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Determination of the crystal structure of the hydrobromide of 3-carbomethody-trans-3, 5-dimenthyl-D-pyrazoline… Luth, Hartwig 1965

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THE DETERMINATION OF THE CRYSTAL STRUCTURE OF THE HYDROBROMIDE OF 3-CARBOMETHOXY-TRANS-3,5-DIMETHYL-A1-PYRAZQLINE BY X-RAY DIFFRACTION by HARTWIG LUTH B.S.A., University of Toronto, 1960 M.S.A., University of Toronto, 1962 A Thesis submitted in P a r t i a l Fulfilment of the Requirements for the Degree of Master of Science in the Department of Chemistry We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February, 1965 I n p r e s e n t i n g 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 r e q u i r e m e n t s 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 t h a t 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 r e f e r e n c e and s t u d y , I f u r t h e r agree t h a t p e r -m i s s i o n f o r e x t e n s i v e c o p y i n g 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 g r a n t e d by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g 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 g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n * ABSTRACT The hydrobromide of 3-carbomethoxy-_trans-3, 5-dimethyl-Z^^-pyrazoline, C7Hi3N202Br, c r y s t a l l i s e s in the monoclinic system with a = 8.28, b = 10.31, c = 13.92$ and ^ = 122.4°. The space group i s P2^/c and there are four molecules per unit c e l l , thus each molecule forms an asymmetric unit in the c e l l . The i n t e n s i t i e s of 580 r e f l e c t i o n s were estimated from films exposed to CuK <x radiation. The structure determina-tion was based on the heavy atom Patterson and Fourier methods and least squares refinement. The f i n a l discrepancy, R, for the 409 observed r e f l e c t i o n s i s 0.116. The compound was found to contain a bromide ion and a cation with no double bond, with a t r i g o n a l C.(5) atom, and a positive charge d i s t r i b u t e d between N(l) and C(5). The five-membered ring i s non-planar with N(2) displaced 0.32 8 from the plane of the remaining four atoms, or N(l) and N(2) displaced above and below the plane of the three carbon atoms and the methyl group on C(5) lying almost on these planes. A l l other molecular dimensions are normal. The shortest o intermolecular approach i s a C(5)...0(3) distance of 2.76 A, which re s u l t s from the a t t r a c t i o n between the p o s i t i v e l y -charged carbon and the r e l a t i v e l y negative oxygen. The shortest approach involving .a bromide ion i s a Br~---H-N(2) o hydrogen bond of 3.22 A; the next shortest approach i s a Br~...N(2) distance of 3.31 A*. The other intermolecular distances are normal. ACKNOWLEDGEMENTS The author wishes to express his sincere appreciation to Dr. J. Trotter for guidance and, above a l l , encouragement received in a l l stages of t h i s work. Appreciation i s also expressed t o D r . D. E. McGreer for a help f u l discussion and the c r y s t a l sample, to Mr. W. Griba for the i l l u s t r a t i o n s in t h i s thesis, and to the National Research Council of Canada for f i n a n c i a l support. i i i TABLE OF CONTENTS PAGE TITLE PAGE i ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES . . iv LIST OF FIGURES v ACKNOWLEDGEMENTS v i INTRODUCTION 1 EXPERIMENTAL . . ... . . . . 4 STRUCTURE ANALYSIS 6 COORDINATES AND MOLECULAR DIMENSIONS 9 DISCUSSION 17 BIBLIOGRAPHY ... . 