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13C NMR spectra and long-range 13CH couplings in substituted ethylenes
JOURNAL
OF MOLKCL~LAR
13C NMR
SPECTROSCOPY
Spectra
37, 252-259 (1971)
and long-Range 13C-H Couplings Substituted Ethylenes’
Ii. AI. CRECELY,
in
R. W. CRECELT, ANI) J. H. GOLDSTEIN
Depart,ment of Chemistry,
Emory
University.
.Itlanta.
Georgiu 50322
Long-range 13C-H coupling constants in a number of vinyl derivatives have been obtained from the analysis of high-resolution W spectra. The substituent effects on these couplings are discussed and correlations are presented between the geminal W-H couplings and both the H-H and directly bonded W-II couplings in vinyl compounds. INTRODUCTION Proton magnetic resonance spect’ra have been report,ed for many vinyl compounds (l-i1 ). In several cases the ‘“C-H sat,ellite spectra have been analyzed t,cl obtain t,he direct)ly bonded 13C-H coupling constant’s and limited informat,ion about differences between long-range 13C-H couplings (G-11). The I’(: chemical shift,s for numerous substitut’ed ethylenes have appeared in the lit’eratlure (1~3-16). The long-range 13C-H couplings have been reported for ethylene (17, 18), vinyl bromide (19), vinyl chloride (20), acrylonitrile ($I), and several polysubstitut,ed ethylenes (18,WO, 22). These couplings have been determined from analysis 13C spectra (SO), prot,on spectra of ‘“C-enriched compounds of high-resolut#ion (17, 19), double resonance techniques (18, 21), and observation of the ‘“C-H inner satellites of the proton spect)ra (2%). Changes in the geminal 13C:-H couplings with substitution in vinyl compounds have been found to bc relatively large> (‘6 t.o 9 Hz in vinyl bromide), indicating that monosubstituted ethylenes would be appropriate systems in which tjo study substit,uent effects on CCH couplings. ‘“C spect,ra of eleven vinyl CO~IIn this paper we describe the high-resolution pounds. The long-range 13C-H couplings are reported. In addition the iwwl ‘“C-H satellite spect’ra of three disubstitutcd ethylenes have been analyzed to obtain t,he long-range 13C-H couplings. Correlations betwwn (11~ I wo-bontl 13C-H couplings and both the H-H and directly bond4 ‘“C-H couplings it) vinyl derivat,ives have been invest*igated.
All of t~ie compounds samples
for which
used
13C spectra
’This work was supported
in this
study
were obtained
in part, by a grant 2.52
werP
commercially
were prepared from the Naiiorlal
trvailablr.
Tllr,
in either
M-mm
Imtittltes
of iIr:d~h.
or
W
NMR
OF ETHYLENES
258
lo-mm NMR sample tubes to which ~15 % acetone by volume was added t.o serve as the internal proton lock. For the prot’on spectra a portion of the above sample was transferred to a 5-mm tube. The 13C spectra of vinyl chloride were obtained at -20” C using a saturated solution in acetone. The 13C spectra were obtained using a Bruker HFX-90 spectrometer operating in the frequency sweep mode at a temperature of -22’ C. Sweep widths of 0.4 and 1.0 Hz/cm were used depending on the complexity of the patterns. Normally ~240 scans were accumulated using a Fabri-Tek 1074 signal-averaging syst#em. The spectrometer was locked to the proton signal of acetone while observing the 13C spectra of t#he vinyl compounds at 22.6 MHz. The proton spectra were taken on a Varian A-60A spectrometer operating at ~38” C using acetone as an internal reference for the 13C samples. The 13C-H satellite spectra of maleic acid were obtained from a saturated acetone solution. Diethyl fumarate and diethyl maleat’e were run as neat. samples. Calibrations were performed by the usual side-band technique. RESULTS
