Nuclear magnetic resonance spectra of vinyl protons of cyclopentadiene and cyclohexadiene from spin decouplin

Elleman, D. D.

Manatt, S. L.

English

NASA Technical Reports Server

' 1  
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. 
> 2 - G  . -  t h a t  described by Freernu: a d  .-LCIYSOK . 
a ted two  phase detectors o f ' tFe  5z.e desL;r, as described by us previously . 
LLs par t icu lar  systea Incorpor- 
6 
locking frequency. 
giver, elsewhere . 
A r.ore dek. l led c.escrils;tior, of t he  corr?iete systex i s  
S2ectra :*-ere :scorixi bg f r e q x r , c g  s ~ e ?  2-5 110st usss. 7 
Cyclopentaaene (I) xas obtzir,ed by crackir-;; t ke  d 5 e r .  Cgclo- 
hexadiene (11) 'was a co,mercial scrnple zca contained an k r p r i t y  of cyclo- 
hexene. About 7-105 tetrzr.ethylsLlanz wis added t o  each s z $ - e  in Varian 
thin-walled 5 rm s a q d e  tubes. Cqgen  m s  reroved by b ~ ' 3 X k g  nitrogen 
. I  through t h e  sarnples f o r  about t k - e z  r x x z e s .  
- The ccxplete m a l y s e s  02 t k s  ?roton n.r.r. spectra of  - azzd I1 
presez: zs;ker f o d d a ' b l e  tesks as i s  evidsnt from obsexat icn  0' t k e  
corr,pler2tles of t h e  vixyl. proton regions for these rnolecilles ( sez  f i g .  l a  
and fig. 3a, respectively). 
l l n e s  a?d the  fac t  t h a t  r ing obscures t'x t m e  posit ions of x z r l y  a l l  ol" 
t k e  vinyl resonance lizes :&e a straig:?; I"crward i terztLve z._=~=.oacfi tc
t h e  analysis of t h i s  spec - lm~  r & t h e r  =at t ract ive.  
I n t k e c m  of I the  great c lu l t ip i lc l ty  cf 
By placing a Izr.ge-fidr2 r.o&Lation at the ne;kylene prot or, 
frequency in a frequency-swee? e;:p,rk.en% -.;z >;ere able t o  bring &out a 
ra ther  gratifying simplification or" the viryl  proton regicc LZ I t o  a?. A 2 2  E 
system as shown i n  fig. 13. 
r e s u l t s  ob taked  i n  a field-sweep expexisent. 
- 
Fig. f c  shows sir?.ilar tkough l e s s  p1easir.g 
Fror. sever& spectra of the 
~~ ~ - 
I .  ? * *  ~ ' 3  
qual i ty  of f ig .  15 it was possible to obtein l i n e  posit ion measurer:ents 
accurate t o  2 0.01 cps. 
To the decou?led spectrm of  I it IJZS possible t o  Lrtroduce a 
second per turbkg field-modulatloc at  varioils l i n e s  of the  A '13 system. 
Two exa?$es of these t r i p l e  i r radiat ion exper&ents a re  shohn 2n figs. 
2 2  
2b and Z C ,  These tr2ple i r radiat ion eqer;inents denonstrated t h a t  l i n e s  
4, 7, ll+ and 17 (as labeled ir, fig. 2a) xera re la ted t o  each othez. These 
t r a s i t i o n s  a re  the  aEtisyzxetriczi ones ar,d each is  doxb1y degenerate, 
The idex t i ty  of s m e t r i c  t r ans i t i o r s  follo; .~s im-eciat ely. F ~ G F  cocsider&lon 
of t h e  nmber o f  otker l l n e s  s91it whez Gach l b e  was i r ra2iated t h e  speci- 
fie assigment based OR She USE& no-,;'uior. fa,- t he  A 3 s?ic system' could 2 2  
be mde  and i s  s-mnerized below: 
1 Line As sigrizent 
1 5 
1 2 
3 
r; 
5 
6 
2 
!?,IO 
6 
7 
7 11, I 2  
9 3 
9 
10 
4 
8 
A f b a l  set, of parsxeters was o5taked using the  Si~alen and Beiley bXRIT 
progran ' : 
&AB 
JAA 
J’AB 
Jm 
%B 
8.079 
+1.944 
+l. 090 
+5.064 
+1.94-4 
? 0.004 
2 0.007 
k 0.006 
2 0,006 
2 0.006 
The average deviatior? between G’oserved ard calculated l i n e  posit ions w a s  
0.006 cps, 
A s  shown i n  fig.  3b we were able t o  sirr..plify the  vinyl  proton 
spectrum of I1 t o  an A2B2 systm hit the res1‘1f.s were r o t  neayly a s  good 
as those obtained for  I. 