21 APPENDIX 22 iv LIST OF TABLES TABLE PAGE I F i n a l p o s i t i o n a l parameters and the i r standard deviations 10 II Last i s o t r o p i c and f i n a l anisotropic temperature factors 11 III Bond distances and valency angles 12 IV Shorter intermolecular distances 14 V LIST OF FIGURES FIGURE PAGE 1 Superimposed sections of the three-dimensional electron-density d i s t r i b u t i o n through the atomic centres p a r a l l e l to (010), (contours at in t e r v a l s of 1^2,3-eA~ 3 for l i g h t atoms 10, 20, 30eA - 3 for Bromine atom), and a perspective drawing of the molecule at the same scale as map ... 8 2 Projection of the structure along b, i l l u s t r a t i n g molecular packing. 16 - 1 -I N T R O D U C T I O N T h e r e a c t i o n o f d i a z o e t h a n e , I I , a n d m e t h y l O C - m e t h a c r y -l a t e , I , y i e l d s a m i x t u r e o f c i s a n d t r a n s - 3 , 5 - d i m e t h y l - 3 ^ c a r b o m e t h o x y - - p y r a z o l i n e , I I I a n d I V , . T h e m i x t u r e i s s e p a r a t e d b y d i s t i l l a t i o n t h r o u g h a s p i n n i n g b a n d c o l u m n w i t h s t i l l p o t a t 8 0 ° - 9 0 ° C . P h o t o l y s i s t o c y c l o p r o p a n e s a n d n u c l e a r m a g n e t i c r e s o n a n c e s p e c t r o s c o p y s h o w t h e l o w e r b o i l i n g c o m p o n e n t t o b e p r e d o m i n a n t l y t h e c i s i s o m e r , I I I , a n d t h e h i g h e r b o i l i n g c o m p o n e n t t o b e p r e d o m i n a n t l y t h e t r a n s i s o m e r , I V . M o r e o v e r , n .m.r. s p e c t r a o f I I I a n d I V s h o w t h e e f f e c t s o f t h e b u l k y m e t h y l g r o u p s o n t h e c o n f o r m a -t i o n o f t h e s e m o l e c u l e s i n t h e c h e m i c a l s h i f t p o s i t i o n s o f t h e h y d r o g e n s o n C ( 4 ) . I n t h e t r a n s p y r a z o l i n e , I V , t h e s e t w o h y d r o g e n s h a v e n e a r l y s i m i l a r s h i f t s ( 8 . 2 8 a n d 8.56 T O . I n t h e c i s p y r a z o l i n e , I I I , t h e s e h y d r o g e n s h a v e n o t i c e a b l y d i f f e r e n t c h e m i c a l s h i f t s ( 7 . 6 8 a n d 9 . 7 4 T ) . T h e c i s r e l a t i o n s h i p o f t h e t w o m e t h y l g r o u p s i s b e l i e v e d t o c a u s e a g r e a t e r f o l d i n g o f t h e p y r a z o l i n e r i n g i n I I I t h a n i n I V , t h u s p l a c i n g t h e h y d r o g e n s i n t o e n v i r o n m e n t s w i t h d i f f e r i n g d e g r e e s o f s h i e l d i n g ^ ) . A k n o w l e d g e o f t h e c o n f o r m a t i o n s o f t h e s e m o l e c u l e s , I I I a n d I V , i s i m p o r t a n t i n t h e e x p l a n a -t i o n o f t h e m e c h a n i s m s o f t h e i r p y r o l y s i s a n d p h o t o l y s i s r e a c t i o n s . T h e r e f o r e t h e h y d r o b r o m i d e o f t h e t r a n s p y r a z o l i n e , I V , w a s p r e p a r e d ; a n c j a n x - r a y a n a l y s i s b a s e d o n t h e h e a v y a t o m m e t h o d wa s u n d e r t a k e n . E a r l y i n t h e c o u r s e o f t h e a n a l y s i s i t b e c a m e a p p a r e n t t h a t t h e h y d r o b r o m i d e o f I I I e x i s t e d a s a b r o m i d e i o n , a n d - 2 -a cation which can best be represented as a resonance hybrid of Via and VIb, i n which the p o s i t i v e charge i s d i s t r i b u t e d between N(l) and C(5), where C(5) i s a t r i g o n a l atom. This l a t t e r feature leaves the question of cis-trans isomerism unanswered and therefore the o r i g i n a l problem unsolved. However, no X-ray analysis of a s i m i l a r cation could be found in the l i t e r a t u r e , and the analysis was continued on t h i s structure. - 3 -/ C H3 C H = C (I) C 0 2 C H 3 + • 0 C h L . 