AND
CALCULATIONS
The 13C spectra of eleven substituted vinyl compounds were obtained. The three long-range 13C-H couplings involving the vinyl prot,ons were determined for seven of these compounds. For the remaining cases only t’he long-range coupling to Cb was obtained. The spectra of the (Y carbon for these compounds could not be analyzed due to coupling between this carbon and protons in the substituent. The analyses of the spectra were carried out using LAOCN3 Q’S) on a Digital Equipment Corporation PDP-10, or LAME (24) on an RCA Spectra 70/46 computer. In some cases it was found that the 13C patterns were dependent on the differences between bhe proton shifts. Therefore the proton chemical shift)s used in the analysis of the 13C spectra were det)ermined on samples containing -15% acetone. In some cases adjustments were made in the proton shifts t,o account for the difference in operating temperatures between t,he Varian A-60A and the Bruker spectrometers. Values for vinyl chloride at - 20’ C were obtained from a previous temperature study (4). It was necessary to vary the proton chemical shifts in order to theoretically reproduce the spectrum of the carbonyl carbon of acrolein. Values chosen from the literat,ure at ~22’ C (5) were found to give a more satisfactory agreement between the calculated and observed frequencies than the values obtained in the present study at -38” C. In several cases it was found that different sets of parameters would predict the observed 13C patterns. To aid in select>ing the correct assignments and signs for t,he CCH couplings information from the 13C-H satellite spectra, additivity relationships, and correlations with other couplings were employed. The 13C spectra of divinyl ether and vinyl acetate are first order. Therefore 13C-H couplings has no effect on t~he prechanging the signs of the long-range
CKECELY,
254 dieted
patterns.
CRECELY,
AND
GOLIMTE:In’
However, by observing the inner ‘“C-H satellit’e spect,rum, ether was found to be positive. The analogous coupling in vinyl acetate was therefore assumed to be positive. In divinyl ether there are three long-range 13C-H couplings to t)he (Y carbon which vary in magnit,ude from 5.0 to 6.5 Hz. Due to the first-order nature of the a pattern it was impossible to assign these couplings to the proper protons or det,ermine their signs. The two long-range 13C-H couplings to the (Ycarbon in vinyl acetate were found to be of nearly the same magnit,ude. On the basis of known CCH couplings in vinyl compounds, we felt it, reasonable to assume that JCoH3 is negative and CJCaHZis positive. Unique analyses could not be obtained for the cr13C spectra of acrolein or acrylic acid even though these spectra are not first order. In bot,h cases eight’ set,s of long-range 13C-H couplings were determined which satisfactorily predicted the 13C spectra. Of these possibilities only one value for Jc,IX, in each compound fol was found tjo be negative. Since t,his coupling is negat,ive in a,11compounds which a unique analysis was obtained, it was assumed also l-o be negative in thrst: two cases. This assumption left two possible values for Jc,rrt in these compounds (1.5ij or -0.2 in acrylic acid and 1.X or -0.6 in acrolein). It has been rshowr~ ($0) that the CCH coupling constants in polysubstitut,ed bromo and chloru et)hylenes can be predicted t)o within 1 Hz of t#he observed value using additivita of substituent effects in the monosub&ituted compounds. Assuming