t o  120 cps fror;.. the te t rane thyls i lme freqwr,cy enough r.ociLation was 
Becacse t h e  r e % k y l e n e  proton frequency was close 
present close t o  t h i s  l a t t e r  freqEency -&en a la rge  noddzi ion - A s  placed 
a t  t h e  fomer  freqcezcy to cause saturation of the  locking s t g a l  and 
sel-ious beats in the  locking h o p .  
m t  recove, tended t o  ULilOlrJc the  s?ectrcr!eter -bile t h e  spec tn? .  of 11 was 
being sxept w i t h  a mLociulation level a5 the  zethylene proton frzqdency 
suf f ic ien t  t o  achieve the  desired mouqt of decouplirg. 
d i f f i c u l t i e s  it m s  Yossible t o  o’c-lain ra ther  sa t i s lac tory  spectra of one 
sLde of the  A 3 
swept through without t h e  spectroreter wilocking. 
gave a set of l h e  posit ion rneasurmer.ts accurate t o  2 0.05 cps. 
Both 05 Shese factors ,  which w e  could 
h s p l t e  5hhese 
spec-lnn of I1 axd iz ssveral cases cor-plete spectra xere 
Oata from these spectra 
2 2  
b!e were cot at  a l l  able t o  iritroduce a sec0r.d large pe:rt~-hL--~ 
f i e l d  in to  the  decoupled s p e c t m  of Ii t o  t r ace  out t he  energy of t t e  -L-2i32 
systex -without h n e d i a t e l y  mLockkg the  spc t roxe te r .  
t h e  A2B2 s p e c t m  of I1 was started Sy recognizing a cer ta in  s k r A l a r i t y  
between the  S ? E C Z X ~  of I1 znd certain A2B2 spectra of 2-disubstituted 
h-.. assigxen-l or’ 
benzene recently discussed by Grant e t  al.’ A s  discussed by the  l a t t e r  
~~ 
authors v a h e s  of N and L ana thus t h e  che7Aca.l s h i f t  were obtained 3x2  
cer tain repe t i t ive  spacing in t h e  s p e c t n x  of the A2B2 systern of Ii. 
assigniients f o r  t he  various re la t ive  sign assigments  between the  long- 
range H-C=C-C=C-H ar,d E-C=C-C-H cou?lings were considered. 
Trial 
The o r ly  assigr,- 
nent which gave a sat isfactory convergence fo r  "X?LIT ar.d which gave agreeTent 
with experinental i n t ens i t i e s  ana sa t i s fac tory  ag ree~~en t  with l ine posit ions 
was t h a t  given below: 
: ,,E.".* 
6,394 It 0.013 
d i5.142 t 0.028 
+LO64 2 0.W J' AB 
JAB 
J3B 
A 3  
AA 
- 
C9.417 2 0,033 
+1.9& 2 0,028 
6,. 
The average deviatior between obssr-ved and calculateL l i n e  posit ions was 
@.OS?. 
we attribu';e t o  incorrplete decoc>.cr.g ~:l:ic:Ci resul ted LT certain, ~f the 
The rxch l u g e r  errors  ir, t he  a rL2ys i s  of 'she d 2 2  B spectrcx of I1 
- .  
J 3 --2 2 lir.es being shif ted fro:- tkeLr t r c e  posi';ion. 
