t a n t s and temperature dependency of them was observed and w i l l be discussed i n section C and D, i n turn. - 107 -Figures26 (a ) - w ( c ) ESR Spectra of 1 , 4 , 5 , 8 -Tetranitronaphthalene Radical in TPAP-DMF ( Fast Scan) (a ) -27 ° C Figures 27 ( a )~ ( c ) ESR Spectra of 1,4,5,8 - Tetranitronaphtalene Radical in TPAP - DMF ( Fast Scan) (a ) - 2 7 ° C 32 66.78 3268.15 3269.13 o 00 3266.95 3267.94 3268.90 ( b ) - | | ° C 3382.81 3 3 8 4 . 9 0 3385.91 (c) 2 0 ° C 1.55 A O A o 1.50 O x 1.45 o - 109 -• <2> • • ,250 to O z O . 2 0 0 150 G A O A A ^ A ^ A A A A © Li - D f w I E O L i -THF & Nc- OWE A N G - T H ^ • TPAP-DMF • • Temperature ( ° C -100 - 5 0 0 Figure 28 Temperature Change of Q N ar.d G H in 1,4,5,8-Tetranitronaphthalene Anion Radical - 110 -B. Hyperfine S p l i t t i n g Constants. S p l i t t i n g constants observed were 1.4~1.5 gauss f o r CL ^  and o. 15*" 0.25 gauss f o r Q. depending upon the temperature and the solvent used. Results of molecular o r b i t a l c a l c u l a t i o n s are shown below. Table 6. S p i n - D e n s i t i e s and S p l i t t i n g Constants f o r Anion •Radical of l ^ ^ o S - T e t r a n i t r o n a p h t h a l e n e . Spin D e n s i t i e s S p l i t t i n g Constants p o s i t i o n Huekel McLachlan ( c a l c . ) (exp.) 1 O.063O ' 0.0707 2 0.0572 0.0606 1.44 1.4 9 0 -0.0193 11(N) ,0 .0356 0.0329 0.15 0.15 15(0) 0.0472 0.0476 — — .. The parameters of (4.1) and equations (4.2), (4.8) were again used. The experimental s p l i t t i n g constants given i n ta b l e 6 are f o r DMF-TPAP system. Since the parameters and equations used f o r MO c a l c u l a t i o n were o r i g i n a l l y determined to be the most s u i t a b l e f o r n i t r o s u b s t i t u t e d benzenes-DMF-TPAP system, the experimental - I l l -values of present r a d i c a l i n the same solvent i s the most s u i t a b l e to be taken f o r comparison w i t h the c a l c u l a t i o n . The agreement seems apparently to be e x c e l l e n t . However, from the s i m i l a r i t y of the molecular s t r u c t u r e of the compound t h that of 1 , 8-dinitronaphthalene i n which the n i t r o group was found to be twis t e d out of the plane of aroma-t i c r i n g by an angle of Q = 6 0 ° , i t i s h a r d l y acceptable to assume the t w i s t i n g angle of the n i t r o group on 1 , 4 , 5 > 8 - t e t r a -nitronaphthalene to be ne a r l y zero. Consider the e f f e c t of t w i s t i n g angle on t h e • c a l c u l a t e d s p l i t t i n g s . In the same treatment, as was employed i n chapter IV, the e f f e c t of the t w i s t i n g angle can be represented as, - 1 fuJ = / ,2/9Co^ { 9 . ( 5 . 1 ) The r e s u l t s of M O c a l c u l a t i o n s employing ^5Q N as given i n the equation (5*1) 'instead of 1 . 2 ^ are tabulated i n Appendix I I I . P l o t of c a l c u l a t e d &^ and Q. versus $ i s shown i n f i g u r e 2 9 . The corresponding angle to the experimental Ct^ ( ^ 0 . 1 5 gauss) was found to be ^ 3 5 ° . Since the c o e f f i c i e n t s of the equation used to c a l c u l a t e CL-^ were determined to achieve the b e s t . f i t to the experimental s p l i t t i n g of n i t r o s u b s t i t u t e d benzenes and the values of the c o e f f i c i e n t haue Splitting Constant I CH I ( calculated, gauss ) - 113 -i n h e r e n t l y considerable inaccuracy, the determined value of the t w i s t i n g angle has a c e r t a i n inaccuracy. The e r r o r was estimated to be tlO°. Thus the t w i s t i n g angle was determined of the MO parameters and equations employed. C. Solvent E f