addit,ivit,y is valid for other disubstit,uted ethylenes, only one of the two possible values fox predict, the CCH ,Jc~II~in acrylic acid (1.55 Hz) can be used to satisfactorily coupling in maleic acid. The value calculat,ed from additivitp (3.35 Hz) is in excellent agreement with the observed coupling (3.36 Hz). The long-range ‘“C-H coupling in fumaric acid is not available. However, the coupling vxlut* predictted from addit.ivit,y (- 2.75 Hz) agrees favorably with the value observed in the diet,hyl ester (-2.77 Hz). Of the two possible values for JCaHs in acrokill, we feel that,, based on t,he assignments in acrylic acid, the larger value is mortt reasonable. The signs of t(he couplings from the vinyl carbons t.o the aldehyde proton in acrolein (d,,, = 26.6, JcaH = 0.95) could not br determined. The carbon?1 pattern was analyzed utilizing differences between the long-range “(J-H couplings det,ermined previously from analysis of the ‘“C-H satellite spectra (8). Due to the near degeneracy of the prot,on chemical shift.s in vinyl trichlorosilane, the 13C-H satellite spectra were analyzed to determine t#hc proton--proton couplings constants. The following coupling psramekrs w(trr obtained: .I,, :; 14.26, Jn = 19.55, Jz = 2.03, J,,, = 152.2, .Jcx2 = 160.9, .JCHR = 159.9, :\11t1 J CCHa - JCCH, ,- 2 Hz. Using these values a unique tit, for the laCI spectra ~1s obtained for this compound. The long-range 13C-H coupling paramet,erx involving the elhylenic carborls are given in Table I and t,hose involving the carbonyl carbons are given in Table
J CBHlin divinyl
13C NMR
255
OF ETHYLENES TABLE
I
LONG-RANGEW2-H COUPLINGCONSTANTSSIN SUBSTITUTED ETHYLENES
H2 \
c
= c
/
1 \
H3 x
H1
X
Cc& 7.5 6.75 4.15 1.8 1.55 7.6 -2.5
Cl Br I COH COOH OAc Sic13
C&l
Cc& -7.9 -8.2 -7.8 -3.4 -4.55 -7.9 -0.8
6.9 6.25 4.0 0.25 -0.6 9.65 -6.85 -7.0 9.75 -0.35 -0.6
Si(GH& OCzHz COCH3 COOCH3 cis di COOH, cis di COOEt, tram di COOEt,
JCCA = 3.36 jcCH = 3.07 -2.77 CCH =
i’1’alues are in Hz. TABLE LONG-RANGE
II
13C-H COUPLING CONSTANTS* INVOLVING IN SUBSTITUTED ETHYLENES
THE CARBONYL
COH COOH cis di COOH
2.2 4.1 2.25
15.9 14.1 13.15
cis di COOEt
2.65
13.55
CARBON
10.1 7.6 -
* Values in Hz.
II. The values obtained in the present study for vinyl chloride and vinyl bromide are in agreement with those that have been reported previously (19, 20). The CCH couplings given here for diethyl maleate and diethyl fumarat,e are considerably different’ from those reported in a previous study (‘2.2). DISCUSSION
In t,he vinyl compounds the largest substituent which varies over a range of 17 Hz. A corresponding
effects are found for J,,,, , trend has also been observed
in monosubstituted et)hyl derivatives (25) (assuming ./eCH is negative) and in the five-membered heterocycles ($6, 27). In the latter compounds JCBH. varies from 6.3 t,o 14 HZ while .IVan,, varies from 6.3 to 7.3 Hz as the hrt,eroatom changes from carbon to oxygen. As has been pointed out previously- (20, 28), tllth substit,uent effects on these couplings can be rat,ionalized in terms of the I’ople :u~(l Bothner-Bv theory of geminal coupling constams (29 ). The substituent effects on ./ oa~lZand Jc,ao observed llert, arc of opposite s&t. Similar observations were noted in the subst>ituted cvclopropanes (JO), but I Ilk” substituent effect’s in t,hese compounds are considerably less pronounced than irk t,he vinyl derivatives. Using molecular orbital iheory, Gil and Formosinllo Simoes (31 ) speculale that, the substit,uent effects on .ICnIly and .I,,rl:i in vinyl compounds are