3 . © : (Ua) 5 © 5 .> C 0 2 C H 3 C H 3 N C H 3 N N C 0 2 C H 3 (III) (IV) (IV) H B r C H 3 N ^ ^ C H 3 ^ C O X H , N H 2 3 (V) C H , 3 H <CH> © B r © 3 H N H C 0 2 C H 3 (Via) (VI b) - 4 -E X P E R I M E N T A L C r y s t a l s o f t h e h y d r o b r o m i d e o f 3 - c a r b o m e t h o x y - t r a n s -3 , 5 - d i m e t h y l - A ^ - p y r a z o l i n e a r e c o l o u r l e s s p l a t e s w i t h ( 1 0 0 ) d e v e l o p e d a n d s m a l l e r { b l l ^ f a c e s . T h e d e n s i t y w a s m e a s u r e d b y f l o t a t i o n i n a c a r b o n t e t r a c h l o r i d e - b e n z e n e m i x t u r e a n d t h e u n i t c e l l d i m e n s i o n s a n d s p a c e g r o u p w e r e d e t e r m i n e d f r o m v a r i o u s r o t a t i o n , W e i s s e n b e r g a n d p r e c e s s i o n f i l m s . C r y s t a l D a t a C u K o t = 1 . 5 4 1 8 A*; A > MoK = 0 . 7 1 0 7 A) 3 - c a r b o m e t h o x y - t r a n s - 3 , 5 - d i m e t h y l - A * " - p y r a z o l i n e h y d r o b r o m i d e , C 7 H 1 3 N 2 0 2 B r ; m o l . w t . 2 3 7 . 1 , m . p t . 1 5 2 - 1 5 3 ° C . M o n o c l i n i c , a = 8.28 + 0 . 0 3 , b = 1 0 . 3 1 + 0 . 0 3 , c = 1 3 . 9 2 + 0 . 0 3 A, £ = 1 2 2 . 4 + 0 . 3 ° . V o l u m e o f u n i t c e l l = 1 0 0 3 X3 D x ( Z = 4) = 1.57 g c m - 3 D m = 1.56 g c m - 3 A b s o r p t i o n c o e f f i c i e n t f o r C u K d , X - r a y s , X = 1 . 5 4 1 8 8, JUL = 5 9 . 0 5 c m " 1 A b s e n t r e f l e c t i o n s : hO-/ w h e n / i s o d d OkO w h e n k i s o d d 5 S p a c e g r o u p : P 2 ] / c ( C 2 n ) T o t a l n u m b e r o f e l e c t r o n s p e r u n i t c e l l : F ( 0 0 0 ) = 4 8 0 . F o r t h e c o l l e c t i o n o f i n t e n s i t y d a t a a c r y s t a l , w i t h e d g e 0.3 mm p a r a l l e l t o [ o i l ] a n d t h i c k n e s s 0.1 mm, w a s m o u n t e d w i t h b a x i s p a r a l l e l t o t h e a x i s o f r o t a t i o n o f t h e s p i n d l e o f t h e o W e i s s e n b e r g c a m e r a . E q u i - i n c l i n a t i o n p h o t o g r a p h s o f t h e h o i , h i / , h 2 / , h 3 i , h 4 / , a n d h 5 / w e r e t a k e n w i t h C u K o ( r a d i a t i o n w h i c h w a s made m o n o c h r o m a t i c b y a N i f i l t e r . - 5 -The i n t e n s i t i e s were estimated visually and corrected for Lorentz and p o l a r i z a t i o n factors and the structure amplitudes were derived. The photographs showed a rapid decrease i n int e n s i t y with increasing Bragg angle, so that only 409 r e f l e c t i o n s had measureable i n t e n s i t i e s . The various layers were scaled by careful timing of the expo^ sures and by s l i g h t adjustment of the scale factors at one stage i n the analysis, i . e . by comparison of the observed with the calculated structure factors. Because of the small s i z e of the c r y s t a l , errors due to absorption were small and no corrections were applied. - 6 -STRUCTURE ANALYSIS The position of the bromide ion was determined from a three-dimensional Patterson synthesis as (0.1208, 0.2025, 0l0175). Structure factors were calculated, (discrepancy R = X | F q - F c | / 21|F0J was 0.39 for the 409 re f l e c t i o n s ) where the temperature factor B was 5.0 A*2, and the scattering factors were derived from those of Br in the International T a b l e s . A three dimensional Fourier series was summed with signs of the structure amplitudes based on the bromide ion contributions. Peaks corresponding to a l l the atoms of the molecule (except hydrogen) appeared on the electron-density map. The structure factors for a l l 12 atoms were calculated (R .