The dlf lererxe between 
one pa i r  of observed. sr.d calcda=ed llces was 0.24 cps ( i l rxs  7 a d  ' 1  :i. 
k a l y s e s  of t he  A2B2 spectra f o r  the  vinyl  p r o x x s  sl I and -- 
does not detemine whether the  A o r  B protons a re  cpf ie lc  I n  these r o l e ~ - d e s  
and in fac t  t h e  assignrent of  soze of t he  coupling cons%ncs i s  based on 
zr,alogy t o  other rrolecdes . 
Vinyl protons in I and II a r e  adj2cer.t t o  -ethylene grol;ps CZY be rLade. 
1 However, a deterxination 02- ;;.:C.ich se t  of 
1 assignxxnt of the cpfield v i ~ y l  protons as those adjacent uo 
t h e  methylene group f o r  I, was based on the  f a c t  t ha t  t h i s  group of virqrl 
protons i s  more strongly coupled ;o the  xethylene protons as evidenced f r o n  
t h e  undecouplea spectrmi (see fig. 3a),  
we expect a posi t ive coupling of about 3-4 cps and i n  t h e  case of  the  down- 
In the case of t he  l a t t e r  protons 
f i e l d  vinyl protons a negative coupling of about 1-2 cps as est izated fror& 
data f o r t h e  cycloolefins . 9 
6 In our previous reported asalysis  of the spectrzn of ixdeze , 
which contains a Kethylene group adjacent to two doable bonds and par t  of 
a five-nembered r ing and which should be closely analogous t o  I, we fomd 
t'nat i n  the  five-mernbered r ing the H-C-C=C-II coupling was  a different  sign 
than the  H-C=C-H a ~ d  H-C-C-E coczplings, wlnich a r e  both presm-ed t o  be posi- 
t i v e  h sign 
and JAx and Jgy a re  0rJ.y s l igh t ly  difi'erent. 
of t he  v k y i  proton each l i n e  or" the decoupled AsB2 spec tn i i  sho-dd be 
s p l i t  in to  1:2:1 t r i p l e t s .  
first order. 
methylene W t e t  we should be i r radiat ing t rans i t ions  having one se t  of 
t he  Vinyl protons in spin s t a t e  ria and the other set i? spin s t a t e  89 
reasoriing from the  r e su l t s  for hdene . 
Tie colr,plete p;.oton spectra7 of i i s  a "2 3 2- Y2 spec t rm 
In t he  undecoqled spectrux 
The zethylene protors  of I give a q - a t e t  t o  
Or, se lect ive i r radiat ion o f  the  low-field inenber of  t he  
t 
Fron detai led consicieration of the  s>in states of 5 i e  v a r b u s  
l i n e s  of the -L232 eecoupled spec;rm w e  would exTect in t k e  sxperinerx 
described above t o  see perturbation i n  the  do;vnfieid portion of t h e  :?df of 
t h e  vinyl proton spectrum assignable t o  t h e  protons with t h e  cegative hng- 
range E-C-C=C-E coupling a d  s0r.e perturbation i n  the upfield portion of 
t h e  half  o f  the vinyl proton s p e c t m  assignable t o  the  vinyl protons 
adjacent t o  the  niethylene group. 
from the  experbent  indicated that  t he  upfield v h y l  protons were those 
adjacent t o  the  methyler,e group. 
upfield menber of the xethylene q c k t e t  was  i r rad ia ted  confimed t h i s  
resu l t .  
Reasoning i n  t h i s  manner the  r e s u l t s  
An additional experheEt where t h e  
These r e s u l t s  w i l l  be described in nore d e t a i l  elsewhere. 
.7 
ziscussioc 
Recently there  has been considerable i rkeres t  in t h e  na twe  of  
long-raxge proton-proton spin-spin couplings. We define "long-range" 
couplings as  those existing between protons nore than thFee bonds apart 
(i.e. 'J's and 5J1s, where the  superscript denotes the  nmber of cher5cal 
bonds separating coupled nuclei). A t  present several possible mechanisms 
have been postulated f o r  these couplings. 
coupling i s  thought t o  be transmitted through the  0-Sond frm.ework jus t  
as t h e  v ic ina l  3J coupling 
'J and 
distances a re  SrTdU enough13. 