f e c t . As e x h i b i t e d i n f i g u r e 27, a pronounced solvent e f f e c t was observed. • The n i t r o g e n s p l i t t i n g is. the s m a l l -est i n DMF and the l a r g e s t i n THF5 i t i s w e l l known that the n i t r o g e n s p l i t t i n g constant of n i t r o group e x h i b i t s unusually strong solvent dependency (84, 85). The s i m i l a r solvent e f f e c t was a l s o observed f o r diphenyl n i t r i c oxide (DPNO) (86) and d i - p - a n i s y l n i t r i c oxide (87), and the l 4 N s p l i t t i n g constant of DPNO was expressed (73) i n terms of the d i p o l e moment jji of a solvent as; to be 35 =10°, assuming the v a l i d i t y f o r the present r a d i c a l To e x p l a i n the e f f e c t , the o l l o w i n g e q u i l i b r i u m ; \ / N > < IOI9 101 ( i ) ( i i ) was proposed. - 114 -In a nonpolar solvent the e q u i l i b r i u m w i l l move to the r i g h t hand side and the s p i n d e n s i t y on the n i t r o g e n n u c l e i w i l l decrease, thence OL ^  w i l l decrease. In a p o l a r s o l v e n t , the e q u i l i b r i u m w i l l move to the l e f t , and & N w i l l i ncrease. The s i m i l a r e f f e c t can be expected f o r the s p l i t t i n g of n i t r o group. However the s i t u a t i o n i n the n i t r o group i s somewhat complicated. Gendell e t a l ( 8 0 ) 14 showed that the N s p l i t t i n g i n the nitrobenzene anion would be expected to be more solvent dependent than the proton s p l i t t i n g s because the "^N s p l i t t i n g . i s very sentive to the s p i n d e n s i t y d i s t r i b u t i o n and the s o l v a t i o n i s more l i k e l y to occur i n the neighborhood of the n i t r o group than elsewhere i n the molecule. As was shown i n the equation (4.2) i n chapterZTV, the s p l i t t i n g depends on two terms of opposite s i g n but comparable magnitude, one of which i s p r o p o r t i o n a l to the sp i n d e n s i t y on n i t r o g e n nucleus and the other to the s p i n d e n s i t y on the oxygen n u c l e i , so that the small change i n the s p i n d e n s i t y d i s t r i b u t i o n over the n i t r o group caneexhibit 14 l a r g e s h i f t s i n the N s p l i t t i n g . G r e n d e l l et a l a l s o showed the solvent e f f e c t on the -^N s p l i t t i n g can be represented i n MO c a l c u l a t i o n as the increase of the oxygen Coulomb i n t e g r a l w i t h the increase of solvent p o l a r i t y . - 115 -Rieger and Fraenkel (37) a p p l i e d t h i s kind of treatment to the n i t r o s u b s t i t u t e d aromatics, and showed the change of s p l i t t i n g constants from DMF to a c e t o n i t r i l e (MeCN) would be accounted hy c a l c u l a t i o n in- which the oxygen Coulomb i n t e g r a l c o e f f i c i e n t (fQ was increased by 0.05 f o r MeCN. The same method was a p p l i e d to the present r a d i c a l . The c a l c u l a t e d s p i n d e n s i t i e s f o r cfQ=1.5 and 1.3 are shown i n Appendix IV. C a l c u l a t e d CL™ and (X„ are shown i n f i g u r e H 30 along w i t h the values f o r </"G=1.4 f o r the cases when ^ C N = l . 0 4 f , and ^ C N = 1 . 2 f 3 . The r e s u l t shown on f i g u r e 30 c l e a r l y i n d i c a t e s that (2^ i s m u c n i n f l u e n c e d whereas & H i s l e s s s e n s i t i v e to the environment. The f i g u r e a l s o showa the l a r g e r values of Q, JJ 'with simultaneously the l a r g e r CL ^ values are only obtainable i n the more p o l a r • s o l v e n t s than.DMF to which the value 1.4 of (To corresponds. Since the d i e l e c t r i c constants of DMF and THF are 7.15 and 7 . 