= 0.28), set t i n g B = 5.0 8 2 for a l l atoms and using the 0, N, C scattering factors from the Interna-t i o n a l Tables(4); -the scattering factors for B r - were corrected for anomalous dispersion according to the expression, fBr-corrected = \J ( f ° B r _ + ^ f ' B r ) + ( ^ f " B r ) 2 using the values of A f'Br a f l d A f"Br f o r A7CuKo< given in the International T a b l e s ^ ) _ The p o s i t i o n a l and thermal parameters and an o v e r a l l scale factor were refined by block-diagonal least squares refinement, where the function to be minimized was I w ( F 0 - F c ) 2 with yTw = /F o//60 when / F o / 60 and J~¥ = 60/JFQJ when j FQj ^ 60.. After three cycles of refinement using i s o t r o p i c temperature factors, the scale factors of the i n t e n s i t i e s for the in d i v i d u a l layers were adjusted s l i g h t l y by comparing the sums of jFQj and of jFcj for - 7 -each layer. Also the temperature factor of N(l) (see f i g . 1) was found to be much higher than that of N(2), which fact lead one to suspect a po s i t i v e charge on N ( l ) . Accordingly a N + scattering curve (derived from N scattering curve in a s i m i l a r fashion as the B r - scattering curve) was used for t h i s atom in the subsequent cycles. Refinement of the posi-t i o n a l and thermal parameters was continued through four more cycles of least squares using anisotropic temperature factors for a l l atoms, reducing R to 0.116. A sixth cycle did not reduce R any further. The F D values and the F c values calculated from the output parameters of the f i f t h cycle are l i s t e d in the Appendix. The electron density projection on (010) from the improved (scaled) structure amplitudes with signs from the contributions of a l l atoms i s shown in f i g . 1. : l l 1 1 1 1 I I I 0 1 2 3 4 & S u p e r i m p o s e d s e c t i o n s o f t h e t h r e e - d i m e n s i o n a l e l e c t r o n - d e n s i t y d i s t r i b u t i o n t h r o u g h t h e a t o m i c c e n t r e s p a r a l l e l t o ( 0 1 0 ) , ( c o n t o u r s a t i n t e r v a l s o f 1 , 2 , 3 -eA~ 3 f o r l i g h t a t o m s 1 0 , 2 0 , 3 0 e A ~ 3 f o r B r o m i n e a t o m ) , a n d a p e r s p e c t i v e d r a w i n g o f t h e m o l e c u l e a t t h e same s c a l e a s map. - 9 -COORDINATES AND MOLECULAR DIMENSIONS The f i n a l p o s i t i o n a l and thermal parameters are given in Tables I and II; x/a, y/b and z/c are the coordinates referred to monoclinic c r y s t a l axes, (x) , (y) and €f> (z) are the standard deviations of the coordinates (in 8) computed from the least square residuals. B are the i s o t r o p i c temperature factors from the t h i r d least squares cycle,, and b j j are the anisotropic temperature factors in the expression: exp ~ ( b l l h 2 + b 1 2 h k + b 1 3 n ^ + b 2 2 k 2 + b 2 3 k ^ + b33^2J • The detailed v a r i a t i o n of these bjj values i s of l i t t l e s i g n i f i -cance, because they are affected by systematic errors, such as absorption errors, and because the values are somewhat dependent on each other. For example, rescaling the i n t e n s i -t i e s of the layers tends b 2 2 to approximate the mean of and b33. Hence the anisotropic temperature factors w i l l not be discussed any further. The bond distances and the valency angles in the molecule are given in Table III. The average standard deviation for bonds i s 0.06 8 and for angles i s 3 degrees. A l l the planes through the five-membered ring, which were calculated, i n d i -cated the ring to be non-planar. Two planes with an angle of 0.6 degrees between them describe the geometry of the rin g equally well. These planes are: Plane 1 through N ( l ) , C(3), C(4) and C(5) with equation 0.0127 X' + 0.9525 Y + 0.3043 Z' = 1.1693 plane 1, where the maximum deviation of a l l four atoms i s 0.03 8 and the deviation for N(2) i s 0.32 A. - 10 -Table I FINAL COORDINATES (FRACTIONAL) WITH STANDARD DEVIATIONS Atom x/a y/b z/c ^ ( x ) <S (y) ^5"(z) Br- 0 .1222 0, . 