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UBC Theses and Dissertations

Circular dichroism of nitrate esters Barton, Richard Edgar 1971

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CIRCULAR DICHROISM of NITRA.TE ESTERS by B.Sc.f  RICHARD EDGAR BARTON U n i v e r s i t y o f B r i t i s h Columbia;,  1966  A THESIS SUBMITTED I N PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  i n the  Department of  CHEMISTRY We a c c e p t t h i s to  t h e s i s a.s c o n f o r m i n g  the r e a u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA June,  1971  iv  In presenting t h i s requirements British  thesis  in partial  f o r an a d v a n c e d d e g r e e a t  Columbia,  freely available  I agree t h a t for  that permission for  the  fulfillment  of  the U n i v e r s i t y  of  Library  r e f e r e n c e and s t u d y . extensive  s h a l l make I  copying of t h i s  further thesis  the  it agree for  s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e Head o f my D e p a r t ment o r by h i s r e p r e s e n t a t i v e s . ing or p u b l i c a t i o n s  of t h i s  It  thesis  n o t be a l l o w e d w i t h o u t my w r i t t e n  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, B.C.  Columbia  i s understood for  that  f i n a n c i a l gain  permission.  copyshall  A B S T R A C T The c i r c u l a r hexyl-,  bicyclo  measured. the  optically  heptyl-,  \Z,2.1J  A chirality  stereochemistry  their is  dichroism of  rule  of  active  alkyl  and o x o l a n y l n i t r a t e s  i s proposed which  the n i t r a t e  in  right-handed  esters w i t h the  w i t h the a l k o x y l  oxygen a t  z axis,  and t h e n i t r o  sign of  the  rectangular the o r i g i n ,  The r u l e  c a n be e f f e c t i v e l y  conformation of forty-eight predicted  the n i t r a t e  nitrate  esters  i n the p o s i t i v e  applied ester  coordinates  yz p l a n e ,  d i c h r o i s m band w i l l  when t h e p e r t u r b i n g a t o m s l i e  be  positive  favoured  c a n be d e t e r m i n e d .  examined, the r u l e the  c o n t r a d i c t i o n s were  conformations  formational  250-330  [2.2.l] heptyl nitrates, for  gave  In a series a positive  of  seven  trato  b a n d was o b s e r v e d f o r  of  con-  alkylbicyclo-  2 3 0 nm band was  compounds c o n t a i n i n g a 2 - e n d o n i t r a t o  negative  No  "double-humped"  nm s p e c t r a l r e g i o n and e v i d e n c e  equilibria.  of  observed.  M e n t h y l and c a r v o m e n t h y l n i t r a t e s bands i n t h e  Of  correctly  e i g h t e e n and t h e band s i g n s o f two r e m a i n u n c e r t a i n . direct  the  x-direction.  o n l y when a  t h e band s i g n o f t w e n t y - e i g h t ;  of  C - 0 bond on t h e  moiety i n the p o s i t i v e  2 3 0 nm c i r c u l a r  sign  chromophore  cartesian the  was  correlates  2 3 0 nm CD b a n d s : when t h e p l a n a r n i t r a t o  oriented  cyclo-  observed  group w h i l e  compounds w i t h a 2 - e x o  a ni-  group. The i n f l u e n c e  ellipticity  of  the  of  temperature  and s o l v e n t  on t h e  2 7 0 and 2 3 0 nm CD b a n d s o f n i t r a t e  molecular esters  iii  was e x a m i n e d .  The 270 nm band i s  vironmental effects,  and i n some c a s e s i t s  versed by changing the tributed  to rotation  t h e more s e n s i t i v e  solvent  s i g n may be  or temperature.  of the n i t r a t o  bond, a l t h o u g h n o n - c o n f o r m a t i o n a l  to  This is  group about the  e f f e c t s may a l s o  0-C be  important. S t u d i e s on m e n t h y l and f e n c h y l n i t r a t e s appreciable  influence  270 nm e l e c t r o n i c  of  solvent  .transition.  showed no  on t h e e n e r g y o f  the  enreat-  V  TABLE OF CONTENTS Page Abstract List  of Tables  List  of Figures  <>....o  ii „  0........0  ......<> 0  Acknowledgments INTRODUCTION  vi  <>  o..  viii  0  ......  xii  o....  1  .  C h i r a l i t y Rules <>.... 000 Environmental Effects CD o f N i t r a t e E s t e r s Chromophores R e l a t e d t o R 0NCr2 Conformation of the N i t r a t o Group... Transitions In Nitrate Esters..o.0.. B o n d i n g Of The N i t r a t o G r o u p . 0 . o . . . o 0  6 Ik, 35  43 55 65 73  RESULTS AND DISCUSSION c  80  U l t r a v i o l e t S p e c t r a Of N i t r a t e E s t e r s 80 C h i r a l i t y Rule For N i t r a t e E s t e r s . . . 84 Alkylcyclohexyl Nitrates.•0...o 9k N i t r a t e s Of A l k y l b i c y c l o [ 2 , 2 , f l heptanols o o I l k N i t r a t e s W i t h Oxolane R i n g s . l4l Steroidal Nitrates. 155 Acyclic  Nitrateso..•o•.••0••o.•.•.o•  Summary. •  EXPERIMENTAL  ••.<>•.  o •. • • •  . . . . o .. o . . . . . . . . . . . . . . . . . . . . . . . . . . . . Source o f C h i r a l C a . r b i n o l s . . . o . . o . . . Synthesis of N i t r a t e E s t e r s . . . . . . . . . UV S p e c t r a . . . . . . 0 0 . . . . .  CD Measurements Source o f I n s t r u m e n t E r r o r . . . . . . . . . . Low T e m p e r a t u r e C D . M e a s u r m e n t s . . . • • o  160  165  167 168 168 173  173 174 176  vi  L I S T OF TABLES  Page I  Some E n v i r o n m e n t a l E f f e c t s  II  C o n f i g u r a t i o n a.nd t h e S i g n s o f t h e C o t t o n Of N i t r a t e s  Seen i n CD S p e c t r a . • • Effect  o  of. G l u c o s i d e s  17  o . . 36  III  CD o f S t e r o i d a l N i t r a t e s  in Ethanol.  40  IV  Chromophores C o n t a i n i n g N i t r o g e n - O x y g e n . . . . . . . . •  44  V VI  UV S p e c t r a , o f N i t r a t e E s t e r s Probable E l e c t r o n i c T r a n s i t i o n s Responsible The CD Bands Of N i t r a t e E s t e r s . . .  66 For  0  72  VII  L e n g t h o f N i t r o g e n Bonds  VIII  UV S p e c t r a , o f N i t r a t e E s t e r s , c . . .  IX  CD o f N i t r a t e s W i t h One C y c l o h e x a n e  X  Alkylcyclohexyl Nitratesi Predicted C h i r a l i t y  XI  AG V a l u e s o f V a r i o u s S u b s t i t u e n t s . . . . . . . . . •  XII  V a r i a b l e T e m p e r a t u r e S t u d y o f 1R»3R14S-Menthyl Nitrate ( I ) . 0 .o . . . . . . . .  106  C i r c u l a r D i c h r o i s m o f 1R»3R»4S-Menthyl Solvent E f f e c t s . . . . . ° o . . . . o . . . . . . . . . .  109  XIII  81 Ring.oo...o.  0  0  Nitrate  0  XIV  CD Of N i t r a t e s  XV  Band S i g n s and C h i r a l i t y R u l e P r e d i c t i o n s F o r N i t r a t e s o f A l k y l b i c y c l o [2.2.1] h e p t a n o l s . . . o • o .  XVI XVII  LTCD o f Effect  100  Of A l k y l b i c y c l o [ 2 . 2 . l ] h e p t a n o l s . oll6  Bornyl,  I s o b o r n y l and F e n c h y l  o f S o l v e n t s on t h e CD o f Nitrates..  Nitrate...123  . . . . . 0 . 0 . 0  XVIII  LTCD o f C a . m p h a . n e - 2 , 3 - d i o l - d i n i t r a t e s  XIX  CD o f L - T h r e i t a . n  Dinitrate  0II8  Alkylbicyclo-  [2.2ol] h e p t y l  131  (MeOH).o...137  and o f D- and L-<x-  Nitrato-^'/^-dimethyl-lf-butyrolactone.  XX  96  CD Band S i g n s and <, 0 . . . . . . . . » .... « ... 98  0  0  76 •  CD o f N i t r a t e s W i t h O x o l a n e R i n g s  oooo.......143  0.  145  vii  L I S T OF TABLES  (CONTD)  Page XXI  CD o f L - T h r e i t a n  Dinitrate  (30°C)  XXII  CD o f S t e r o i d a l N i t r a t e s , . o » '  XXIII  Nitrates  XXIV  230 nm S i g n P r e d i c t i o n s  ..  o  . . . »  of o(-Hydroxy A c i d s . . . . Nitrato  Rule.oo..o.....«««oo««..oa..*..«o....*.oooo  Sources o f C h i r a l A l c o h o l s . . . . . .  XXVI  Elemental Analysis  of N i t r a t e  156 l6l  by...Planar  XXV  1^9  o • « , . . . . . . . .  Esters..0.0oo  l65  169 172  viii  L I S T OF FIGURES  Pa.ge 1.  R e l a t i o n s h i p Between t h e A b s o r p t i o n , ORD and CD  Ultraviolet 3  2.  Three C l a s s e s o f Chromophores  3«  Spheres o f P o s s i b l e Dissymmetry. • o  4.  The O c t a n t R u l e . . . . . . . . . . . . . . . .  5.  C C h a r a c t e r T a b l e and t h e A Representation.  6.  E n v i r o n m e n t a l CD E f f e c t s  7.  CD o f ( - ) Menthone i n D e c a l i n a t + 2 5 * C , - 7 4 * C a.nd + l 6 2 * C (A) and i n V a r i o u s S o l v e n t s a t  2 v  2 5 °C  7 11  Pseudoscalar .  2  . . o . .  0  6  0  •  12  .<>...  16  ( B ) . . . c . o . . . . . o . . a o o o s . o o a . . . . . o o . . o . . . o « o  21  8.  G e n e r a t i o n o f a Double-Humped CD C u r v e . . . . o o . c •  9.  ORD and CD o f 2 , 3 , 4 , 6 - T e t r a - 0 - a . c e t y l - l - o N i t r o - o i - D - g a l a c t r o p y r a n o s e (A) and M e t h y l 4 i 6 - 0 Benzylidene-Q(-D-altropyra.noside 3-Nitra.te ( B ) . o 37  10. 11.  Free R o t a t i o n i n the N i t r i t o , N i t r a t o Chromophores.  Nitro  and 43  CD o f ? * - C h l o r o - 7 > S - N i t r o - 5 o ( - C h o l e s t a . n e a t +22- C (50)..  48  Sector R u l e . . o . . .  49  a.nd - 1 8 8 ° C 12.  Nitro  13. 14.  A p p l i c a t i o n o f the N i t r o Sector Rule •• A p p l i c a t i o n o f Rule R e l a t i n g C o n f i g u r a t i o n o f C - n i t r o A l c o h o l s t o t h e S i g n o f t h e 3 1 0 nm CD band ( 6 5 ) . . . . . . < > . . . • * . . . . . • • • • o . • . . . . . . . . . . . . . o  15c  22  Sector Rule f o r  the Nitrosoamine  (upper  (64). ....  sectors)  0  16.  C o n f i g u r a t i o n of S t e r o i d a l  17•  Proposed S t r u c t u r e s  for  50  52  Chromophore 53  0  Acetates.  Nitrate  Esters.........  55 57  ix  Pa.ge 57  18.  Bond R o t a t i o n s  in Nitrate  19.  Methyl N i t r a t e  Energy Surface  20.  Some T r a n s i t i o n s  21.  UV S p e c t r u m o f M e t h y l N i t r a t e R e s o l v e d i n t o i t s Component Bands ( 8 9 ) . . . . . . . o . . . . . » . . o o . o  22  Esters  o f MeON0 . . . . . o  .  2  68  E n e r g y L e v e l s and T r a n s i t i o n s o f t h e N i t r o Chromophore a n d N i t r a . t e I o n . • o o . . . . . o o . .  24.  Ethyl Nitrate Bands  68  . . o o  •  0  23.  19  ( 8 9 ) ° . . . . . . . . . . . o .  as V i e w e d f o r C h a r g e - T r a n s f e r <>..  N o n b o n d i n g and T r o r b i t a l s  71  of the Nitrato  G r O U p . . o . . . . . . . . . s . . . . . . . * . . . o . . « e . e . . . e . . o . e . . .  25.  260  UV S p e c t r u m o f M e n t h y l N i t r a t e  27.  N o d a l P l a n e s o f t h e TT a n d N o n b o n d i n g of  30.  the N i t r a t o  0  (A) and Nodal  0 0  ».o..o.  82  84  Surface  C o o r d i n a t e s a n d D i p o l e Moment o f t h e N i t r a t o Group . . . . . . . o o . . . . . . . o . . 0 . 0 . 0 . 0 0 . . o . . . . Planar Rule  75  Orbitals  C —ONO2 ( B ) o o . . o . o . e o . o o o o . . . o . . o o e . Q . . . o . * . . a .  86  . . .  86  o.o......  87  ( f r o m Cs p o i n t group) f o r t h e o  N i t r a t o Group.. 31.  (MeOH) o  Group••.•<>•••.......o.o..oe...o..  Antibonding Orbitals Of  29.  7^  M o l e c u l a r O r b i t a l D e n s i t y C o n t o u r Maps f o r M e t h y l N i t r a t e , a c c o r d i n g t o Csizma.dia. e_t a . l . (89). . * ° .0 . 0 0 .a o o . o . o o . e « o . . . . « . o . . . o o o « . . o . e . . .  28.  69  Possible Positions  o f t h e n and I T * Nodal Group.o.o.......o..oo...  89  32.  V i e w i n g t h e N i t r a t © Group A l o n g t h e 0-C b o n d . . o .  90  33.  Application of the Nitrato C h i r a l i t y  Surfaces  of the Nitrato  ISs2R—Bornyl  Rule t o  Nitra.te«.ooo.».o..oeo»o.»9B»..oo...  of the Nitrato  Group................  91 92  34.  Projections  35. 360  CD o f C y c l o h e x y l N i t r a t e s ( i n CH-^CN). ........ 99 R e s o l v e d Bands ( n o t t o s c a l e ) o f t h e 270 nm T r a n s i t i o n o f M e n t h y l and C a r v o m e n t h y l N1 ~tr*3."t 6 S • e o c o o o o o o o » o f i o o * o e « o o » o o o o o o o o o o o o » o o o o 99 0 0 0  X  Page  37.  CD ( b a n d I )  38.  LTCD o f M e n t h y l N i t r a t e  39.  V a r i a t i o n o f t h e 270 nm Band o f M e n t h y l N i trate (I) with Temperature..... •  40.  Menthyl N i t r a t e ( I ) J R e l a t i o n o f [e] . . . . . . . • • • • 2  41.  7  of Isocarvomenthyl N i t r a t e  102  0...00  (I) in Methanol...........  0  £ ?ry  •  to • •  n  •  106  o 108 •  •  1  0  8  P l o t o f D i e l e c t r i c C o n s t a n t (A) and Z V a l u e (B) Against M Menthyl N i t r a t e ( I )  113  42.  CD o f I s o b o r n y l ,  117  43.  CD o f C a m p h a n e - 2 , 3 - d i o l - d i n i t r a t e s  44.  C h i r a l i t y Rule P r o j e c t i o n s X I I and X I V  2  7  0  o  f  Bornyl, Penchyl N i t r a t e s (CH^CN)  120  o f N i t r a t o Groups  in 121  45.  LTCD o f L S i 2 R - B o m y l N i t r a t e  (MeOH)  46.  T e m p e r a t u r e V a r i a t i o n (Band I ) B o r n y l N i t r a t e s (MeOH).  126  o f I s o b o r n y l and o . . . 0 • . • • o .  127  47.  LTCD o f I S i 2 R - B o r n y l N i t r a t e  48.  CD o f l R » 2 R - I s o b o r n y l N i t r a t e  (Solvent  49.  CD o f B o r n y l  (X) N i t r a t e s . . . . . . . 133  50o  LTCD o f C a m p h a n e - 2 , 3 - d i o l - d i n i t r a t e s  (MeOH)......  51.  LTCD o f C a . m p h a . n e - 2 , 3 - d i o l - d ' i n i t r a . t e s  ( M e O H ) . . . . . . 140  52.  CD o f L - T h r e i t a . n D i n i t r a t e a n d L - C k - N i t r a t o 0, ^ - d i m e t h y l - * - b u t y r © l a c t o n e . • • o . . . . o .  ( I X ) and F e n c h y l  (IX)...  i  129 Study)..  53•  P r o j e c t i o n s f o r I s o i o d i d e and I s o m a n n i d e N i t r a t e s and I s o s o r b i d e D i n i t r a t e ( X I X )  54.  Projections Dinitrate  of Nitrato  . . . . 1 4 4  Mono-  146  Groups i n L - T h r e i t a . n •  . . . o o o . . . . . . . . . e . . . . . . . . . . . . . . o . . o . . . . o .  55«>  CD o f L - T h r e i t a n D i n i t r a t e  56.  LTCD o f L - T h r e i t a n  Dinitrate. 1  139  . . . . . o .  147  150 151  xi  Page 57.  CD o f L - T h r e i t a n D i n i t - r a t e w i t h P o s s i b l e R e s o l u t i o n (MeOH a t 3 G * C ) . . o ..  Band  0  58.  LTCD o f D - « - N i t r a t o - ^ , ^ - d i m e t h y l - y - . b u t y r o lactone. . . . . . . . o . . . . . 0  59.  CD o f N i t r a t e s  of o(-Hydroxy Acids  o  e  o . . . .  (CH-CN).......  152  153 162  xii  ACKNOWLEDGMENTS  To ray m e n t o r and g u i d e , P r o f e s s o r L . D . i n t r o d u c e d me t o t h e f i e l d s nitrate  esters,  of c i r c u l a r  H a y w a r d , who d i c h r o i s m and  and t o whom I am d e e p l y i n d e b t e d  h i s g u i d a n c e and  for  encouragement,  to Professor J . T r o t t e r  for valuable discussions  x-ray analysis of n i t r a t e  on t h e  esters,  t o D r . R.No T o t t y ' s p r e s e n c e i n t h e l a b o r a t o r y and h i s willingness  to offer  valuable  help,  t o P r o f e s s o r s S . S c h r o e t e r and S . A n g y a l f o r g i f t s chiral  of  earbinols,  t o my w i f e ,  P e g g y , who s p e n t h o u r s o f t i m e  my h a n d w r i t i n g i n t o n e a t  typescript.  deciphering  xiii  1.  I N T R O D U C T I O N  2  INTRODUCTION A most c h a r a c t e r i s t i c  p r o p e r t y o f a l a r g e number and  v a r i e t y of n a t u r a l l y - o c c u r r i n g o p t i c a l r o t a t o r y power, polarized  light.  that  is,  To e x h i b i t  (l)  a g o , when he s a i d , of points  "I  only  has c h i r a l i t y  if  its  symmetry e l e m e n t s Sn, t h a t a l t e r n a t i n g axis of  To be c h i r a l , is,  it  measure o f m o l e c u l a r  l i g h t known as c i r c u l a r  dichroism  coefficients  1).  the or  is  the  (CD).  The CD  between  the  cir-  light.  a b s o r p t i o n , At,  t h e CD s p e c t r u m o f t h e c h i r a l  on t h e i r a b s o l u t e  against  compound  The s i g n o f At depends on t h e c h i r a l i.e.  that  circularly  f o r t h e two f o r m s o f  of the d i f f e r e n t i a l  the molecules,  in co-  center,  or l e f t  molar absorption  (Figure  one  chirality  e x p r e s s e d as t h e d i f f e r e n c e  wavelength i s  image  must l a c k  o f t h e sample i s  A plot  group  translations  have no p l a n e ,  p r e f e r e n t i a l absorption of the r i g h t  cularly polarized  or  symmetry.  The most d i r e c t  polarized  years  c a n n o t be b r o u g h t t o  Thus a c h i r a l m o l e c u l e i s  (2a).  mole-  over seventy  i s n o n s u p e r i m p o s a b l e w i t h i t s m i r r o r image b y and r o t a t i o n s  with  the  c a l l any g e o m e t r i c a l f i g u r e  ideally realized,  incide with i t s e l f . "  interaction  their  chiral.  defined c h i r a l i t y  c h i r a l and s a y i t  a plane m i r r o r  their  optical activity,  c u l e s o f t h e compound must be Lord K e l v i n  o r g a n i c compounds i s  sense  configuration.  of  3  i  Figure  1.  Relationship ORD and CD.  The d i f f e r e n t i a l circularly polarized persion  dispersion of r i g h t light,  and  absorption,  left-handed  known a s o p t i c a l r o t a t o r y  (ORD), may be measured w i t h a  and l i n e a r l y p o l a r i z e d chiral  between t h e u l t r a v i o l e t  light  sample i s t r a n s p a r e n t .  spectropolarimeter  i n s p e c t r a l r e g i o n s where  transform.  phenomena o f ORD and CD t o g e t h e r a r e known as t h e from t h e i r  discoverer,  The r e l a t i o n s h i p  t h a t the  CD band i s  Cotton  The Cotton  (I895) ( 2 b ) .  of the e l e c t r o n i c a b s o r p t i o n ,  of a chiral transition is  the  The two phenomena, CD and  ORD, a r e r e l a t e d b y t h e K r o n i g - K r a m e r s  effect  dis-  illustrated  i n Figure  1.  confined t o the area under the  ORD and Note ultra-  4.  violet  a b s o r p t i o n band, w h i l e the  retically)  over the e n t i r e  ORD c u r v e e x t e n d s  (theo-  spectrum.  C i r c u l a r d i c h r o i s m d a t a are a l s o expressed as molec u l a r e l l i p t i c i t y , [e] , w h i c h i s r e l a t e d a b s o r p t i o n by the  d i s p e r s i o n has*  differential  expression  = 3300 A t  [9] The g e n e r a l f i e l d  to the  of  circular  d i c h r o i s m and o p t i c a l  been r e v i e w e d b y s e v e r a l a u t h o r s  rotatory  (3-7).  The w a v e l e n g t h w e i g h t e d a r e a u n d e r t h e CD band i s p o r t i o n a l to the r o t a t i o n a l of the dissymmetry of the of the  pro-  s t r e n g t h , R, w h i c h i s a measure  c h r o m o p h o r e and o f t h e  intensity  dichroism. A  Each t r a n s i t i o n al for  o f t h e chromophore w i l l  s t r e n g t h and t h e r e f o r e  have i t s  t h e c a l c u l a t i o n c a n be  compounds w i t h o v e r l a p p i n g CD b a n d s .  strength,  R,  rotation  difficult  rotational  i s a s i g n e d q u a n t i t y and s e r v e s as a measure  o f the chromophore*s i n t e r a c t i o n w i t h i t s vironment.  This quantity i s also  theoretical  significance.  perimental quantity. R , k  dissymmetric  important  en-  because o f  Through the r o t a t i o n a l  the theory of o p t i c a l a c t i v i t y  transition,  The  own  its  strength,  can be r e l a t e d t o an e x -  The r o t a t i o n a l  strength of  the  is  (c.g.s. 'o  units)  where c i s t h e v e l o c i t y o f l i g h t ,  h i s Planck*s  constant,  i s t h e number o f o p t i c a l l y a c t i v e m o l e c u l e s p e r cm 3 , 6  K  i s the p a r t i a l  i s also important rotational  f o r the k^  to note t h a t  h  transition.  the experimentally  solvent.  o f t h e m e d i c i n a l and t e c h n i c a l i m p o r t a n c e  esters  ( R 0 N 0 ) , knowledge o f t h e i r p h y s i c a l 2  p e r t i e s and m o l e c u l a r  structure  nitrato  i s an e a s i l y a c c e s s i b l e  group  It  obtained  s t r e n g t h w i l l v a r y w i t h t e m p e r a t u r e and  In spite nitrate  ellipticity  (-0N0 ) 2  is relatively  w h i l e the h y d r o x y l group from which i t  spectrophotometer can be r e a d i l y  or polarimeter.  limited.  cular dichroism of the n i t r a t e  derived  would c o r r e l a t e  esters  group,  the  For  dichroism  cir-  these  to devise a c h i r a l i t y r u l e  circular  group  o f the wide range  the stereochemistry of a n i t r a t e  to the signs of i t s  usual  Since the h y d r o x y l  n a t u r a l l y o c c u r r i n g a l c o h o l s may be s t u d i e d . was d e s i r a b l e  The  chromophore,  is usually  converted i n t o the n i t r a t o  bands.  of  pro-  a b s o r b s a t t o o l o w a w a v e l e n g t h t o be r e a c h e d b y t h e  reasons i t  and  that  ester  of  6  Chirality Circular  dichroism i s  mination of absolute that  Rules  of unique value  configuration  depends d i r e c t l y  on t h e  since  chirality  When c h i r o p t i c a l p r o p e r t i e s a r e phores are divided i n t o  a)  Dissymmetric chromophore  Figure  2.  three  b)  f o r the  it  is a  of the  property  molecule.  considered,  chromo-  (Figure  2).  Coupled-Oscillators T r o g e r ' s base  c)  Three classes of  classes  chromophore i s  c h i r a l by i t s e l f  exhibit  dichroism;  coupled-oscillator  the  t w o c h r o m o p h o r e s w h i c h become o p t i c a l l y a c t i v e mutual i n t e r a c t i o n ; by i t s e l f ,  of i t s  is  molecular o r b i t a l s  i n which i t  longs to t h i s  third  Snatzke  (8a)  is  situated.  type of  s y m m e t r i c a l and i t s  a c t i v e when i t  active  by a by the  transitions w i l l  requires  is  their inactive  chiral group  The n i t r a t o o n l y be  i s placed i n a dissymmetric  will  dissymmetric  The n i t r a t o  chromophore.  and  by  s y m m e t r i c a l chromophore  b u t becomes o p t i c a l l y  perturbation vironment  the  symmetric chromophore 3-methylcyclohexanone  chromophores.  The d i s s y m m e t r i c circular  deter-  enbegroup  optically  environment.  c o n s i d e r e d t h e m o l e c u l e as d i v i d e d i n t o  spheres  7  of influence symmetric  and p o s t u l a t e d t h a t  extent  (Figure  1st 3»  In effect,  3).  sphere  Spheres o f p o s s i b l e the p e r t u r b a t i o n  dissymmetry.  o f a chromophore w i l l  f u n c t i o n o f t h e d i s t a n c e between i t atoms ( 8 b ) . to  » 2 7  tional  the  c h r o m o p h o r e d e t e r m i n e s t h e s i g n o f t h e CD band  to the greatest  Figure  t h e sphere n e a r e s t  Thus t h e r o t a t i o n a l i x  y  j7  7  JX  D;  and t h e  perturbing  strength is  proportional  w h e r e t h e 7's a r e t h e  cosines of the  line  be a  direc-  j o i n i n g t h e oxygen atoms o f  the  c a r b o n y l g r o u p w i t h t h e p e r t u r b i n g a t o m , and D i s a  function  o f t h e d i s t a n c e b e t w e e n t h e p e r t u r b i n g a t o m and t h e  chromo-  phore. Thus t h e i n h e r e n t l y the  c a r b o n y l Or n i t r a t o ,  accessible,  symmetric chromophore, whose t r a n s i t i o n s  are  s u c h as  readily  can be used as a s t e r e o c h e m i c a l p r o b e when  placed i n a dissymmetric deduce t h e a b s o l u t e  environment.  It  c o n f i g u r a t i o n of the  Ascertaining the absolute  may be used compound.  configuration of a  chiral  compound c o n t a i n i n g a s y m m e t r i c c h r o m o p h o r e r e q u i r e s comparison of i t s  to  CD s p e c t r u m w i t h t h e s p e c t r a o f  the  reference  8.  compounds o f known a b s o l u t e  configuration.  spectrum of a c o n f o r m a t i o n a l l y ulation-weighted conformers uration,  labile  S i n c e t h e CD  compound i s t h e  average o f the s p e c t r a o f i t s  (vide i n f r a ) ,  pop-  individual  to determine the absolute  config-  t h e c o n f o r m a t i o n a l e q u i l i b r i a o f t h e compound must  be k n o w n .  On t h e o t h e r h a n d , when t h e a b s o l u t e  configur-  a t i o n o f a compound i s k n o w n , CD m e a s u r e m e n t s can g i v e f u l i n f o r m a t i o n about the absolute  configurations  the present  conformational e q u i l i b r i a .  of the n i t r a t e  s t u d y a r e k n o w n , and i t  would form a set o f reference  was hoped t h a t  these  configuration.  r u l e s a r e b a s e d on t h e i m p l i c i t  Consequently,  for  s t a n d a r d s on w h i c h t o base a  assumption  o f an i n t e r a c t i o n b e t w e e n a c h r o m o p h o r e and i t s environment.  The  esters selected  r u l e r e l a t i n g t h e s i g n s o f t h e CD bands t o Chirality  use-  molecular  a careful evaluation of  the  mechanism o f o p t i c a l a c t i v i t y must p r e c e d e t h e d e s i g n o f chirality rule  (13).  Over t h e y e a r s ,  mechanisms have been p r o p o s e d  three  O n e - e l e c t r o n mechanism K i r k w o o d c o u p l i n g mechanism  3.  