nechanlms could be inportant i n  addition t o  a coctrlbciion transmitted 
through the  n-electron s y s t e m u .  This n-electror- P.echar,isn involving 
6-n configuration interact ion i s  usually t'ne largest  contributlon t o  
long-range coupllr-gs -2n con,jugated molecules. 
repwted here cor.?kried with saze other r e c e ~ t  r e su l t s  on %rz.s-1,3-dienes 
Ir. saturate6 molecules 'J 
12 . 9r. addition there  i s  some evidence tha t  
5 J coupling can be t ra - i sd t ted  through space i f  the  intra-proton 
h unsa-luated zolecules both of  these 
The r e s u l t s  fo r  I and I1 
15, 
16,17 provide soixe i r l r " o r ~ & l o ~  CT, t he  rela-live bportances cf i;:*.sse rechanims. 
In Table I a re  given dzta fo r  several open chain trsns-dienes. 
Ir, these molecules there  a re  several 4J1s a d  5J1s. The theory of t he  
propagation of spin-spin coupling through a rr-electron systexu predicts  
t h a t  t he  coupling w i l l  be positive when a pa i r  of protons a r e  separated by 
ar odd nmber of bonds and negative when they a re  separated by an even 
nii.ber of bonds. 
butadienes are  i n  agreenent with t he  theory. 
The sign results f o r  t h e  4Jts and *Jrs fo r  ";he tras-1,3- 
In the  case of I z.d I1 both 
these  types of long-range couplings are found t o  be posit ive.  
i f  the values for  the 4J1s of  l,+butadiene of about -0.1 cps 
are taken t o  be character is t ic  of t h i s  n-contribution in &enas then iz I 
and I1 the measured 4J1s (not considering J BB in I f o r  t h e  mment) nust  
I ' 8  - -  . 
be the  sum of a -0.8 cps n-contribution and a +1.9 cps contribution fron? 
other mechanisms. 
0.1 t o  0.3 cps13 o r  considerably l e s s  i n  ragnitude than t h i s  1.9 cps 
contribution. 
each other when compared with other nolecules in which a through-space 
contribution t o  
protons13. 
have been observed in saturated r d e c u l e s  when the  angulzr disposit ion 
between the t w o  C-II bonds i n  a H-C-C-C-H 2rap.ent I s  sixilar t o  t h a t  fourid 
ir, I and Is3 even though the intra-proton distance i s  r e l a t ive ly  great 
i .e.  greater  than about 3 8. Fle ascribe the  rragnitudes of t h e  4J1s 
(excluding JBB in I) i n  I and I1 as a r i s ing  from a +l.9 cps contribution 
from a coupling mechanisn which is signif icant  when t h e  angular disposit ion 
of the  C-E! bonds i s  suck tha t  l i c e s  through these bonds w i l l  nearly cross 
somewhere behiEd the  carbon ators  t o  give ar, angle I n  ;'.e range of ?O-leO". 
This kind of coupling zechanis;r.is probably the  sa-ce or,e respozsible fo r  t h e  
very large (3-14 cps) 4Jts observed in soEe bridged r ing systerr.s13; i f  t h i s  
i s  the  case then it i s  l i k e l y  that  these large couplings are also posit ive.  
4 The usual o-coctribution t o  J 's appears t o  be about 
The protons involved i n  I and I1 are  rather  dis tant  froxn 
4 J is  believed t o  exist because of closely disposed 
Long-range couplings i n  t he  range of a posi t ive 1-2 cps have 
4 The JBB in I, which i s  a J, although coupling via the  n-electron 
5 5 would involve J, and t h e  J i n  I1 a r e  about 1 cps different  from each other  
and both positive. It :.< 
about +0.7 cps'. 
Seen estimated tha t  the 'J rr-coupling w i l l  be 
Although it would be expected t h a t  this n-coupling 
should be independent of orientation f o r  a butadiene and depend OT? t h e  
rr-bond order between the  couplec! protons, experbenta l  evidence shows tha t  
5Jtt ( the J between l,&-protons each t r ans  t o  t he  f o d  single bond of a 
trans-lJ-diene) i s  about twice as l a rge  as t h e  other  5Jfs  (i.e. 'JCc 2nd 
JtC)l6,l7. The Jcc and Jtt for  trans-lJ-dienes a re  i n  the  range of 
+0.5 t o  +0.8 cps which i s  in rather close agrement with the  theory. 