2.002 0, ,0180 0, .006 0, .006 0 .006 N(l) -0 .1812 0, ,0642 0, .1647 0, ,043 0. .048 0 .041 N(2) -0 .0067 0, ,0271 0 .1662 0, ,032 0. ,035 0 .029 C(3) 0 .1834 0. ,0136 0, ,2867 0. ,042 0, ,045 0 .041 C(4) 0 .0907 -0, .0073 0 . 3627 0, .049 0, ,047 0 .045 C(5) -0 . 1059 0. .0170 0, ,2821 0, ,049 0, ,051 0 .043 CH 3(3) 0 .2971 -0, ,1053 0, .2878 0, .035 0. .039 0 .033 CH 3(5) -0 .2740 0, ,0339 0, ,3061 0, .055 0, .061 0 .047 C(3') 0 .2456 0, . 1510 0, .3130 0, .038 0. ,040 0 .035 0(3) 0 .1625 0 .2575 0 .2735 0 .032 0 .046 0 .031 0(3') 0 .4395 0, , 1482 0 .3997 0, .034 0, .036 0 .033 CH 3(3') 0 ;5212 0 .2712 0 .4393 0 .047 0., .039 0 .053 - 11 -Table II LAST ISOTROPIC (8 2) AND FINAL ANISOTROPIC (x 10 ) TEMPERATURE FACTORS AND DEVIATIONS FROM RING PLANE K A - , A) AND RING PLANE 2 ( A 2 A) Atom B b l l b12 b13 b22 b23 t>33 Ai A 2 Br" 5 .05 309 - 55 204 139 - 11 75 N(l) 9 .50 464 123 386 278 147 136 +0.016 +0.132 N(2) 2 .05 195 18 112 188 - 7 31 -0.324 -0.221 C(3) 3 .58 182 222 117 200 - 33 62 -0.018 0 C(4) 3 .68 190 119 93 176 4 75 +0.031 0 C(5) 5 .86 364 151 248 333 -120 68 -0.031 0 CH 3(3) 2 .312 142 160 117 91 - 21 42 -&J170 -1.177 CH 3(5) 6 .24 392 111 234 459 - 13 71 +0.201 +0.224 C(3') 2 .82 200 134 148 154 - 1 42 +1.430 +1.451 0(3) 5 .95 400 -116 222 551 14 71 . 0(3') 8 .92 408 -160 312 295 63 139 CH 3(3') 5 .20 296 -136 136 20 - 49 134 — — - 12 -Table III OBSERVED BOND LENGTHS(d o b s ) AND SOME BOND LENGTHS FROM THE LITERATURE (d-, , t ) <4> AND VALENCY ANGLES Bond d o b s 8 d i i t . ^ Angle Degrees CH 3(5) - C(5) 1 .60 1 .54 CH 3(5) - C(5) - N(l) 107 . C(5) - N(l) 1 .48 — CH 3(5) - C.(5) - C(4) 128. C(5) - C(4) 1 .42 — N(l) - C(5) - C(4) 124. C(4) - C(3) 1 .62 — C(3) - N(2) - N(l) 116 . N(l) - N(2) 1 .48 — N(2) - N(l) - C(5) 94. CH 3(3) - C(3) 1 . 54 1 .54 C(5) - C(4) C(3) 102 . C O ' ) - C(3) 1 .48 1 .52 C(4) - C(3) - N(2) 98. C(3') - 0(3) 1 .26 1 .23 C(4) - C(3) - C(3') 101. C(3*) - 0(3*) 1 .40 1 .36 C(4) - C(3) - CH 3(3) 113. CH 3(3') - 0(3') 1 .40 1 .36 N(2) - C(3) - C(3') 101. N(2) - C.(3) 1 .58 — N(2) - C(3) - CH 3(3) 110. C(3' ) - C(3) - CH 3(3) 129. Br" - N(2)' 3 .31 — C(3) - C.(3') - 0(3) 134. Br~ - 0(3) 3 .44 — C(3) - C(3') - 0(3') 106. Br~ - N(l) 4 .24. — 0(3.) - C(3«) - 0(3') 120. Br _ - C(3') 3 .70 - - C(3') — 0(3.') - CH3(3') 114. 13 -P l a n e 2 t h r o u g h t h e t h r e e c a r b o n atoms w i t h e q u a t i o n 0 . 0 0 8 7 X' + 0 . 9 6 8 9 Y +• 0.2437 Z' - 0 9639 p l a n e w h e r e N(l) a n d N(2) a r e d i s p l a c e d 0. A3 A a b o v e a n d 0,22 A b e l o w t h e p l a n e r e s p e c t i v e l y (see T a b l e 1 1 ) . I n b o t h e q u a t i o n s X', Y a n d Z' a r e c o o r d i n a t e s i n 8 r e f e r r e d t o a s e t o f o r t h o g o n a l a x e s , a , b a n d c * . A l l t h e s h o r t e r i n t e r m o l e c u l a r d i s t a n c e s a r e l i s t e d i n T a b l e I V a n d t h e p a c k i n g o f the m o l e c u l e s i s shown i n f i g . 2. - 14 -T a b l e IV SHORTER I N T E R M O L E C U L A R D I S T A N C E S ( A l l d i s t a n c e s ^ 4 X b e t w e e n m o l e c u l e 1 a t x , y, z a n d n e i g h b o u r i n g m o l e c u l e s a r e l i s t e d ) A t o m ( o f m o l e c u l e 1) t o A t o m O f M o l e c u l e # D i s t . ( A ) Br" N ( 2 ) 1 3 . 