of opposite sign. Their prediction that, .I ontr3 would clecrtuscb and of the subatituent incrrasec: i> J CaH3would increase as t.he electronegntivity contrary to t,he experiment,allp observed changes. ‘I%(~ model of ,Jamesori rin(.l Gutowsky (32) has been used t,o calculate geminal ‘“C---H coupling const:uitS ( SS) and is successful in explaining many of the observed trends. In the C:I,Wof the couplings to C, in the vinyl compounds t’he observed change in ,~~.,rFiri.4 correctly predicted. However, because of both positjive and negative contributions to the couplings, predictions could not be m:& concerning the subst,itucwt, effects on J,,,,:, . In previous studies of long-range ‘“C-H couplings, relationships 11ave btltbii investigated between C-H and H-H coupling constants (26, SO, ,~4-~3i’). ; ‘l‘lre long-range ‘Y-H couplings in aromat,ic compounds have been correlated witli geometrically similar H-H couplings (26, 3i’ ). In the subst itutrd cycloprop:u~e:: it, was found that correlations existed between J ccl1 and a linear combinatioir of the geminal H-H coupling and a vicinal H-H coupling (30 ). In t,he present study correlations have been investigated bet,ween the 101ig. range ‘“C-H couplings and both the geminal and vicinal H---H couplings in 111tb vinyl compounds. Although general trends :w observed betlveen JCC, :~n(d .J,cH , much better correlations are found between J,2C:H and the vicinal H- H couplings. There is an inverse croportionality betwtn Jo,,, and both the I./,< and t,he tram vicinal H-H couplings. A plot of JcBII, iis tlicl reciprocal of th(a :IV~‘I’ implies ;I age of these two H-H couplings is shown in Fig. 1. This correlation linear relationship bet,ween e1 CcHand clcctronegativity since it has been noted 1~~ Schaefer and Hutton t,hat t,he prot,onproton couplings in vinyl compounds art’ linearly related to t,he inverse of t,he substituent, elcct,ronegat,ivit,~ (&s ). Figures 2 and 4 show plots of each of t’he long-range C’-H couplings to (‘, IL\ the average of t,he vicinal H-H couplings. Since .I,:,,, was found to correlate inversely wit811.JHCCH, correlations between JonN and the reciprocal of ?I,,,,:, \vere also investigated. There was esseruiully no difference bt%ween the con&t ioil coefficient, obtained for eit’her case. Figure 4 shows a plot of ‘JCaHa z’s the directly bonded coupling ./CnWI ‘l‘llip
. I\;
l3C NMR
6.0
JW
257
OF ETHYLENES
\
.
.
-\;
-^IL_.___l
I J HCCH
1.0
0.6
FIG. 1. Jcgnl us l/Jnccn. (-3.67)
are included.
The CCH coupling values for ethylene (-2.4) H-H couplings are from Refs. (I-8,6-8, 10,17).
and acrylonitrile
8.0 I
-2.01----II.0
I8.0
J
HCCH
FIG. 2. JCYH~us ~HCCH.The CCH coupling values for et,hylene (-2.4) (0.29) are included. H-H couplings are from Refs. (2-4, 6-8, 17).
and acrylonitrile
correlation is considerably better than t,hat between Jcaaa and JHCCH, alt,hough much better correlations are found with t’he proton-proton for JGH%and JGJCBH1 couplings. Both t,he geminal and vicinal 13C-H couplings to the carbonyl carbon in acrolein and acrylic acid were found to be positive. As is observed for vicinal H-H couplings in vinyl compounds, the trans CCCH couplings are larger than the cis CCCH couplings, Karabatsos et al. (3.9) have noted that the dependence
CRECELY,
258
CRECELY,
AND GOLDSTEIN
0.0
. /
Jw
,r’,’
?? /
/’
.
3
I
- 6.0
I
I
IO.
I 7.
J
HCCH
Fra. 3. .Jcan3 2’sJn,,,,n. The CCH coupling values for ethylene (-2.4) -4.42) are included. I3-H couplings are from Xefs. (&SP 6-8, f7).
\
and acrylouitrilr~
‘\\
- 8.0 -
FIG. 4. Jca~I vs. Jc~FI~.