Magnetic-electric  of the e l e c t r i c  complementary  (l4)»  1. 2.  The a m p l i t u d e  a  coupling  mechanism  o f t h e CD band depends on t h e  magnitude  and m a g n e t i c t r a n s i t i o n moments and t h e  co-  s i n e o f t h e angle between them. I n t h e o n e - e l e c t r o n m e c h a n i s m , t h e m a g n e t i c and transitions  o c c u r i n t h e same c h r o m o p h o r e and t h e  o f t h e m o l e c u l e a c t s as a p e r t u r b i n g f i e l d w h i c h  electric  remainder partially  9  b r e a k s down t h e s y m m e t r y o f t h e n e t i c and e l e c t r i c  transitions  chromophore. are  "mixed".  I n the Kirkwood coupled o s c i l l a t o r requires at  least  itions dipolar  molecule  dissymmetrically  The c h r o m o p h o r e s have e l e c t r i c  and t h e s e e l e c t r o n i c fields  model, the  two c h r o m o p h o r i c g r o u p s  o r i e n t e d i n space.  T h u s t h e mag-  transitions  are  t o p r o d u c e a m a g n e t i c moment.  theory i s a special  case o f t h i s  The m a g n e t i c - e l e c t r i c two c h r o m o p h o r e s .  trans-  c o u p l e d by The  their  exciton  mechanism.  c o u p l i n g mechanism a l s o  One g r o u p has a n e l e c t r i c  t h e o t h e r has a m a g n e t i c t r a n s i t i o n .  involves  transition  while  These t r a n s i t i o n s  coupled i n the molecule t o give r o t a t o r y  strength to  are  both  transitions. A m o l e c u l e w i t h o n l y one i m p o r t a n t  chromophore  be a d e q u a t e l y t r e a t e d b y t h e o n e - e l e c t r o n t h e o r y . (13)  states that  if  the d i p o l e - d i p o l e  the Cotton e f f e c t  Schellman  the t r a n s i t i o n under c o n s i d e r a t i o n  weak and e s s e n t i a l l y m a g n e t i c , ignore  should  it  i s usually allowable  c o u p l i n g t h e o r y e n t i r e l y and  is to treat  by t h e o n e - e l e c t r o n mechanism.  A s t r o n g a b s o r p t i o n band i s u s u a l l y a s s o c i a t e d w i t h electrically  allowed t r a n s i t i o n while only a shoulder  f o r a m a g n e t i c a l l y a l l o w e d one. many o r g a n i c m o l e c u l e s t i a l l y p-p  appears  The l o w e s t e n e r g y bands  c o n t a i n i n g h e t e r o atoms a r e  essen-  t r a n s i t i o n s w i t h l a r g e m a g n e t i c moments  (n—>n*  transitions)  and can be c o n s i d e r e d i n t h e f r a m e w o r k o f  one-electron  theory.  an  of  the  10*  If  the Cotton e f f e c t  electric and i f  arises  f r o m a band w i t h a  d i p o l e and no m a g n e t i c d i p o l e  (fT-*rffor  t h e r e a r e no m a g n e t i c t r a n s i t i o n s  violet,  it  is a fairly  example)  i n the  safe assumption t h a t  large  near-ultra-  the  rotatory  s t r e n g t h i s developed l a r g e l y from the d i p o l e - d i p o l e l i n g mechanism (13a).  Thus t h e C o t t o n e f f e c t s  of  strong  a b s o r p t i o n bands a r e t r e a t e d by t h e c o u p l e d - d i p o l e although the p o s s i b i l i t y such bands i s u s u a l l y A chirality  rule  of one-electron  coup-  theory,  contributions  to  present. can be d e v e l o p e d b y e x a m i n i n g  the  t r a n s i t i o n i n v o l v e d , and t h e n d i v i d i n g t h e space a r o u n d chromophore i n t o  signed regions t h a t  tical activity.  I n the  case o f t h e  contribute carbonyl  t h e s y m m e t r y and n o d a l p l a n e s o f t h e o r b i t a l s i t i o n are the surfaces t h a t chromophore i n t o devised  (3).  o f the c a r b o n y l group i s to the octant however, behaviour  i n which i t  is  located  trans-  the  rule  is  dissymmetry  c h a r a c t e r i z e d by a s i g n (Figure 4 ) .  been an i n c r e a s i n g number o f r e p o r t s (13b).  of the  Thus, an o c t a n t  o f a n a t o m on t h e  op-  chromophore,  d i v i d e up space a r o u n d  eight regions.  The i n f l u e n c e  to the  the  of  according There  has,  antioctant  11  Back  Octants  +  Front  Octants +  A.  C.  B.  Figure 4.  The O c t a n t R u l e s A. n v r r ' t r a n s i t i o n . B. O c t a n t projection. C. S i g n o f t h e o c t a n t r e g i o n s .  S y m m e t r y r u l e s have b e e n d e v e l o p e d f o r a s u r p r i s i n g l y number o f  chromophores,  of authors  and have b e e n r e v i e w e d b y a number  (9-12).  Schellman,  on t h e o t h e r h a n d , h a s u s e d a  approach to generate transitions,  chirality  application  rules  different  (13a, 15).  For  the  a group t h e o r y approach i s a p p l i e d w i t h i n  o n e - e l e c t r o n mechanism.  S c h e l l m a n ' s method c o n c e r n s  o f group t h e o r y f o r g e n e r a t i n g the s i g n  mining regions associated with perturbers symmetric  large  chromophores.  strength i s given R p a  The e q u a t i o n f o r t h e  by - Vqp =  of  the  the deter-  inherently rotatory  12.  Reps  rotatory  M = electric  dipole  vector  m = magnetic d i p o l e  vector  a  v  strengh  , P = s t a t e s a and P  a,p=  p e r t u r b a t i o n energy between t h e two e x c i t e d s t a t e s which produces  coupling  The f o r m o f V w h i c h i s r e q u i r e d t o i n d u c e c h r o m o p h o r e depends on t h e s y m m e t r y o f t h e group i t s e l f .  In particular,  chirality  i n the  chromophoric  S c h e l l m a n shows t h a t  a part  o f V must b e l o n g t o t h e p s e u d o s c a l a r r e p r e s e n t a t i o n rotatory  s t r e n g t h i s a p s e u d o s c a l a r w h i c h changes s i g n on  r e f l e c t i o n and i n v e r s i o n i n t h e The c a r b o n y l c h r o m o p h o r e , C  2 V  p o i n t group. 2  potential  (Figure 5 )  A,  1  1  1  1  A  1  1 -1  -1  2  o  B  1 -1 -1  C  2 V  reveals of the  o" Vlxi.) VtyjL)  1 -1  F i g u r e 5«  character table  1  B, 2  2 V  J  C  2  f o r example, belongs t o t h e  representation i s the pseudoscalar p a r t  E  2 V  origin).  Consulting the C  that the A  c  (the  + t  +  1 -1 1  c h a r a c t e r t a b l e and t h e A representation.  A  2  2  representation  pseudoscalar  13.  Thus a q u a d r a n t r u l e by t h i s  approach.  is predicted  It  f o r the carbonyl  s h o u l d be n o t e d , h o w e v e r ,  group  that  S c h e l l m a n * s method can s p e c i f y o n l y a minimum number  of  s p a t i a l regions  T h e r e may be a d d i t i o n a l n o d a l  sur-  f a c e s , n o t d e t e r m i n e d b y s y m m e t r y , w h i c h can l e a d t o  fur-  ther  (l6).  subdivisions. The t h i r d a p p r o a c h t o a c h i r a l i t y  e m p i r i c a l one. solute  A l a r g e number o f  rule  looking for  the  purely  compounds o f known a b -  c o n f i g u r a t i o n a r e e x a m i n e d and t h e i r  ism spectrum r e c o r d e d .  is  circular  A r u l e may t h e n be d e v e l o p e d  correlations  dichroby  b e t w e e n c o n f i g u r a t i o n and CD band  sign. Whatever t h e r u l e , correctly predict  the f i n a l t e s t  the absolute  of the Cotton e f f e c t ,  configuration  or vice versa.  can be c o n s i d e r e d i n t h e d e v e l o p m e n t nitrate  esters.  is its  ability from the  These t h r e e  to sign  approaches  of a c h i r a l i t y rule  for  14  Environmental In the a p p l i c a t i o n of development, t e m p e r a t u r e , t o r s are i n v o l v e d . intermolecular  chirality  solvent,  r u l e s and i n  The i n t r a m o l e c u l a r  and c o n f o r m a t i o n  Temperature  effects;  it  is  conformational,  i s due t o  can a f f e c t  can a f f e c t  both of these  the conformation of the  i n t h e CD s p e c t r u m may be o b s e r v e d  (Figure  chromophore,  sign  2.  doubled-humped peaks changing i n  changes  marked changes i n t h e i n t e n s i t y  4.  induced c i r c u l a r  dichroism.  5«  frequency s h i f t s  o f CD b a n d s .  t h e cause and s i g n i f i c a n c e  w i l l n o t be c o n s i d e r e d i n d e t a i l .  intensities,  one peak  3.  of  The f i r s t  (28).  o f CD b a n d s .  frequency s h i f t s four  effects  to:  E q u i l i b r i u m b e t w e e n an u n a s s o c i a t e d and a n associated  form  (self-association).  C o n f o r m a t i o n a l changes i n t h e m o l e c u l e e q u i l i b r i u m b e t w e e n two o r more  3.  five  reversal.  p e r h a p s even m e r g i n g i n t o  2.  solvent.  6).  1.  1.  inter-  environmental  When t h e t e m p e r a t u r e a n d / o r s o l v e n t i s v a r i e d ,  have been a s c r i b e d  and  while  solvent—solute  and a l s o t h e i n t e r a c t i o n o f t h e c h r o m o p h o r e w i t h  study,  fac-  effects.  effect  effect  action.  In t h i s  their  These may be c o n s i d e r e d as i n t r a -  environmental  the intermolecular  Effects  -  an  conformers.  Assymmetric s o l v a t i o n - v a r i a t i o n s  i n the  sol-  15  vent 4.  E q u i l i b r i u m b e t w e e n a s o l v a t e d and ated  5.  cage. unsolv-  form.  A combination of  c o n f o r m a t i o n a l and  solvation  effects. These e f f e c t s  are not  just  as c a n be seen f r o m T a b l e I . example, esters, nitrites  i n ketones,  xanthates  benzyl sulphoxides (49), n i t r o  c o n f i n e d t o one  These e f f e c t s  are seen,  for  (49), ot-hydroxy a c i d s (39),  ( 2 1 ) , a z o x y compounds  steroids  chromophore,  (20),  ( 5 0 ) , and o ( - a m i n o e s t e r s  (18).  16  C. INTENSITY FIGURE  CHANGE.  D. INDUCED  6. E N V I R O N M E N T A L  CD  CD.  EFFECTS.  17.  Table I Some E n v i r o n m e n t a l E f f e c t s Seen i n CD S p e c t r a  Compound  Effect  P o s t u l a t e d Cause Ref  trans-2-chloro-5-methylcyclohexanone  double-humped peak  conformational  28  menthone  double-humped peak  conformational  28  2-oxo-1-p-menthanol  double-humped peak  conformational  48  3/5-acetoxyhexanordammar20-one  i n t e n s i t y change c o n f o r m a t i o n a l - 22 w i t h AT r o t a t i o n a l isomerism  isofenchone  double-humped peak  asymmetric vation  sol-  25  epiisofenchone  double-humped peak  asymmetric vation  sol-  25  5-hydroxy-epiisofenchone  double-humped peak  asymmetric vation  sol-  2  camphenylone  double-humped peak  asymmetric vation '  sol-  25  K-acetoxy-camphor  double-humped peak  asymmetric vation  sol-  25  oC-hydroxy-epiisof enchone  double-humped peak  asymmetric vation  sol-  25  2 -methyl-adamantanone  sign  solvent  lactic  double-humped peak  a  acid  reversal  5  effect  19  conformati o n a l (rotational isomerism)  39 42  camphor  i n t e n s i t y change asymmetric with AT vation  L-malic a c i d  double-humped peak  sol-  conformational (rotational isomerism)  43 39  18.  Table  I  contd.  Some E n v i r o n m e n t a l E f f e c t s Compound  Seen I n CD S p e c t r a  Effect  Postulated  Cause i ief.  dimethyl-L(-)-malate  double-humped peak  conformati onal  39  ethyl-L(+)-lactate  double-humped peak  conformational  4o  ( * - p u l e g o n e o x i d e and /3-pulegone o x i d e  double-humped p e a k and s i g n reversal  conformational and s o l v a t i o n equilibria  17  s(-amino  double-humped peak  conformational  18  LL-BH8?2o( and e l a i o m y c i n ( a z o x y chromophore  double-humped peak  solvation equilibrium  20  benzyl methyl  sign  conformational (rotational isomerism)  21  esters  C-g=N-C)  sulphoxide  <<-chloro-benzyl sulphoxide  methyl  reversal  sign reversal i n 220 nm transition  21 conformational equilibrium and/ or asymmetric solvation of a r o m a t i c chromophore  i n t e n s i t y change c o n f o r m a t i o n a l w i t h temp.  34  ci s-(S)-4-methyl—2-hexene and t r a n s - ( S ) - 4 - m e t h v l - 2 hexene  double-humped peak  conformational  35  N-dithiocarbethoxy-Laspartic acid  sign reversal with solvent  conformational ( r o t a t i o n about C-0 b o n d )  49  cholestan-3£-ol xanthate  sign reversal w i t h AT  conformational (rotamer e q u i l ibrium)  49  Etianic  a c i d s and  esters  methyl  19'•  Table  I  contd.  Some E n v i r o n m e n t a l E f f e c t s  Compound  Seen I n CD S p e c t r a  Effect  Postulated  Cause R e f  N-phthaloyl-20rt-amino-5tfpregnan-3£-ol  shape change w i t h sign r e v e r s a l o f one p e a k w i t h AT  conformational or solvation' : equilibria  49  cholestan-X-ol  sign reversal with AT  rotational merism  iso-  4-9  sign reversal w i t h AT  rotational merism  iso-  50  nitrite  7<*-chloro-70 - n i t r o - 5 < r t cholestane  20;  The p r o b l e m i n many c a s e s i s  to  separate pure  m a t i o n a l from pure s o l v a t i o n e f f e c t s . fect,  it  i s meant t h a t  confor-  By c o n f o r m a t i o n a l  t h e changes i n t h e CD s p e c t r u m  f r o m changes i n e i t h e r t h e c o n f o r m a t i o n o f t h e w h o l e (eg. menthone), chromophore.  o r changes i n t h e  The r o t a t i o n o f t h e n i t r o  o i d s i s an example o f t h i s fect.  conformation of  latter  Even t h o u g h a change o f  r i u m between two c o n f o r m e r s i n s o l u t i o n ,  just  it  is  the  the steref-  equilib-  still  - an i n t r a m o l e c u l a r  classienviron-  mental e f f e c t .  A CD s o l v e n t  defined i n t h i s  t h e s i s a s a v a r i a t i o n i n t h e CD s p e c t r u m due  to the solvent alone, In this bitals  case,  transition.  or to  f r o m any c o n f o r m a t i o n a l  so as t o  effects  A whole s e r i e s  f o r the r i g i d b i c y c l o  [2,2, l]  the molecular  change t h e i r  of e f f e c t s  heptanones  dissymmetric  have been  and a l l  (Figure 6 - A ) .  pure solvent  c o m p l e t e CD s p e c t r u m i s  effect  reversed,  T h i s can t h e r e f o r e  - an i n t e r m o l e c u l a r  in  reported  conformational  c o n c e i v e d , y e t on c h a n g i n g f r o m d i o x a n e t o  the  the  ( 2 5 ) (Figure 6 - B ) .  a  octane,  or-  a r e most e a s i l y d e t e c t e d  case o f 2 - m e t h y l - a d a m a n t a n o n e , no  freedom i s  is  change.  change t h e e n e r g y r e q u i r e m e n t s o f  Pure s o l v e n t  compounds.  I n the  on t h e o t h e r h a n d ,  the solvent molecules a f f e c t  o f t h e chromophore  perturbation,  rigid  apart  effect,  molecule  conformational  s o l v e n t may a l t e r  f i e d as a c o n f o r m a t i o n a l e f f e c t  result  group i n n i t r o  type of  ef-  fine  iso-  structure  be a t t r i b u t e d  environmental  to  a  effect.  21.  In compounds which have c o n f o r m a t i o n a l m o b i l i t y , s o l v e n t e f f e c t w i l l be superimposed upon the effect.  any  conformational  These c o n f o r m a t i o n a l e f f e c t s o c c u r because the  CD  band i s v e r y s e n s i t i v e to p o p u l a t i o n v a r i a t i o n .  The  spectrum  rotational  i s a population-weighted  average  of the  CD  c o n t r i b u t i o n s o f the separate s p e c i e s i n s o l u t i o n . One  of the most commonly encountered  f o r c o n f o r m a t i o n a l l y f l e x i b l e molecules  t y p e s of s p e c t r a  i s the  humped curve e x e m p l i f i e d by the CD spectrum  double-  of (-)-menthone  shown i n F i g u r e 7»  F i g u r e 7«  CD o f (-)-menthone i n d e c a l i n a t +25*C, - 7 4 C and +l62*C (A) and i n v a r i o u s s o l v e n t s a t 25*C ( B ) . e  D j e r a s s i e t a l . (28) showed t h a t a complex CD w i t h two  curve  o p p o s i t e l y signed extrema could a r i s e whenever  Cotton e f f e c t s o f s i m i l a r a m p l i t u d e s ,  two  but o p p o s i t e s i g n , are  22.  superimposed w i t h t h e i r 20 nm.  i n d i v i d u a l maxima s e p a r a t e d b y 1  I n the ketones s t u d i e d ,  a r a t e d b y a b o u t 30 nm. species i n  at a s l i g h t l y  different  sign  (Figure  humped o n e .  Figure  8.  8).  solution,  and e a c h s p e c i e s  w a v e l e n g t h w i t h CD p e a k s o f The r e s u l t a n t  absorbed oppo-  CD c u r v e i s a d o u b l e -  G e n e r a t i o n o f a d o u b l e - h u m p e d CD c u r v e . 1 nm f o r p e a k s o f  amplitude,  the r e s u l t i n g apparent r o t a t i o n a l  o n l y about  1/25  o f those of the  contributing  similar  strengths  are  species.  t h e r e i s an e q u i l i b r i u m between two c o n f o r m e r s ,  rotational R  where R  least  .  F o r a s e p a r a t i o n (A,-A^of a b o u t  If  sep-  I n o t h e r w o r d s , t h e r e were a t  two d i f f e r e n t  site  t h e two extrema were  A  to  the  s t r e n g t h a t t e m p e r a t u r e T i s g i v e n by  T  = ( R  A  - R ) ( l b  + exp(-AG°/NkT))"  and R ^ a r e t h e r o t a t i o n a l  1  strengths  + R  F E  of the  dual conformers, A G * i s the f r e e energy d i f f e r e n c e  indivi-  between  the  23.  conformers, k i s number.  Boltzman's  By p l o t t i n g R  constant,  against  T  t h e c o r r e c t AG°.  If  constant  and  this  &  i n the  corresponding Therefore,  So i t  conformers  is  i n t h e case o f  (-)-menthone  (diaxial) (-)-menthone  changed, t h i s p r o b a b l y r e f l e c t i n g the  change.  l i b r i u m w o u l d be s h i f t e d  Figure  7 also  t o t h e s i d e o f t h e more is  lowered.  c o n f o r m e r had been f r o z e n o u t .  the  effect equi-  stable  I n EPA s o l v e n t  has a n i n t e n s e p o s i t i v e  no n e g a t i v e hump was d e t e c t e d ,  change  shows t h e  I t w o u l d be e x p e c t e d t h a t  c o n f o r m e r as t h e t e m p e r a t u r e (-)-menthone  (-)-  compounds.  conformer p o p u l a t i o n s .  at -192*C,  by  calculated.  7 shows t h e changes i n t h e CD c u r v e o f  of temperature  to  ;  (diequatorial)  as s o l v e n t i s  dif-  e q u i l i b r i u m i s e x p e c t e d t o be a f f e c t e d b y  m e n t h o n e , and many o t h e r  Figure  for  1  be o b t a i n e d ,  e s t a b l i s h e d b e t w e e n two  b o t h s o l v e n t and t e m p e r a t u r e .  (-)-menthone  -  c a n be o b t a i n e d and t h e  can be e a s i l y  an e q u i l i b r i u m i s  in solution,  line,  The i n t e r c e p t w i l l be R^. 0  equilibrium  curves w i l l  be a s t r a i g h t  t h i s g r a p h i c a l m e t h o d , AG , R  Avogadro's  l+exp(-aG°/NkT)  f e r e n t v a l u e s o f AG*, a f a m i l y o f o n l y one o f w h i c h w i l l  and N i s  CD c u r v e ;  i n d i c a t i n g t h e more  stable  In nonpolar solvents,  axial  24.  or b o a t l i k e  forms sometimes p r e d o m i n a t e  chloro-5-niethylcyclohexanone of equilibrium  i s a n o t h e r example o f t h i s  type  (27).  ( + ) CD i n p o l a r  In polar  Trans-2-  (29).  solvents  solvents,  (-)  the d i e q u a t o r i a l  producing a positive  CD i n n o n p o l a r  conformer  solvents  predominates,  CD b a n d , w h i l e t h e d i a x i a l  conformer  p r e d o m i n a t e s i n a n o n p o l a r medium, p r o d u c i n g a n e g a t i v e CD band.  The a c t u a l i n t e r a c t i o n mechanism c o u l d i n v o l v e a d i -  polar interaction  of the solute molecule w i t h the f i e l d  duced b y t h e s o l v e n t m o l e c u l e s , w h i c h c o u l d l i b r i u m of the conformers, trum.  change t h e  ethyl-L(+)-lactate.  (18),  lactic  and m a l i c a c i d  S(+)-lactic  240 nm w h i c h have been a t t r i b u t e d respectively  (23).  equi-  and t h e r e b y change t h e CD s p e c -  S i m i l a r d o u b l e - h u m p e d CD c u r v e s a r e s e e n , f o r  i n «A-amino e s t e r s  in-  (39),  example, and  a c i d has bands a t 210  and  t o t h e r o t a m e r s A and B  25.  V '  0.  OH  H 0  V  x  H O — C — H  H 0 - —  6Hmore  P — H  6*  stable S (+)-Lactic  Acid  Double-humped peaks a r e a l s o seen i n r i g i d m o l e c u l e s and a r e a s c r i b e d t o (Figure 6B).  /  0  conformationally  solvation  equilibria  Some a u t h o r s have e x p l a i n e d t h i s phenomenon a s  a n e q u i l i b r i u m b e t w e e n s o l v a t e d and u n s o l v a t e d  species  (24-27). solute + solvent  ^  ,T  [so l u t e - s o l v e n t ]  The s h o r t - w a v e l e n g t h band has been a s s i g n e d t o  the  s o l v a t e d s p e c i e s w h i l e t h e l o n g - w a v e l e n g t h band has been attributed  to the unsolvated  o f t h e system i s  species.  As t h e  l o w e r e d , t h e band due t o  temperature  solvated  species  t h e n s h o u l d grow a t t h e expense o f t h e band a s s o c i a t e d the unsolvated  species.  W i t h t h e more p o l a r  ( w h e r e t h e r e w o u l d be g r e a t e r a s s o c i a t i o n o f solvent)  with  solvents solute  one w o u l d e x p e c t t h e s o l v a t e d band t o be  and larger.  Thus b o t h c o n f o r m a t i o n a l and s o l v a t i o n e q u i l i b r i a  can  26.  p r o d u c e a d o u b l e - h u m p e d CD s p e c t r u m . has a r i g i d  conformation,  it  Unless the  i s very d i f f i c u l t  molecule  to  distinguish  b e t w e e n s o l v a t i o n and c o n f o r m a t i o n a l e q u i l i b r i a .  One c a n -  n o t always argue t h a t  be much  conformational effects w i l l  larger than solvation e f f e c t s . of  (-)-menthone  spectrum o f  The a m p l i t u d e s o f t h e  and e p i i s o f e n c h o n e a r e s i m i l a r ,  (-)-menthone  h a s been e x p l a i n e d v i a a  mational equilibrium while that attributed et a l . with  of  state  (-)-menthone  at  that  However,  solvent effects  lower temperatures.  are  was Djerassi operative  There are  number o f p o s s i b l e ways t o d i s t i n g u i s h b e t w e e n t h e effects.  One w o u l d p o s t u l a t e  the low temperature  show t h a t  two  conformational e q u i l i b r i a  the  shorter-wavelength  s h o u l d i n c r e a s e a t t h e expense o f t h e  will  a  CD m e a s u r e m e n t s w e r e i n c o n s i s t e n t  the solvation hypothesis that  as t h e t e m p e r a t u r e  the  confor-  epiisofenchone  to a solvation equilibrium.  (28) also  yet  is  lowered.  for  if  with band  longer-wavelength  band  An e x a m i n a t i o n o f F i g u r e 7  t h i s was t h e r e a s o n a c o n f o r m a t i o n a l  r i u m was p o s t u l a t e d  spectra  equilib-  (-)-menthone.  A n o t h e r p o s s i b l e method f o r d i s t i n g u i s h i n g between  the  two e q u i l i b r i a i s t o examine t h e CD s p e c t r u m o f t h e  vapour.  If  the  d o u b l e - h u m p e d p e a k s a r e seen i n t h e v a p o u r ,  solvent  i s not the sole  m u s t a l s o be i n v o l v e d .  cause and c o n f o r m a t i o n a l It  i s also possible  f o r m a t i o n a l and s o l v a t i o n e q u i l i b r i a equilibria  then  equilibria  f o r both  con-  t o be o p e r a t i v e .  can be d e t e c t e d t h r o u g h v a r i a b l e  temperature  Two  27.  studies.  If  the  CD band p a s s e s t h r o u g h a maximum and  begins to  decrease a g a i n ,  f o r m a t i o n a l and s o l v e n t Djerassi  et a l .  this  is  evidence  range  have a l s o  (28).  shown t h a t  low  out  the p o s s i b i l i t y  possibily  decide  if  Self-association high  show i n -  of  one s h o u l d n o t  self-association  same t e m p e r a t u r e  self-association  is  entirely By m o l e -  (17). of  range,  CD, ORD  one  could  an i m p o r t a n t  s h o u l d become a more d o m i n a n t  factor.  factor  at  concentrations. The s e c o n d t y p e o f  r e v e r s a l of the ketones  (antioctant  complete  This occurs,  for  is a  complete  example,  in  some  ( 1 9 ) , i n b e n z y l m e t h y l s u l p h o x i d e and i n o c - c h l o r o  tanone-4-(IS)  (303nm).  environmental effect  CD b a n d .  benzyl methyl sulphoxide  (21).  The r i g i d  2 -methyl-adamana  h a s a r e l a t i v e l y weak p o s i t i v e  behaviour).  On g o i n g t o  CD i n  I t s most i n t e n s e peak i s  the nonpolar  solvent,  structure.  (most i n t e n s e  b e h a v i o u r was n o t S n a t z k e and h i s  Again,  the  band, AG-0.052  AC+0.093  still  CD s p e c t r u m was  (19) s t u d i e d .  the  showing relatively  (300nm).). H o w e v e r ,  seen i n t h e o t h e r adamantanones  co-workers  dioxane  isooctane,  CD s p e c t r u m (340-235nm) i s r e v e r s e d ,  vibrational weak  low-temp-  seems t o  c u l a r w e i g h t d e t e r m i n a t i o n s and by an a n a l y s i s a n d UV s p e c t r a o v e r t h e  sol-  temperature.  For a thorough i n v e s t i g a t i o n , rule  con-  the degree o f  over the  5^-Cholestan-3-one  creased s o l v a t i o n a t  both  effects.  