3 1 B r ~ N ( l ) 1 4.24 B r ~ 0 ( 3 ) 1 3 .44 B r " C ( 3 ' ) 1 3 . 7 0 B r ~ N ( l ) 2 3 . 9 3 B r ~ N ( 2 ) 2 3 .22 Br"" C H 3 ( 3 ) 2 3 . 9 1 0 ( 3 ) B r ~ 4 3.62 .0(3) N ( l ) 3 3 . 2 6 0 ( 3 ) N ( 2 ) 3 3 . 3 6 0 ( 3 ) C H 3 ( 5 ) 3 3 . 3 6 0 ( 3 ) C ( 5 ) 3 2 ,76 0 ( 3 ) C ( 4 ) 3 3 . 1 0 0 ( 3 ) C ( 3 ) 3 3 . 6 5 0 ( 3 ) C H 3 ( 3 ) 3 3 . 7 1 0 ( 3 ' ) 0 ( 3 ' ) 6 3 . 8 9 0 ( 3 ' ) C H 3 ( 5 ) 5 3.47 0 ( 3 ' ) C ( 4 ) 6 3 . 7 9 0 ( 3 ' ) C H 3 ( 3 ) 6 3 . 7 0 l - N ( l ) C H 3 ( 3 ) 3 3 ,70 C ( 6 ) C H 3 ( 3 ) 3 3 . 9 1 - 15 -Atom (of molecule 1) to Atom of Molecule # Dist (A) C(8) Br" 4 3.76 C(8) CH 3(3') 6 3,98 c(io-) B r - 4 3.83 C(10) C(5) 3 3.96 CH 3(3') N(l) 3 3.84 CH 3(3') CH 3(5) 3 3.96 CH 3(3') CH 3(5) 5 3.96 CH3(3,') CH 3(3) 6 3.67 CH 3(3) CH 3(5) 5 3.70 Molecule 1 at X y z 2 at -x - y -z 3 at - X J + y 2 Z 4 at X 2 y i+z 5 at 1+x y z 6 . at 1-x - y 1-z 0 °Br~ F i g . 2. P r o j e c t i o n of the s t r u c t u r e along b, i l l u s t r a t i n g m olecular packing. - 17 -DISCUSSION The analysis has shown the compound to be ioni c (this fact w i l l be dealt with later) and the five-membered ring to be s l i g h t l y buckled, but d e f i n i t e l y not planar. The five-membered ring i s best described in terms of either a plane through the four atoms N(l) , C(3) , C(4) and C(5) , with N(2) displaced +0.32 8 from t h i s plane, OJT the plane through the three carbon atoms, Tvith N(l) and N(2) displaced — 0.13 8 and +0.22 A respectively. For both cases the dev-i a t i o n of CH3(3) from the plane i s -1.2 8, and of CH"3(5) i s o +0.2 A, with the re s u l t that the two methyl groups appear to be in a trans-configuration. While the displacement of the CH3(3) i s reasonable for a group bonded to a tetrahedral atom, C(3), the displacement of CH3(5), however i s much too small for C(5) to be a tetrahedral atom and indicates C(5) to be a t r i g o n a l carbon atom. In fact, the small displace-ment of CHg(5) from the plane probably re s u l t s from c r y s t a l packing forces (to be discussed) d i s t o r t i n g a perfect t r i g -onal configuration about C(5). There i s therefore no question of cls - t r a n s isomerism or of fo l d i n g of the molecule along a l i n e j o i n i n g C(3) and C(5), v i z . from n.m.r. the angle between plane 2 and the plane through C(5), N(1), N(2) and C(3) i s greater than 18° for the non-hydrobrominated pyrazoline as compared to 2° for the hydrogen bromide pyrazoline, so that the analysis has not resolved the o r i g i n a l problem of the configuration of the parent l\ ^ -pyrazoline. - 18 -The interatomic distances and valency angles do lack in accuracy, as a r e s u l t of (1) the presence pf the bromide ion, ( i i ) possible absorption errors, ( i i i ) the. rather smail number of observed r e f l e c t i o n s . In s p i t e of t h i s lack of accuracy, the absence of a double bond in the r i n g i s estab-l i s h e d . The N(l) - N(2) bond, a double bond i n the non-hydrobrominated pyrazoline, measures 1.48 + 0.06 8, where 1.20 A i s the calculated length for N=N . The shortest o ri n g bond i s C(4) - C(5), measuring 1.42 + 0.06 A. But a o simple carbon-carbon double bond measures 1.34 A. Moreover chemical considerations do not permit a double bond i n t h i s p o s i t i o n . The sum of the angles N(l) - C(5) - CH 3(5), N(l) - C(5) - C(4) and C(4) - C(5) - CH3.