3 9 ' r e s p e c t i v e l y , these solvents are f a r l e s s p o l a r than DMF the d i e l e c t r i c constant of which i s ~ 4 0 . Experimentally t h l a r g e C L M ' S and O 's were observed i n ' H these l e s s p o l a r s o l v e n t s , and the experimental r e s u l t s might appear to be c o n t r a d i c t o r y to the expectation from MO C a l c u l a t i o n s . - 1 1 6 -However one can take the e f f e c t of the c a t i o n present i n the solvents i n t o account. Since the c a t i o n s d i d not e x h i b i t any hyperfine c o u p l i n g w i t h the anion, one cannot expect any strong e f f e c t of the c a t i o n on the anion as i s observed i n contact i o n - p a i r s . However, although the e f f e c t of the c a t i o n i s r a t h e r weak, the p e r t u r b a t i o n on the anion r a d i c a l due to the a l k a l i metal c a t i o n beuldrbagstronger than that of the s o l v a t i o n . A p o s s i b l e s t r u c t u r e which can cause the weak i n t e r a c t i o n between the a l k a l i metal c a t i o n and the anion r a d i c a l i s "solvent-separated i o n - p a i r s " proposed by Hogen-Esch and Smid (46) f o r f l u o r e n y l - a l k a l i metal i o n -p a i r s . I n the solvent-separated i o n - p a i r s , the anion and the c a t i o n are separated by i n t e r v e n i n g solvent molecules, and the c a t i o n i c charge i s t r a n s f e r r e d to the anion through the i n t e r v e n i n g solvent molecules, the p e r t u r b a t i o n of which would be s t i l l c o n s i d e r a b l y l a r g e i n comparison w i t h the solvent e f f e c t i n the present anion r a d i c a l . Since the distance between the c a t i o n and anion i s s u f f i c i e n t l y l a r g e , the d i f f e r e n c e i n the c a t i o n i c r a d i i of Na + and L i + would give l i t t l e change i n the i n f l u e n c e s of the c a t i o n on the anion as was observed experimentally on the system i n DME and THF. The change i n s p l i t t i n g from DME to THF may be a t t r i b u t e d to the change i n p o l a r i t y of the s o l v e n t s . - 317 -1.50 i H £ C N - 1 . 0 « £ / 3 C N « i .zP 1.3 1.4 1.5 Oxygen Coulomb Integral Coefficient, <f( Figure 30 Effect of Oxygen Coulomb Integral Parameter on Calculated Splitting Constants of 1,4,5,8-Tetranitro--naphthalene Anion Radical - 118 -D. Temperature Dependency of S p l i t t i n g Constants. The s p l i t t i n g constants increase w i t h temperature as i l l u s t r a t e d i n f i g u r e 2 8 . Very few works have been p u b l i -shed on the temperature dependency of the hyperfine s p l i t t i n g oft'the n i t r o group of aromatic compounds. Freed and Rieger measured the temperature change of "^N s p l i t t i n g of 4-nitroacetophenone i n the DMF-TPAP system. The s p l i t t i n g are ( i n gauss); & N = 6 . 2 0 (at -32°C) and 0-^=5.86 r o o m temperature). Rieger and Fraenkel gave a b r i e f comment on the behavior and suggested that lowering the temperature r e s u l t s i n the formation of a t i g h t e r complex w i t h s o l v e n t , hence CL^ i n c r e a s e s . E v i d e n t l y t h i s mechanism i s not the predominant one f o r the present r a d i c a l , because the tendency observed i s the rev e r s e , namely, the l a r g e r ^ i s obtained at the higher temperatures. Since the temperature dependency i s a l s o observed i n DMF-TPAP system, the presence of a small c a t i o n i s not a c r i t i c a l f a c t o r f o r ther behavior, The f a c t that the c o