(-4.42)
are included.
of CCCH couplings vicinal proton-proton
The CCH coupling values for ethylene (-2.4) and acrylonitrilr Directly bonded *3C-H couplings are from Refs. (6’~9, I7j.
in sp” compounds couplings.
on dihedral
angle
is similar
to tbat
of
ACKNOWLEDGMEST The authors are grateful RCA Spectra 70/46. RECEIVED:
to the Emory University
(‘ompufer
(lenter
for the use of the
July 22, 1970 REFERENCES
1. 2. 8. 4, 5.
C. N. BANWELL .\ND N. SHEPPIHD, Mol. Phys. 3, 351 (1960). E. 0. BISHOP AND R. E. RICH~~RDS, Mol. Phys. 3, 114 (1960). Y. AMT.%, H. SHIMIZU, AND S. FIJJI~.~R.\, J. Chem. Phgs. 36, 1951 (1962). W. S. BREY, JR., K. N. SCOTT, :~ND I>. K. WHITM~\N, .I. Phys. Chem. 72, 4351 11968~. J. I<. n.kVIES, J. No!,. &?ctrosc. 2% 399 (1969).
l3C NMR 6. 7. 8. 9. 10. If. 12. 15.
R. R. A. G. L. P. G. G.
OF ETHYLENES
250
T. HORGOOD,JR., R. E. Mayo, AND J. H. GOLDSTEIN,J. Chem. Phys., 39,25Ol (1963). E. MAYO AND J. H. GOLDSTEIN,J. Mol. Spectrosc. 14, 173 (1964). W. DOUGLASAND J. H. GOLDSTEIN,J. Mol. Spectrosc. 16, 1 (1965). C. GRAHAM, Ph.D. Dissertation, University of California, San Diego, 1967. LUNAZZI AND F. TADDEI, Spectrochim. Acta, Part A 26, 553 (1969). KREBS AND H. DREESKAMP,Spectrochim. Ada, Part d 26, 1399 (1969). B. SAVITSKYAND K. Na~rKaw.4, J. Phys. Chem. 68, 1956 (1964). B. SAVITSKY, P. D. ELLIS, K. NAMIKA~~‘.~,.\ND G. E. MAC’IEL, J. Chem. Ph,ys. 49, 2395 (1968). 14. G. E. MACIEL, J. Phys. Chem. 69, 1947 (1965). 15. T. HIGASHIMURA, S. OUMUR~, L. MORISHIM.~, .\ND T. Y~NEz.\I~.I, J. Polynl. SU’., Part B 7, 23 (1969). 16. E. LIPPMAA, T. PEHK, K. ANDERSON,.~NDC. R,IPPE, Org. Atag. Iles. 2, 109 (1970). 17. R. M. LYNDEN-BELL AND N. SHEPP~IRD, Proc. Roy. Sot., Ser. 11 269, 385 (1962). 18. Cf. GOVIL, J. Chem. Sot., 11 1967, 1420. 19. R. M. LYNDEN-BELL, Mol. Phys. 6, 537 (1963). 20. F. J. WEIGERT AND J. D. ROBERTS,J. Phys. Chem. 73, 449 (1969). 21, It. FREEMAN, J. Chem. Phys. 40, 3571 (1964). 2%. N. MILLER, J. Chem. Phys., 37, 2729 (1962). .%!j. A. A. BOTHNER-BY ‘IND S. CASTELLANO,private commuriicatio~i. 2.4. C. W. H.~IGH AND J. W. WILLIAMS, J. $101. Speclrosc. 32, 398 (1969). $5. G. MIYAZIM.~, Y. UTSUMI AND K. T.4K.4H.\SHI,J. Phys. Chem. 73, 1370 (1969). 26’. F. J. WEIGEI~TAND J. I). ROBERTS,J. gnher. Ch,em. Sot. 90, 3543 (1968). 97. It. W. CHECELY,K. M. CRECELY,4ND J. H. GOLDSTEIN,Znorg. Chem. 8, 252 (1969). 88. K. A. MCLAUCHLAE~ AND T. SCHAEFER,(‘an. J. Chem. 44, 321 (1966). 29. J. A. POPLE AND A. A. BOTHNER-BY, J. Chem. Phys. 42, 1339 (1965). 30. K. M. CRECELY,1~. W. CRECEL~, .~NDJ. H. GOLDSTEIN,J. Phys. Chem. 74, 2680 (1970). $1. 17. M. S. GIL x~~~ S. J. S. FOHMOSINHOHIMOES, Mol. Phys. 16, 639 (1968). 52. C. J. J~MES~N .IND 11. S. GUTOWSKY, J. Chem. Plays. 