v a t i o n does n o t a l w a y s r e m a i n c o n s t a n t erature  for  then  this  that  Since the  adaman-  28.  tanone has a r i g i d solvent  structure,  the e f f e c t  must be due t o  the  alone.  A s e c o n d example o f a c o m p l e t e r e v e r s a l o f t h e CD s p e c trum i s  benzyl methyl sulphoxide,  Vibrational  aromatic t r a n s i t i o n s ists  trans-  n-TT* t r a n s i t i o n o f t h e s u l p h o x i d e w e r e o b -  i t i o n s and t h e served.  i n which aromatic  s t r u c t u r e was a l s o (250-270  nm).  seen i n one o f  the  Since f r e e r o t a t i o n  a b o u t t h e C-C and C-S b o n d s , t h e r e v e r s a l o f t h e  ex-  spec-  O II  C H  2  - £ j S — C H  3  t r u m i n g o i n g f r o m e t h a n o l t o i s o o c t a n e was a t t r i b u t e d the existence ution.  of d i f f e r e n t  The a r o m a t i c  f o r benzyl t - b u t y l steric  proportions  250-270  sulphoxide  of  rotamers i n  nm t r a n s i t i o n was n o t  to sol-  reversed  i n w h i c h t h e r e w o u l d be more  hindrance to i n t e r n a l r o t a t i o n .  s o l v e n t and c o n f o r m a t i o n a l e f f e c t s  Therefore,  can g i v e r i s e  both  to  the  d o u b l e - h u m p e d CD s p e c t r u m and t h e c o m p l e t e r e v e r s a l o f a CD spectrum.  The most r e c e n t l y i n v e s t i g a t e d  t h a t of induced stance, mixture) ition  S,  circular  solvent  effect  d i c h r o i s m where an i n a c t i v e  is  sub-  ( e i t h e r a symmetrical molecule or a racemic  i s dissolved i n a chiral  of the substrate  I n other words,  solvent,  C, and t h e  becomes o p t i c a l l y a c t i v e  chirality  trans-  (36-38).  has been i n d u c e d b y t h e  solvent,  29.  C, i n t h e s u b s t r a t e , does n o t r e q u i r e  S.  I t was c o n c l u d e d t h a t  s p e c i f i c b o n d i n g b e t w e e n C and S  Theories of Solvent  substrate  dichroism,  i s recorded  more a t t e n t i o n h a s b e e n d e v o t e d t o  e x a m i n a t i o n o f t h e p o s s i b l e mechanisms o f interactions  (38).  i n induced c i r c u l a r  w h e r e t h e CD s p e c t r u m o f a n a c h i r a l solvent,  effect  Effects  With the current i n t e r e s t  a chiral  this  and how s o l v e n t s a f f e c t  an  solute-solvent  CD s p e c t r a .  The t h e o r y o f an e q u i l i b r i u m b e t w e e n a s o l v a t e d unsolvated  species i s  one o f t h e more common e x p l a n a t i o n s .  Some s u c h e q u i l i b r i a have been n o t e d , p o r t e d by R i t c h i e nitriles  and  and P r a t t  (30)  for  and k e t o n e s w i t h d i m e t h y l  s u c h as t h e one  re-  complex f o r m a t i o n  of  sulphoxide.  Is 1 complex They a l s o  state  that the bulk  proach c l o s e l y to the bulk  o f t h e s o l v e n t need n o t  of the solute  c o m p l e x f o r m a t i o n m i g h t have i m p o r t a n t formations of the  solute.  In addition,  m a t i o n m i g h t be e x p e c t e d t o be q u i t e effects.  species.  effects the  T h i s c o u l d cause a marked e f f e c t  Such  on t h e  complex  sensitive  to  i n the  ap-  con-  for-  steric CD s p e c -  in  30.  trum.  Complex f o r m a t i o n w i t h camphor h a s e v e n b e e n  f o r the nonpolar Klyne, Kirk theses f o r theses,  solvents  not  effects  theories).  dissymmetric  C C l ^ and c y c l o h e x a n e ( 3 1 ) .  and W a l l i s  solvent  ( 2 9 ) have p r o p o s e d t w o (note:  these are  The f i r s t  solvation.  In this  solute molecule.  turbs the solute cules  chromophore.  (nonpolar),  o n l y due t o t h e s o l u t e m o l e c u l e associating molecules, the dissymmetry of  itself,  the p e r t u r b a t i o n  solvent  For a c h i r a l molecule,  cage t h e n  of the  for  solvent  effect  state,  s h o u l d be g r e a t e s t  polar to  molecule.  The  result  " t h e magnitude o f  than the other;  be l a r g e r . "  Thus t h e r e  for  fenchone than f o r  more h i n d e r e d i n  the  f o r t h o s e compounds w h e r e  one s i d e o f t h e c a r b o n y l g r o u p i s much more h i n d e r e d substituents  is  u s u a l l y be a p r e f e r e n c e  o f a s s o c i a t i o n f r o m one s i d e o f t h e m o l e c u l e . (29)  mole-  i s a l s o due  cage a r o u n d t h e s o l u t e  there w i l l  should b e , as Klyne e t a l .  per-  chromophore  while  is  molecules  For non-associating  the p e r t u r b a t i o n  of  the e f f e c t  solvent  The s o l v e n t  hypo-  is that  hypothesis, of  hypo-  called  hypothesis  due t o t h e t i m e - a v e r a g e d a r r a n g e m e n t around the  reported  the dissymmetry would  s h o u l d be a g r e a t e r  solvent  by  then effect  norbornanone.  side of carbonyl fenchone by g e m i n a l m e t h y l  groups.  31.  However, of t h i s  i n t h e compounds s t u d i e d ,  t h e y f o u n d no  nature.  In their increments", bation of the which i s ,  second h y p o t h e s i s , the  solvent  effect  "solvent-dependent results  from the  chromophore by t h e s o l u t e m o l e c u l e  i n t u r n , p e r t u r b e d by the s o l v e n t .  solvent-influenced compound.  dissymmetric  T h i s c o u l d be t h e  c a r b o n y l group i s  features  itself  Thus t h i s  just  carbonyl  However,  solute-solvent  "hypotheses",  and s t i l l  t h e s o l v e n t molecule approached the s o l u t e ,  anism o f p e r t u r b a t i o n  any d i s t o r t i o n effect  a great v a r i a t i o n of  the f i e l d  re-  to the f i e l d  CD w i t h s o l v e n t  and  by  this  solute  Since t h e r e  in rigid  V e l l u z e t a l . ( 4 4 ) have s u g g e s t e d t h a t t h e  The mech-  s t r e n g t h (44).  o f t h e chromophore o r  it's o p t i c a l a c t i v i t y .  it  induced  the solute molecule,  d i s t o r t i o n w o u l d be p r o p o r t i o n e d  molecule w i l l  chromophore.  could involve  the solvent which d i s t o r t s  Of c o u r s e ,  inter-  study.  could d i s s y m m e t r i c a l l y p e r t u r b the  results  various  i n an u n h i n d e r e d e n v i r o n m e n t .  These a r e  quire additional  of the  pro-  d o m i n a n t f a c t o r when t h e  t h e r e was no d e f i n i t i o n o f a s p e c i f i c action path.  group  pertur-  p o s e d i n t e r a c t i o n i s b e t w e e n t h e c h r o m o p h o r e and  If  trend  is  molecules,  solvent  effect  f r o m a d i r e c t v i c i n a l a c t i o n o f t h e s o l v e n t on t h e  chromophore.  Actually,  dipole  forces are thought  the p e r t u r b i n g f i e l d w i t h i n the framework o f the theory of o p t i c a l  activity.  t o be one-electron  32.  If  the nature of solute-solvent  mainly e l e c t r o s t a t i c , w i t h the d i e l e c t r i c  interaction  were  t h e n one w o u l d e x p e c t some  correlation  c o n s t a n t s and Z v a l u e s o f s o l v e n t s .  the molecule i s considered a r i g i d shown t h a t t h e r o t a t i o n a l  sphere,  then i t  s t r e n g t h should v a r y  If  can be  linearily  with  "a  d  9  K -1 K +2  w h e r e M i s t h e d i p o l e moment o f t h e s o l u t e ,  K i s the  0  tric  constant  dielec-  and d i s t h e mean d i s t a n c e b e t w e e n t h e  chiral  s o l u t e m o l e c u l e and t h e s o l v e n t m o l e c u l e s i n a d i l u t e ution  (44).  I f the i n t e r a c t i o n  is electrostatic,  sol-  there  s h o u l d be a l i n e a r r e l a t i o n b e t w e e n Afi and K - l / K + 2 . does seem t o be s u c h a r e l a t i o n s h i p tones  (44).  f o r many s t e r o i d a l k e -  This correlation i s not general,  Wellman e t a l . cholestan-3-one  There  however.  ( 2 8 ) , w e r e n o t a b l e t o c o r r e l a t e Ag o f 5oCand 5 « - a n d r o s t a n - l 6 - o n e  constant or solvent p o l a r i t y  (Z v a l u e ) .  R a s s a t and Coulombeau ( 2 5 , 4 5 )  with  dielectric  On t h e o t h e r  did correlate  CD m i n i m a o f i s o f e n c h o n e w i t h t h e p o l a r i t y  hand,  the negative of the  solvent  (Z v a l u e ) . One i s n o t , a t t h i s p o i n t , shifts  o f t h e n - rr* t r a n s i t i o n s  concerned w i t h  frequency  i n t h e UV a b s o r p t i o n  w h i c h have b e e n c o r r e l a t e d w i t h d i e l e c t r i c  constants.  spectra Here  33  t h e more p o l a r  solvents result  s t a t e due t o e l e c t r o s t a t i c  interactions  s o l v e n t m o l e c u l e s and r e s u l t of isofenchone,  in stabilization  i n a blue  peaks*  these i n t e n s i t y  Z values.  shift.  frequency  of the  (28),  r e l a t i o n between the r o t a t i o n a l  and  I n t h e CD shifts,  double-humped  changes w e r e c o r r e l a t e d t o  Wellman e t a l .  ground  between s o l u t e  t h e r e w e r e no a p p r e c i a b l e  but only the changing of i n t e n s i t i e s  of the  Kosower*s  found only a rough strength of  cor-  (-)-menthone  and Z v a l u e s . Weigang ( 4 6 ) a l s o for  rotatory  rections cules.  studied the solvent  s t r e n g t h and f o u n d t h a t  even f o r r a n d o m l y o r i e n t e d The s o l v e n t  volved the Lorentz the r e f r a c t i v e  field field  field  corrections  t h e r e are nonzero  cor-  s o l u t e and s o l v e n t  correction  factor not only  mole-  in-  c o r r e c t i o n which i s a f u n c t i o n  index of the solvent,  but also  f u n c t i o n o f t h e i n d u c t i v e and d i p o l a r  contained  solute-solvent  vent  For a randomly o r i e n t e d  system, the e f f e c t  static  of the solvent  d i p o l e moment o f t h e s o l v e n t  in optical activity.  field  due t o  the  a decrease  Because o f t h e c o m p l e x i t y o f t h e  on a p u r e l y q u a n t i t a t i v e  foothold.  field  From t h e p r e v i o u s  concerning dissymmetric about a c h i r a l molecule,  orientation  His considerations  it  considerations of solvent  pro-  correction  v o l v e d a p e r t u r b a t i o n by s o l v e n t m o l e c u l e s w h i c h were domly o r i e n t e d .  con-  solute-sol-  i s to predict  b l e m , Weigang c o u l d n o t p l a c e t h e s o l v e n t  a  inter-  actions which involved a term i n c l u d i n g the d i e l e c t r i c stant of the solvent.  of  inran-  presented  molecules  may v e r y w e l l be t h a t  the  sol-  3*.  vent molecules are not solvent  field  constant it  randomly o r i e n t e d .  correction w i l l  and t h e r e f r a c t i v e  involve  usually  constant  considered,  a l w a y s be  both the  o f t h e CD band  or r e f r a c t i v e  Therefore,  intensity  index f u n c t i o n  even though such c o r r e l a t i o n s  could a f f e c t  t h e CD s p e c t r u m .  degree o f e l e c t r o n i c - v i b r a t i o n a l  may n o t  path i n which  This involves  coupling  to  optical activity,  a r e known t o be s e n s i t i v e  Vibronic  (32).  S t i g t e r and S c h e l l m a n effect solvent  related effects  and v i b r a t i o n a l  to the nature  of the  of isotropic  solvent. solvent  strain in  a b s o r p t i o n bands.  of the  between s o l u t e  and s o l v e n t m o l e c u l e s w o u l d be  Until  the present,  mental e f f e c t s b e e n made.  chromophore.  Again,  no s y s t e m a t i c  close  of  the  contact  postulated.  study of the  o n t h e CD s p e c t r u m o f n i t r a t e  the  T h i s mech-  anism could p o s s i b l y i n v o l v e a d i r e c t p e r t u r b a t i o n wave-functions  con-  frequencies  ( 3 3 ) voice a possible  t o t h e p a c k i n g and o r i e n t a t i o n  the  the  c o m p o n e n t s o f t h e m a g n e t i c moment c a n make i m p o r t a n t tributions  are  found.  W e i g a n g h a s p r o p o s e d an a l t e r n a t i v e solvent  the  dielectric  index of the solvent.  c a n be s e e n why c o r r e l a t i o n s  with a dielectric  Nonetheless,  esters  environhas  35  CD Of N i t r a t e  Up u n t i l  Esters  1 9 7 1 , t h e r e h a s been no p a p e r p u b l i s h e d  r e l a t i n g the configuration of the n i t r a t e signs of t h e i r  CD s p e c t r a .  analogous t o the " o c t a n t The f i r s t nitrate  nitrates  of glucopyranose.  chromophore.  ketones.  to the  Even f r o m t h e f i r s t  ORD was i n e x a m i n i n g t h e  paper  seen a r o u n d 3 0 0 nm.  and  were t h e o n l y  L a t e r t h e y made a  (52,53).  nitrato  group)  They f o u n d ,  exhibit positive effects  nitrates  g r o u p on t h e r i n g , © ( - g l y c o s i d e s w i t h a C - 0 N 0  w h i l e those w i t h a C-0N0 Cotton e f f e c t s .  2  II.  the  2  Cotton  group of a ^ c o n f i g u r a t i o n The s i g n s o f t h e  o f ^ - g l y c o s i d e s were r e v e r s e d .  a r e summarized i n T a b l e  effect  of the p o s i t i o n of  c h r o m o p h o r e o f an O C c o n f i g u r a t i o n ; showed n e g a t i v e effects,  ef-  correlation  o f h e x o s e and g l u c o s e  irrespective  one  o n l y t o 2 6 5 nm.  b e t w e e n t h e c o n f i g u r a t i o n and t h e s i g n o f t h e C o t t o n (due t o t h e n i t r a t o  di-  nitrato  had s t r o n g b a c k g r o u n d r o t a t i o n ,  shoulders or i n f l e c t i o n s  of  al.(51).  ORD o f mono and  They were a b l e t o p e n e t r a t e  These s u g a r n i t r a t e s i n most c a s e s ,  rule  1 9 6 5 b y T s u z u k i et  p a p e r was r e s t r i c t e d  c o u l d see how l i m i t e d  fect  for  the  study of the o p t i c a l r o t a t o r y d i s p e r s i o n  e s t e r s was r e p o r t e d i n  Their f i r s t  esters with  T h e r e h a s a p p e a r e d no  rule"  cor-  Their  Cotton  conclusions  3&.  Table  II  C o n f i g u r a t i o n And The S i g n s Of The C o t t o n E f f e c t Of Configuration  C-ONO2  C  x  of  Ci  Of  Nitrates  Glucosides Configuration  S i g n Of C o t t o n , Effect  oL  CX - a n o m e r  (-)  c<  0 -anomer  (+)  fi  ck - a n o m e r  (+)  /S - a n o m e r  (-)  = *  C  1  ft  =  0  1  C  = o<  1  = ft  C = 0N0 =«<  c = 0N0 = o< C-j = 0N0 =/3 C^ = 0N0 =^  Cotton e f f e c t (-)  Cotton E f f e c t (+)  2  2  2  2  2  :•. C o t t o n e f f e c t (+)  2  Cotton (-)  effect  37.  Because o f t h e pounds, the  s t r o n g background r o t a t i o n  It  ( 5 5 ) reported the f i r s t  Figure 9 i t  was a l s o i n  1966 that  CD o f n i t r a t e  esters.  can be seen how much more u s e f u l CD i s  i n determining the sign of the Cotton e f f e c t esters.  com-  s i g n o f t h e C o t t o n e f f e c t was a s c e r t a i n e d by-  a p p l y i n g t h e Drude e q u a t i o n . Tsuzuki  of the  of  T h a t i s why CD was c h o s e n o v e r ORD f o r  From  t h a n ORD  nitrate the  present  study.  Figure 9 .  ORD and CD o f 2,3,4,6-tetra-0-acetyl-l-0-nitro-ctD - g a l a c t o p y r a n o s e ( A ) and m e t h y l 4 i 6 - 0 - b e n z y l i dene-ot-D-altropyranoside 3 - n i t r a t e (B).  Tsuzuki et a l . o f hexose n i t r a t e s  ( 5 4 ) d e v o t e d a second p a p e r t o i n which they confirm t h e i r  t h e CD  correlation  38  between the  ORD and t h e s t e r e o c h e m i s t r y o f t h e  They a l s o r e p o r t red-shifted  that  t h e CD maximum  by s t e r i c h i n d r a n c e .  t r i b u t i o n to the e l l i p t i c i t y t h e o r d e r C > C^ > C^ > C , j . 2  Their  In addition,  the  is  con-  conforms  to  s t u d y w o u l d have b e e n much  b e t t e r , i f t h e y c o u l d have p e n e t r a t e d t o a t t h e CD.  nm r e g i o n )  (260-270  in polynitrates  nitrates.  least  2 2 0 nm i n  T h e y n e v e r d i d see t h e 2 3 0 nm band o f t h e  nitrate  chromophore. A second c l a s s o f n i t r a t e s carboxylic  acids  ORD d a t a .  E i g h t n i t r a t e s w e r e e x a m i n e d , and n i t r a t e s  (53).  cl-D-hydroxy-carboxylic tive  Cotton e f f e c t s ,  acids  acids  while  (S-configuration)  Again,  However,  t h e y s t u d i e d was t h e e c - h y d r o x y they only presented  (R c o n f i g u r a t i o n )  those of  of  showed p o s i -  oc-L-hydroxy-carboxylic  showed n e g a t i v e  they only penetrated t o about  limited  Cotton  265-270  effects.  nm w i t h ORD,  and i n some c a s e s t h e r e was u n c e r t a i n t y i n d e t e r m i n i n g sign of the Cotton e f f e c t circular  due t o t h e n i t r a t o  group.  dichroism of three c(-hydroxy-carboxylic  been i n c l u d e d i n t h i s p r e s e n t  the  The  acids  have  study.  U n t i l 1 9 6 6 t h e r e was no r e p o r t o f CD bands o t h e r  than  t h e 2 7 0 nm one r e c o r d e d b y T s u z u k i and c o - w o r k e r s ( 5 * 0 . It  was i n 1 9 6 7 t h a t a c o m m u n i c a t i o n a p p e a r e d b y Hayward and  Claesson nitrate  ( 5 6 ) r e p o r t i n g t h e d i s c o v e r y o f t h e 2 3 0 nm band esters.  Thus t h i s  " h i d d e n " t r a n s i t i o n had been  of  39.  d i s c o v e r e d and t h i s transitions  not  showed t h e v a l u e  of  seen i n t h e u l t r a v i o l e t  b e i n g o b s c u r e d b y more i n t e n s e  ones.  CD i n  revealing  s p e c t r a because  In their  communication,  H a y w a r d and C l a e s s o n d i s c u s s e d t h e  CD s p e c t r a o f  trate  of isosorbide,  e s t e r s - mono and d i n i t r a t e s  and i s o m a n n i d e , and t h a t found t h a t the  the  the  and n e g a t i v e  for  those w i t h e x o - ( S ) - n i t r a t o  compounds w i t h e n d p _ - ( R ) - n i t r a t o  During the year 1969, a third  band o f  while  the present  probably not strengths  the n i t r a t o  effects  located  c h r o m o p h o r e was Laurent  reported  characteristic  as w e l l as t h e  III.  in  is  steroidal  l o c a t i o n of the of the group.  some t y p e s o f  and  different.  combination of the  configuration  t h e CD b a n d s o f  are presented i n Table  of the  re-  rotational  CD d a t a f o r a s e r i e s o f the  in  seen  The band  since the  2 1 0 and 2 3 0 nm b a n d s a r e  and c o n c l u d e d t h a t  are  signs of  a t a b o u t 2 1 0 nm.  due t o e x c i t o n s p l i t t i n g  et a l .  nitrates,  group,  and i s  of the  of  groups  s t u d y was  ( 5 7 ) . T h i s was a n o t h e r b a n d w h i c h was n o t  UV s p e c t r a ,  was  groups.  p o r t e d b y a g r o u p o f German w o r k e r s - S n a t z k e ,  Snatzke  It  o f t h e o ( - c a r b o n a t o m , b u t t h e 2 3 0 nm band  for  Wiechert  ni-  isoiodide  of 3j3-cholesteryl n i t r a t e .  was p o s i t i v e  progress,  eight  s i g n o f t h e 2 6 5 nm band was i n d e p e n d e n t  configuration  of  steroidal  Cotton  nitrato The nitrates  TABLE  III  CD Of S t e r o d i a l N i t r a t e s (Nitrato  bands  Steroid  ONO2 P o s i t i o n  In  Ethanol  only)  Configuration  S i g n s o f CD Bands I  3£>  (equatorial)  A/B  trans  3d  (axial)  A/B  trans  II  III  +  -  + (weak]  -  +  -  +  +  A./B c i s  -  +  17/8  A/B  trans  +  +  19  A/B  trans  +  +  19  A/B  cis  3*  A/B c i s  5*  A/B  HP  Notei  (5/8-androstan)  trans  adapted from data o f Band I  - 3r270nm  Band I I  - »230nm  Band I I I  - «210nm  (weak)  +  (57)  —  41  However, which i s  o n l y f o u r t e e n s t e r o i d a l n i t r a t e s were  r e a l l y t o o few t o p e r m i t  characteristic  was p o s s i b l e groups.  chromophore.  No d e t a i l e d  solvent  chemical l i t e r a t u r e .  I n most c a s e s  I n most c a s e s b a t h o c h r o m i c  t h a t a r e seen i n n i t r i t e  Snatzke e t  al.  the i n t e n s i t y  other n i t r a t e s ,  tensity  it  solvent.  esters.  o f band I I  decreased.  No  changes i n t h e  e q u i l i b r i u m of the n i t r a t o  group.  trato  on t h e CD o f n i t r a t e  Because o f t h e group.  present a sector rule  (230 nm).  For  increased,  while  The  conformational  This facet  of the  e s t e r s w i l l be  sol-  discussed  of the  r e l a t i n g the c o n f i g u r a t i o n  group t o the signs o f  did not  s t u d y t h e low t e m p e r a t u r e  in-  intensity  c o - w o r k e r s were n o t a b l e  nitrato  of  greatest  conformational mobility  S n a t z k e and h i s  all  vibrational  I n some c a s e s t h i s  change was no d o u b t due t o  later.  The  change o f band I I amounted t o 300%,  vent effects  iso-  s h i f t s were seen f o r  changes i n i n t e n s i t y were s e e n i n band I I some compounds,  keto  has  s t r u c t u r e was d e t e c t e d i n a n y o f t h e t h r e e bands  nitrates  it  esters  i n b o t h e t h a n o l and  t h r e e bands i n g o i n g t o t h e n o n p o l a r  for  configuration  study of n i t r a t e  m e a s u r e d a few s t e r o i d a l n i t r a t e s  fine  a  t o d e t e c t t h e CD bands i n t h e p r e s e n c e o f  y e t appeared i n the  octane.  conclusions r e l a t i n g  CD s p e c t r u m t o t h e p a r t i c u l a r  and p o s i t i o n o f t h e n i t r a t o  studied,  t h e CD b a n d s .  of  These  CD o f n i t r a t e  nito  the authors  esters ( 5 7 ) .  42.  In 1970, the  there  appeared an a d d i t i o n a l r e f e r e n c e  CD of n i t r a t e e s t e r s .  studying various  the  Snatzke and  CD o f c h i r a l adamantanones and  s u b s t i t u e n t s on t h e i r CD.  directed at n i t r a t e esters. ported.  Eckhardt  were  the e f f e c t of  T h i s was  not a  study  Three k e t o - n i t r a t e s were r e -  I t i s i n t e r e s t i n g to note t h a t a n i t r a t o group i n  an e q u a t o r i a l p o s i t i o n obeys the o c t a n t  r u l e f o r ketones,  whereas an a x i a l s u b s t i t u e n t shows a n t i o c t a n t T h i s has on a P  (58)  to  behaviour.  been shown, however, o n l y f o r n i t r a t e s p o s i t i o n e d  carbon atom to the  carbonyl  group and  not  for  other  positions.  4 -Nitryloxy-adaman tanone-(2)-(lS).  4-Nitryloxy-adamantandione-(2,6) -(1R).  a  U n t i l the p r e s e n t , r e l a t i n g the  there  there  has  been no r u l e p r e s e n t e d  c o n f i g u r a t i o n o f the n i t r a t o group t o  s i g n o f i t s CD band; t h e r e s t u d y o f the  has  has  been no d e t a i l e d  e f f e c t o f s o l v e n t on t h e i r CD  been no v a r i a b l e temperature  systematic  spectra,  study.  the  and  43.  Chromophores R e l a t e d t o R0N0  Useful information the c i r c u l a r  can a l s o he o b t a i n e d b y  dichroism of other  chromophores r e l a t e d  2  studying  nitrogen-containing  to the n i t r a t o  group.  Some o f  these  chromophores are p r e s e n t e d i n Table I V . 1.  Nitrito  Group  The n i t r i t o  and n i t r o  chromophores a r e p r o b a b l y t h e  nitrogen-oxygen  c h r o m o p h o r e s most c l o s e l y r e l a t e d t o  nitrato  A l l three  group.  c h r o m o p h o r e s have f r e e  a b o u t a C-0 o r C-N b o n d . ( F i g u r e  Figure  10.  Free r o t a t i o n chromophores.  Djerassi  and h i s  10).  nitro  rotation  and  nitrato  c o - w o r k e r s have r e p o r t e d b o t h CD and esters,(40,59,60).  c h r o m o p h o r e a b s o r b s a b o u t 3 2 0 - 4 0 0 nm and shows Because o f i t s  used t h e v a r i a b l e  the  0 ii  i n the n i t r i t o ,  ORD d a t a f o r a number o f n i t r i t e  structure.  two  free rotation,  temperature  technique  This  vibrational  Djerassi  (40)  i n studying  the  CD and ORD o f n i t r i t e  esters.  Generally,  in steroidal  t r i t e s where t h e f r e e  r o t a t i o n was i m p a i r e d ,  ni-  only a lim-  44.  Table  IV  Chromophores C o n t a i n i n g Name  Structure  Nitrogen-Oxygen  Absorption (nm)  Notes  Ref.  nitrato  270,230,210 f r e e r o t a t i o n 0-0 bond  RONO  nitrito  320-440  RN0  nitro  270-290,330 f r e e r o t a t i o n ; sector rule  60,26,65,  500-700  monomers u n s t a b l e ; m u l t i p l e peaks; free rotation  67  sector  64  R0N0  2  2  R-NO  C-nitroso  R f  \)  N - n i t r o s o - 370 amine (N-nitrosc  %  +.0"  R«P  ~>I-0'  •^C=N'NC 2  ?  a b o u t 51-57  vibrational structure; free r o t a t i o n ; no g e n e r a l r u l e proposed  rule  40,59,60  50,64,63  nitrone  2 7 0 , 2 4 0 , 2 1 0 2 7 0 , 2 4 0 bands s t r ongly solvent shifted  68  nitroxide  450,320  69  camphenyl t - b u t y l nitroxide radical; bathochromic s h i f t i n nonpolar s o l vents  nitrimino •  45  ited in  change was seen on l o w e r i n g t h e t e m p e r a t u r e .  steroidal nitrites  free  rotation,  magnitude lowered  where t h e r e  ol n i t r i t e ,  little  t h e r e was o b s e r v e d a l a r g e  of the r o t a t i o n a l  (40).  