(5) (see Table III) 359 degrees, i n d i c a t i n g that C(5) i s a t r i g o n a l atom, which fact i s also supported by the small displacements of the atoms from the plane of the r i n g (already mentioned). The structure of the cation can how be deduced. From the refinement of the structure N(l) was found to carry some p o s i t i v e charge, N(1> - N<2) was found to approximate a sin g l e bond rather than a double bond, and C(5) proved to be a t r i g o n a l atom, s u c h t h a t V i a may represent one plausible structure of the cation. This structure can only be par-r-t i a l l y correct, because a C(5) - N(l) double bond has already been ruled out. The fi n a l - evidence to resolve t h i s incon-sistency i s that, C(5) has a r e l a t i v e l y low density ( f i g . 1) and the temperature factor of t h i s atom i s somewhat higher than those of C(3) and C(4) (Table II); these facts suggest - 19 -that C(5) c a r r i e s some of the posit i v e charge, so that the f i n a l structure i s a resonance hybrid of the contributing structures Via and VIb. Although.VIb i s an unusual formu-l a t i o n , i t i s supported by the various points already mentioned, and one further point: C(5) i s involved in an unusually short intermolecular contact of 2.76 8 to 0(3) of a molecule related to the molecule at x, y, z by a screw axis. This distance, about 0.S^shorter than the usual Van o der Waals distance (3.1 A), i s j u s t i f i e d on consideration of the force of at t r a c t i o n between the p a r t i a l p o s i t i v e charge on C(5) and the r e l a t i v e l y negative oxygen atom. The reaction of IV with HBr must involve an i n i t i a l rearrangement to a / X^-pyrazoline^V, a chemically reasonable acid rearrangement process, followed by formation of the hydrobromide. Evidence for such a rearrangement was obtained by treating the hydrobromide with NaHC03; the product was d i f f e r e n t from the o r i g i n a l Z^-pyrazoline, IV, and the n.m.r. spectrum was consistent with structure V ^ \ The angles in the rin g are somewhat ir r e g u l a r which i s not too surp r i s i n g in such an unusual ring system. The external angles, and the bond lengths in the carbomethoxy group, do not d i f f e r markedly from the expected orders of magnitude as shown in Table I I I . The intermolecular distances require some s p e c i a l comment;' o The shortest contact between the molecules of 2.76 A, which has already been discussed, r e s u l t s in several other short contacts, also involving 0(3), in the range of 3.1 - 3.4 8 - 20 -(Table IV). One of these contacts i s between 0(3) and CH3(5) where the distance i s 3.36 8; i f CH3(5) lay in the o best r i n g plane, t h i s distance would be 0.2 A shorter, so that the non-planarity at C(5), as already mentioned, may be ascribed to c r y s t a l packing forces. The shortest d i s -tance involving the bromide ion i s with N(2) and not with N(l) or with C(5). In fact there are two Br~---N(2) con-tacts, 3.22 A* and 3.31 8 (Table IV). In order to accommodate a l l hydrogen atoms, one of these distances must represent a N-H.-.Br~ hydrogen bond. A l l the evidence mentioned so far rules out the p o s s i b i l i t y of two N(2) - H-•-Br" bonds and of a p o s i t i v e charge on N(2). Consideration of the angles of approach, Br-(l) • • -N(2.) - N(l) = 83° Br"(2) • • -N(2) - N(l) = 118° B r - ( l ) • • *N(2.) - C(3) = 114° Br"(2) • • -N(2) - C(3) = 119° where B r ~ ( l ) i s the bromide ion at (x, y, z) , and Br~C2) i s the bromide ion at (-x, -y, - z ) , suggests that Br~(2), involving the equal angles i s hydrogen-bonded to N(2) (bond length 3.22 8), rather than B r ~ ( l ) which involves the small angle of 83°. The Br"(1)•••N(2) distance i s s l i g h t l y shorter than the sum of the i o n i c radius of Br~ and the van der Waals o radius of nitrogen (3.45 A). A l l the other intermolecular distances are normal, the shortest Br~'°-N(l) contact i s 3.93 8. - 2 1 -BIBLIOGRAPHY 1. McGreer, D. E., Morris, P. and Carmichael, G., Carl. J . Chem. 41, 726 (1963). 