e f f i c i e n t s of the temperature change i s approximately the same f o r any system i n v e s t i g a t e d leads one to the view that the temperature change of (X ^ May Be of an i n t r a m o l e c u l a r o r i g i n . - 119 -Consider the hindered r o t a t i o n of the n i t r o group and r e f e r again to f i g u r e 2 9 . In the r e g i o n of values of greater than 30° where the a c t u a l t w i s t i n g angle p o s s i b l y drops, the curve of Q, ^ increases monotonously and i s concave upwards. I f the curve i s denoted as & N*f ( c 9 )> both f ' ( 0 ) and f"($> ) ( f ' ( 0 ) = f M (<9 )=^T) are p o s i t i v e i n t h i s r e g i o n of Q . I t i s e a s i l y shown that i f the hindered r o t a t i o n occurs the e f f e c t i v e value of Q i s l a r g e r than the angle QQ which i s the center of the hindered r o t a t i o n when f ' ( 6 > ) > 0 , f " ( ( 9 ) > 0 . The e f f e c t i v e t w i s t i n g angle i s obtained by time-averaging the value of $• during one c y c l e of r o t a t i o n . The e f f e c t i v e t w i s t i n g angle w i l l be l a r g e r f o r a l a r g e r amplitude of the hindered r o t a t i o n which i s a t t a i n a b l e at higher temperature. Since i t i s the e f f e c t i v e t w i s t i n g angle that determines, the & N i n f i g u r e 29, one would observe a l a r g e r Cl™ at higher temperature. I t would be p o s s i b l e to c a l c u l a t e the amplitude of the hindered o s c i l l a t i o n by using the experimentally ob-tained value of Q,N and assuming an appropriate motion (say, simple harmonic) f o r the o s c i l l a t i o n of the n i t r o group, i f a very r e l i a b l e curve of f ( (9 ) should be a v a i l a -b l e . However i t i s too much to do t h i s k i n d of c a l c u l a t i o n s w i t h the curve i n f i g u r e 29 because the accuracy of i t i s not h i g h enough. - 120 -E. Asymmetry of the ESR spectrum. The spectrum of the TNN anion showed a pronounced asymmetry w i t h lower i n t e n s i t i e s of l i n e s at higher f i e l d as shown, say, i n f i g u r e 22 (d). The pheno-menon i s more remarkable at higher temperatures and was observed i n a l l spectra of TNN anion r a d i c a l s i n v e s t i g a t e d and was observed f o r both the hydrogen and the n i t r o g e n hyperfine s p l i t t i n g s . A p o s s i b l e mechanism which may cause asymmetry of spectra i s the co-existence of two (or more) kinds of r a d i c a l s each of which has a s l i g h t l y d i f f e r e n t g-value and s l i g h t l y d i f f e r e n t s p l i t t i n g constants from those of : ; the other. I f the exchange r a t e between the two species i s s u f f i c i e n t l y l a r g e , one obtains a spectrum w i t h time averaged s p l i t t i n g constant, and the same l i n e width f o r e each l i n e as i s u s u a l l y observed. However i f the exchange r a t e i s slow enough to make the spectrum from each species d i s t i n g u i s h a b l e , one can observeda-spectrum which i s merely a s u p e r p o s i t i o n of spectra from each species. When the r e s o l u t i o n of the spectrometer i s not s u f f i c i e n t l y high to r e s o l v e the small d i f f e r e n c e of the l i n e p o s i t i o n s f o r the two specie s , any adjacent two l i n e s w i l l emerge as a s i n g l e l i n e w i t h smaller i n t e n s i t y and l a r g e r l i n e width i n the - 121 -case f o r l a r g e r d i f f e r e n c e between the two l i n e p o s i t i o n s . One of the p o s s i b l e causes f o r the mechanism might be a mixture of