61, 2790 (19WI). 35. C. J. JAMESONAND M. C. DAM.~SCO,Mol. Phys. 18, 491 (1970). 34. (:. J. KAR.IH.\TSOS,J. .4mer. Chem. Sot. 83, 1230 (1961). 35. G. J. KARAUATSOS,J. I). GR,~H.uI, .IND F. M. VANE, J. Phys. Chem. 66, 1657 (1961). 36. (:. J. KARAI~~~TROS, J. I). GR.\H.\MAND F. M. V.\NE, J. Amer. Chem. Sot. 84, 37 (1962). 37. F. J. WEIOEHT -4~1) J. 1). ROBERTS,J. Amer. Cheni. Sot. 89, 2967 (1967). 38. T. SCHAEFEKAND H. M. HUTTON, Can. J. Chem. 46, 3153 (1967). .!?Y. (;. J. KARAHATSOS,C. E. OHZECH,JIM.,‘INI) N. HSI, J. :lmer. Chem. Sot. 88, 1817 (1966).
OF MOLKCL~LAR
13C NMR
SPECTROSCOPY
Spectra
37, 252-259 (1971)
and long-Range 13C-H Couplings Substituted Ethylenes’
Ii. AI. CRECELY,
in
R. W. CRECELT, ANI) J. H. GOLDSTEIN
Depart,ment of Chemistry,
Emory
University.
.Itlanta.
Georgiu 50322
Long-range 13C-H coupling constants in a number of vinyl derivatives have been obtained from the analysis of high-resolution W spectra. The substituent effects on these couplings are discussed and correlations are presented between the geminal W-H couplings and both the H-H and directly bonded W-II couplings in vinyl compounds. INTRODUCTION Proton magnetic resonance spect’ra have been report,ed for many vinyl compounds (l-i1 ). In several cases the ‘“C-H sat,ellite spectra have been analyzed t,cl obtain t,he direct)ly bonded 13C-H coupling constant’s and limited informat,ion about differences between long-range 13C-H couplings (G-11). The I’(: chemical shift,s for numerous substitut’ed ethylenes have appeared in the lit’eratlure (1~3-16). The long-range 13C-H couplings have been reported for ethylene (17, 18), vinyl bromide (19), vinyl chloride (20), acrylonitrile ($I), and several polysubstitut,ed ethylenes (18,WO, 22). These couplings have been determined from analysis 13C spectra (SO), prot,on spectra of ‘“C-enriched compounds of high-resolut#ion (17, 19), double resonance techniques (18, 21), and observation of the ‘“C-H inner satellites of the proton spect)ra (2%). Changes in the geminal 13C:-H couplings with substitution in vinyl compounds have been found to bc relatively large> (‘6 t.o 9 Hz in vinyl bromide), indicating that monosubstituted ethylenes would be appropriate systems in which tjo study substit,uent effects on CCH couplings. ‘“C spect,ra of eleven vinyl CO~IIn this paper we describe the high-resolution pounds. The long-range 13C-H couplings are reported. In addition the iwwl ‘“C-H satellite spect’ra of three disubstitutcd ethylenes have been analyzed to obtain t,he long-range 13C-H couplings. Correlations betwwn (11~ I wo-bontl 13C-H couplings and both the H-H and directly bond4 ‘“C-H couplings it) vinyl derivat,ives have been invest*igated.