2. McGreer, D. E., Chiu, N. W. K. and Vinje, M. G.,(in preparation), 1965. 3. Chiu, N. W. K., M. Sc. Thesis, July 1964, Department of Chemistry, University of B r i t i s h Columbia. 4. International Tables for X-ray Crystallography, Vol. I l l Kynoch Press (1962). 5. Pauling,,L., The Nature of the Chemical Bond (1960) p. 160, Cornell University Press. 6. Chiu, N. W. K., Private Communication. - 22 -APPENDIX h k I ^obs^calc I I . V -)T.I -25.7 19.1 -21.8. i;3.4 i;.# -jr.* o . l •140.0 I . l -88.0 -42.1 -[0«.2 - j ' i . V -7.6 -kT. I 4.0 -16.4 47.4 -44.2 10.1 -41.3 24.7 "24.9 • l i . J 56.J 20.1 46.0 _24.B JO.* 9.1 44.0 it. * 10.9 14.4 21.9" 19.1 II. T 64. t 20.2 22.1 94.8 -14.0 4 i . a" 42.1 27.e 40. I 2>. 2 __62.9 2 7.2 7.1 16. 7 - I t . I 25.4 20.4 27.0 14.4 J9.2 69.2 77.1 J. 1 24. 7 27.4 _24.4 Jl.O 14.2 -74.1 •76. 7 -47.2 • I l fO St.I -*i(>. 2N.6 9.0 42.1 16. 7 29.6 42.0 — 24.0 11.6 U . 3 28. 6 19.0 _ 5.0 - i o . 6 -19. » 10.2 22.1 24.1 16. * 11.8 11.4 JO.6 ; I .JI IT.» 24". 4 16.6 10.2 92.4 - t 1.8 6.2 •12 11.7 14.9 -2 0. -9.2 -4 13.4 -14.4 • 4 18.7 ' 13.* -6 21.8 7. 0 0. -*.7 -2 17.4 -11.* 2 19.4 ' -16.4 -4 0. -11,1 -6 U. -It 24.1 -21." 7 10 0. -7.9 12 U. -1 .a |4 0._ -1.7 0 0." i.l -2 I'?. 2 -i->.* - o . ' -4 1W.6 -18.8 -4.4 -14.6 12 0. -2. 1 1 7 1,4 T2.« 1 6". 7 66. 2 42.2 7 2).fl *9.4, 1 25.5 *4,1 42.6 - J 78.1 f t . 7 ] 24.6 21.9 -9 46.4 31.6 -7 54.4 42. 7 "-1 24.9* 26.6 -1 .20.8 16.4 -5 10.6 27.7 -T 41.0 17.3 -« '29.1 27.1 \ 36.2 -16. 1 -1 26.r -26.4 J 41 .4 -42.4 -J JO.6 -10.3 -3 0. 1. 7 -1 44.4 - 19.4 -1 ' 47.0 -18.8 -4 47./" ~-» 1.3 -T JJ.B -14.9 -1 14.1 -11.8 -5 41.4 -16.2 -T 14.0 -24,6 -9 44.0 - IB.I 2 20.6~ 11. 1 4 JB.2 - 1 1 .i 6 10.4 -ID. 1 8 40.2 -42.1 10 24.6 -29.5 12 11.9 -20.9 0 76. T -10 1.6 -2 10.6 -12.0 2 as.3 -98. 1 -4 12.1 -11.4 4 a s . * -96.4 -6 0. -8,0 -0 0. 10.9 8 40.9 -41.4 10 0. 4.7 10 21.5 -20.1 1? 0. 17.t 0 98.4 -108.7 -2 99.* -92,6 2 47.4 -91.0 -4 1(0.1 -154.4 4 92.1 -52.a. -6 49.1 -48.9 6 22.1 -12.1 -A IS.4 -19.3 10 16.1 -20. 1 12 0. I . l 0 54.2. -60.1 -2 36.6 -47.7 2 91.6 -46.6 -4 11.6 -78.1 4 0. -14.4 •6 91.9 -46.1 -8 101.4 -94. 7^  10 4 1 .9 -42 .V 12 19.1 -16.* 0 16.9 11.9 -2 34.7 -40.7 -4 29.1 -14.1 •6 T1.4 -69.7 -B 36.4 -52".'4 10 12.0 -24.4 12 32.4 -51.1 14 17.0 -IT.7 0 19.H 24.0 •2 14.6 IT.4 -4 11.1 10.9 -6 |4.2 ' -9.2 -a o. 9.4 10 28.4 -14.1 11 14. • -17.* 10,2 20.3 "17.1 14.1 22.7 22.1 22.4 29.1 28.4 10.2 0. 2.4 0. 19.4 " * l , 4 "-44.B " 60.2 19.6 19.9 16.0 -1 7.2 -40. 7 24.0 -24.9 -1.4 -24.2 14.6 -4.0 i o . e ' 16.1 12. T 62.6 -46. ) -40.6 -10. 1 -I 7.T -a.T -4.9 -3.0 -42. B -T.9 90.6 18. S 26.1 0. 14.1 10.9 19.6 14. T 15.4 22.8 I 7.9 IB.9 I 7.9 71.I 14. 7 22.3_ "14.T 39. I 0. 16.r _18. 1„ 94.9 l». l -^9.8 •11.0 -10.4 MO.', 4.1 14.6 -19.9 , -4.0 -43.4 -26.8 -14.2 11.6 8.9 12.9 28.1 11.6 20.0 -9.6 Zll'A. 10.9 9.9 18.9 76.9 4.8 36.9 -0.2 J ' ^ 16.4 -9.1 4.9 _66.0_ 90/2 19.3 91.T 22. T >*.*.*. 16.2 -T. 1 12.9 11 .4 11.1 _21.4_ 19.4 67.0 64.4 28.6' -2.2 -28.0 -6.0 -^.4 - I I . * 1. 1 2.4 -6. 1 28.1 16.0 . _24. 7_, 16.9 64.T 67.1 29.0 2.2 __*9,0_ 19". a 61.0 15. a 18.4 11.6. 67.6 14.9^ 2J.6 18.T 42.1 14.6 27.2 2.1.2 21.9 21.2 _ 22.8 18. I 10.6 42.6 -21.9 17.6 12.4 -13. 1 -17.8 , -24.8 . -IT.6 -12.1 -15.6 1.9 -12.2 10.2 

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