ground and e x c i t e d s t a t e s as was proposed f o r toluenide anion (88). The energies and the squares of c o e f f i c i e n t s of the lowest and next to the lowest unoccupied molecular o r b i t a l s obtained by Hiickel method f o r the TNN anion r a d i c a l below. Molecular O r b i t a l Lowest Next to the Lowest " -energy p o s i^tloTr----^,^^ -0.026 £ -0.316 $ 1 0.0630 0.0239 2 0.0571. O.OI38 9 0 0.0551 11 (N) 0.0356 O.063.9 •15(0) 0.0472 O.O605 The energy d i f f e r e n c e between the two l e v e l s i s approximately 5 k c a l which might be thermally accessable. However the spi n d e n s i t y d i s t r i b u t i o n i s e n t i r e l y d i f f e r e n t between two l e v e l s and one can h a r d l y expect there to be ne a r l y the same magnitude of s p l i t t i n g constants f o r the two l e v e l s . Therefore i f more than two r a d i c a l species should be present at a l l , the mixture i s not the one of ground and ex c i t e d s t a t e s , but i s of d i f f e r e n t types such as mixtures of i o n - p a i r s or solvated molecules. - 122 -However the v i s i b l e r e g i o n o p t i c a l spectra of TNN anion r a d i c a l i n DME-Na system ( f i g u r e 31) e x h i b i t s only . one absorption maximum that can be r e f e r e d to the r a d i c a l s p e c i e s , and therefore the mixture-mechanism seems to be a l e s s f a vorable one f o r the i n t e r p r e t a t i o n - o f the asymmetry of the spectrum. I f one can assume the spectrum i s due to only one r a d i c a l s p e c i e s , the broadening may be r e f e r r e d to the so c a l l e d motional broadening. McConnell pointed out (89) that the e l e c t r o n s p i n would be subject to a f l u c t u a t i n g . f o r c e as the r a d i c a l undergoes Brownian motion i f an a n i s o t r o p i c i n t e r a c t i o n between e l e c t r o n i c and nuclear s p i n were present. The s p i n system i s perturbed by t h i s time-dependent fl u c t u a t i o n , and the l i n e width of components on the ESR spectrum shows a systematic broadening. The theory of the e f f e c t was extended by K i v e l s o n (90) and Stephen and Praenkel (91) f o r the case where the s p i n Hamiltonian i s . a x i a l l y symmetric. C a r r i n g t o n and Longuet-Higgins (92) extended the theory f o r any Hamiltonian i r r e s p e c t i v e of the symmetry, The theory w i l l be b r i e f l y summarized and the r e s u l t s of the theory w i l l be a p p l i e d to i n t e r p r e t the asymmetric broadening of the spectrum of the present r a d i c a l 1 I 1 . 1 t — • 5000 4500 4 0 0 0 3500 Wave Length ( A) Figure 31 Optical Spectrum of TNN-Na-DME System - 124 -N e g l e c t i n g the nuclear Zeeman and quadrupole terms, a Hamiltonian f o r S=-| p a r t i c l e s and i n u c l e i i s w r i t t e n as K •+ ZT}T«£SP (5.2) where H^is the magnetic f i e l d , Q; i s the g-^tensor, the f i c t i o u s s p i n of the unpaired e l e c t r o n , 1^  and ', the s p i n and the hyperfine s p l i t t i n g tensor of the i t h nucleus r e s p e c t i v e l y . (5-2) i s r e w r i t t e n as % = Vot W (5.3) where ^ g j3.