All of t~ie compounds samples
for which
used
13C spectra
’This work was supported
in this
study
were obtained
in part, by a grant 2.52
werP
commercially
were prepared from the Naiiorlal
trvailablr.
Tllr,
in either
M-mm
Imtittltes
of iIr:d~h.
or
W
NMR
OF ETHYLENES
258
lo-mm NMR sample tubes to which ~15 % acetone by volume was added t.o serve as the internal proton lock. For the prot’on spectra a portion of the above sample was transferred to a 5-mm tube. The 13C spectra of vinyl chloride were obtained at -20” C using a saturated solution in acetone. The 13C spectra were obtained using a Bruker HFX-90 spectrometer operating in the frequency sweep mode at a temperature of -22’ C. Sweep widths of 0.4 and 1.0 Hz/cm were used depending on the complexity of the patterns. Normally ~240 scans were accumulated using a Fabri-Tek 1074 signal-averaging syst#em. The spectrometer was locked to the proton signal of acetone while observing the 13C spectra of t#he vinyl compounds at 22.6 MHz. The proton spectra were taken on a Varian A-60A spectrometer operating at ~38” C using acetone as an internal reference for the 13C samples. The 13C-H satellite spectra of maleic acid were obtained from a saturated acetone solution. Diethyl fumarate and diethyl maleat’e were run as neat. samples. Calibrations were performed by the usual side-band technique. RESULTS
AND
CALCULATIONS
The 13C spectra of eleven substituted vinyl compounds were obtained. The three long-range 13C-H couplings involving the vinyl prot,ons were determined for seven of these compounds. For the remaining cases only t’he long-range coupling to Cb was obtained. The spectra of the (Y carbon for these compounds could not be analyzed due to coupling between this carbon and protons in the substituent. The analyses of the spectra were carried out using LAOCN3 Q’S) on a Digital Equipment Corporation PDP-10, or LAME (24) on an RCA Spectra 70/46 computer. In some cases it was found that the 13C patterns were dependent on the differences between bhe proton shifts. Therefore the proton chemical shift)s used in the analysis of the 13C spectra were det)ermined on samples containing -15% acetone. In some cases adjustments were made in the proton shifts t,o account for the difference in operating temperatures between t,he Varian A-60A and the Bruker spectrometers. Values for vinyl chloride at - 20’ C were obtained from a previous temperature study (4). It was necessary to vary the proton chemical shifts in order to theoretically reproduce the spectrum of the carbonyl carbon of acrolein. Values chosen from the literat,ure at ~22’ C (5) were found to give a more satisfactory agreement between the calculated and observed frequencies than the values obtained in the present study at -38” C. In several cases it was found that different sets of parameters would predict the observed 13C patterns. To aid in select>ing the correct assignments and signs for t,he CCH couplings information from the 13C-H satellite spectra, additivity relationships, and correlations with other couplings were employed. The 13C spectra of divinyl ether and vinyl acetate are first order. Therefore 13C-H couplings has no effect on t~he prechanging the signs of the long-range
CKECELY,
254 dieted
patterns.