is  For example,  inhibition  increase  of  i n the  a complete i n v e r s i o n  largest  course,  attributed  case o f  o c c u r r e d b e t w e e n -74° and - 1 9 2 * C .  is  small.  barrier  to  to  isomerism.  rotation  in nitrate  to note that  Djerassi  higher  found t h a t  This  nitrites that  energy  it  is  Even impor-  t h e most s t a b l e  f o r m a t i o n was u s u a l l y a l r e a d y p r e d o m i n a n t a t  the  bond  (RONO2) e s t e r s .  isomers present,  seen  The  f r e e r o t a t i o n a b o u t t h e C-0 s i n g l e  though there are r o t a t i o n a l tant  was  -192* C.  This indicates  One w o u l d e x p e c t a s l i g h t l y free  the  o f t h e CD s i g n a l was  to r o t a t i o n a l  to  cholestan-3<< -  changes i n t h e CD s p e c t r u m o f s t e r o i d a l  energy b a r r i e r  in  s t r e n g t h as t e m p e r a t u r e  as t h e t e m p e r a t u r e was l o w e r e d f r o m - 7 4 ' C t o was,  However,  con-  room t e m p -  erature. As i n t h e  case o f n i t r a t e  appeared r e l a t i n g the  e s t e r s , no g e n e r a l r u l e  configuration  of the n i t r i t e  (RONO) t o t h e s i g n o f t h e CD a b s o r p t i o n . that  the value  t o use t h e  Because o f t h e it  ORD/CD o f n i t r i t e  characteristic nature  differentiation  esters,  of measuring the  Djerassi  of the  between e p i m e r i c p a i r s  i s not always p o s s i b l e  to  ester suggests esters  Cotton e f f e c t of alcohols  c o m p l e x n a t u r e o f t h e CD band o f  has  is  for  (59).  nitrite  characterize  the  whole  46  o f t h e band b y a s i n g l e (61)  sign.  Velluz,  relative  They were a l s o a b l e t o d i s t i n g u i s h between configurations  of epimers.  of the center bearing the n i t r i t o then i n v e r s i o n of the again,  cular dichroism.  construct  configuration to  example)  gave r i s e  For s t e r o i d s where t h e n i t r i t o  general.  Legrand r e p o r t s t h a t  nitrites  of 17-hydroxy s t e r o i d s  from the n i t r i t o  cir-  group  is  However,  this  the opposite (ie.  of t h a t  rule  is  is true  center gave  not for  on f i v e - m e m b e r e d  changes i n t h e m o l e c u l e  as  (jfi - n i t r i t o ,  b a n d , w h i l e an R - c o n f i g u r a t i o n  t o a n e g a t i v e band ( 6 l ) .  structural  re-  e x a m p l e ) as w e l l  seemed t h a t an S - c o n f i g u r a t i o n  to a positive  In addition,  However,  sign of the  g r o u p s a t t a c h e d t o 6-membered r i n g s it  inverted,  a general rule  the  for  the  configuration  c h r o m o p h o r e was  attached to a chain ( 2 0 « < - n i t r i t o , for n i t r i t o  When t h e  s i g n o f t h e CD o c c u r r e d .  t h e y were n o t a b l e t o  l a t i n g the absolute  rise  Grosjean  c o n f e r t h e s i g n o f t h e most p r e p o n d e r a n t peak i n t h e CD  spectrum.  for  L e g r a n d and  rings).  even remote  g r o u p can r e v e r s e t h e s i g n o f i t s  CD ( 6 1 - 6 2 ) .  47.  Hayward and T o t t y nitrite  esters.  rules of Velluz contradicted  (66) r e p o r t e d  Of t h e n i n e , et a l . :  four  CD d a t a f o r  fitted  the  tentative  ( 6 1 ) , one ( ( - ) - R - 2 - o c t y l  these r u l e s *  nine  nitrite)  w h i l e t h e o t h e r f o u r w e r e am-  biguous. The s i m i l a r i t i e s group prompted Snatzke  between t h e n i t r i t o (57) t o  b u t he f o u n d no c o r r e l a t i o n  and t h e  examine t h e  between t h e  nitrato  CD d a t a f o r  both,  s i g n s o f t h e i r CD  bands. 2.  Nitro  Chromophore  A second chromophore s i m i l a r the n i t r o  group.  to that  As w i t h t h e n i t r i t o  of the n i t r a t o  group,  an e q u i l i b r i u m b e t w e e n c o n f o r m e r s w h i c h w i l l dependent. it  In the  was f o u n d t h a t  going to  low t e m p e r a t u r e the  change i n r o t a t i o n a l  hindrance  be  of the n i t r o  be  temperature  study of n i t r o  l o w e r t e m p e r a t u r e s was s m a l l f o r  t h e r e was s t e r i c  there w i l l  is  steroids,  strength  in  compounds w h e r e  group  In  (26).  compounds w h e r e t h e r e was o n l y a w e a k l y h i n d e r e d r o t a t i o n the n i t r o al  group,  t h e r e was f o u n d a g r e a t  change i n  rotation-  s t r e n g t h as t h e t e m p e r a t u r e was l o w e r e d . F o r n i t r o  oids,  the  strongest  changes i n t h e CD o c c u r r e d  was t h e o n l y n i t r o  ster-  between  - 5 0 ' C and - 1 7 0 ' C w h e r e a h i g h p o p u l a t i o n o f t h e m o s t conformer i s o b t a i n e d .  of  stable  7o\-Chloro-7/S-nitro-5oC-cholestane  s t e r o i d w h i c h showed i n v e r s i o n o f s i g n  on  48.  cooling  (Figure  11).  350 22 C -0.5- -  Figure  at at 11.  22*C -188«C  CD o f 7 ° < - c h l o r o - 7 ^ - n i t r o - 5 < < - c h o l e s t a n e and - 1 8 8 ' C ( 5 0 ) .  T h i s i n v e r s i o n i s a p p a r e n t l y caused b y t h e teraction  of the 15-methylene group  for  to t u r n the n i t r o  (26).  There i s a  w h a t w o u l d n o r m a l l y be i t s m o s t f a v o u r e d T h e r e have been no g e n e r a l r u l e s  relating  esters,  b u t t h e r e has been one p r o p o s e d f o r r u l e was a n o c t a n t  t h e one p r o p o s e d f o r t h e  considering a l l  orbitals  i n the n - T T * t r a n s i t i o n ,  involved  has e v o l v e d i n t o  a sector rule  tendency  and  nitrite  one s i m i l a r (63).  the nodal planes of  (64).  from  configura-  the n i t r o  c a r b o n y l chromophore  made r e f i n e m e n t s ,  chlor-  conformation.  t h e s i g n s o f t h e CD b a n d s f o r n i t r a t e  The o r i g i n a l  in-  g r o u p away  t i o n to  (63,64).  +22*C  steric  c a r b o n and t h e g e m i n a l  ine w i t h the a x i a l n i t r o the geminal c h l o r i n e  at  and now t h e  group to Snatzke the rule  49.  n A.  B.  C.  ORBITALS  V AND  SECTOR RULE SECTORS.  NODAL  FIGURE 12.  AND  TT*  NODAL  FOR  NITRO  SYMMETRY  NITRO  PLANES  OF  n—^TT*.  CHROMOPHORE—UPPER  PLANES  SECTOR  OF  RNG>.  RULE.  Figure  1 2 shows t h e s e c t o r s f o r t h e N i t r o R u l e , w h i l e  ure 13 i l l u s t r a t e s  (+T Figure  the  application.  CD e x p e r i m e n t 13»  ( + ) CD e x p e r i m e n t  Application  For these n i t r o  of the N i t r o  steroids,  Sector  t h e most f a v o u r e d  was s e l e c t e d b y e x a m i n i n g m o l e c u l a r m o d e l s . type o f r u l e t h a t nitrito  is  Fig-  Rule. conformer This i s  desired f o r both the n i t r a t o  the  and  chromophores.  Another, l a t i n g the  simpler  set of r u l e s ,  configuration  of  has been p r o p o s e d  carbohydrate  t o t h e s i g n o f t h e CD a b s o r p t i o n  (65).  C-nitro  re-  alcohols  51.  These t h r e e r u l e s 1.  state:  Carbohydrate metric  C-nitro  a l c o h o l s i n w h i c h t h e asym-  carbon atom a d j a c e n t t o t h e  group belongs t o the S - s e r i e s Cotton e f f e c t s  and p o s i t i v e  whereas the C - n i t r o cent  2.  exhibit  CD maxima ( o r  alcohols  i n which the  Cotton e f f e c t s  and n e g a t i v e  by a h y d r o x y l o r an a c e t a m i d o The a b s o l u t e  configurations  c e n t e r s do n o t Cotton  contribute  show  C-nitro  C-2,  whether  group.  of other  to the  asymmetric  sign of  the examination of  c u l a r models t o determine t h e p r e f e r r e d group.  ellipticity  the  effect.  These r u l e s do n o t r e q u i r e  hydrate  adja-  CD maxima  or the  i s n o t a f f e c t e d by substitution a t  the n i t r o  shoulders),  shoulders).  The s i g n o f t h e C o t t o n e f f e c t  3.  positive  c a r b o n a t o m has t h e R - c o n f i g u r a t i o n  negative (or  nitromethyl  mole-  conformation  They a r e v e r y e a s y t o a p p l y t o t h e alcohols  (Figure  14).  of carbo-  52.  NO?  I  I  NO,  NO,  I  CH,  2  CHo  AcHN-C-H  I  H-C-OH  I  )-AH  HO-  H-C-NHAc  I  HO-GH  I  HCOH  HO-CH  I  I  HCOH  I  HCOH  HCOH I 0H CH HCOH  HCOH CH 0H 2  CH 0H  2  S-configuration  at  2  S-configuration  C-2  at  C-2  R-configuration  at  C-2  (+)-CD p r e d i c t e d (+)-CD e x p e r i m e n t a l  (+)-CD p r e d i c t e d (+)-CD e x p e r i m e n t a l  (-)-CD (-)-CD  1-deoxy-l-nitro-Dglucitol  2-acetamido-l,2dideoxy-l-nitroD-glucitol  2-acetamido-l,2dideoxy-l-nitro-Dmannitol  Figure  14.  A p p l i c a t i o n of Rule R e l a t i n g C o n f i g u r a t i o n of C - n i t r o a l c o h o l s t o t h e s i g n o f t h e 3 1 0 nm CD band ( 6 5 ) .  No d e t a i l e d vent  s t u d y h a s b e e n made o f t h e e f f e c t  on t h e CD s p e c t r a o f n i t r o  s h i f t was o b s e r v e d i n  the  solvent  compounds.  changing the  t o dioxane t o isooctane that  predicted experimental  (60).  could a f f e c t  It  solvent  Snatzke  c e r t a i n t y between s o l v e n t  from methanol however,  the dissymmetry of the  ( 2 6 ) states effects  sol-  No w a v e l e n g t h  is possible,  i t i o n w h i c h w o u l d be m i r r o r e d i n t h e t h e CD b a n d s .  of  trans-  changing i n t e n s i t y  "To d i f f e r e n t i a t e and t h o s e  with  caused b y  f o r m a t i o n a l m o b i l i t y many more m e a s u r e m e n t s need s t i l l be m a d e . "  of  conto  53.  This statement solvent  sums up t h e e x t e n t  effects  of n i t r o  very l i t t l e but t h i s  study.  (R-^N-NO).  The C - n i t r o s o  j u s t presented p r e l i m i n a r y r e s u l t s  trogen-oxygen  C-nitroso has had 1970,  ( 6 7 ) . The  bands i n t h e r e g i o n o f 5 0 0 t o 7 0 0  The monomers a r e u n s t a b l e ,  tation.  chromophores are t h e  The most r e c e n t p a p e r a p p e a r e d i n  c h r o m o p h o r e has m u l t i p l e nm.  about  compounds.  Two o t h e r n i t r o g e n - o x y g e n (R-NO) and t h e N - n i t r o s o  o f t h e knowledge  and a s w i t h t h e o t h e r  chromophores s t u d i e d  so f a r ,  it  The o n l y c o n c l u s i o n was t h e " n i t r o s o  shows shape and s i g n i n d i v i d u a l l y  ni-  has f r e e  ro-  absorption  characteristic  of  the  p o s i t i o n o f t h e c h r o m o p h o r e on t h e s t e r o i d n u c l e u s " ( 6 7 ) . The CD o f t h e N - n i t r o s o  group,  on t h e o t h e r h a n d ,  had a f a r more t h o r o u g h i n v e s t i g a t i o n has been p r o p o s e d c o r r e l a t i n g t h e  (64).  A sector  configuration of  has rule  N-nitroso-  a m i n e s t o t h e i r n-TT* C o t t o n e f f e c t ? * ( F i g u r e 1 5 ) .  Figure  15.  Sector Rule f o r the Nitrosoamine ( u p p e r s e c t o r s ) (64),  chromophore  These a r e t h e n t h e most f a m i l i a r n i t r o g e n - o x y g e n p h o r e s and t h e ones t h a t nitrato  group.  a r e most c l o s e l y r e l a t e d  Generally,  they a l l  have f r e e  chromoto  the  rotation.  55.  Conformation of the N i t r a t o  If  a chirality  absolute their  Cotton e f f e c t ,  i n f o r m a t i o n about the  When t h i s  lactone,  then there  since i t  cannot r o t a t e  The c a r b o x y l  freely. lactones  (70),  acids  ( 7 2 ) . In steroidal acetates,  steroidal acetates  chromophore,  conformation.  in solution  it  and i t  was  Figure  16.  was f i r s t  the  confor-  ( 7 3 ) » and t h e n  (Figure 1 6 ) .  of Steroidal  possible  necessary  EQUATORIAL  Conformation  then  because o f t h e  Principally,  rule  carboxylic  !  AXIAL  acids  conformation  ( 7 1 ) and  m a t i o n was d e d u c e d f r o m x - r a y a n a l y s i s t o the molecule  sector  The c a r b o x y l s e c t o r  applied to  of the  of  chromophore a p p e a r s as a  later  to' analyze t h e i r  conformation  i s u s u a l l y no p r o b l e m o f  developed f o r  rotation  of  s t e r o i d a l a c e t a t e s and c a r b o x y l i c  a good a n a l o g y .  free  the  esters to the sign  g r o u p s h o u l d be k n o w n .  r u l e as a p p l i e d t o  was f i r s t  i s t o "be d e r i v e d r e l a t i n g  configuration of nitrate  the n i t r a t o  is  rule  Group  Acetates.  applied  56.  There i s  always a danger i n a p p l y i n g conformations  crystal to  conformations  suggested t h a t  (73)  i n the s o l i d  the  solution.  conformation  state w i l l  i s o l a t e d molecule.  in  acetates  also probably predominate  in  of the e s t e r  16 correspond t o the  the  Mathieson  of s t e r o i d a l  The c o n f o r m a t i o n s  a s shown i n F i g u r e  However,  in  favoured  the  group  trans  c o n f o r m a t i o n d i s c u s s e d b y O k i and N a k a n i s h i ( 7 ^ ) . In the  case o f n i t r a t e  compounds i n w h i c h t h e cyclic  structure.  nitrato  held r i g i d l y  What we know a b o u t t h e n a t u r e  group,  lie  (Figure  i n a plane  c o n f o r m a t i o n come f r o m  17).  I n an e l e c t r o n :  a  the spec-  d a t i n g back t o  completely eliminate  completely planar  structure  a b o u t t h e N-0 b o n d o f t h e n i t r a t o study  (76).  b y D i x o n and W i l s o n  Free  A more r e c e n t m i c r o w a v e  the N0  ?  of  a  rotation a  s t u d y was made  ( 7 7 ) , where t h e y found t h a t a l l  showed t h a t  did  g r o u p was f a v o u r e d i n  heavy atoms o f m e t h y l n i t r a t e  Calculations  17).  nitrato  They  the p o s s i b i l i t y  (Figure  all  1 9 3 7 , P a u l i n g and  ( 7 5 ) favoured a c o n f i g u r a t i o n of a planar  however,  atoms  diffraction  group w i t h the methyl group out o f t h i s plane.  five  of  a l o n g w i t h t h e oc-carbon atom,  study of methyl n i t r a t e ,  later  in  q u e s t i o n t o be a n s w e r e d was w h e t h e r t h e  of the n i t r a t o  not,  available  measurements.  The f i r s t  Brockway  t h e r e a r e no  chromophore i s  c h r o m o p h o r e and i t s  troscopic  esters,  were c o m p l e t e l y  g r o u p was n o t e v e n  the planar. twisted  PLANAR CARBON  NITRATO-WITH IN P L A N E .  FIGURE 17. PROPOSED NITRATE  CARBON MOIETY OUT P L A N E OF NITRATO  STRUCTURES FOR ESTERS.  FIGURE 18. BOND ROTATIONS ESTERS.  OF BROUP.  IN  NITRATE  58.  as l i t t l e  a s one d e g r e e f r o m t h e  Trotter  and h i s  planar n i t r a t o  co-workers  groups i n x - r a y  plane. similarly  studies  of  found  relatively  2-0-(p-bromo-  benzenesulphonyl)-li4,3:6-dianhydro-D-glucitol-5-nitrate, in  cis-1,2-acenaphthenediol  cyclobutene-l,2-diol  dinitrate,  dinitrate  show t h a t  the  0.1 A out  of the plane  (78-80).  carbon atom o f t h e of the  of  different  ONOg a t o m s .  conclude  that  from p l a n a r i t y  in  is  crystal packing.  a result  of  then, without  structure  evidence  be p l a n a r  of n i t r i c  However,  in  It  is  to the  e n e r g y minimum w h i c h i s  groups  Csizmadia et a l .  seen b y there  at 4 . 9 Kcal./mole i n the  to  that  assume the the  (81). conformation examining  is a  ( 8 9 ) , have shown t h a t  s t r u c t u r e w i t h the «-carbon  dinitrate  closer  oxygen o f t h e  t u r e w i t h t h e <X-carbon atom l y i n g i n a p l a n e t o the nitrato group l i e s  It  In addition,  i s not the  For methyl n i t r a t e ,  are  distortion  contrary,  easily  that  as a r e -  reasonable  solution.  structure  about  environments.  slight  approach of the methyl hydrogens t o the  the  just  a c i d was shown t o be p l a n a r  this planar  molecular models.  the  only  seems  cis-benzocyclobutene-l,2-diol  further  C-OMOg g r o u p w i l l  moiety.  It  and n o t  c h e m i c a l and c r y s t a l  i s more l o g i c a l t o  w i t h the  Calculations  c r y s t a l packing since planar n i t r a t o  seen f o r  cis-benzo-  C-ONOg g r o u p i s  t h e C-ONOg a t o m s w a n t t o be p l a n a r , sult  and i n  the  nitro  struc-  perpendicular  below t h a t  same p l a n e a s  of the  59* nitrato  group.  Therefore,  t h e r e must be o t h e r  factors,  such as b o n d i n g p e r h a p s , w h i c h would f a v o u r such a ture  since s t e r i c  structure. Dixon's  considerations  But i n l i g h t  (77) microwave  planar n i t r a t o  study,  (Figure  The e f f e c t  it  investigation.  c o n s i d e r e d t o be  18). i s o m e r i s m a b o u t C-C bonds  in nitrate  e s t e r s has been o b s e r v e d v i a i n f r a r e d  troscopy.  In a series of n i t r a t e  steric  hindrance  bands were s p l i t to r o t a t i o n a l  substituent,  to r o t a t i o n , (82-86).  spec-  esters,  and t h u s t h e r e w o u l d be  t h e 1630  cm"  1  and 1280 cm""  T h i s s p l i t t i n g was  gauche.  ©BOg  GAUCHE  1  attributed  i s o m e r s - t h e t r a n s i s o m e r and t h e  ONOg  TRANS  planar,  and C-C b o n d s need now be  of rotational  w h e r e X was a l a r g e  and  was d e c i d e d t o use a  stereochemical  group i s  o n l y r o t a t i o n a b o u t t h e C-0 considered  perpendicular  of the recent x-ray analysis  group i n t h i s  Since the n i t r a t o  favour the  struc-  60.  The t r a n s i s o m e r s have l o w e r TP as NOg and "Vs NO^ t h a n gauche i s o m e r s .  However,  is  seen when t h e s t e r i c  is  o n l y one p r o b a b l e  benzyl n i t r a t e . studied  band ( n o t  such as i n t h e  there  case  of  (82,83) b a s i c a l l y  and d i n i t r a t e s ,  but  t h e r e was a b a r e l y d e t e c t a b l e  c y c l o h e x y l n i t r a t e w h i c h was a t t r i b u t e d  differences  split)  i s not great or i f  U r b a n s k i and W i t a n o w s k i  simple a l i p h a t i c n i t r a t e s  ting for  2  hindrance  conformation,  was a l s o r e p o r t e d t h a t  0N0  only a single  the  to  b e t w e e n a x i a l and e q u a t o r i a l p o s i t i o n s  it split-  steric of  the  group. In a l l  the  cases where r o t a t i o n a l i s o m e r i s m a b o u t  C-C b o n d i s p o s s i b l e ,  there  i s also the p o s s i b i l i t y  r o t a t i o n a b o u t t h e C-0 b o n d .  ortant  i n the n i t r a t e  esters of the present  moment and s p e c t r o s c o p i c in pentaerythritol  tetranitrate  D i x o n and W i l s o n  there i s  rotation  study of methyl  oxygen o f t h e n i t r a t o  ni-  group.  the  They e x p l a i n e d ,  interaction,  steric  "that  hindrance,  b e t w e e n t h e m e t h y l h y d r o g e n s and t h e n e a r b y o x y g e n . " "steep" barrier,  (83).  showed t h a t t h e h y d r o g e n a t o m s  (77)  a steep r e p u l s i v e  Dipole  molecules i n s o l u t i o n  o f the methyl group are staggered w i t h r e s p e c t t o nearest  C-0  be i m p -  study.  s t u d i e s f a v o u r such f r e e  On t h e o t h e r h a n d , i n t h e m i c r o w a v e trate,  of  The r o t a t i o n a b o u t t h e  bond i s t h e t y p e o f r o t a t i o n a l i s o m e r i s m t h a t w i l l  a  t h e y mean s t e e p i n c o m p a r i s o n t o  By  other  61.  CH<j-0- b a r r i e r s .  The b a r r i e r  group i n m e t h y l n i t r a t e Csizmadia et a l . surface  for  results,  it  rotation  i n methyl n i t r a t e  (Figure  can be s e e n t h a t  In Figure  sketched  in at  would favour  the value  the t h e o r e t i c a l to  rotation  one.  a b e a r i n g on r o t a t i o n  be g r e a t e r  dinitrates  Zhanov  group.  steric  and t h e n i t r a t e s  isomerism about the  The m o l e c u l a r  ring.  In  found o n l y 2 . 9 A between a n i t r o oxygen i n the o t h e r Waal's r a d i i  distance,  for  containthat  has  relatively oxygen  calculations  c h a r g e on t h e  Trotter  of  oxygen  oxygen atoms i s greater  indicating attractive  et a l . ( 7 8 )  g r o u p o x y g e n and t h e  five-member r i n g .  only a l i t t l e  negative n i t r o oxygen.  hindrance  2-0-(p-bromobenzensulphonyl)-l,4:3,  6-dianhydro-D-glucitol-5-nitrate,  is  than  C-0 bonds.  orbital  electronic  one  esters.  i s a second i n t e r a c t i o n  ( 8 6 ) show a p o s i t i v e  o f an o x o l a n e  (2.9A)  been  a l k o x y l o x y g e n and t h e r e l a t i v e l y n e g a t i v e  the n i t r o  their  group  spectra rather  seems t o be an i n t e r a c t i o n b e t w e e n t h e  positive of  to methyl  For methyl n i t r a t e ,  (89).  from microwave  there  energy  By a n a l y z i n g  l i n e s have  i n t h e more c o m p l e x n i t r a t e  i n g oxolane r i n g s ,  +  1 5 - 1 6 Kcal/mole  contour  There w i l l  I n some c a s e s o f  There  19 t h e  5 Kcal/mole  esters.  about  methyl  a potential  the b a r r i e r  is  of the  2 . 3 Kcal/mole  calculated  a number o f n i t r a t e  19).  rotation  was s e t a t have  (89),  to  2.8A.  The sum o f v a n The  0 . . . . 0  than the van der  der-  contact  Waal's  f o r c e s between t h e  o x y g e n and t h e r e l a t i v e l y p o s i t i v e  alkoxyl  relatively alkoxyl  63.  ONO.  • A *  V  H R-0  2.94 A separation between oxygen atoms  2.86 A s e p a r a t i o n between oxygen ' atoms  T h i s same i n t e r a c t i o n was a l s o d e t e c t e d i n a n red study  ( 8 ? ) , where d i f f e r e n t  band appeared f o r t h e n i t r a t e drohexitols. trato  The T ? s ( N 0 ) 2  frequencies  esters of the  C-0 bonds.  theVs(N0 ) 2  .l,4:3»6-dianhy-  (•)  the  The d i h e d r a l angle,<|>, i s t h e a n g l e  be-  g r o u p and t h e C - 0 bond  "ps(N0 )  = 1282  cm"  1  <j) exo  -ps(N0 )  =  cm"  1  attributed  in  ring.  <fr endo = 0 * + 3 0 *  The s h i f t  ni-  between  t w e e n t h e C - 0 bond o f t h e n i t r a t o the adjacent  for  infra-  f r e q u e n c y o f endo and exo  groups v a r i e d w i t h the d i h e d r a l angle  adjacent  \  =  120°+  to higher to the  30  frequencies  2  2  1274  o f t h e endo i s o m e r i s  c l o s e a p p r o a c h and i n t e r a c t i o n  again  of the  ring  64.  oxygen w i t h t h a t  of the n i t r a t o  group.  T h i s same t y p e o f i n t e r m o l e c u l a r a t t r a c t i o n has been r e p o r t e d t o be p r e s e n t dinitrate  in  also  cis-l,2-acenaphthenediol  (?9).  Both n i t r a t o  groups are i n c l i n e d t o the plane of the  a t o m s , and b o t h i n c l i n e d  i n t h e same d i r e c t i o n .  i n t e r m o l e c u l a r nonbonding distance g e n a t o m o f one n i t r o oxygen ( ? 8 ) . trans nitro  is  Again, the frequency l)s(N0 ) 2  tween n i t r a t o  groups  (88).  u s e f u l i n analyzing the  The  closest  2 . 9 l A between an o x y -  g r o u p and t h e n e i g h b o u r i n g  g r o u p s was r e l a t e d  carbon  of the  alkoxyl cis  to the d i h e d r a l angle  be-  These c o n s i d e r a t i o n s w i l l  conformation of the n i t r a t o  i n d i n i t r a t e s and i n n i t r a t e s  c o n t a i n i n g oxolane  and  be  groups  rings.  65-  Transitions  A chirality the t r a n s i t i o n s  rule  In Nitrate  i s u s u a l l y developed by  and t h e o r b i t a l s  t h e case o f n i t r a t e  Esters  esters,  o f the  examining  chromophore.  there i s a lack  of  definite  i n f o r m a t i o n about the nature of the t r a n s i t i o n , and t h e o r b i t a l s  of the  the  esters,  d e t e c t i n g two o f t h e s e .  was f i r s t trato  The f i r s t  e s t e r s and i s  detected i n a c i r c u l a r  first  dichroism study of the The  d e t e c t e d t h r o u g h CD s p e c t r o s c o p y ,  193  nm ( £  and 2 1 0 nm t r a n s i t i o n s w e r e n o t these t r a n s i t i o n s  den u n d e r t h e i n t e n s e data of  some n i t r a t e  ni-  third  trans-  i t i o n d e t e c t e d was f o u n d i n t h e UV s p e c t r a o f e t h y l  spectra;  seen  The second band  l o c a t e d n e a r 2 1 0 nm ( 5 7 ) . The f o u r t h and l a s t  w h i c h had a maximum a t  in  characterized  l o c a t e d n e a r 2 3 0 nm ( 5 6 ) .  s p e c t r a l band, also is  s p e c t r a l band was  o r s h o u l d e r a r o u n d 2 7 0 nm.  g r o u p and i s  the  and. CD has been i n v a l u a b l e  i n t h e UV s p e c t r a o f n i t r a t e a s an i n f l e c t i o n  bonding  chromophore.  F o u r s p e c t r a l b a n d s have now been o b s e r v e d i n spectra of n i t r a t e  In  =5800)  The  (90).  seen i n t h e  nitrate, 230  ultraviolet  a r e r e l a t i v e l y weak and a r e  1 9 3 nm t r a n s i t i o n .  nm  hid-  T a b l e V l i s t s UV  esters.  Ungnade and S m i l e y  (91) report  that  l a r g e r molecules  of  secondary a l k y l n i t r a t e  had h i g h e r £ v a l u e s t h a n l o w e r m o l e -  cular weight n i t r a t e s .  