%H«S« -f £ TclJ-S* ( i s o t r o p i c term) H' = + ZTj-tJp *f ( a n i s o t r o p i c term) and 3 '** T r e a t i n g -y^ as a p e r t u r b a t i o n term, the f o l l o w i n g expressions f o r the transverse r e l a x a t i o n time T ' - L and the l o n g i t u d i n a l r e l a x a t i o n time T'2 were obtained. • 1 _ xP  T{ ]L0fu ( l + ^ T 1 ) 1 = T2 .15 -V where (5.4) - 125 -Since the h a l f height l i n e width i s closely-r e l a t e d w i t h T|' and T 2' , and i . increases w i t h the increases of the sura of 1/T]_' and l / T 2 ' , A\jJ i i s d i r e c t l y r e l a t e d w i t h P. . Thus AUT± increases w i t h the value of P. For sets of equivalent n u c l e i , P i s expanded to give three terms. The f i r s t i s independent of Mij:, the second i s l i n e a r i n the and the t h i r d term i s b i l i n e a r i n the Mij:. The t h i r d term a f f e c t s both sides of the spectrum i n the same manner. I t i s the second term that c o n t r i b u t e s to the asymmetric broadening. This term i s expressed as Z ^ i l M ^ t j i T ^ j ( 5 - 5 ) where M^1) denotes the sum of the values f o r a l l n u c l e i i n the set represented by the symbol ( i ) and T ^  (•*-) i s the hyperfine tensor for-any nucleus i n the set. Equation (5'5) shows that i f we consider a p a r t i c u l a r m u l t i p l e t of l i n e s d i f f e r i n g only i n t h e i r v a l u e s , the l i n e s w i t h p o s i t i v e M£ ' w i l l be broader or narrower than those w i t h negative 4 l ) M^1) according as the inner product 1 T ^ Is p o s i t i v e or negative. C a r r i n g t o n e t a l (92) c a l c u l a t e d the p r i n c i p a l compo-nents of t ^  f o r a n i t r o g e n n-electron and the n i t r o g e n nucleus to be t„ = +76, t v = t = -38 Mc/s. *z y - 126 -I f we assume g x =gy> &z f ° r the present anion r a d i c a l , g ^  g 1 t ^ w i l l be negative according to the equation 8 oc p ' = ( g„ - gj_ ) t z (5.6) Thus the l i n e s for negative M-j-'s w i l l be broadened and the l i n e s for posit i v e !s w i l l be sharp. Experimentally sharper l i n e s were observed at lower f i e l d . I t means l i n e s at lower f i e l d correspond to posit i v e M 's. Simce i t i s the sign of the i s o t r o p i c hyperfine tensor T 1 which determines whether a l i n e corresponding to a certa i n Mj appears at lower high f i e l d and l i n e s for posit i v e Mj's appear i n lower f i e l d for the p o s i t i v e . T 1 , the i s o t r o p i c part of nitrogen hyper-fine tensor i s p o s i t i v e . Stephen and Fraenkel suggested that the g-tensor for C5H5" has g^ > g | ( (9I)» McConnell and Strathdee (93) calculated the three p r i c i p a l components of t ^ for a CH proton, and found them to be t x = +43f , t y = -38J> , t z = - 5 f Mc/s where J> i s the amount of unpaired spin i n .the C2p 7 r o r b i t a l . 'Assuming these s i t u a t i o n i s also tfaue for the proton of the present r a d i c a l , i t i s possible to determine the sign of g ^ ^ ' t . Now i f g has a x i a l symmetry, equation (5-6) holds, Since g|( -gJ_<0 and t & < 0 , g ^ ' - t ^ may be po s i t i v e . I f i t i s sc:^ the l i n e s for posit i v e M-r1 s w i l l be - 127 -broadened. Experimentally broadened l i n e s appeared at higher f i e l d which i n d i c a t e s that the i s o t r o p i c h y perfine tensor on the hydrogen nucleus of a CH proton i s negative. As was mentioned by Carring t o n and Longuet-Higgins there i s a s l i g h t u n c e r t a i n t y as to the s i g n of t7. I f t i s • ^ z p o s i t i v e , the i s o t r o p i c hyperfime tensor w i l l be p o s i t i v e . Since the value of t z f o r the CH proton i s much smaller compared w i t h the t 7 f o r the n i t r o g e n nucleus, the magnitude of g ^  1 * ^  <?tp i s much smal l e r , and hence the broadening w i l l be much l e s s pronounced f o r the CH proton compared w i t h l i n e s due to the n i t r o g e n s p l i t t i n g . This was a c t u a r y observed i n the present i n v e s t i g a t i o n . - 128 -BIBLIOGRAPHY. (1 (2 (3 (4 (5 (6 (7 (8 (9 (10 ( l l (12 (13 (14 (15 (16 (17 (18 Z a v o i s k i i , J . Phys. U. S. S. R, 8, 377 (1944) , i b i d . , Q_, 211 (1945) A. N. Holden, C. K i t t e l , F. R. M e r r i t and W. A. Yager Phys. Rev. ZL> 147 (1950) C. H. Townes and J . T u r k e v i t c h , i b i d . , JJ_y 148 (1950) H. S. J a r r e t t and G. J . Sloan, J . Chem. Phys., 22, 1783 (1954) A. 