5 
5 5 
If 
'. , . .  
9 
. 
couplings in truls-dienes a r e  Jtt we assume tha t  e f fec ts  present i n  the 
absent i n  t h e  case of I and 11 then the  observed nagnitudes of  JBB i n  I 
and t h e  5 J i? I1 can be explained as ar i s ing  f ro2  +0.7 cps n-contribktions 
and +1.2 cps and M.2 cps contributions, respectively, from other mechanism. 
4 A 
( i . e ,  0.1-0.3 cps)13, 
J o-contribution t o  JBB of I through the  methylene group should be small 
The angular disposit ion between the  C-H bonds invol- 
ving t h e  B protons of I i s  sirriilar t o  t h a t  f o r  t h e  protons involved i n  the  
other  4 J t s  i n  t h i s  molecule, which were discussed above, except t ha t  t he  
intra-carbon distance i s  s l i g h t l y l a r g e r  here. 
through-space mechanism i s  again operaiive it i s  about ~1.2 cps in rragnitude, 
possibly ref lect ing the  s l i gh t ly  larger  iqtra-carbor, distaxce in this case. 
Assuming t h a t  t h i s  sane mechanisn i s  presext i n  11, che much Siraller contri- 
If a s w l a r  cross-ring 
bution of +0,2 cps t o  'J again probably r e f l e c t s  mainly the  s ignif icant ly  
grea te r  intra-carbon distance, 
5Jts in II are  very similar t o  t h o s e  faux2 i n  - o-disubstituted bezzenes 
which a re  p-ost cer tainly related t o  t he  similar geometry ana sug;_sst t ha t  
s k d a r  coupling xechanisxs a r e  operative i n  both types of r ing compcunds. 
The magnitudes and signs of  t t e  4Jts and 
1 
The - cis-vinylic couplings i n  1,3-but&iene i s  +10.17 cps ar,d t h a t  
i n  I1 is  +9,42 cps which shows t h a t  t h e  electronic s t ructure  i n  these t w o  
types of double bonds i s  only s l igh t ly  different ,  The much smaller value 
of +5,06 cps i n  I apparently re f lec ts  the  e f fec t  of r ing  contract: ion or. 
vicinal. coupling as has been observed when g o b g  from a six- t o  a five- 
nenbered r ing , 
respectively, r e f l ec t  this sane effect .  
v inyl ic  couplings i n  1,3-butadiene i s  about 1.7 while the  r a t i o  of t he  t rans-  
coupling between protons on the  formal single bond of butadiene t o  t h e  
corresponding &-coupling in  I1 i s  1,8. 
9 The values of Ju f o r  I and 11, +1.94 cps and +5.W cps, 
The r a t i o  of the  trans- t o  - cis-
This r e su l t  nay indicate  t h a t  
.. . * .  
- 
there  is a close electronic similari ty i n  the  s tmc tu re  of the  two f o d  
s ingle  bonds in butadiene and II and also in general t he  sane terms 
determine t h e  coupling between vicinal protons separated by two z2 carbon 
atoms except f o r  a scale fac tor  which may be related t o  the n-bond orde$. 
That such a re la t ion  exists may be indicated from the  observation of t he  
parallelism between the sum of the two vicinal  couplings in I1 which i s  
U.6 cps and i n  naphthalene which is U.6 cps16 and the  sums of the 
corresponding n-bond order fo r  the two adjacent bonds of 1.34 arid 1.33, 
respectively, as calculated by tfie molecular orbi ta l -e thod . This corcpari- 
son would not seem t o  support the  recent contentions of Dewar and Schneising 
t h a t  appreciable conjugation does not exist i n  unsaturated systems such as 
19  
19 
1,3-di=es. 
The analyses o f t h e  corqlete spectra of I and II a re  i n  progress 
and w i l l  be reported subsequently. 