Additionally,  Csizmadia  reported  66.  Table V UV S p e c t r a o f N i t r a t e E s t e r s Nitrate  Solvent  Ethyl  nitrate  pet.  Ethyl  nitrate  n-heptane  ether  i  Ref.  270  17  99  193  5800  90  EtOH  270  15  91  EtOH  270  16,20  91  EtOH  270  16  91  2-Butyl n i t r a t e  EtOH  270  17  91  4-Heptyl  EtOH  270  28  91  EtOH  270  37  91  EtOH  270  22  91  EtOH  270  33  91  MeOH  270  19  100  1-Octyl  nitrate  Cyclohexylmethyl n i trate Cyclopentylmethyl nitrate  2-0ctyl  nitrate nitrate  Cyclohexyl  nitrate  5-Methyl-2- o c t y l nitrate Isoamyl n i t r a t e  67.  that,  i n the  intensity  series  CH^ONOg t o EtONOg t o i - p r O N 0  band was s h i f t e d  Although four  It  absorption  is uncertainty  s h o u l d a l s o be n o t e d t h a t curve  Csizraadia e t a l . eight nitrate five  there  concerning  their  an a p p a r e n t l y  calculated the t h e o r e t i c a l  esters,  oneTT"-»TT* t r a n s i t i o n ,  and m e t h y l n i t r a t e , 5 ev.  simple  al.  acid a t r a n s i t i o n  nonbonding o r b i t a l  of  f o r example  had  and o n e t f - ^ t f * ) .  Eremenko et  a n+TT*transition.  spectra  ( t h r e e n-»Tf t r a n s i t i o n s ,  There i s g e n e r a l agreement t h a t  orbital.  group  can have a c o m p l e x band p a t t e r n ( 8 9 ) .  r e s o l v e d b a n d s up t o  band o f n i t r i c  low  lower energy (89).  s p e c t r a l bands o f t h e n i t r a t o  have b e e n d e t e c t e d , nature.  to  the  2  t h e 270 nm band call  (92)  265 nm  o f an e l e c t r o n f r o m  o f oxygen t o an a n t i b o n d i n g  Lao ( 9 3 ) s i m i l a r l y  the  identifies  is  the  molecular  t h i s a s a n-flT*  transition. Csizmadia's transitions possible molecular V I I of  at  (89) t h e o r e t i c a l  274 a n d 249 nm.  transitions orbital  F i g u r e 20 shows some o f  i n methyl n i t r a t e .  co-workers  t h e UV s p e c t r a o f m e t h y l n i t r a t e component b a n d s .  The n-vr? band i s  nitro  (270 n m ) .  levels  The d a t a f o r  e n e r g i e s were t a k e n f r o m T a b l e s  C s i z m a d i a and h i s  chromophore  s t u d y i n d i c a t e s n-»TY*"  of the n i t r o  (89).  resolved  Figure into  its  similar to that  Figure  22 d e p i c t s t h e  g r o u p and n i t r a t e  ion for  IV,  the  the V and  21 shows Gaussian of  the  energy  comparison.  68.  +•2  A ev 1-3 3n  2n m  IT  FIGURE 2 0 . SOME  FIGURE 21.  TRANSITIONS OF MeONO-,.  UV SPECTRUM OF METHYL NITRATE RESOLVED INTO ITS COMPONENT BANDS (8 9)  69.  A.  TRANSITIONS  IN  RN0  2  (94).  2  FIGURE 2 2.  ENERGY  B.  T R A N S I T I O N S IN T H E NITRATE J O N (93,9S)  LEVELS OF T H E NSTRO  70.  L e s s i s known a b o u t t h e 230 nm t r a n s i t i o n ; n o t even an i n f l e c t i o n  i n t h e UV; t h e band i s  h i d d e n u n d e r t h e more i n t e n s e  transitions.  o f t h e UV e n v e l o p e a t 230 nm v a r i e d f r o m the s e r i e s methyl to n - b u t y l n i t r a t e be t h e t r u e i n t e n s i t y  nm ( £ = 2 8 )  (89).  The  This w i l l  (89).  The  not  overlap  The l o w i n t e n s i t y ,  4  however,  theoretical  shows a n-*Tr* t r a n s i t i o n a t 230  Thus C s i z m a d i a e t a l .  nm CD band o f n i t r a t e  intensity  £=100 t o 200 f o r  o u t a tr-^Tf t r a n s i t i o n .  spectrum of methyl n i t r a t e  is  completely  o f t h e t r a n s i t i o n because o f  o f t h e much more i n t e n s e b a n d s . would tend t o r u l e  there  referred  t o t h e 230  e s t e r s as r e s u l t i n g f r o m a n n-*T? t r a n s -  ition. T h e r e has been c o n s i d e r a b l e e n e r g y bands o f n i t r a t e  esters or n i t r a t e  transition  of the n i t r a t e  transition  (£=9,700 o r  nm ir-»T? pounds  transition (92,97,98).  2500)  i-propyl,  (89).  this region, transfer nitrato  ion.  of n i t r i c  (95,96),  as  has  higher  The 200 nm  i o n has been a t t r i b u t e d  12,500)  t o a ir—Tr*  the  a c i d and o r g a n i c n i t r o  C s i z m a d i a and h i s  1 7 — T? band n e a r 207 nm f o r n-butyl,  discussion of the  210  com-  co-workers expect  the series of methyl,  n - b u t y l and t - b u t y l n i t r a t e s  ethyl, (£=1300  They a l s o e x p e c t more l o w i n t e n s i t y b a n d s some o f w h i c h w i l l  be a s s o c i a t e d w i t h a  f r o m t h e a l k y l g r o u p t o t h e TT* o r b i t a l s  a  of  to in  chargethe  group.  Kaya e t a l .  (90), investigated  the p o s s i b i l i t y  c h a r g e - t r a n s f e r bands i n t h e s p e c t r a o f n i t r a t e  of  esters (90).  The e t h y l n i t r a t e m o l e c u l e was d i v i d e d  i n t o two p a r t s -  e t h o x y l g r o u p as e l e c t r o n d o n o r and t h e n i t r o electron acceptor  200 nm.  t h e TT e l e c t r o n e n e r g y l e v e l s  and e x p e c t e d t h e f i r s t  a t 208 nm.  g r o u p as an  (Figure 23).  They c a l c u l a t e d nitrate,  the  of  Tt—*-TT* t r a n s i t i o n t o  ethyl appear  A s e c o n d s t r o n g hand was e x p e c t e d t o o c c u r  The f i r s t TT-*-tT*band, a c c o r d i n g t o K a y a , may be  garded as an i n t r a m o l e c u l a r  charge-transfer  near re-  caused b y t h e  i n t e r a c t i o n b e t w e e n t h e e l e c t r o n d o n a t i n g C H ^ d - g r o u p and 2  the electron accepting  -N0 . 2  The t r a n s i t i o n s p r o b a b l y r e s p o n s i b l e  f o r t h e t h r e e CD  bands a r e summarized i n T a b l e V I .  •NT  ELECTRON  F i g u r e 23t  DONOR  Ethyl Nitrate bands.  ELECTRON  as viewed f o r  ACCEPTOR  charge-transfer  72.  Table Probable E l e c t r o n i c  VI  Transitions  F o r The CD Bands Of N i t r a t e Band  (nm)  n-TT*  230  n-TT*  .3190-200  Esters  Transition  270  210  Responsible  fT—fT*(charge  rr-rf  transfer)  73B o n d i n g Of The N i t r a t o  Group  There are t h r e e resonance s t r u c t u r e s group t o  of the  consider!  II  I  III  T h e r e has been some q u e s t i o n a b o u t t h e i m p o r t a n c e structure  III.  D i x o n (77)  group supports a r o l e need t o c o n s i d e r  for  showed t h a t structure  2  o . .  (101).  structure orbitals  III.  us,  III.  as t h e i r  However,  oxygen.  oxygen i f  one i s  On  nitrates  substituted properties  nitro are  to accept  con-  about  one w o u l d ha.ve t o c o n s i d e r  the the  band ( a l k o x y l g r o u p e l e c t r o n d o n a t i n g ;  t r o group e l e c t r o n a c c e p t i n g ) .  There i s c o n s i d e r a b l e  c e r t a i n t y concerning the o r b i t a l s  involved.  orbitals  a r e d r a w n as i f  the n i t r a t o  alkoxyl  substituted nitro  compound  one f i n d s  nitrato  I n o t h e r w o r d s , he s a y s t o f o r g e t  of the alkoxyl  charge-transfer  spectroscopic  of  Thus one w o u l d  "the organic  c a n be c o n s i d e r e d as a l k o x y l  compounds as f a r cerned"  a. p l a n a r  the T Y bonding of the a l k o x y l  the other hand, M u r r e l l t e l l s R0-N0  nitrato  statements  niun-  Sometimes  g r o u p were j u s t  (102,103),  s u c h as " t h e MO l o c a l i z e d  the  an  while other on t h e  times  nitrato  74.  g r o u p c o u l d c l e a r l y be i d e n t i f i e d w i t h t h e MO o f t h e ion"  ( 8 9 ) ( F i g u r e 24 and 2 5 ) .  Figure 24.  N o n b o n d i n g and T T o r b i t a l s  In Figure  24A,  the  TT  delocalized over the n i t r o the d e r e a l i z a t i o n If then i t  the  of the n i t r a t o  e l e c t r o n s a r e shown a s  over the e n t i r e  if  t h i s were t h e  The bond l e n g t h s  that  g r o u p has t h e u s u a l  However,  of a nitrogen-oxygen  the  its  nitro  nitrogen-oxygen  l e n g t h o f t h e RO-NC  s i n g l e bond.  of  As can be  t h e l e n g t h o f t h e N=0 bond o f t h e  portion of the n i t r a t o d o u b l e bond l e n g t h .  of  c a s e , t h e n one w o u l d  v a r i o u s N=0 and '0-N b o n d s a p p e a r i n T a b l e V I I . Table,  ONOg g r o u p ,  c h r o m o p h o r e and a l l  e x p e c t a s h o r t e r RO-N bond d i s t a n c e .  seen i n t h i s  being  ONOg g r o u p .  d e r e a l i z a t i o n were o v e r t h e e n t i r e  But,  group.  g r o u p , w h i l e F i g u r e 24B d e p i c t s  would e x p l a i n the p l a n a r  transitions.  is  nitrate  Therefore,  bond it  is  75.  1  i  I  I  3n (n..Q',)|  n—i—r  FIGURE 25.  MOLECULAR ORBITAL DENSITY •S CSIZMADIA et al. (89).  76.  Table  VII  Length of N i t r o g e n  Molecule  N-OR  (A)  Bonds  N=0 ( A )  Method  Ref.  RONOo Compounds methyl n i t r a t e (CH 0N0 )  1.36  1.26  electron diffraction  1.405  1.206  m i crowave  81  cis-1,2-acenaphthenediol d i n i t r a t e  1.41  1.19  X-ray  79  pentaerythritol tetranitrate C(CH 0N0 )^  1.404  1.2205,  X-ray  108  2-0-(p-bromobenzenesulphonyl)-l,4:3,6d i anhyd r o - D - g l u citol 5-nitrate  1.53  1.16  X-ray  78  cis-benzocyclobutene-1,2-diol dinitrate  1.387, 1.411  1.198, 1.190  X-ray  80  3  nitric  2  acid  2  (H0N0 ) 2  1.203  2  nitrate  ion  Nitrite  Esters  (0N0 ")  methyl n i t r i t e (CH -0-N=0) 3  75.104  2  1.37  1.218  105  1.22  104  77-  Table V I I  contd.  Lengths of N i t r o g e n Molecule O t h e r N-0  N-OR (A)  Bonds  N=0 1  Method  Ref.  Compounds  N 0  1.197  106  nitromethane  1.22  104  N0 C1 2  1.202  106  N0  2  1.19 3^  107  2  (CH N0 ) 3  2  (CH ) ^0  1.388  107  (CH^NO-HCI  1.425  107  H N-CHtN0H  1.41  106  3  2  3  78' concluded t h a t ,  despite  Csizmadia's  (89) c a l c u l a t i o n s ,  RO-N "bond c a n n o t have much d o u b l e bond c h a r a c t e r and bonding i n t h i s , p o r t i o n of the n i t r a t o like  that  of the n i t r a t e  ion.  group w i l l n o t 1  the  the be  79  R E S U L T S  a n d  D I S C U S S I O N  80.  A.  Ultraviolet  Ultraviolet nitrate  Spectra of N i t r a t e  a b s o r p t i o n s p e c t r a l d a t a f o r a number  esters are presented i n Table V I I I .  were c a l c u l a t e d  mum, a s can be seen f r o m F i g u r e are the instrument esters  c o r r e s p o n d t o a n y UV m a x i 26.  The c u r v e s i n F i g u r e 26  t r a c e s and a r e t y p i c a l  acetonitrile  curves f o r  was s e l e c t e d as t h e p o l a r  was e x a m i n e d i n s i x  solvents of  I t was g e n e r a l l y f o u n d t h a t  greater in acetonitrile  than i n  i n cyclohexane.  This indicates  types of t r a n s i t i o n s .  action affects  differently  of the molecule. transition is  Normally,  c y c l o h e x a n e a t 270 and 230  the presence of  electronic  states,  Menthyl n i t r a t e  greater different of  the ground s t a t e  solvent  inter-  states n-rjr*  of the  interactions  molecules.  had an a b n o r m a l l y l a r g e £270  hexafluoroisopropanol.  elec-  solvent  the v a r i o u s e l e c t r o n i c  s t a b i l i z e d by the e l e c t r o s t a t i c  b e t w e e n s o l u t e and p o l a r  1R:3R*4S-  t h e a b s o r p t i o n was  Because o f t h e v a r i a t i o n s  tronic density in different  sol-  varying  nm, w h e r e a s , t h e i n t e n s i t y a t 210 and 200 nm was  interaction  the  cyclohexane r e p r e s e n t e d a n o n p o l a r one.  Menthyl n i t r a t e polarity.  intensities  studied.  Generally, vent while  The  of  f o r t h e w a v e l e n g t h s 2 7 0 , 2 3 ^ , 210 and 200  nm, b u t t h e s e w a v e l e n g t h s do n o t  nitrate  Esters  v  a  l  u  T h i s can o n l y be a t t r i b u t e d t o  caused b y t h e e l e c t r o n - w i t h d r a w i n g  e  i  n  the  trifluoromethyl  Table  VIII  UV S p e c t r a Of N i t r a t e  Nitrate  menthyl n i t r a t e  Esters  Solvent  270 nm 230 nn 210 nm 200 nm  HFIP CHC1, MeOH  44 31 28 30 30 25  1400  4200  5000  830 9^0 1000 650  3900 3900 3800 3800  4800 4900 4600 5300  3900.  7700  CHoCN  TMP C6H  1 2  p-menth-l(7)-transene-2-ol-riitrate  CH^CN  38  860  cis-3-methylcyclohexyl nitrate  CH^CN  28  336  trans-3-methylcvclohexyl nitrate  CH^CN  35  CH^CN  3^ 26  1140 800  3800 3900  4400 4100  37 30  1100 830  3800 3900  4500 5100  60 37  1600 1200  3200 3200  4100 4400  65 58  1700 1300  5900 6700  7600 9700  6^12  52 47  1400 1200  5100 6000  6700 8700  6*12  59 50  i860 1260  7200 7400  9500 9900  c t - n i t r a t o - / , ^ - d i m e t h - CH3CN yl-^ -butyrolactone 6%2  25 25  670 642  2100 2200  3400 3600  threitan  28 28  700 550  4700 5200  7700 8900  bornyl  nitrate  C  isobornyl  nitrate  CHoCN C  e(-fenchyl  nitrate  camphane-2-endo, 3endo-diol-dinitrate camphane-2-endo,3exo-diol-dinitrate  6%2  CHc.CN C  camphane-2-exo,3exo-diol-dinitrate  6*12  6*12  CHoCN CHoCN W l Z  C  CHoCN C  C  dinitrate  CHoCN C H 6  1 2  82.  210  FIGURE 26.  +  UV SPECTRUM OF MENTHYL NITRATE (MeOH).  83.  g r o u p s on t h e s o l v e n t m o l e c u l e . normal i n t h i s  The l v a l u e  a t 200 nm was  solvent.  In the series b o r n y l ,  i s o b o r n y l , and f e n c h y l  nitrates,  a l l w i t h t h e same e m p i r i c a l f o r m u l a , t h e i n t e n s i t y a t nm (CH^CN s o l v e n t ) the n i t r a t o  i n c r e a s e d as t h e s t e r i c h i n d r a n c e  group i n c r e a s e d .  exo-diol-dinitrate, had t h e h i g h e s t  i n which the n i t r a t o  £ value  2,3-diol-dinitrates  Similarly,  of  camphane-2-exo,3groups are  a t 270 nm among t h e t h r e e  studied.  270  cis,  camphane-  84.  B.  C h i r a l i t y Rule For N i t r a t e  Assuming a p l a n a r n i t r a t o  Esters  g r o u p , and w i t h a t t e n t i o n  cused on t h e . . n i t r o p o r t i o n o f t h e n i t r a t o  chromophore,  d a l and s y m m e t r y p l a n e s o f t h e c h r o m o p h o r e w e r e The n o d a l p l a n e o f t h e TT o r b i t a l s w i l l t a i n i n g the n i t r a t o symmetry p l a n e  group.  Nodal.planes  F i g u r e 27.  be t h e p l a n e  (Figure  of the nonbonding o r b i t a l s  N o d a l p l a n e s o f theTT and n o n b o n d i n g o f the n i t r a t o g r o u p .  t h e no  determined.  This i s also the only  o f t h e p l a n a r chromophore  fo-  con-  molecular 27).  of  the  orbitals  85.  The n o n b o n d i n g o r b i t a l s  of  t h e t e r m i n a l oxygens a r e a l s o  in  this plane.  The n o d a l p l a n e s o f t h e s e n o n b o n d i n g o r b i t a l s  of  the t e r m i n a l  oxygens are p l a n e s p e r p e n d i c u l a r t o t h e plane  of  the n i t r a t o  g r o u p and l i e  There w i l l  a l o n g t h e N-0  bonds.  a l s o be n o n b o n d i n g e l e c t r o n s a s s o c i a t e d  the a l k o x y l oxygen.  with  One o f t h e n o d a l p l a n e s a s s o c i a t e d  with  these o r b i t a l s w i l l  p r o b a b l y be c o i n c i d e n t a l w i t h t h e m o l -  ecular plane  chromophore.  of the  The n o d a l s u r f a c e s o f t h e a n t i b o n d i n g T T * o r b i t a l s more a m b i g u o u s ,  principally  the bonding i n the n i t r a t o  because o f t h e u n c e r t a i n t y group.  Sometimes t h e  s u r f a c e s a r e a p p r o x i m a t e d by p l a n e s , curved surfaces  (Figure  A p l a n a r group w i l l symmetry. and t h e  28)  of the  C  s  point  group i s  are  (63,64). least  g r o u p has o n l y t h e  chromophore t h e n b e l o n g s t o t h e C  s y m m e t r y e l e m e n t s E and g".  of  antibonding  but they a c t u a l l y  a l w a y s have a t  A planar n i t r a t o  are  In Figure  adapted t o the  29  s  one p l a n e symmetry  point the  group,  of plane, with  character  coordinate  system  table of  86.  FIGURE 2 8 . ANTIBONDING ORBITALS (A) AND NODAL SURFACE OF e-ON0 (B). 2  E  C  FIGURE  8  v.j.  A'  1  1  », ,R*  A"  1  ~1  Rii  CHARACTER  Z  xy.xz  TABLE.  29. COORDINATES AND DIPOLE MOMENT  87. the n i t r a t o plane,  group.  and do n o t  The x a x i s ,  The y a n d z a x e s a r e i n t h e change s i g n on r e f l e c t i o n  a s do t h e s i g n s o f t h e 1*  TT* a n t i b o n d i n g o r b i t a l s . a l s o be i n t h i s  symmetry p l a n e .  Using Schellman's  (15) rule  reflection  b o n d i n g and  For the n i t r a t o  of the p o t e n t i a l  chirality  plane.  The d i p o l e moment o f t h e g r o u p  pseudoscalar p a r t  being that  i n the  on t h e o t h e r h a n d , d o e s change s i g n on  through the plane,  planar  symmetry  is  t h e A"  approach t h e n , t h e r e f o r the n i t r a t o  group,  30.  should e x i s t  group, w i t h the  of the nodal plane of the TT o r b i t a l s  P l a n a r r u l e ( f r o m Cs p o i n t n i t r a t o group.  will the  representation.  group)  for  the  a  plane  (Figure  y  Figure  the  30).  88.  However,  this  approach from group t h e o r y  t h e minimum number o f to the molecular  s p a t i a l regions  symmetry p l a n e ,  can o n l y In  (16).  specify  addition  t h e r e may be o t h e r  nodal  s u r f a c e s n o t d e t e r m i n e d b y symmetry w h i c h can l e a d t o ther  subdivisions. For the n i t r a t o  group,  o n l y be t h e n o d a l s u r f a c e s (Figure  these a d d i t i o n a l planes  could  o f t h e n and T T o r b i t a l s  The n o d a l p l a n e B ( F i g u r e  31).  nonbonding o r b i t a l s it  fur-  31)  of the  oxygen  i s n o t e x p e c t e d t o be i m p o r t a n t  seldom passes t h r o u g h t h e p e r t u r b i n g m o l e c u l e .  t h e TT* a n t i b o n d i n g o r b i t a l n o d a l • s u r f a c e  only  since Similarly,  occasionally  p a s s e s t h r o u g h t h e m o l e c u l a r bonds o f t h e compound. only the nodal plane A (Figure  31)  rule,  turbing part  of  the per-  molecule.  The d i t h i o c a r b a m a t e to the n i t r a t o  the nature  s i n c e t h i s p l a n e does p a s s t h r o u g h t h e  of the  is  o f t h e oxygen nonbonding  o r b i t a l which could appreciably a f f e c t chirality  It  chromophore i s  similar  group.  I  c  DITHIOCARBAMATE  I N  NITRATO  in  structure  FIGURE  31. POSSIBLE POSITIONS S U R F A C E S OF T H E  OF THE n AND TT* NODAL NITRATO GROUP.  The n i t r a t o  g r o u p h a s o n l y one s y m m e t r y p l a n e , w h i l e  dithiocarbamate  has t w o -  the molecular plane,  p e r p e n d i c u l a r p l a n e l y i n g a l o n g t h e N-C b o n d . of dithiocarbamates (109).  and a s e c o n d The CD s p e c t r a  have b e e n i n t e r p r e t e d b y a q u a d r a n t  Analogously,  t h e CD o f t h e n i t r a t o  t h e n be d e s c r i b e d b y a p l a n a r  group  should  "planar rule"  to  nitrate  t h e g r o u p i s v i e w e d down t h e 0-C bond ( F i g u r e  +  rule  rule.  In the a p p l i c a t i o n of t h i s esters,  the  (P)  32).  0  \ VIEW  F i g u r e 32.  If  Viewing the n i t r a t o  g r o u p a l o n g t h e 0-C b o n d .  t h e m a j o r i t y o f t h e p e r t u r b i n g atoms are t o t h e r i g h t  of  91  the plane,  the molecule i s  chirality;  if  compound i s  s a i d t o have p o s i t i v e  the m a j o r i t y are to the l e f t  s a i d t o have n e g a t i v e  In applying the r u l e ,  it  (-)  (+)  of the plane,  the  chirality.  must be r e a l i z e d  that  free  ro-  t a t i o n a b o u t t h e C-0 bond i s p o s s i b l e and t h e most  sterically  favoured  models.  conformation i s  s e l e c t e d by e x a m i n i n g t h e  T h i s t e c h n i q u e has a l s o b e e n a p p l i e d t o n i t r o The s t e r i c a l l y  f a v o u r e d c o n f o r m e r w i l l most l i k e l y be  p r e d o m i n a n t i s o m e r e v e n a t room t e m p e r a t u r e . however,  the "most s t e r i c a l l y  n o t be d e f i n i t e l y possibilities  steroids  selected,  Figure  to lSs2R-bornyl  the  I n some c a s e s ,  conformation"  so a number o f  were c o n s i d e r e d .  a p p l i c a t i o n of the r u l e  favoured  (63).  could  alternative  33 i l l u s t r a t e s  the  nitrate.  NITRATE  (-)  F i g u r e 33•  CHIRALITY  A p p l i c a t i o n of the N i t r a t o to lSi2R-bornyl n i t r a t e .  Chirality  S i n c e b o t h t h e 270 and 230 nm t r a n s i t i o n s  rule  are thought  to  berr-*i/,  c o r r e l a t i o n was a t t e m p t e d w i t h t h e s i g n s o f  o f these bands. w i t h the  Empirically,  a c o r r e l a t i o n was o n l y  obtained  s i g n o f t h e 230 nm b a n d .  In a d d i t i o n to the p r o j e c t i o n probable  both  conformation,  o f t h e most  four other possible  sterically  correlations  were  examined* 1.  With the configuration (R o r S) t o w h i c h t h e  2.  With -0N0 (Figure  2  of the 0N0  2  chiral  group i s  c i s to the geminal  center bonded.  hydrogen  3^A)  3.  With -0N0  4.  W i t h t h e p r o j e c t i o n v i e w e d down t h e  2  trans to the geminal  o f t h e O-N-0 g r o u p  (Figure  hydrogen bisectrix  34C)  (D n  -0N0 i s cis the geminal hydrogen. 2  F i g u r e 34.  to  Projections  Bo - 0 N 0 i s t r a n s t o the geminal hydrogen. 2  of the n i t r a t o  C.  group.  -0N0 group i s viewed through t h e 0N0 m o i e t y . 2  93.  T h e r e was no c o r r e l a t i o n the three dichroic those p r e d i c t e d  found between t h e s i g n s o f any  transitions  of the n i t r a t o  from the three p r o j e c t i o n s  of  g r o u p and  of Figure  34.  The c i s and t r a n s p r o j e c t i o n s w e r e n o t e x p e c t e d t o be favoured from s t e r i c  considerations.  Additionally,  c o r r e l a t i o n o f CD s i g n was seen w i t h t h e the c h i r a l  c e n t e r t o which the n i t r a t o  no  configuration  group i s  of  attached.  9k  C.  Seven a l k y l were s t u d i e d  Alkylcyclohexyl  substituted  (I-VII,  Table  a r e shown i n F i g u r e 35*  Nitrates  chiral  cyclohexyl  I X ) and r e p r e s e n t a t i v e  spectra  As seen f r o m T a b l e X , t h e r e  no c o r r e l a t i o n o f t h e c o n f i g u r a t i o n w i t h CD band s i g n .  nitrates  of the c h i r a l  There i s , however,  is  centers  f a i r l y good  cor-  r e l a t i o n b e t w e e n t h e s i g n o f t h e 230 nm band ( b a n d I I ) and the sign of the c h i r a l i t y predicted  from the planar  nitrato  rule. In the menthyl, hexyl n i t r a t e s ,  c a r v o m e n t h y l , and  t h e m o l e c u l e s were c o n s i d e r e d i n t h e  form, w i t h a l l substituents and F r a n k l i n  cis-3-methylcyclo-  equatorially oriented.  (110) made a n NMR s t u d y o f t h e  Feltkamp  conformations  o f m e n t h o l and c a r v o m e n t h o l i n w h i c h t h e y d e t e r m i n e d the population o f the e q u a t o r i a l W i t h f e w e r g r o u p s on t h e r i n g , a x i a l isomer p r e s e n t . nitrate  chair  that  c o n f o r m e r was c l o s e t o 100$.  t h e r e w o u l d be more o f t h e  I t has been r e p o r t e d t h a t  h a s 73$ e q u a t o r i a l n i t r a t o  g r o u p a t +25*C  B o t h m e n t h y l and c a r v o m e n t h y l n i t r a t e s  have  cyclohexyl (ill). negative  p e a k s n e a r 320 nm w h i c h do n o t c o r r e s p o n d t o a n y known i t i o n of nitrate  esters  (Figure 35).  trans-  These s m a l l p e a k s a r e  s e p a r a t e d b y a b o u t 50 nm f r o m t h e t r a n s i t i o n a t 270 nm and a r e n o t s e e n i n t h e CD s p e c t r a o f t h e r i g i d [2.2.1] h e p t y l n i t r a t e s . proportion of a x i a l nitrate  this  They may a r i s e  from the small  conformers i n s o l u t i o n .  320 nm peak h a s a  value  alkylbicyclo-  For menthyl  0.8$ o f t h a t  of the  96 Table  IX  CD Of N i t r a t e s W i t h One C y c l o h e x a n e R i n g Nitrate I  menthyl  nitrate  Solvent CH^CN cyclohexane  X i n nm. »([©]) 3 2 0 ( - i o ) , 3 i M o ) , 2 7 1 (+1230)" 250(0),232(-3260>224(0), 215(+7300) 319(-18),312(0),27K+910), 250(0),232(-3230),220(0), 2l4(+5800)  II  carvomenthyl nitrate  CH CN  3l8(-0),312(0),270(+630), 248(0),235(-870),227(0), 2l6(+5000)  III  isocarvomenthyl nitrate  CH CN cyclohexane  285(+6o),267(+49),229(+870) 292(+30),269(0),264(-6), 259(0),226(+1100)  IV  p-menth-l(7)ene-cis-2-olnitrate  CH^CN  276(+920),247(+250),219 (+9200)  V  p-menth-l(7)ene-trans-2ol-nitrate  CH CN 3 cyclohexane  283(-610),262(0),237(+6400), 227(0),218(-12,000) 277 ( - 1 0 9 0 ^ 5 4 ( 0 ) , 233 (+6340), 224(0),215(-9300)  VI  cis-3-methylcyclohexyl n i trate*  CH3CN cyclohexane n-heptane  268(+65),255(+55)»240(+90) inc. 298(-4),280(0),265(+10)inc. 268(+32),260(+31),228(+200)  CH CN cyclohexane  268(+33),245(0),235(-70)inc. 292(-8),263(-2),240(-35)inc.  VII  trans-3-methylcyclohexyl n i t r a t e *  *by R.N. T o t t y i n c . - and i n c r e a s i n g  3  3  3  97.  