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Deguchi and H. Takaki, i b i d , 36, 560 (1963) (88) T. R. T u t t l e , J r . J . Am. Chem. Soc. 84, 1492 (1962) (89) H. M. McConnell, J . Chem. Phys. 2^ _, 709 (1956) (90) D. K i v e l s o n , J . Chem. Phys. 2£, 1087 (1957) (91) M. J..Stephen and G. K. Fra e n k e l , J . Chem. Phys. 32, 1435 (I960) (92) A. C a r r i n g t o n and H. C. Longuet-Higgins, Mol. Phys. 5_, 447 (1962) (93) H.M. McConnell and J . Strathdee, Mol.Phys. 2, 129 (1959) - 133 -Appendix I. Atomic Numbering System. The f o l l o w i n g numbering systems were used throughout the present work. - 13^ -Appendix I I . C o e f f i c i e n t s of the Lowest Unoccupied  Molecular O r b i t a l of 1 , 8-Dinitronaphthalene (Hiickel) P o s i t i o n C i 1 - 0 . 1 8 8 6 2 0 . 3 5 0 4 3 0 . 0 9 7 6 4 - 0 . 3 7 5 8 5 0 . 3 7 5 8 6 - 0 . 0 9 7 6 7 - 0 . 3 5 0 4 8 0 . 1 8 8 6 9 0 10 0 11 - 0 . 2 5 1 2 12 0 . 2 5 1 2 13 0 . 2 5 2 8 14 O . 2 5 2 8 15 - 0 . 2 5 2 8 16 - 0 . 2 5 2 8 - 135 -Appendix I I I . , E f f e c t of Tw i s t i n g Angle on Spin D e n s i t i e s  of 1,4,5^8-Tetranitronaphthalene Anion R a d i c a l . 2y? (<9=o c ) £ C N = l . i o £ ( 6>=2 3°) p o s i t i o n . HMO McL ICL 1 HMO McL • 1 2 O . O 6 3 O 0.0571 0 . 0 7 0 7 O.O606 1.44 0.0650 0.0545 0.0751 0.0560 1.33 9 0 -0.0193 0 -0.0195 11(N) 0.0356 0.0329 0.151 0.0370 0.033^ 0.10 15(0) 0.472 0.0476 0.0466 0.0476 CN=1-04^3 ( & = 3 0 ° ) /CN=0-95^ ( £ = 3 8 ° ) 1 2 1 0.0662 0.0535 0.0763 0.0545 1.29 0.0681 0.0515 0.0791 0.0509 1.21 9 1 0 -0.0195 0 -O.OI89 11(H) 0.0379 0.0352 0.13 0.0392 O.0367 0.31 15(0) 0.0462 0.0468 0.0456 0.0464 - l 3 6 -85 f (8 = 45°) r W 0 - 7 5 ? ( ^ = 5 0 ° ) p o s i t i o n HMO McL i a i HMO McL \CL\ 1 0.0701 0.0827 0.0720 O.O856 2 o . 0 4 9 4 ' 0.0476 1.13 000472 0.0439 i . o 4 9 .0 -0.0146 0 -0.0192 11 (N) o.o4o8 0.0392 0.65 o .o424 o.o4o8 0.85 15(0) o .0449 0.0452 0.0442 0.0446 *p C N = 0 * 60 ^  (r>=6o°) £ C N = o . 4 o p ((9=64?) l 0.0747 0.0900 0.0775 0.0954 2 o.o44o 0.0394 0.93 0.0396 0.0322 0.76 9 0 -0 .0299 0 -0 .0204 11 ( N ) 0.0449 0.0454 1.45 0.0488 0.0506 Q.08 15(0) 0.0432 0.0425 0.0421 0.0409 - 137 -Appendix IV. E f f e c t of Oxygen Coulomb I n t e g r a l Parameter  on Spin D e n s i t i e s and C a l c u l a t e d S p l i t t i n g Constants i n 1 , 4 , 5 , 8 - T e t r a n i t r o n a p h t h a l e n e Anion R a d i c a l . p o s i t i o n HMO McL \CL\ HMO McL • l a i <*"o=1-5 <f0=1.3 1 0 . 0 5 8 8 0 . 0 6 5 0 0 . 0 6 7 3 0 . 0 7 6 2 2 0 . 0 5 7 4 0 . 0 6 1 8 1.46 0 . 0 5 6 9 0 . 0 5 9 4 1 .41 9 0 - 0 . 0 1 8 7 0 - 0 . 0 2 0 0 11(N) O .0389 0 . 0 3 6 3 .136 0 . 0 3 2 3 0.0306 0 . 3 4 1 5 ( 0 ) 0 . 0 4 7 4 0 . 0 4 8 3 0 . 0 4 6 8 0.04.70 •cf 0=l . 5 . ^ o = 1 ' 3 1 O .0616 0 . 0 7 0 1 0 . 0 7 1 1 0 . 0 8 2 7 2 0 . 0 5 3 3 0 . 0 5 5 1 1 .31 0 . 0 5 3 9 0 . 0 5 3 9 1 . 2 8 9 0 - 0 . 0 1 8 8 0 - 0 . 0 2 0 1 11(N) o . o 4 i 6 . o . o 4 o o . 5 9 0 . 0 3 4 2 0 . 0 3 0 6 0 . 2 9 1 5 ( 0 ) 0 . 0 4 6 8 0 . 0 4 7 1 0 . 0 4 5 4 0 . 0 4 6 4 where WQ = tf + . The c a l c u l a t e d values f o r the case where </"0=1.4 are shown i n Appendix I I I . 

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