* 
The couplings i n  I1 will embody cer ta in  s t e r i c  e f f ec t s  charac te r i s t ic  
of six-menbered r ings which allow more useful cozparison t o  couplings i n  
benzene derivatives. 
s l i gh t  difference of t he  &-vhyEc couplings between butadiene and 11. 
These s t e r i c  e f fec ts  probably account f o r  t h e  
References 
1. D. M. Grant, R. C. Hirst and H. S. Gutowsky, J. Chem. Irnys. 3s, 470 
(1963 1. 
2. 
3. 
R. J. Abraham and H. J. Bernstein, Can. J. Chem. 39, 905 (1961). 
R. A. Hoffman and S. Gronowitz, Ark. XerL, a 45 (1959) and other 
papers by these authors. 
4 .  14. L. Heffernan and A. A. Hmffroy, Nole. F'hss. 
5. 
6. 
7. 
527 (1964). 
R. Freeman and W. A. Anderson, J. G'nem. Phss. z, 2053 (1963). 
D. D. EXlerran and S. L. Xanatt, ibid.  36, 1945 (1962). 
D. D. Elleman, S. L. Manatt and C. D. fearce, ibid,  i n  press (1964). 
8. J. D. Swalen and C. A.  Reilly, ibid.  2, 21 (1962). 
9. (a) 0. L. Chapman, J. Am. Chen. SOC. 85, 2034 (1963); (b) v. S d t h  
and H. Krihoff, ibid.  3, 2016 (1963)7(c) P. Laszlo and P. R. Schleyer, 
ibid.  85 2017 (m. --7 
10. 
ll. 
12. S. Koide ar,d E. Duval, J. Chem. Phys. 
13. See discussion in ref. 7. 
If+. 
15. E. 0. Bishop and J. I. Nusher, Mol. Phss. 
16. 
P. C, Lauterbur and R. J. Kurland, ibid.  84, 3405 (1962). 
A. I). Buckhgham and K. A. Nclauchlan, Proc. Chem. SOC., lA.4 (1963). 
11. Xarplus, J. Chem. Fhys, 2, 1842 (1960). 
621 (1963). 
R. A. Harris and A. A. Bother-By, private cornmication. 
17. 
18. 
R. T. Hobgood and J. H. Goldstein, J. Xol. Spect. l2, 76 (1964). 
J. A. Pople, W. G. Schneider and H. J. Bernstein, "High-Ftesolution 
Nuclear Magnetic Resonance, pp. If+7-l49, McGraw-Hill, Xew York, 1959. 
19. A.  B, Pullman and A. pullnan, "Les Theories Electroniques de l a  ChLiAe 
Orgsnique,'l Masson e t  Cie, Paris, 1952. 
20. M. J. S. Dewar and H. N. Schmeising, Tetrahedron 2, 166 (1959). 
I 
0 1 + 
c\ 5 $ 1  I I I 1 I I I 
rl 
1 I rl c: 
c r l o  c o o  I 
9 7 ! 
o\ 
rl 
I 
2 
I 
I I 
I + + 
3 t a 0  0 0  
. 
Fig. 1. Spectrum of the Vinyl protons of cyclopentadiene (I) at 60 Mc. 
(a) Undecoupled and frequency swept. (b) Decoupled from 
methylene protons and frequency swept. (c) Same as (b) except 
f i e l d  swept. 
! 
. 
1 
Fig. 2. Spectrum of the vinyl protons of cyclopentadiene (I) at  60 Mc. 
(a) Decoupled from methylene protons and frequency swept. 
(b) Same as (a) i n  addition to i r radiat ion of l i n e  18. (c) Same 
as (a) i n  addition to irradiation of l ine 17. 
1 
. J. . * .* c 8 . 
* 
. 
Fig. 3. Spectrum of the vinyl protons of cyclohexadiene (11) at 60 Mc. 
(a) Undecoupled and frequency swept. (b) Decoupled from 
methylene protons and frequency swept, 
according t o  the usual convention for +B2 spin systems; see 
ref. 1. 
Transitions labeled 
- J  
c n 
Y 


Analyses of the Nmr Spectra of the Vinyl Protons of Cyclopentadiene and Cyclohexadiene Using Spin Decoupling

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