A 8" •  n  i  3 •2--  -4-  • 6- •  -8- •  -10"  -12 X  MENTHYL NITRATE f-MENTH-IC7)-ENE- 'R AM-2-OL-NITRATE i p ^ O L - NITRATE •CARVOMENTHYL NITRATE NITRATE  98.  Table X Alkylcyclohexyl  Nitrates  CD Band S i g n s and P r e d i c t e d Compounc #  NITRATE  Configuration  Chirality CD Band S i g n I  II  Ill  Predicted Sign  1R:.3RI4S  +.  1R:2R:4R  +  -  isocarvomenthyl  ,1SS2SJ4R  +  +  +  IV  p-menth-1(7)-enecis-2-ol-nitrate  2RI4R  +  +?  +  V  p-menth-l(7)-enetrans-2-ol-nitrate  2S:4R  -  +  VI  cis-3-methylcyclohexyl n i t r a t e  1S«3R  +?  +  VII  trans-3-methy1cyclohexyl n i t r a t e  os  +?  I  menthyl  II  carvomenthyl nitrate  III  nitrate  I S  +  +  -  -  + + + 1  -f  99.  270 nm p e a k . recorded f o r  It  is  s i m i l a r t o t h e double-humped  (-)-menthone  spectrum  ( 2 8 ) . F i g u r e 36 i l l u s t r a t e s  t h e d o u b l e - h u m p e d peak f o r m e n t h y l and c a r v o m e n t h y l  how  nitrates  may be g e n e r a t e d .  F i g u r e j6.  R e s o l v e d b a n d s ( n o t t o s c a l e ) o f t h e 270 nm t r a n s i t i o n o f m e n t h y l and c a r v o m e n t h y l n i t r a t e s .  (+)-cis-3-Methylcyclohexyl  nitrate  larger proportion of the a x i a l peak was d e t e c t e d i n i t s to solvent. nm ( [e] - 4 )  conformer.  spectrum, but i t  In cyclohexane, while  it  No d o u b l e - h u m p e d was v e r y  has a n e g a t i v e  in acetonitrile,  a completely p o s i t i v e  i s e x p e c t e d t o have a  n-heptane  band a t  298  and m e t h a n o l ,  s p e c t r u m was o b t a i n e d .  t o s o l v e n t no d o u b t r e f l e c t s v a r i a t i o n s  sensitive  i n the  This  sensitivity  equilibrium  100.  5  b e t w e e n a x i a l and e q u a t o r i a l f o r m s . no d o u b t has a p o s i t i v e negative  one.  The e q u a t o r i a l  270 nm band w h i l e  t h e a x i a l has a  Even t h o u g h t h e proposed c h i r a l i t y r u l e  n o t a p p l i e d t o t h e 270 nm t r a n s i t i o n , opposite  conformer  the rule  does  is  predict  s i g n s f o r t h e e q u a t o r i a l and a x i a l i s o m e r s o f  3-methylcyclohexyl The c o r r e c t  nitrate.  s i g n o f t h e 230 nm band i s a l s o  f o r isocarvomenthyl n i t r a t e . stituents  cis-  In this nitrate,  all  c a n n o t be i n t h e e q u a t o r i a l p o s i t i o n .  s i d e r i n g t h e AG v a l u e s o f v a r i o u s  predicted  substituents  sub-  After (Table  i s o c a r v o m e n t h y l n i t r a t e was d r a w n w i t h a n a x i a l  conXI),  isopropyl  group.  Table  XI  AG V a l u e s Of V a r i o u s S u b s t i t u e n t s  C  6 n axiaT H  *" 6 n eqatorial  X  Substituent -GHo -GH<CH-) -0N0p  J  c  X  0  c  -OH  The a s s u m p t i o n i s made t h a t i s the  (112)  H  X  , A G r  1.70 2.15 0.59 0 „ 52  the AG v a l u e o f the  sum o f t h e A G v a l u e s o f t h e i n d i v i d u a l  molecule  substituents.  101.  T h i s i s t h e same a s s u m p t i o n made b y F e l k a m p and who f o u n d e x p e r i m e n t a l l y t h a t  (110)  70$ w i t h an e q u a t o r i a l  OH.  It  isocarvomenthol  exists  i s expected then t h a t  carvomenthyl n i t r a t e would e x i s t w i t h a s l i g h t l y t h a n 70$ e q u a t o r i a l n i t r a t o  Franklin  iso-  greater  group.  The 270 nm CD band o f i s o c a r v o m e n t h y l n i t r a t e  (III)  i s much w e a k e r t h a n t h o s e o f m e n t h y l o r c a r v o m e n t h y l trate.  In acetonitrile  does n o t e x h i b i t  solvent,  isocarvomenthyl  t h e s m a l l peak a t 320 nm.  h a v i n g a much w e a k e r 270 nm b a n d , i t sensitive  (Figure  37).  i s also  ni-  nitrate  However,  besides  solvent  The s m a l l n e g a t i v e peak i n  cyclo-  hexane i n d i c a t e s t h e p r e s e n c e o f a n e g a t i v e band w h i c h p r o b a b l y due t o t h e l e s s s t a b l e  PREDICTED LESS  TO  conformer.  BE  FAVOURED  The CD s p e c t r u m o f i s o c a r v o m e n t h y l  f r o m 250 t o 350 nm  is  102.  103  c a n be l o o k e d u p o n a s one s i m i l a r  to that  o f m e n t h y l and  c a r v o m e n t h y l n i t r a t e s w i t h t h e s m a l l p e a k on t h e wavelength side.  The l o w i n t e n s i t y  short-  o f t h e 270 nm b a n d ,  w h i c h seems t o be t h e m o s t s e n s i t i v e  to  conformation,  p r o b a b l y due t o t h e g r e a t e r p r o p o r t i o n o f o t h e r l e s s conformers w i t h o p p o s i t e l y signed peaks. it  i s the thermodynamic s t a b i l i t y  that  By " l e s s  group,  is referred  trans-3-methylcyclohexyl  to.  nitrate  was d r a w n i n t h e p r o j e c t i o n w i t h a n a x i a l 0 N 0 e q u a t o r i a l CH^.  2  trans-3-MethyIcyclohexyl n i t r a t e to  pected.  solvent  (VII)  sterically  c o n f o r m a t i o n c o u l d n o t be made, and  t h e s i g n s f r o m two p r o j e c t i o n s a p p e a r i n T a b l e  sitive  than  and an  Even s o , a d e c i s i o n on t h e most  favourable n i t r a t o  stable  stable",  Because o f t h e l a r g e r v a l u e o f -AG f o r a m e t h y l a nitrato  is  that  is  X.  e v e n more  the c i s isomer, which i s  thus  sen-  t o be  ex-  The t r a n s i s o m e r h a s w e a k e r CD b a n d s t h a n t h e  cis  and h a s s i g n r e v e r s a l o f t h e 270 nm band on g o i n g f r o m a c e tonitrile  to  cyclohexane.  Again,'this  p l a i n e d as a c o n f o r m a t i o n a l It  i s more d i f f i c u l t  can e a s i l y be  ex-  effect.  to select a favoured  for p-menth-l(7)-ene-trans-2-ol-nitrate  (V).  conformation  104  Conformation A i s  favoured over B since the n i t r a t o  i n B w o u l d be v e r y c l o s e t o t h e Tr* o r b i t a l s group.  The NMR s p e c t r u m i n d i c a t e s  group  o f t h e C=CH  the n i t r a t o  group  2  to  be a x i a l ;  t h e g e m i n a l p r o t o n resonance^ w h i c h a p p e a r s as a  distorted  triplet,  jection A predicts  h a s a band w i d t h o f o n l y a positive  10 c p s .  Pro-  b a n d , and a p o s i t i v e  230 nm  CD band was o b s e r v e d . The 230 nm band o f (IV)  is  p-menth-l(7)-ene-cis-2-ol-nitrate  completely hidden under the t r a n s i t i o n  W i t h l o w t e m p e r a t u r e and s o l v e n t to  c o r r e c t l y ascertain the  a p p e a r s t o be  chromic s h i f t s  possible  s i g n of t h i s band, a l t h o u g h  ( I V and V) a l s o  show m a r k e d  it  batho-  ( a b o u t 5 nm) i n g o i n g f r o m c y c l o h e x a n e  solvent.  to  Another unusual property of t h i s  when compared t o t h e o t h e r n i t r a t e i s the very strong i n t e n s i t y trate  may be  III.  positive.  These two n i t r a t e s  acetonitrile  studies i t  o f band  esters in this  o f band I I I  V has a m o l e c u l a r e l l i p t i c i t y  of  (218 n m ) . 2 1  pair,  series, Ni-  g-12,000  in  105.  acetonitrile.  T h i s c o u l d be due t o e l e c t r o s t a t i c  a c t i o n s between t h e t r a n s i t i o n s chromophores;  of o l e f i n i c  the increased i n t e n s i t y  t r a n s i t i o n moment c o u p l i n g .  It  and  inter-  nitrato  could r e s u l t  i s thought t h a t  transition  moment c o u p l i n g a l s o a c c o u n t s f o r t h e i n c r e a s e d o f t h e CD bands o f /3  nitrate  (I)  temperature  As t h e t e m p e r a t u r e w h i l e a t t h e same t i m e ,  Study  s t u d y was c a r r i e d o u t on m e n t h y l  i n methanol over the temperature  90*C ( T a b l e X I I , F i g u r e  intensity  (113).  -unsaturated ketones  !Ri3Rt4S-Menthyl N i t r a t e V a r i a b l e Temperature A variable  r a n g e +30*C t o  38). is  l o w e r e d , t h e 320 nm band  is  Since i t  c o n s i s t e n t w i t h b o t h a s o l v a t i o n and a I n t h e case o f  i s true  is  the  (-)-menthone,  this  behaviour  conformational it  was t h e  w a v e l e n g t h peak t h a t grew a s t e m p e r a t u r e was l o w e r e d The o p p o s i t e  in-  i s t h e s h o r t w a v e l e n g t h peak  increases w i t h lowering of temperature,  equilibrium.  This  i s o c c u r r i n g and w h a t one  s e e i n g i s t h e i n c r e a s i n g p o p u l a t i o n o f one f o r m a t  that  decreases,  t h e 270 nm band i n c r e a s e s .  dicates that equilibration  expense o f a n o t h e r .  from  i n t h e case o f m e n t h y l n i t r a t e .  long (28). The  o n l y t i m e d o u b l e - h u m p e d p e a k s were o b s e r v e d i n t h e CD s p e c t r a of n i t r a t e possible,  e s t e r s was when a c o n f o r m a t i o n a l e q u i l i b r i u m was a s i n t h e case o f m e n t h y l n i t r a t e ,  was t h e p o s s i b i l i t y tratopropanoic  acid.  of rotamers i n s o l u t i o n , Therefore,  o r where as w i t h  the e q u i l i b r i u m  there D-cfr-ni-  seen i n  the  106,  Table X I I V a r i a b l e Temperature Study o f lRj3R«4S-Menthyl N i t r a t e Tempererature  CO 30 20  320 nm Band >(nm) [e]  Band >• (nm)  321 322  271 271-2  +1080 +1120  270-2  +1350  271-2  + 1480  -8.8  -55 -90  324-5  -2.2  I [6]  (I) Band X (nm  II  232 232  -3100 -3100  233  -3520  * a t 15°C  A. BAND X (270 nm) .  FIGURE 38.  B. 320 nm BAND  L T C D OF MENTHYL IN M E T H A N O L .  NITRATE (1)  10?.  CD s p e c t r u m o f m e n t h y l n i t r a t e mational  equatorial  is  230 nm b a n d ) .  as t e m p e r a t u r e explanation  is  for  lipticity  of  However, changed i s  confor-  still  w e r e n o t made Band I I I  39)•  the increase  nitrate.  the molecular  linearly with  (II),  although the  el-  temp-  T h i s same t y p e o f b e h a v i o u r was  also  shows a n i n c r e a s e is  seen  measurements  1R; 3R14S-IV!enthyl N i t r a t e  as t h e n e a t  Solvents  solvents,  (band  Solvent  The CD o f m e n t h y l n i t r a t e solvents,  i n molecular  ellipticity  l o w e r e d , b u t n o t n e a r l y as g r e a t  i n t h e 270 nm band  (Table X I I I ) .  alternative  quantitatively.  as t h e t e m p e r a t u r e  halogenated  studied,  (nega-  population  a very probable  t h e 270 nm band i n c r e a s e s  (Figure  while  conformer decreases  a change i n r o t a m e r  range  the  270 nm b a n d )  t h e d o u b l e - h u m p e d peak o f m e n t h y l  carvomenthyl n i t r a t e  fifteen  (positive  less stable  Over t h e t e m p e r a t u r e  for  t o be a  lowered, the population of  conformer increases  the population of the  erature  thought  one.  As t h e t e m p e r a t u r e  tive  is  as  I).  Study  (I)  was a l s o e x a m i n e d  in  l i q u i d and i n t h e v a p o u r  i n c l u d e d p o l a r and n o n p o l a r  and s o l v e n t s w i t h a w i d e  state  types,  variety  108. 15-r  FIGURE 39.  TEMPERATURE  CcV  VARIATION OF THE 270 nm. BAND OF MENTHYL NITRATE (I) WITH TEMPERATURE. an*©  270  FIGURE 40. MENTHYL NITRATE OF e^o TO zei 270  RELATION '  109.  Table  XIII  C i r c u l a r D i c h r o i s m o f 1R:3R»4S-Menthyl Solvent  Effects  Band 320 [el  S O L V E N T  Nitrate:  Band  I  Band  Hexafluoroisopropanpl  323  -6.4  271  + 1590  Dimethylsulphoxide  324  -9.3  271  +1410  272  +1350  Trifluoracetic  acid  II [e]  234 - 2 8 8 0  Chloroform  321  - 1 2 . 0 270  +1300  Dimethylforamide  323  -10.1  271  +1260  Acetonitrile  320  -10.  271  +1230  Acetic  321  - 1 0 . 5 271  +1190  322  - 1 0 . 4 273  +1150  233 -3080  Isopropanol  322  - 1 2 . 3 271  +1100  234 -3150  Methanol  321  -11.7  271  +1080  232 -3100  Tetrahydrofuran  322  - 1 4 . 4 272  +1080  235 -2820  cis-1,2-Dimethyl-1carbomethoxycyclopropane  323  - 1 2 . 3 271  +1030  n-Hexane  321  269  +1000  cis-Pinane  324  -16.7  272  +980  234 -3030  Cyclohexane  319  -18  271  +910  232 -3230  NEAT LIQUID  320  -12.6  271  +1130  269  (+)  acid  Trimethyl  phosphate  VAPOUR  * concentration  (pressure)of  sample u n k n o w n .  *  232 -3230  233  (-)  *  110.  of f u n c t i o n a l groups. ultraviolet  i s not possible  spectra of n i t r a t e  wavelength s h i f t , bands I and I I possible  It  but i t  that  from  the  esters whether there i s  any  is quite  e v i d e n t b y e x a m i n i n g CD  t h e r e i s no s u c h s h i f t ,  e x p e r i m e n t a l e r r o r o f +2 nm.  dependence o f w a v e l e n g t h w i t h s o l v e n t , t h e r e i s no e l e c t r o s t a t i c to a l t e r  to t e l l  within  the  Since t h e r e i s it  indicates  that  i n t e r a c t i o n of the solvent  the energy of the  no  so a s  transition.  T h e r e i s no e v i d e n c e o f h y d r o g e n b o n d i n g i n  hexafluoro-  i s o p r o p a n o l s o l v e n t w h i c h h y d r o g e n bonds v e r y s t r o n g l y  with  ketones. The i n f o r m a t i o n f r o m t h e s o l v e n t t h e p r e s e n c e o f an e q u i l i b r i u m .  study also  indicates  G e n e r a l l y t h e 320 nm peak  i s most i n t e n s e i n t h e n o n p o l a r h y d r o c a r b o n s o l v e n t s and • its  i n t e n s i t y decreases as t h e p o l a r i t y o f t h e s o l v e n t  creases.  The o p p o s i t e  i s t r u e o f t h e 270 nm b a n d , w h i c h  most i n t e n s e i n t h e h i g h l y p o l a r  s o l v e n t s and w e a k e s t  the nonpolar hydrocarbon solvents.  T h i s can be  r e s u l t s were o b t a i n e d f o r  chloro-5-methylcyclohexanone  (-)-menthone  a b s o r p t i o n a t t h e same w a v e l e n g t h  ition,  and  t h e UV i n t e n s i t y  but i s also the r e s u l t  solvents.  trans-2-  molecular  o f t h e 270 nm band w i t h t h e i n t e n s i t y  remembered t h a t  in  (114).  There i s a l s o a rough c o r r e l a t i o n o f the ellipticity  is  interpreted  a s an i n c r e a s e d amount o f t h e a x i a l f o r m i n n o n p o l a r Similar  in-  (Figure 40).  o f t h e UV  I t must be  i s n o t due t o a s i n g l e  of other overlapping  trans-  bands.  Ill  The v a l u e s i n h e x a f l u o r o i s o p r o p a n o l curve.^Additionally, tense i n t h i s  f a l l along  the molecular e l l i p t i c i t y  fluorinated  by o t h e r a u t h o r s  do n o t  (29)  solvent.  It  t h a t the greatest  i n ketones occurred w i t h f l u o r i n a t e d  the  is very  in-  has a l s o been n o t e d solvent  effects  solvents.  This  in-  d i c a t e s t h e n t h a t h e x a f l u o r o i s o p r o p a n o l may a f f e c t  not  the conformer p o p u l a t i o n s ,  trans-  ition.  However,  but also the e l e c t r o n i c  t h e r e was no w a v e l e n g t h s h i f t  of  either  band I o r I I , b u t o n l y i n c r e a s e d i n t e n s i t y o f band I . may be p o s s i b l e t h a t t h e e l e c t r o n - w i t h d r a w i n g atoms w o u l d a f f e c t  to various solvent parameters. of the molecular e l l i p t i c i t y fractive  index,  It  fluorine  the e l e c t r o n d e n s i t y of the n i t r a t o  The m o l e c u l a r e l l i p t i c i t y  polarity,  was a l s o e x a m i n e d i n T h e r e was no  perhaps,  and Z v a l u e  correlation  o f t h e 270 nm band w i t h  o r d i p o l e moment o f t h e  a rough c o r r e l a t i o n w i t h d i e l e c t r i c (Figure  group.  relation  re-  solvent.  T h e r e was no c o r r e l a t i o n w i t h t h e r e l a t i o n K - l / K + 2 . is,  only  There  constant  4l).  Summary Of t h e s e v e n a l k y l c y c l o h e x y l n i t r a t e s , 230 nm bands t h a t  five  can be c o r r e l a t e d w i t h t h e s i g n  by a p l a n a r n i t r a t o  rule;  f o r t h e two o t h e r s ,  band  a s s i g n m e n t o r c h i r a l i t y p r e d i c t i o n was u n c e r t a i n . able solvent  shift  have predicted sign No a p p r e c i -  o f bands I and I I was d e t e c t e d i n a w i d e  variety of solvents.  Low t e m p e r a t u r e and s o l v e n t  studies  112.  indicate  the presence  of a conformational e q u i l i b r i u m  m e n t h y l , and c a r v o m e n t h y l n i t r a t e s , of a solvation equilibrium  although the  c a n n o t be c o m p l e t e l y  in  possibility eliminated.  113.  ii4;  D.  Nitrates  Of A l k y l b i c y c l o r 2 , 2 , i " l H e p t a n o l s  The CD s p e c t r a o f s e v e n n i t r a t e s heptanols  (VIII-XIV,  T a b l e X I V ) were r e c o r d e d .  have t h e s i g n s o f t h e i r  This series i s not subject  chirality  rule  to a skeletal  changes may be a t t r i b u t e d  t a t i o n of the n i t r a t o  All  230 nm CD band (band I I )  c o r r e c t l y by t h e p l a n a r n i t r a t o  Any c o n f o r m a t i o n a l  o f a l k y l b i c y c l o [ 2 . 2 . lj-  predicted  (Table  equilibrium. solely to  i n s e l e c t i n g the  favoured conformation f o r bornyl  ( I X ) and i s o b o r n y l  Isobornyl n i t r a t e  d o e s n o t have d i s t i n c t  II  as b o r n y l n i t r a t e  does, but i t  a r e n e g a t i v e and o v e r l a p  (VIII) bands  seems t h a t  both  ( F i g u r e 42). Low t e m p e r a t u r e CD  (LTCD) m e a s u r e m e n t s c o n f i r m t h a t  isobornyl  t h e 230 nm band i s  negative.  r u l e p r e d i c t s a n e g a t i v e 230 nm CD band  for  nitrate.  I t was more d i f f i c u l t  to select the s t e r i c a l l y  c o n f o r m a t i o n f o r D-Q(-fenchyl n i t r a t e favoured conformations -  (X).  favoured  There were  one p r e d i c t i n g a n e g a t i v e  and t h e o t h e r c o n f o r m a t i o n a p o s i t i v e  chirality.  tween atoms, i t dicts a positive  Using  was f o u n d t h a t t h e c o n f o r m a t i o n t h a t 230 nm CD band (band I I )  voured s t e r i c a l l y .  Experimentally,  is  slightly  a positive  two  chirality  P e t e r s o n m o l e c u l a r m o d e l s and m e a s u r i n g t h e d i s t a n c e s  observed.  ro-  sterically  nitrates.  The c h i r a l i t y  XV).  g r o u p on t h e C-0 b o n d .  T h e r e was no d i f f i c u l t y  and I I I  seven  beprefa-  CD band was  116  T a b l e XIV CD Of N i t r a t e s  Of A l k y l b i c y c l o [ 2 . 2 . 1 . ]  Nitrate  #  Solvent  heptanols >-(nm),[©j  VIII  1 R i 2 R - I s o b o r n y l CH CN 3 Nitrate cyclohexane  270(+130),252(0),223-4 (-2200) 265(-90),245(-20)min.,220 (-1800)  IX  ISi2R-Bornyl Nitrate  CH CN  270(-260),232(-3300),221 (0),212(+2900) 270(-245),231(-3400)  D-cC-Fenchyl Nitrate  CH^CN cyclohexane  277(-740),260(0),232 (+11,200)222(0),212(-12,700) 277(-475),262(0),233 (+10,5000),222(0),210(9800)  XI  Camphane-2-exo, 3-exo-diol d i nitrate  CH CN cyclohexane  273(-590),222(0),210(+920) 266(-425)  XII  Camphane-2-ejco, CH^CN 3-endo-diol d i nitrate  28l(+101),267(0),228-9 (-5100),221(0),21l(+7200)  XIII  C a m p h a n e - 2 - e n d o , CH-jCN 3-^ndo-diol d i nitrate cyclohexane  275(+400),229(+4l00),2l8(0), 206(-2000?) 290(+34),270(0),228(+3600)  XIV  Camphane-2-endo 3-exo-diol dinitrate  X  min, -  minimum  * n o t a maximum  3  cyclohexane  CH CN 3  cyclohexane  270(+200)*230(+9000),217(0), 209(-9000) 285(-148),266(0),229(+7100)  117.  118.  T a b l e XV Band S i g n s And C h i r a l i t y R u l e P r e d i c t i o n s Nitrates  Of A l k y l b i c y c l o [ 2 . 2 . l ] h e p t a n o l s  Nitrate  #  For  Configuration  I  Band S i g n II III  1RI2R.  +  (-)  (-)  -  1S:2R  ±  -  +  -  1RJ2R  -  +  -  +  -  +  -  -  +  VIII  Isobornyl  IX  Bornyl  X  D-d-Fenchyl  XI  Camphane-2-exo,3-exodiol-dinitrate  1RI2SI3R  XII  Camphane-2-exo,3-endodiol dinitrate  1R:2S«3S  XIII  Camphane-2-endo,3-endodiol dinitrate  1RJ2RS3S  +  +  XIV  Camphane-2-endo,3-exodiol dinitrate  1R J 2R:3R  -b  +  Nitrate  Nitrate Nitrate  a.  ( + ) a t low t e m p e r a t u r e . ( - ) a t room t e m p e r a t u r e .  b.  (+)  in  CH3CN,  (-)  in  CgH  a  +  Predicted Sign  (+)  +  -  + + (-)  119.  The f o u r c a m p h a n e - 2 , 3 - d i o l have t h e i r band s i g n s rule.  dinitrates  (band I I )  T h e r e was no d i f f i c u l t y  (XI-XIV)  p r e d i c t e d by t h e i n s e l e c t i n g the  chirality favoured  c o n f o r m a t i o n o f t h e 2 - e x o , 3 - e x o and 2 - e n d o , 3 - e n d o ( X I and X I I I ) .  The n i t r a t o  conformations,  of the n i t r o  Besides being the  these also a l l o w f o r  o x y g e n o f t h e C-2 n i t r a t o  o x y g e n o f t h e C-3 n i t r a t o  ( p a g e s 61-64  Camphane-2-exo,3-exo-diol negative  be  close  contact  group w i t h the of t h i s  dinitrate  222 nm i s  o f a weak n e g a t i v e  therefore  h a s a v e r y weak  indicates  230 nm b a n d . B o t h n i t r a t o  p r o j e c t i o n s which p r e d i c t  a negative  T h e r e was no d i f f i c u l t y  viewed f o r  t h e 2 and 3 n i t r a t o  If  predict  presence give II.  sterically (2-endo,3-exo; groups,  opposite  when  chirality  t h e numbers o f atoms i n t h e p o s i t i v e  sectors are a l g e b r a i c a l l y  summed t h e n t h e  of the t o t a l gives the c o r r e c t p r e d i c t i o n addition,  until  the  s i g n f o r band  i n s e l e c t i n g the  the r u l e a p p l i c a t i o n ,  (Figure 44). negative  However,  XIV).  groups  favoured conformation of the trans d i n i t r a t e s 2-exo,3-endo).  alkoxyl  thesis).  does n o t become p o s i t i v e  r e a c h e d , and t h i s  t h e second n i t r a t o  g r o u p s a r e 0C t o e a c h o t h e r ,  the prime source of  chromophoric  and  sign  o f CD s i g n .  group always f a l l s  s e c t i o n w i t h t h e s i g n o f t h e 230 nm b a n d .  in-  sterically  CD a b s o r p t i o n a t 230 nm ( F i g u r e 4 3 , T a b l e  The m o l e c u l a r e l l i p t i c i t y  nitrato  isomers  g r o u p s a r e c i s and w i l l  c l i n e d i n t h e same d i r e c t i o n . favoured  also  Since  in  In  the  the  they are expected t o  be  perturbation.  A second t y p e o f c o n f o r m a t i o n w h i c h a l l o w e d even a  closer  120.  FIGURE  43.  CD OF CAMPHANE- 2,3DIOL DINITRATES (CH-CN).  121  +  +  + C)  +  O  9  6  A.  3-endo  2-exo  T o t a l atomss  (+)  9  (-)  15  Experimentally(-) A.  ( + ) 14 (-) 9 E x p e r i m e n t a l l y ( + ) Band  II  B.  o f a l k o x y l oxygens w i t h n i t r o  In these  conformations,  t h e same s i g n , and t h a t  2-endo,3-exo  of n i t r a t o  groups  in  o x y g e n v/as e x a m i n e d .  t h e s e were n o t t h e most s t e r i c a l l y  formations.  3-exo  T o t a l atoms:  C h i r a l i t y Rule P r o j e c t i o n s X I I and X I V .  interaction  predict  2-endo  2-exo,3-endo  F i g u r e 44.  However,  Band  B.  favoured  both n i t r a t o  con-  groups  s i g n was t h e s i g n o f  the  230 nm CD b a n d . CD S p e c t r a o f B o r n y l , In this  I s o b o r n y l and F e n c h y l  series of three mononitrates  spectrum o f D-o(-fenchyl n i t r a t e three,  it  has t h e most i n t e n s e  (VIII-X),  t h e CD  (X) i s o u t s t a n d i n g . CD b a n d s ;  t e n s e 230 nm band o f a n y m o n o n i t r a t e 11,200K  Nitrates  T h i s no d o u b t r e f l e c t s  it  has t h e most  so f a r r e p o r t e d  the s t e r i c  Of t h e in-  ( [©]232  hindrance  of  +  II  122  the geminal d i m e t h y l group adjacent which would r e s t r i c t Temperature  C-0 bond  Effects i s o b o r n y l and f e n c h y l  t r a t e s i s temperature dependent. and i s o b o r n y l n i t r a t e s  reverse  band o f f e n c h y l n i t r a t e  It effects.  (Table  The 270 nm band o f  nibornyl  s i g n on c o o l i n g , w h e r e a s  i n c r e a s e s as t h e t e m p e r a t u r e  this  is  XVI).  is difficult  t o separate  conformational  from  There are t h r e e p o s s i b l e e x p l a n a t i o n s  s i g n r e v e r s a l s as t e m p e r a t u r e i s 1)  group  rotation.  The 270 nm band o f b o r n y l ,  lowered  to the n i t r a t o  of  solvent  these  loweredt  S i n c e r o t a t i o n a b o u t t h e C-0 bond i s p o s s i b l e ,  a  lowering of temperature would a l t e r the p r o p o r t i o n of  rot-  amers.  of  As t h e t e m p e r a t u r e  t h e most t h e r m o d y n a m i c a l l y 2)  interaction,  mation of the n i t r a t o The e f f e c t  lowered, the population  s t a b l e rotamer would  As t h e t e m p e r a t u r e  creased s o l v e n t  3)  is  is  lowered, there  effects  D-oc-Fenchyl n i t r a t e while  the  confor-  group. solvation alone;  f o r m a t i o n a l mechanism need n o t be i n v o l v e d .  and s o l v e n t ,  c o u l d be i n -  which would a l t e r  c o u l d be due t o  s i m i l a r to the solvent  increase.  i s the  a con-  T h i s w o u l d be  i n b i c y c l o ( 2 . 2 . l j heptanones l e a s t a f f e c t e d by  t e m p e r a t u r e v a r i a t i o n has t h e  (25).  temperature greatest  123.  Table XVI LTCD Of B o r n y l , Solvent  I s o b o r n y l And F e n c h y l  TempBand erature >(nm)  I  !St2R-Bornyl  Band I I nm, m  "Mm* at  [e]  Cc)  Nitrate  Nitrate  CH-jCN  +30 0 -40  270i 275 286  -26O -230 -80  232  -3300  MeOH  +30 +20 -20 -35 -50 -65 -75 -90 ~-100  270i 270i 270i 280 270 271 270 268 269 272i 270 269  -250 -240 -140 -55 0 +101 +160 +290 +430  233  •3300  261 260 265 265  230  -6600  -200 +80 +330  263 258  230  -7000  270i 270i 2701  -430 -408 -380  270i 288  -210 -40  EPA  CHC1.  -10 -95 -145 30 0 -6o  n-pentane  o  -125 1R»2R-Isobornyl MeOH  n-pentane  Nitrate  +30 +20 -15 -30 -4o -60 -75 -90 -95  265i 270i 270 269 268 268 268 268 268  -75 -70 0 +31 +80 +170 +260 +370 +440  +20 -115  273i 269  -22 +130  256 252 248 248 247 246  124.  Table XVI c o n t d . LTCD Of B o r n y l , Solvent  Temperature  Cc)  I s o b o r n y l And F e n c h y l  Band > (nm]  I  X (nm!  [e]  D-*-Fer i c h y l  Btf 0  +5 -95  277 276  -660 -960  261 . 260  n-pentane  0 -125  276 276  -675 -730  260 260  =  inflection.  Band TTT % (nm)  OS  Nr ;rate  Me OH  i  Nitrate  233 233  +11000 +15000  125.  effect  on t h e I n t e n s i t y  trend also r e f l e c t s  of the b o r n y l n i t r a t e  bands.  the increased s t e r i c hindrance to  t r a t o group r o t a t i o n from b o r n y l t o i s o b o r n y l t o nitrate.  Bornyl n i t r a t e  hindrance  of the gem-dimethyl bridge;  rotation.  Therefore,  explained v i a a conformational The l o w t e m p e r a t u r e shown i n F i g u r e  positive  group which  is  has  the  severely  the observed e f f e c t  can be  mechanism.  CD (LTCD) o f b o r n y l n i t r a t e  sensitivity  t r a t e s to temperature flips  isobornyl nitrate  is  45.  The r e l a t i v e  trate  the  D-«(-fenchyl n i t r a t e  g e m - d i m e t h y l g r o u p ot t o t h e n i t r a t o  ni-  fenchyl  i s e n d o , and does n o t have  h i n d e r e d by the 7 - m e t h y l g r o u p ;  restricts  This  o f b o r n y l and i s o b o r n y l  can be s e e n i n F i g u r e 4 6 ,  Bornyl  s i g n a t -50*C, w h i l e i s o b o r n y l n i t r a t e  a t -10*C.  This could i n d i c a t e  nini-  becomes  the presence of  a  g r e a t e r p r o p o r t i o n o f l e s s s t a b l e r o t a m e r s a t room t e m p e r a ture  for bornyl nitrate.  A t -95*C t h e m o l e c u l a r  o f b o r n y l and i s o b o r n y l n i t r a t e s ellipticity dicate  are s i m i l a r .  ellipticities  The  molecular  i s i n c r e a s i n g r a p i d l y a t -90*, which would  the b a r r i e r  in-  t o r o t a t i o n i s b e i n g a p p r o a c h e d and an  i n c r e a s i n g number o f m o l e c u l e s a r e a d o p t i n g t h e conformation of the n i t r a t o  preferred  group.  Varying the concentration of i s o b o r n y l n i t r a t e 0.036 m o l a r t o 0 . 1 m o l a r gave e s s e n t i a l l y t h e same  from curve  128.  FIGURE  4 5 . LTCD  OF  B-2R BORNYL (MeOH).  NITRATE  127.  FIGURE 46. TEMPERATURE VARIATION (BANDI) OF ISOBORNYL AND BORNYL NITRATES (MeOH)  128.  ( F i g u r e 4 6 ) when t e m p e r a t u r e was p l o t t e d a g a i n s t cular e l l i p t i c i t y  o f band  mole-  I.  S o l v e n t does have a n a p p r e c i a b l e nitrates VIII-X  the  e f f e c t on t h e LTCD o f  (Table XVI, Figure 4?).  In n-pentane,  the  270 nm band was s t i l l n e g a t i v e a t - 1 1 5 C f o r b o r n y l  nitrate,  w h i l e t h e s i g n o f t h i s band had a l r e a d y f l i p p e d f o r  iso-  s  bornyl nitrate  b y t h e t i m e t h i s t e m p e r a t u r e had b e e n r e a c h e d .  T h e r e was l i t t l e  v a r i a t i o n i n chloroform, while the  e f f e c t was seen i n  methanol.  P u r e c o n f o r m a t i o n a l and p u r e s o l v a t i o n e f f e c t s be s e p a r a t e d .  It  seems, t h o u g h , t h a t  e f f e c t w i l l predominate. could a r i s e  camphor and f e n c h o n e ,  was v a r i a t i o n i n  solvent  n o r were a n y d e t e c t e d i n t h e LTCD the parent ketones,  although  t h e bands o f  in bornyl  as t e m p e r a t u r e was  one w o u l d e x p e c t t h e e f f e c t  D-«*-fenchyl n i t r a t e .  ni-  -95*Ci  f e n c h y l and i s o b o r n y l n i t r a t e s  did  lowered.  d i s s y m m e t r i c s o l v a t i o n were t h e p r i n c i p a l  CD v a r i a t i o n ,  there  intensity.  not appreciably s h i f t If  the  detected  (MeOH) as t h e t e m p e r a t u r e was l o w e r e d f r o m 0° t o  similarly,  effect  conformation of  T h e r e was no a p p r e c i a b l e w a v e l e n g t h s h i f t trate  cannot  conformational  T h e r e were no " d o u b l e - h u m p e d " p e a k s  i n any o f t h e s e n i t r a t e s , of  the  The l o w t e m p e r a t u r e  from s o l v e n t a f f e c t i n g the  chromophore.  greatest  cause  of  t o be g r e a t e s t  S i n c e a p p r o a c h t o one s i d e o f t h e  t r a t o group i s b l o c k e d by the g e m - d i m e t h y l g r o u p ,  for ni-  solvent  34  130.  m o l e c u l e s w o u l d be a b l e t o p e r t u r b o n l y one s i d e o f chromophore.  The r e s u l t s do n o t  support t h i s  the  hypothesis.  I n b o t h t h e c y c l o h e x y l n i t r a t e s and t h e n i t r a t e s bicyclo [2.2.l] heptanols, band changed s i g n .  of  t h e r e was no case w h e r e t h e 230 nm  The 270 nm band i s t h e most  sensitive  to temperature and/or solvent.  However,  preciable  o f t h e 230 nm bands o f  increase i n i n t e n s i t y  b o r n y l and f e n c h y l n i t r a t e s ; percentage  the  t h e r e was an a p -  bornyl nitrate  increase than fenchyl n i t r a t e ,  both  had a g r e a t e r  again  reflecting  the g r e a t e r s t e r i c hindrance to r o t a t i o n i n the  fenchyl  nitrate. Room T e m p e r a t u r e  CD S t u d i e s .  The same t r e n d t h a t was seen i n t h e v a r i a b l e e x p e r i m e n t was a l s o study  (Table X V I I ) .  seen i n t h e room t e m p e r a t u r e  was p o s i t i v e  s e v e n ( F i g u r e 4-9). nm b a n d ; i n f a c t , t e n s i t y o f band  Of t h e e l e v e n , t h e  showed  varied was e x -  molecular  i n f o u r o f t h e m , and n e g a t i v e  T h e r e was no s i g n r e v e r s a l o f t h e  s o l v e n t had v e r y l i t t l e  effect  in 230  on t h e  in-  II.  I n D-oC-fenchyl n i t r a t e , i n e i t h e r bands I o r I I , static  o f t h e s o l v e n t was  The 270 nm band o f i s o b o r n y l n i t r a t e  amined i n e l e v e n s o l v e n t s . ellipticity  solvent  B o t h b o r n y l and f e n c h y l n i t r a t e s  no s i g n r e v e r s a l as t h e n a t u r e ( F i g u r e 48).  temperature  interaction  no w a v e l e n g t h s h i f t was  confirming that  of solvent  t h e r e i s no  so as t o a l t e r  detected electro-  the energy  re-  131.  Table XVII E f f e c t Of S o l v e n t s On the CD Of Alkylbicyclo £ 2 . 2 . 1 J h e p t y l Nitrates Solvent  lRi2S-IsobornlR»2S-Borny] D-ot-Fenchyl Nitrate v l Nitrate Nitrate X (nm) x(nm] X(nm)  T r i m e t h y l phosphate  270  +170  274 232  -230 -3000  Acetonitrile  270 223  +130  270  233  -260 -3300  Dimethylsulphoxide  270  a  +120  274  -370  Dimethylforamide  275  a  +100  274  Hexane  260  Acetic acid  265  Methanol  265  Cyclohexene  260  -90  220  265  -90 -1800  270  266  -260  -2200  a  e  277  -740 +11,200  -660 . +11,000°  232  -270  -36 -74  270  -258  -75  270  -250 -3260  277  231  -2^5 -34oo  277  233  +10,500  270 234  -440 -3180  277 234  -690 +11,100  Hexafluoroisopropanol  270 234  -570 -3300  277  -1050  Carbon t e t r a chloride  270  -320  270  -290  277  -560  276  -575°  Cyclohexane Chloroform  NEAT 'n-pentane  a1 bt c«  a  270  -130  270  -22  233  not a maximum, but end a b s o r p t i o n , a t +5*C. a t 0*C.  233  233  b  -475  +12,500  132.  1 3 3.  FIGURE 4 9 . CD OF BORNYL OX) AND FENCHYL - O NITRATES.  134.  quirements of the e l e c t r o n i c relation  o f t h e band I  transition.  intensity  normal solvent parameters,  of  T h e r e i s no  fenchyl n i t r a t e  nor w i t h the  cor-  with  size of the  the  solvent  molecule. At low t e m p e r a t u r e s , bornyl nitrate  (VIII)  r e s u l t s w e r e due t o p e c t more o f t h e the  less  stable  the  bands  (IX)  (band I ) .  conformational mobility,  If  so a s t o  could be, t h e n ,  so as t o r e v e r s e  its  Fenchyl n i t r a t e nitrato  band  that  the  the  clear,  at  sign of i t s  action is.  2?0 nm CD  from the s o l v e n t .  pure  solvation  n o t be e l i m i n a t e d a s a cause o f t h i s Camphane-2,3-diol The f o u r characteristic cation  an  molecules  sign. the  is  to  still  solvent  effects  un-  inter-  still  can-  phenomenon.  dinitrates  camphane-2,3-diol  dinitrates  e a c h have  CD s p e c t r u m w h i c h c a n be u s e d f o r  (Figure 43).  2-endo n i t r a t o  It  what the exact n a t u r e o f the  Additionally,  canof  g r o u p and t h e r e f o r e w o u l d be l e s s s u s c e p t i b l e  however,  than  solvent  h a s t h e g e m - d i m e t h y l g r o u p ot t o  conformational influence  ex-  to exist  o n a s m a l l e r number o f i s o b o r n y l n i t r a t e reverse  the  rotamers of bornyl n i t r a t e  On t h e o t h e r h a n d , s o l v e n t w o u l d have t o e x e r t  influence  iso-  one w o u l d  rotamers of i s o b o r n y l n i t r a t e It  and  c o n f o r m a t i o n o f enough o f t h e r o t a m e r s  bornyl nitrate band.  have n e g a t i v e  less stable  room t e m p e r a t u r e . not affect  both bornyl n i t r a t e  groups  Additionally,  all  (IX,X,XIII,XIV),  the  identifi-  compounds  and r e l a t e d  to  with the  135.  configuration  of  (+)-camphor,  The l S i 2 R - b o r n y l n i t r a t e I t s enantiomer,  (-)-camphor.  w i l l have a CD  be t h e m i r r o r image o f t h e CD s p e c t r u m  of lSi2R-bornyl n i t r a t e . groups  230 nm CD b a n d s .  examined i s d e r i v e d f r o m  derived from (+)-camphor,  spectrum which w i l l  nitrato  have p o s i t i v e  The t h r e e  (VIII,XI,XII)  all  compounds w i t h  have n e g a t i v e  2-exo  230 nm CD  bands. A relatively  s t r o n g 210 nm CD band ( b a n d I I I )  tected f o r the 2-exo,3-endo ever,  the 2-exo,3-exo  and 2 - e n d o , 3 - e x o  and 2 - e n d o , 3 - e n d o  t i v e l y weak 210 nm CD b a n d s . t o be a  Tr-^Tr*  transition,  i s o m e r s have  coupled e l e c t r o n i c a l l y .  strong  invokes  are  o f t h i s model i s no r o t a t i o n  (14).  chromophores  situated i n a molecule,  the e l e c t r o n i c  that  results  transition  closely of  the  one c h r o m o p h o r e a p p e a r s t o be a m a g n e t i c t r a n s i t i o n t o second c h r o m o p h o r e ,  and v i c e v e r s a .  i s p r o p o r t i o n a l to the product  with  electronically  when two c h r o m o p h o r e s a r e c o p l a n a r , When t h e r e a r e t w o i d e n t i c a l  elec-  contrast  i n w h i c h two c h r o m o p h o r e s One f e a t u r e  rela-  are  Thus one u s u a l l y  t h e K i r k w o o d c o u p l i n g mechanism f o r (15),  in  How-  believed  and t h e s e t r a n s i t i o n s  t r o n i c a l l y a l l o w e d and a r e u s u a l l y s t r o n g ,  allowed t r a n s i t i o n s  isomers.  The 210 nm band i s  t h e f o r b i d d e n n-*Tr* t r a n s i t i o n s .  was d e -  the  S i n c e t h e CD a m p l i t u d e  of the e l e c t r o n i c  moment and t h e m a g n e t i c t r a n s i t i o n moment and t h e  transition cosine  of  136.  t h e angle between them, i t there w i l l  i s a symmetry r e q u i r e m e n t  that  be no r o t a t i o n f o r c o p l a n a r c h r o m o p h o r e s .  The  two n i t r a t o  g r o u p s a r e e x p e c t e d t o be n e a r l y c o p l a n a r f o r  2-exo,3-exo  and 2 - e n d o , 3 - e n d o - d i o l  dinitrates,  f o r e a weak CD band w o u l d be e x p e c t e d . i n the 2-endo,3-exo  and 2 - e x o , 3 - e n d o  t o be r e l a t i v e l y p e r p e n d i c u l a r , tronic  couplings  i n t h e CD.  there-  The n i t r a t o  isomers are  and t h e r e s u l t  o f t h e two n i t r a t o  and  of the  g r o u p s s h o u l d be  elecevident  B o t h o f t h e s e i s o m e r s have s t r o n g 210 nm b a n d s . (exciton)  detected.  The 270 nm band i s environmental e f f e c t s . and c y c l o h e x a n e  t h e one t h a t  i s most s e n s i t i v e  I n t h e two s o l v e n t s , a c e t o n i t r i l e  isomer.  The 2 - j § n d o , 3 - e n d o - d i o l  had a v e r y weak p o s i t i v e  there i s also the p o s s i b i l i t y  band I i n  r e v e r s a l f o r the 2-exo,3-exo  isomer.  I  di-  cyclohexane,  of the existence  n e g a t i v e band n e a r 270 nm ( T a b l e X I V ) .  the 2-exo,3-exo  to  ( C ^ H ^ g ) , t h e r e was s i g n r e v e r s a l i n band  f o r the 2-endo,3-exo nitrate  groups  expected  Because o f o t h e r o v e r l a p p i n g b a n d s , t h e s p l i t t i n g c o u l d n o t be  the  and  o f a weak  T h e r e was no Of t h e f o u r  has. t h e g r e a t e s t , s t e r i c h i n d r a n c e  sign  isomers, to  ro-  t a t i o n because o f t h e 7 - m e t h y l g r o u p . Over t h e t e m p e r a t u r e o f the 2-endo,3-endo  r a n g e +30* C to- -9.0* C, t h e  and 2 - e x o , 3 - e n d o  (Table X V I I I , F i g u r e s 50, 51)•  i s o m e r s changed  There were i n t e n s i t y  i n t h e 270 nm bands o f t h e o t h e r t w o i s o m e r s , b u t no r e v e r s a l was n o t e d .  The i n t e n s i t y  bands  change i n band I  signs changes sign  of  the  137*  Table  XVIII  LTCD Of Camphane — 2 , 3 - D i o l D i n i t r a t e s Isomer 2-exo,3-exo 2-exo,3-endo  Temperature  (XI) (XII)  +20 -90  •  (*C) "  (MeOH) X i n nm,(  [ej )  270(-640) 272(-600)  +10 -36 -90  280(+190),262(0),229(-4800) 282(+84),264(0) 280(-68) ,229(-4600)  2-endo,3-endo(XIII)  +15 -60 -90  270-5(+l40) ,230(+4000) 270(-190) 265(-480),230(+7400)  2-endo,3-exo  +10 -5 -90  280(-95),266(0) 230(+7600) 272(-120),261(0),230(+8l00)  a«  (XIV)  n o t a maximum.  a  a  138.  2-6X0,3-6X0 i s o m e r was v e r y s m a l l o v e r t h e r a n g e o f +30*C t o -90*C, perhaps again r e f l e c t i n g t h e s t e r i c t a t i o n of the n i t r a t o  groups.  I n c o n t r a s t w i t h band I , w i t h temperature tensity  hindrance to r o -  o f band I I  t h e r e was no s i g n  reversal  (Table X V I I I ) , n o r g r e a t i n -  change i n t h e 2 - e x o , 3 - e n d o  and 2 - e n d o , 3 - e x o  di-  n i t r a t e s. I n summary, t h e n i t r a t o p l a n a r r u l e h a s been f u l l y a p p l i e d t o t h e 230 nm band o f t h e dinitrates.  success-  camphane-2,3-diol  E n v i r o n m e n t a l e f f e c t s have been a n a l y z e d and  can p a r t i a l l y of the n i t r a t o  be e x p l a i n e d b y t h e c o n f o r m a t i o n a l groups.  mobility  139.  140'.  FIGURE  5).  LTCD OF CAMPHANE-2,3- DIOL DINITRATES (MeOH).  E  N i t r a t e s W i t h Oxolane  The n i t r a t o nitrates  Rings  p l a n a r c h i r a l i t y r u l e was a p p l i e d t o  c o n t a i n i n g oxolane r i n g s .  The CD o f  t o X X I I have been r e p o r t e d p r e v i o u s l y  compounds XV  t h e CD o f  (56);  pounds X X I I I t o XXV a r e b e i n g r e p o r t e d h e r e f o r t h e time  (Table XIX,  Figure  Since the r i n g s will  in this  s e r i e s are not b r i d g e d ,  b i c y c l o [2.2.3T) h e p t y l n i t r a t e s .  than i n the  S e l e c t i o n of the  group i n t h i s  (XVI)  of n i t r a t e s ,  the n i t r a t o  (78).  For n i t r a t e s predicted  mono-  group  with  in this  series  conformations  possible. rule  s i g n o f t h e 230 nm CD band  s i g n p r e d i c t e d by the r u l e ,  b e a r i n g on n i t r a t o  c o n f o r m a t i o n was k n o w n .  ( X I X ) and i s o m a n n i d e d i n i t r a t e  g r o u p s gave t h e same s i g n p r e d i c t i o n . (XIX),  was  I n t h e s e compounds t h e r e was no a m b i g u i t y  CD s i g n n o r o f  dinitrate  confor-  X V - X V I I I , XX, and X X I , t h e c h i r a l i t y  t h e same s i g n a s t h e  (Table XX).  Therefore,  g r o u p s were p l a c e d i n  where s u c h an i n t e r a c t i o n w o u l d be  alkyl-  intramolecular  oxygen o f t h e n i t r a t o  t h e oxygen o f t h e o t h e r r i n g  there  of isosorbide  i n w h i c h t h e r e was f o u n d an  i n t e r a c t i o n of the n i t r o  first  series of n i t r a t e s  a i d e d by t h e x - r a y s t u d y o f a d e r i v a t i v e nitrate  com-  52).  be a g r e a t e r d e g r e e o f f l e x i b i l i t y  mation of the n i t r a t o  eleven  (Figure  53).  For  information isoiodide  (XXI), both  In isosorbide  on the. o t h e r hand, t h e two n i t r a t o  sign predictions  since  of  g r o u p s gave  nitrato dinitrate opposite  For the 2-exo p r o j e c t i o n ,  the  143  Table CD Of L - T h r e i t a n and  XXIV  Dinitrate ,  r  L-Threitan  Solvent  d i n i t r a t e CH^CN  D - « t - n i t r a t o - £ ,& butyrolactone  *  L - « . - n i t r a t o - ^ ,$ dimethyl-tfbutytolactone  ! n o t a maximum.  "X i n nm,  ( [0j )  259(-520),250(-490) min,240(-570)23l(0), 210(+l6,000)  Cyclohexane  263C-690),239(0), 210(+l6,000)  CH^CN  270 (+600 )*,2 32 (+6500) 222(0),208(-17,000)  Cyclohexane  270(+480),230(+3500), 221(o),210(-6200)  CHjCN  270(-600)*,232(-6500) 222(0),208(+17,000)  Cyclohexane  270(-500)*,232(-3500), 221(0),210(+7000)  dimethyl-Tf-  XXV  And Of D-  L-°\-Nitrato- i,^-dimethyl- tf-butyrolactone Nitrate  XXIII  XIX  145.  T a b l e XX CD Of N i t r a t e s W i t h Oxolane NITRATE  Rings  Configuration  CD Band S i g n I  II  •  Predicted Sign  III  XV  Isosorbide  mononitrate  2S:5R  +  -  -  XVI  Isosorbide (5-endo)  mononitrate  2S:  5R  +  +  +  XVII  Isoiodide (2-exo)  2Ss5S  +  -  -  XVIII  Isomannide (2-endo)  mononitrate  2R:5R  +  +  +  XIX  Isosorbide  dinitrate  2Ss5R  +  +  +  XX  Isoiodide  2Ss5S +  -  -  XXI  Isomannide  2R:5R  +  +  +  XXII  1,2»5»6-Di-0-isopropylidene-cx-D-glucofuranose-3-nitrate  3S  +  —  +  XXIII  L-Threitan  2S»3S  -  +  +  +  XXIV  D - ^ - N i t r a t o - ^ -dimethyl"tf-butyrolactone  R  +  +  -  +  XXV  L - « - N i t r a t o - / S ,$ - d i m e t h y l tf-butyrolactone  S  -  -  +  -  (2-exo)  mononitrate  dinitrate dinitrate  Dinitrate  \  HoXoJ  A  8)  /0~C f  —/---^ h  o  *  5-endo Isoiodide mononitrate  Figure  (XVII)  53 •  Isomannide mononitrate  Isosorbide d i n i t r a t e (XIX)  P r o j e c t i o n s f o r i s o i o d i d e and i s o m a n n i d e monon i t r a t e s and i s o s o r b i d e d i n i t r a t e ( X I X ) .  5-endo n i t r a t o  group i s  of the 5-endo n i t r a t o , positive  (XVIII)  2-exo  sector.  i n the plane, while  i n the  projection  the 2-exo group i s w h o l l y w i t h i n  Isosorbide  dinitrate  the  has a p o s i t i v e 2 3 0  nm CD b a n d . One f a v o u r e d XXII.  c o n f o r m a t i o n c o u l d n o t be s e l e c t e d  The 5 , 6 - i s o p r o p y l i d e n e g r o u p can r o t a t e  C-C bond and t h e n i t r a t o in either  of  group  the i s o p r o p y l i d e n e  For L - t h r e i t a n t h e s i g n o f band I I  dinitrate, and t h e  could i n t e r a c t  about with  for the  oxygens  groups. t h e r e was u n c e r t a i n t y i n  sign of the  chirality  both  prediction.  14?;  If  the n i t r a t o  allows tive  groups are placed i n a conformation  which  close i n t e r a c t i o n w i t h the r i n g oxygen, then a p o s i -  chirality  i s p r e d i c t e d by b o t h n i t r a t o  groups  (Fig-  u r e 54 A ) .  A. g r e a t e s t i n t e r a c t i o n w i t h r i n g oxygen.  F i g u r e 54.  Projections dinitrate.  However,  steric  if  B. b o t h ONOg g r o u p s i n c l i n e d i n t h e same d i r e c t i o n .  of n i t r a t o  groups i n  L-Threitan  f a c t o r s a r e c o n s i d e r e d and t h e  groups are both i n c l i n e d i n the  same d i r e c t i o n ,  negative  (Figure  chirality  is predicted  1  54 B ) .  nitrato  then a  148  T h e r e was no d i s t i n c t nitrate  detected.  230 nm CD band o f L - t h r e i t a n  In polar solvents,  a n e g a t i v e peak i s  n e a r 238 nm, and t h e n t h e m o l e c u l a r e l l i p t i c i t y s h a r p l y t o become p o s i t i v e ure 55)•  diseen  decreases  a t a b o u t 230 nm ( T a b l e X X I ,  Fig-  I n t h e n o n p o l a r s o l v e n t s t h e r e i s no s i g n o f band  at a l l .  It  i s b e l i e v e d t h a t t h i s band i s  very strong positive The d i f f e r e n c e s  210 nm CD band ( [@j  1  Q  + 16,000,  as an e q u i l i b r i u m b e t w e e n  CH^CN). sol-  conformers.  g r o u p s have f r e e r o t a t i o n a n d , i n a d d i t i o n ,  o l a n e r i n g s have a d e g r e e o f f l e x i b i l i t y known t o be  2  the  i n t h e CD s p e c t r a i n p o l a r and n o n p o l a r  v e n t s can be i n t e r p r e t e d The n i t r a t o  hidden under  6x-  t h e m s e l v e s and a r e  nonplanar.  The l o w t e m p e r a t u r e  CD s p e c t r a o f L - t h r e i t a n  dinitrate  i n EPA and i n m e t h a n o l a l s o add a d d i t i o n a l i n f o r m a t i o n . i s no s i g n o f a 230 nm band i n EPA. lowered,  As t h e t e m p e r a t u r e  t h e i n t e n s i t y o f band I d e c r e a s e s ,  u n t i l at  by -105*C, t h e c r o s s o v e r p o i n t  I n other words, the molecular become more p o s i t i v e . cular e l l i p t i c i t y indicates larly,  e  How-  ellipticity  n e a r 230 nm has  Between - 1 1 5 ° C and - l 4 5 ' C ,  the  mole-  o f band I b e g i n s t o i n c r e a s e a g a i n .  This Simi-  t h e i n t e n s i t y o f band I i n m e t h a n o l d e c r e a s e s as is  is  has moved t o 247+3 nm.  t h e p r e s e n c e o f more t h a n one e q u i l i b r i u m .  temperature  There  -60 C,  t h e c u r v e c r o s s e s t h e b a s e l i n e a t 236 nm ( F i g u r e 5 6 ) . ever,  II  lowered  (Figure 56).  T h e r e i s no d o u b t ,  the how-  149,  Table XXI CD Of L - T h r e i t a n D i n i t r a t e  S O L V E N T  Band I >- (nm M  Band >>• (nm)  (30»C)  II  _  Cyclohexane  263  -690  n-heptane  264  -602  n-pentane  263  -580  -  THFicyclohexane (14.86)  263  -738  -  CH^CN  259  -520  240  -570  MeOH  258  -500  237  2,2,2-Trifluoroethanol  261  -490  239  THF  263  -740  Ether-PentaneE t h a n o l (EPA) (5'5«2)  260  -534  -  £3 =° Mnm, Mnm; 241  TTT "9]  1 1  210  +16,000  231  210  +16,000  -640  228  208  +12,000  -390  232  -  -  241 242 237  238 236  >  150.  FIGURE  55.  CD  OF  L-THREITAN  DINITRATE.  151 .  152.  ever,  t h a t a t room t e m p e r a t u r e ,  dinitrate  Figure  in polar  solvents,  h a s a n e g a t i v e 230 nm CD band ( F i g u r e  57.  L-threitan  57).  CD o f L - T h r e i t a n d i n i t r a t e w i t h p o s s i b l e r e s o l u t i o n (MeOH a t + 3 0 - C ) .  Since the i n t e n s i t y  o f t h e 210 nm band i s  b o t h p o l a r and n o n p o l a r s o l v e n t s ,  band  similar  in  one c a n n o t a r g u e t h a t  the  a b s e n c e o f t h e hump a t 238 nm i n t h e n o n p o l a r s o l v e n t s i s to g r e a t e r overlap of the strong p o s i t i v e appears,  i n the l i g h t  nm band has f l i p p e d  o f t h e LTCD m e a s u r e m e n t s ,  sign at  low t e m p e r a t u r e ,  n o n p o l a r s o l v e n t s a t room t e m p e r a t u r e , w e a k e r o r has a l s o f l i p p e d of the n i t r a t o dict  opposite  210 nm b a n d .  sign.  it  is either  The p o s s i b l e  It  t h a t the  and t h a t  due  230  in  much  conformations  g r o u p s p r e s e n t e d i n F i g u r e 5kk and 5^B" p r e s i g n s f o r t h e 230 nm b a n d .  153.  (MeOH)  •5  154.  The c h i r a l i t y positive rolactone  hand I I  rule  f o r the n i t r a t o  a strong negative  CD band (^ j  (CH^CN); a l s o  a r e n o n p l a n a r and i n d i c a t e  moderately high b a r r i e r  solvent  (Table X I X ) .  there  V-  of  s e p a r a t e d by a (115). the  i s m o s t p r o n o u n c e d i n t h e 210 nm less  lactone  absorption.  i s a l m o s t a 100$ i n c r e a s e  i n the  o f band I I a s t h e t e m p e r a t u r e  f r o m +5*C t o - 9 0 * C ( F i g u r e 5 8 ) . decreases i n  the  i n t h e CD s p e c t r a o f XXIV and XXV  This effect  cular e l l i p t i c i t y  the existence  to the planar s t r u c t u r e "  band, a r e g i o n where t h e r e i s Additionally,  ^219  occurs a t  o f t h e r i n g no d o u b t a c c o u n t s f o r  effect  has  t h e r i n g atoms i n  "two equivalent nonplanar c o n f i g u r a t i o n s  large  compound,  ester.  s t u d i e s have shown t h a t  This f l e x i b i l i t y  positive  The CD maximum o f band I I  expected frequency f o r a n i t r a t e  butyrolactone  is  the parent  -8200  22  - 1 3 7 0 i n HC1 (116)).  Microwave  ellipticity  D(-)-Pantolactone,  2  a  for D-^-nitrato-^, A-dimethyl-lf-buty-  (XXIV); the molecular  ( j © J 3 3 +6500).  group p r e d i c t s  is  mole-  lowered  On t h e o t h e r h a n d , band  I  intensity.  I n summary, e i g h t had c o r r e c t  o f the eleven n i t r a t e s w i t h oxolane s i g n s p r e d i c t e d by t h e  For the o t h e r t h r e e , p r e d i c t i o n s were  chirality  rings,  rule.  t h e CD band s i g n s o r t h e c h i r a l i t y  ambiguous.  rule  155.  F  Steroidal  The CD o f t w e n t y - t h r e e amined. (57)»  steroidal nitrate  e s t e r s was e x -  T w e n t y - t w o o f t h e s e were r e p o r t e d b y S n a t z k e  while  et  compound X X X I I was r e p o r t e d b y Hayward and  The f i r s t  (56).  Nitrates  seven n i t r a t e s a r e a l l  F o r t h e s e v e n , two c o n f o r m a t i o n s  3-nitrato  of the n i t r a t o  e q u a l l y f a v o u r e d , and t h e s e gave o p p o s i t e N i t r a t e s X X X I I I and XXXIV a r e 5 - n i t r a t o  al.  Claesson  steroids.  group  chirality  steroids.  seemed  predictions. The  nitrato  g r o u p i s m o r e s t e r i c a l l y h i n d e r e d i n t h e s e s t e r o i d s and ope c o n f o r m a t i o n was f a v o u r e d . t h e s e two n i t r a t e s  c o r r e s p o n d s t o t h e s i g n o f band  T h e r e were e i g h t to X L I I ) .  The s i g n o f t h e p r o j e c t i o n  17-nitrato steroids  For n i t r a t e s  when t h e p l a n a r n i t r a t o  II.  considered  (XXXV  XXXV t o XXXIX, one s t e r i c a l l y  oured c o n f o r m a t i o n of the n i t r a t o  fav-  g r o u p was s e l e c t e d ,  r u l e was a p p l i e d ,  the  of  and  signs of  their  p r o j e c t i o n s were t h e same a s t h e 230 nm band s i g n s .  A single  nitrato  compounds  g r o u p c o n f o r m a t i o n c o u l d n o t be s e l e c t e d f o r  XL t o X L I I ,  but a p o s i t i v e  I n these three n i t r a t e s ,  c h i r a l i t y was s l i g h t l y  t h e r e were p r o b l e m s w i t h t h e  f o r m a t i o n o f t h e 17/J g r o u p , trato  The CD s p e c t r a o f t h r e e  con-  t h e c o n f o r m a t i o n o f t h e l?o{ n i -  g r o u p , and t h e f l e x i b i l i t y  XLV) w e r e e x a m i n e d .  favoured.  of the five-membered D r i n g .  11-nitrato steroids  (XLIII  T h e r e was u n c e r t a i n t y i n t h e s i g n  the p r o j e c t i o n of X L I I I .  T h i s was due t o t h e n e a r l y  to of  equal  156.  Table  XXII  CD Of S t e r o i d a l Compound #  N I T R A T E  3-nitrato  Nitrates  Nitrato 3roup Configuration  CD Band S i g n s I  II  III  Sign From Projection  steroids  XXVI  3d-nitrato-5^- cholestane  3R  -  +  +  XXVII  3<rt-nitrato-l?A-acetoxy-5*-androstane  3R  -  +  +  +  +  X X V I I I 3<<-nitrato-5fX-androstan-17-one  3R  XXIX  3cX-nitrato-17£-acetoxy-5^ -androstane  3R  XXX  3/#-nitrato-5ct-cholestane  -  -  +  +  3S  +  -  +  XXXI  3 ^ - n i t r a t o - 1 7 4 - a c e t o x y - •3S %• a n d r o s t a n e  +  +  XXXII  3/-cholesteryl  +  +  5-nitrato  n i t r a t e 3S  steroids  XXXIII 5-nitrato-3/3-acetoxy5«\-cholestan-6-one XXXIV  +  5R  +a  -b  +  5 - n i t r a t o - 3 ^ » 6 ^ - d i a c e - 5S t o x y - 5<< - cho l e s t a n e  +c  +  +  +  -  +  +  -  +  +  -  +  17-nitrato  steroids  XXXV  17/S-nitrato-4-androstene-3-one  17R  XXXVI  170 - n i t r a t o - 17<<-ethinyl-4-estrene-3-one  17S  X X X V I I 17^ - n i t r a t o - 5 « ( - a n d r o s - 17R tan-3^-ol  +  +  157.  Table XXII (continued) CD Of S t e r o i d a l N i t r a t e s Compound #  N I T R A T E  Nitrato Group Configuration  CD Band S i g n s I  III  +  -  +  -•  +  17/* - n i t r a t o - 5 ° ( - a n d rostan-3-one  17R  XXXIX  V7B - n i t r a t o - 3 0 - a c e toxy-5°(-androstane  17R  +  +  XL  17-nitrato-19-nor4-pregnen-3»20-dione  17R  +d  +f  XLI  17-nitrato-4-pregnen-3»20-dione  17R  XLII  17-nitrato-21-acetoxy-4-pregnen-3»20dione  17R  US  110-nitrato-3<<» 17*diacetoxy-5^-androstane  XLIV  6rt-f l u o r o - l L y - n i t r a t o - U S 21-acetoxy-l6«<-methyll,4-pregnadiene-3» 20-dione  XLV  6o(-f l u o r o - l l t x - n i t r a t o 11R -21-acetoxy-l6o(-methyl-l,4-pregnadiene3,20-dione 19-nitrato  XLVI  +  +  +  +  +  +  +  +  —  +  —  +?  +g  +g  -g  +  -g  +g  steroids  XLIII  steroids  19-nitrato-3r -acetoxy5<<-cholestane ?  -  +  +  v  1  Sign from Projection!  II  XXXVIII  11-nitrato  i  158.  Table X X I I (continued) CD Of S t e r o i d a l N i t r a t e s Compound  N I T R A T E  Nitrato Group Configuration  CD Band S i g n s I  II  III  19-nitrato steroids (continued) XLVII  19-nitrato-3»4-acetoxy-5^-cholestane  XLVIII  19-nitrato-54-cholestan-3-one  a . max. a t 247 nm. b. a t 2 2 1 nm. c. i n f l e c t i o n a t 244 nm. d . a t 287 nm. f . a t 240 nm g . u n c e r t a i n i f due to n i t r a t o absorption.  a., mm  + —  Sign From Projection  •  159.  distribution group. XLV.  o f atoms t o t h e r i g h t  and l e f t  of the  nitrato  One f a v o u r e d c o n f o r m a t i o n was s e l e c t e d f o r XLIV and However,  the sign of the n i t r a t o  band was i n  s i n c e t h e p a r e n t a l c o h o l o f XLIV a l s o h a s a b s o r p t i o n o f t h e same s i g n i n t h i s Three 1 9 - n i t r a t o  spectral  question bands  region.  s t e r o i d s were p r e p a r e d by Snatzke  b u t a g a i n no f a v o u r e d c o n f o r m a t i o n o f t h e n i t r a t o  group  be a s s i g n e d b e c a u s e o f f r e e r o t a t i o n a b o u t t h e C-C bond t h e 19yS - g r o u p .  The CD b a n d s o f t h e s e 1 9 - n i t r a t o  s t e r o i d s are v e r y weak.  et a l . could of  160.  G.  Acyclic  Nitrates  The CD o f t h r e e n i t r a t e s l y examined  o f c t - h y d r o x y a c i d s were  brief-  (Table X X I I I , Figure 5 9 ) .  C00H  C00CH CH o  2  H-C-ONO,  C00CH_CH  3  2  0 N0-C-H  0 N0-C-H  2  CH,  3  2  CHgCOOCHgCH^  H-C-ONO, C00CH CH o 2  XLIX  LI  3  T h e i r complete  CD s p e c t r a down t o 200 nm w e r e m e a s u r e d .  Tsuzuki e t _ a l .  ( 5 5 ) , had p r e v i o u s l y measured t h e ORD o f  compounds L and L I down t o 280 nm. B o t h X L I X and L showed t h e e x i s t e n c e CD bands o f D - K - n i t r a t o - p r o p a n o i c this nitrate  and t h e n i t r a t e  of rotamers.  a c i d w e r e w e a k , and  synthesized  from  The  both  diethyl-L-  m a l a t e showed weak l o n g w a v e l e n g t h p e a k s a t 292 nm and 3 1 0 nm r e s p e c t i v e l y . found f o r  lactic  no d o u b t r e s u l t For  This behaviour i s and m a l i c a c i d s from d i f f e r e n t  (-)-lactic  p e c t e d t o be  acid,  (39-41,  to the  117).  rotamers i n  results  These  OH  c; R  H  peaks  solution.  t h e most s t a b l e r o t a m e r i s  (39)  H ( /  similar  ex-  161.  Table Nitrates  # XLIX  L  LI  XXIII  Of «M-Hydroxy A c i d s  N I T R A T E  Solvent  >. i n nm, ( [©] )  D - ^ - N i t r a t o - p r o p a n o i c CH CN acid  292(+22),281(0),249 (-217)242(0),233(+360) 228(0),219(-2300)  Diethyl-L-malate nitrate  CH^CN  310(-9.6),300(0),267 (+170),252(0),232 (-2100),222(0),209 (+4000)  Diethyl-L-tartrate dinitrate  CH^CN  262(+440)i,242(+660), 234(0),210(-11,000)  3  i=  inflection  162.  FIGURE 59. CD OF NITRATES OF *-HYDROXY ACIDS (CH,CN).  163.  and t h i s  i s t h e r o t a m e r b e l i e v e d t o be r e s p o n s i b l e  negative  210 nm band i n t h e CD s p e c t r u m o f D ( - ) - l a c t i c  In the n i t r a t e ity  of D(-)-lactic  acid,  f o r the acid.  there i s also the possibil-  o f r o t a t i o n a b o u t t h e C-0 bond o f t h e n i t r a t o  group.  If  t h e same c o n f o r m a t i o n i s s e l e c t e d f o r t h e n i t r a t e  ester,  then  the conformation would b e ,  <h  \  ONOo C  I  C-  CH,  HO^  and i f t h e s t e r i c a l l y g r o u p were s e l e c t e d , positive  favoured  conformation of the n i t r a t o  then the c h i r a l i t y  r u l e would p r e d i c t  a  230 nm CD b a n d , w h i c h i s w h a t i s o b t a i n e d .  D-<*-NITRATO-PROPANOIC ACID The s e l e c t i o n o f p r e f e r r e d was d i f f i c u l t  conformations  of n i t r a t e s  because o f t h e l o n g e r f l e x i b l e  chain.  L and L I  164.  The CD s p e c t r u m o f t h e d i n i t r a t e (LI)  did not  diethyl-L-tartrate  show a l o n g w a v e l e n g t h CD b a n d .  CD s p e c t r u m o f t a r t a r i c 200 nm ( 3 9 ) . to the n i t r a t e positive  of  Similarly,  a c i d o n l y has a s i n g l e band a t  The 209 nm band o f L c a n n o t be w h o l l y since the parent diethyl-L-malate  band a t t h i s w a v e l e n g t h ( 3 9 ) .  a l s o has a  T h e r e was no  cA-D-hydroxy a c i d s have p o s i t i v e  (55)  evidence  bands.  ORD s t u d y ,  the  that nitrates  Cotton e f f e c t s while  d e r i v e d f r o m « t - L - h y d r o x y a c i d s have n e g a t i v e In his  about  attributed  f r o m t h e CD s p e c t r a o f n i t r a t e s X L I X t o L I t o s u p p o r t c o n c l u s i o n s o f T s u z u k i and c o w o r k e r s  Cotton  effects.  he o n l y saw t h e ORD o f many o v e r l a p p i n g CD,  The o n l y s i m i l a r i t y  270 nm CD b a n d .  a negative  i n t h e CD s p e c t r a o f n i t r a t e s  the  The n i t r a t e  it  was d i f f i c u l t  to these three n i t r a t e s groups.  from D ( - ) - l a c t i c  L  pos-  acid  had  270 nm b a n d .  In general, rule  of  those  and L I , b o t h d e r i v e d f r o m o i - L - h y d r o x y a c i d s , was t h e i r itive  the  t o apply the n i t r a t o  because o f t h e  flexibility  chirality of  165.  H.  Summary  For the planar n i t r a t o successfully,  the n i t r a t o  which r e s t r i c t s , for  specific  situation, may be  chirality  r u l e t o be  g r o u p must be i n an  t o some d e g r e e ,  intramolecular  its  free  interactions.  then a preferred  applied  environment  rotation, or If  this  conformation of the  allows,  is* the  nitrato  selected. The r u l e was a p p l i e d t o f o r t y - e i g h t  four different  chemical series  nitrate  (Table XXIV).  gave t h e c o r r e c t  esters  Of t h e  forty-  eight,  twenty-eight  band.  T h e r e w e r e t w e n t y n i t r a t e s where t h e p r e d i c t i o n  s i g n o f t h e 230 nm could  n o t be made.  Table  XXIV  230 nm S i g n P r e d i c t i o n s b y P l a n a r N i t r a t o Nitrate  Series  Rule  Incorrect Sign Correct Sign Pre- Sign Pre- P r e d i c t i o n dicted dicted Uncertain 6  _  1  bicyclo [2.2.1] heptanol  5  -  2  w i t h oxolane  8  monocyclic  steroid  six-membered r i n g  rings  , 9 28'  in  3  -  14  -  20  166  In most cases t h i s r e s u l t e d from the i n a b i l i t y t o s e l e c t a preferred  c o n f o r m a t i o n o f the n i t r a t o g r o u p .  There were a  few cases where the s i g n o f the 230 nm CD band was u n c e r t a i n . There was no d i r e c t c o n t r a d i c t i o n to the r u l e among the forty-eight  nitrate esters.  f u l l y a p p l i e d to n i t r a t e s formation i s  Thus, the r u l e can be s u c c e s s -  i n which a p r e f e r r e d n i t r a t o  defined.  The CD s p e c t r a o f n i t r a t e e s t e r s a l s o i n d i c a t e d presence o f a s t r u c t u r a l e q u i l i b r i u m .  t o be a c o n f o r m a t i o n a l e q u i l i b r i u m of the  molecule  (eg.  whole  menthyl n i t r a t e ) , w h i l e i n o t h e r cases the  changes i n the CD s p e c t r a appeared o f the n i t r a t o group i t s e l f example).  the  I n some cases t h i s  appeared  for  con-  to r e s u l t  from r o t a t i o n  ( b o r n y l and i s o b o r n y l  nitrates,  167.  E X P E R I M E N T A L  168  Experimental A.  Source o f C h i r a l (-)-IsoDorneol  Alcohols was o b t a i n e d b y r e d u c t i o n o f  w i t h LiAlH^j, ( 1 1 8 ) a t - 6 o * C t o i n c r e a s e t h e exp i s o m e r  ( T a b l e XXV).  After  ments w i t h p h t h a l i c a n h y d r i d e r o t a t i o n was r e a c h e d  ( J«J  33«5»c=8.0 EtOH (123)).  2 2  (+)-camphor  the proportion  three  successive  (119,120) a c o n s t a n t  - 3 3 . 6 , c = 9 . 8 EtOH; l i t .  G.L.C.  (Aerograph A-700;  wax 20 M) showed no ( + ) - b o r n e o l  contaminant  of  treatoptical [oC]  1 9  -  20$ c a r b o -  (<1$).  The s o u r c e s o f t h e o t h e r o p t i c a l l y a c t i v e a l c o h o l s  are  shown i n T a b l e XXV. B.  Synthesis of N i t r a t e A l l the n i t r a t e  Esters  e s t e r s were s y n t h e s i z e d  responding c h i r a l alcohols. pared from fuming n i t r i c ment,  Anhydrous n i t r i c  acid  100 mgm (O.OOO65 m o l e s )  dissolved i n a mixture of acetic anhydride. ice-water bath. a d d i n g 0.125  and 0.125  (124).  cor-  a c i d was p r e -  In a t y p i c a l  experi-  o f t h e c h i r a l a l c o h o l was  o f 0.2 m l o f a c e t i c a c i d a n d . 0 . 2 The s o l u t i o n was t h e n c o o l e d i n  The n i t r a t i n g  ml (0.0035 moles)  to a cooled s o l u t i o n  from the  (0*C)  s o l u t i o n was p r e p a r e d o f anhydrous n i t r i c  o f 0.25 m l o f a c e t i c  ml of a c e t i c a c i d .  This n i t r a t i n g  an by  acid  anhydride  s o l u t i o n was  s l o w l y added d r o p w i s e t o t h e cold s o l u t i o n o f a l c o h o l , a f t e r a d d i t i o n was c o m p l e t e d , stored i n a r e f r i g e r a t o r  ml  the r e a c t i o n m i x t u r e  (+5°C) f o r two h o u r s .  The  and,  was re-  169;  T a b l e XXV Sources o f C h i r a l  Alcohols  Carbinol (-)-lR»2R-isoborneol  Source LiAlHjj, r e d u c t i o n o f ( + ) - c a m p h o r at (118); s e p a r a t i o n from ( + ) - b o r n e o l  -60»C  (119,120)  (-)-lS»2R-borneol  5% KOH-MeOH h y d r o l y s i s acetate (Aldrich)  D-c(-fenchyl  Koch-Light  alcohol  of  1-bornyl  Laboratories  (-)-menthol  Matheson,  carvomenthol  hydrolysis of i t s 3,5-dinitrobenzoate, a g i f t of S . Schroeter (121)  i so c a r v o m e n t h o 1  hydrolysis of i t s 3»5-dinitrobenzoate, a g i f t o f S. S c h r o e t e r (121)  p-menth-l(7)-enetrans-2-ol  hydrolysis of i t s p-nitrobenzoate, a g i f t o f S. S c h r o e t e r (121)  p-menth-1(7)-enecis-2-ol  hydrolysis of i t s 3,5-dinitrobenzoate, a g i f t o f S. S c h r o e t e r (121)  camphane-2,3-diols  a gift  3-methylcyclohexanols  prepared i n t h i s R.N. T o t t y  l a b o r a t o r y by  Tj-threitan  prepared i n t h i s D. Dong •  l a b o r a t o r y by  D- and L - p a n t o lactone  Abbott  D(-)-lactic  Miles  acid  Di e t h y l - L - t a r t r a t e  Coleman and  o f S . J . Angyal  Laboratories Laboratories  Eastman-Kodak  Bell  (122)  170.  a c t i o n m i x t u r e was t h e n p o u r e d on 10 gm o f  crushed i c e .  e x c e s s a c i d s w e r e n e u t r a l i z e d w i t h kofo s o d i u m (pH m e t e r ) , w h i c h was f o l l o w e d b y e x t r a c t i o n w i t h methylene  chloride.  After  u t i o n was d r i e d  over D r i e r i t e ,  solution,  of the  product with  t h e CHgClg  sol-  and t h e s o l v e n t was r e m o v e d .  G e n e r a l l y t h e n i t r a t e s were p u r i f i e d ("v0.5 t o r r ) .  hydroxide  successive washings  w a t e r and $fo s o d i u m b i c a r b o n a t e  The  D-c<-Fenchyl n i t r a t e  by  distillation  and i s o b o r n y l  nitrate  were a l s o p u r i f i e d  b y c o l u m n c h r o m a t o g r a p h y on s i l i c a  gel  (CHCLj d e v e l o p e r ) .  P u r i f i c a t i o n was c o n t i n u e d u n t i l  T.L.C.  ( s i l i c a gel?  CH^CN ( 2 0 i l )  C^H , 1 2  developer)  indicated  no  impurities. lRi3R«4S-Menthyl n i t r a t e  was a l s o p r e p a r e d v i a  its  provided a guide f o r  this  chloroformate.  The p r o c e d u r e synthesis.  o f Boshan (125)  The C-H-N a n a l y s e s o f t h e n i t r a t e  esters  171  are c o l l e c t e d i n Table XXVI. N.M.R.  spectra  ( V a r i a n A-60 and T - 6 0 ,  w e r e r e c o r d e d and t h e i r  analysis  CCl^  showed t h a t  solvent)  chemical  and c o u p l i n g c o n s t a n t s a g r e e d w i t h t h e s t r u c t u r a l ments.  Infra-red  m o d e l s 21 and 137 solvent), stretching  liquid  s p e c t r a were r e c o r d e d on  Perkin-Elmer (CCl^  and p o t a s s i u m b r o m i d e w a f e r s .  frequencies of the n i t r a t o  with published  assign-  s p e c t r o m e t e r s as s o l u t i o n s p e c t r a films,  b a n d s were  IR s p e c t r a l d a t a f o r n i t r a t e  shifts  The  consistent  esters  (82-85,  87,88). Attempted synthesis of  (-)-trans-carve ol  carveol  (LIII),  (+)-trans-carvotanacetol  pulegol  (LV) were u n s u c c e s s f u l .  (LII),  (LIV),  and  Upon a d d i t i o n o f  (-)-cis1-iso-  the  172.  Table Elemental Analysis Nitrate  XXVI Of N i t r a t e  Esters  Calculated  Found  %C  %H  %N  %C  % H  %N  lRt2R-isobornyl nitrate  60.28  8.60  7.03  60.15  8.69  7.08  lS»2R-bornyl  60.28  8o60  7.03  60,12  8.56  7.10  camphane-2-endo,3 -exo-diol-dinitrate  46.15  6.20  10.77  46.25  6.18  io.96  camp h a n e - 2 - e n d o , 3 -endo-diol-dinitrate  46.15  6.20  10.77  46.20  6.12  10.90  camphane-2-exp,3-exo -diol-diriitrate  46.15  6.20  10.77  46.31  6.25  IO.65  D-c^-f e n c h y l n i t r a t e  60.28  8,60  7.03  60.31  8.44  7.02  1R«3R«4S-menthyl nitrate  59.67  9.52  6.96  59.39  9.72  6.92  isocarvomenthyl nitrate  59.67  9.52  6.96  59.99  9.70  6.91  p-menth-1(7)-ene2-ol-nitrate  60.28  8.60  7.03  60.15  8.51  7.10  D-«(-nitrato-4 4-dim e t h y l - c f - bu t y r o l a c tone  41.14  5.18  8.00  41.28  5.16  8.07  nitrate  173.  c o l o u r on s t a n d i n g .  The i s o l a t e d p r o d u c t s were v e r y  and r e d - b r o w n i n d i c a t i n g t h e p r e s e n c e o f n i t r o g e n It  i s evident  t h a t p o l y m e r i z a t i o n had o c c u r r e d .  been r e p o r t e d t h a t c ( , o i - d i m e t h y l a l l y l n i t r a t e -strong tendency to polymerize L  v  a t -25* C was s i m i l a r l y Nitration  mixture,  of cedrol  o r by n i t r i c  Similarly,  nature of a t e r t i a r y d-3-Bromocamphor bromo-ketone  It  has  exhibits  a  carbinol  unsuccessful. ( L V I ) a t -50»C b y a AcgO-HOAc-HNO^  a c i d i n CHgClg a t  -60"C y i e l d e d  cedrene.  chloroformate  These r e s u l t s r e f l e c t  the  labile  carbinol. resisted nitration  i n 100$ n i t r i c  o f bromine by n i t r a t e  dioxide.  Nitration of  an a t t e m p t e d p r e p a r a t i o n v i a t h e  y i e l d e d only cedrene.  C.  (126).  viscous  by d i s s o l v i n g  a c i d , and a l s o b y  i o n (AgNO^ i n  the  replacement  CH^CN).  UV S p e c t r a UV s p e c t r a were r u n on a C a r y 15 s p e c t r o p h o t o m e t e r  10 mm and 1 mm q u a r t z  cells.  Repetitive  made o v e r t h e span o f a y e a r t o  m e a s u r e m e n t s were  check t h e i r  reproducibility.  C o n c e n t r a t i o n s were s e l e c t e d t o m a i n t a i n a s l i t 1 mm and an a b s o r b a n c e b e l o w D.  in  width  below  1.0.  CD M e a s u r e m e n t s C i r c u l a r d i c h r o i s m s p e c t r a were measured on JASCO ORD/  UV/CD-5  (J-5)  and J - 2 0 s p e c t r o p h o t o m e t e r s .  The m a j o r i t y  t h e s p e c t r a were measured on t h e J - 5 w i t h a s e n s i t i v i t y  of of  174.  differential  5x10 paper.  The e n t i r e  flushing. variable  absorbance u n i t s per m i l l i m e t e r o p t i c a l p a t h was u n d e r c o n s t a n t  chart  nitrogen  The i n s t r u m e n t was o p e r a t e d w i t h a programmed slit-width.  The i n s t r u m e n t was c a l i b r a t e d m e n t s were p e r f o r m e d ; ) in  (127)  of  each day b e f o r e  5-<*-chloestan-3-one  measure-  (A^+1.13 a t  295 nm  1,4-dfoxane was c h o s e n a s a s t a n d a r d .  M e a s u r e m e n t s w e r e made i n 10 mm, 1 mm and 0,1 mm q u a r t z cells,  and w e r e r e p e a t e d a t  prepared  intervals  o v e r 3 y e a r s on  freshly  solutions.  To g u a r d a g a i n s t b a s e l i n e r e c o r d e d b e f o r e and a f t e r  shifts,  solvent baselines  sample r u n s .  All  were,  s p e c t r a were  s c a n n e d t w i c e and e a c h compound was m e a s u r e d a t t w o o r more concentrations. bornyl nitrate  I n one e x p e r i m e n t t h e 230 nm band o f was e x a m i n e d e i g h t  the molecular e l l i p t i c i t y  varied  times  1S:2R-  (CH^CM s o l v e n t )  o n l y + 5$ f r o m t h e  and  average  value. E.  Sources o f If  stray  Instrument light  is a significant  would expect d e v i a t i o n s absorbance v e r s u s was n o t  Error source o f e r r o r ,  from Beer's law.  concentration verified  significant  i n t h e J-5  over the  Linearity that  stray  one of light  s p e c t r a l range  210-  300 nm. The o p t i c a l r o t a t i o n  of the  sample o r o f t h e c e l l s  does  175 not influence  the d i f f e r e n t i a l  a b s o r p t i o n measurements,  t h e a p p a r a t u s i s b a s e d on t h e m e a s u r e m e n t o f (128) . sample  Similarly,  birefringences  c e l l and o f t h e e n t r a n c e  no e f f e c t  on t h e m e a s u r e m e n t  (129) .  face of the p h o t o c e l l  (128).  large  However,  and t h e  but these e f f e c t s  discrepancies  the  have  birefringences  sample c o u l d  a r e e x p e c t e d t o be  The CD s p e c t r u m o f b o t h e n a n t i o m e r s o f  dimethyl-tf-butyrolactone  fluxes  o f t h e e x i t window o f  encountered between the p o l a r i z e r t h e measurement,  luminous  since  affect small  e{-nitrato-4»f*-  (XXIV and XXV) w e r e m e a s u r e d and no  i n t h e i r molecular e l l i p t i c i t i e s  were  noted. The a b s o l u t e p r e c i s i o n o f t h e m e a s u r e m e n t s w e r e by the' background n o i s e  of the p h o t o m u l t i p l i e r  The JASCO i n s t r u m e n t s a l s o r e c o r d a t r a c e multiplier  voltage.  unreliable  when t h e p h o t o m u l t i p l i e r  800 v o l t s . instrument  limited  (shot  of the  noise).  photo-  I t was f o u n d t h a t t h e m e a s u r e m e n t s w e r e  When t h i s  occurs,  voltage  the noise  t e n d s t o have a p o s i t i v e  increased  i n c r e a s e s and  the  For t h i s  reason,  a l l m e a s u r e m e n t s w e r e made v / i t h t h e p h o t o m u l t i p l i e r  voltage  b e l o w 800 v o l t s  by d i l u t i n g the  shorter pathlength.  This,  then,  bias.  above  sample o r b y g o i n g t o decreased the  a  instrument  noise. Instrument  artifacts  a b s o r p t i o n peaks are example).  a r e a l s o known t o o c c u r when  scanned  The n i t r a t e  (aromatic  e s t e r s do n o t  transitions,  suffer  omenon, a s s e e n i n t h e UV s p e c t r a o f m e n t h y l  for  from t h i s nitrate  sharp  phen-  176 (Figure 26).  No a r t i f a c t s w e r e d e t e c t e d i n a n y o f t h e CD  spectra. The s l i t 2^5 nm. tropic  was programmed so t h a t  it  opened t o 2 mm. a t  T h i s was n e c e s s a r y b e c a u s e o f t h e i n c r e a s e d a b s o r p t i o n o f t h e sample b e l o w 24o nm. w h i c h  the p h o t o m u l t i p l i e r the increased s l i t  voltage to increase. opening i s  isocaused  A consequence  the increased spectral  w i d t h and t h e d e c r e a s e i n r e s o l u t i o n .  However*  this  bandis  c o u n t e r e d by t h e i n c r e a s e d d i s p e r s i o n o f t h e p r i s m i n spectral region. slit-opening F.  of  this  The s p e c t r a l b a n d w i d t h a t 220 nm f o r  a  o f 2 mm w i l l be a b o u t 2 n m .  Low T e m p e r a t u r e CD M e a s u r e m e n t s Low t e m p e r a t u r e measurements w e r e made i n 10 mm and  1.0mm c e l l s  i n a quartz  of l i q u i d nitrogen  dewar c o o l e d w i t h t h e  (38).  boil-off  B a s e l i n e s w e r e measured a t  r o o m t e m p e r a t u r e and a t l o w t e m p e r a t u r e .  All  low  measurements w e r e c o r r e c t e d f o r v o l u m e c o n t r a c t i o n published solvent  data  (130,131).  both  temperature from  177  BIBLIOGRAPHY 1.  I . U g i , Do M a r q u a r d i n g , H. K l u s a c e k , P. G i l l e ss jp "i e , Angew. Chem. i n t e m a t . 703 ( 1 9 7 0 ,  G. G o k e l and E d i t . . , £,  2a.  R . S . Cahn, C. I n g o l d , and V . 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