CRECELY,
AND
GOLIMTE:In’
However, by observing the inner ‘“C-H satellit’e spect,rum, ether was found to be positive. The analogous coupling in vinyl acetate was therefore assumed to be positive. In divinyl ether there are three long-range 13C-H couplings to t)he (Y carbon which vary in magnit,ude from 5.0 to 6.5 Hz. Due to the first-order nature of the a pattern it was impossible to assign these couplings to the proper protons or det,ermine their signs. The two long-range 13C-H couplings to the (Ycarbon in vinyl acetate were found to be of nearly the same magnit,ude. On the basis of known CCH couplings in vinyl compounds, we felt it, reasonable to assume that JCoH3 is negative and CJCaHZis positive. Unique analyses could not be obtained for the cr13C spectra of acrolein or acrylic acid even though these spectra are not first order. In bot,h cases eight’ set,s of long-range 13C-H couplings were determined which satisfactorily predicted the 13C spectra. Of these possibilities only one value for Jc,IX, in each compound fol was found tjo be negative. Since t,his coupling is negat,ive in a,11compounds which a unique analysis was obtained, it was assumed also l-o be negative in thrst: two cases. This assumption left two possible values for Jc,rrt in these compounds (1.5ij or -0.2 in acrylic acid and 1.X or -0.6 in acrolein). It has been rshowr~ ($0) that the CCH coupling constants in polysubstitut,ed bromo and chloru et)hylenes can be predicted t)o within 1 Hz of t#he observed value using additivita of substituent effects in the monosub&ituted compounds. Assuming addit,ivit,y is valid for other disubstit,uted ethylenes, only one of the two possible values fox predict, the CCH ,Jc~II~in acrylic acid (1.55 Hz) can be used to satisfactorily coupling in maleic acid. The value calculat,ed from additivitp (3.35 Hz) is in excellent agreement with the observed coupling (3.36 Hz). The long-range ‘“C-H coupling in fumaric acid is not available. However, the coupling vxlut* predictted from addit.ivit,y (- 2.75 Hz) agrees favorably with the value observed in the diet,hyl ester (-2.77 Hz). Of the two possible values for JCaHs in acrokill, we feel that,, based on t,he assignments in acrylic acid, the larger value is mortt reasonable. The signs of t(he couplings from the vinyl carbons t.o the aldehyde proton in acrolein (d,,, = 26.6, JcaH = 0.95) could not br determined. The carbon?1 pattern was analyzed utilizing differences between the long-range “(J-H couplings det,ermined previously from analysis of the ‘“C-H satellite spectra (8). Due to the near degeneracy of the prot,on chemical shift.s in vinyl trichlorosilane, the 13C-H satellite spectra were analyzed to determine t#hc proton--proton couplings constants. The following coupling psramekrs w(trr obtained: .I,, :; 14.26, Jn = 19.55, Jz = 2.03, J,,, = 152.2, .Jcx2 = 160.9, .JCHR = 159.9, :\11t1 J CCHa - JCCH, ,- 2 Hz. Using these values a unique tit, for the laCI spectra ~1s obtained for this compound. The long-range 13C-H coupling paramet,erx involving the elhylenic carborls are given in Table I and t,hose involving the carbonyl carbons are given in Table
J CBHlin divinyl
13C NMR
255
OF ETHYLENES TABLE
I
LONG-RANGEW2-H COUPLINGCONSTANTSSIN SUBSTITUTED ETHYLENES
H2 \
c
= c
/
1 \
H3 x
H1
X
Cc& 7.5 6.75 4.15 1.8 1.55 7.6 -2.5
Cl Br I COH COOH OAc Sic13
C&l
Cc& -7.9 -8.2 -7.8 -3.4 -4.55 -7.9 -0.8
6.9 6.25 4.0 0.25 -0.6 9.65 -6.85 -7.0 9.75 -0.35 -0.6
Si(GH& OCzHz COCH3 COOCH3 cis di COOH, cis di COOEt, tram di COOEt,
JCCA = 3.36 jcCH = 3.07 -2.77 CCH =
i’1’alues are in Hz. TABLE LONG-RANGE
II
13C-H COUPLING CONSTANTS* INVOLVING IN SUBSTITUTED ETHYLENES
THE CARBONYL
COH COOH cis di COOH
2.2 4.1 2.25
15.9 14.1 13.15
cis di COOEt
2.65
13.55
CARBON
10.1 7.6 -
* Values in Hz.
II. The values obtained in the present study for vinyl chloride and vinyl bromide are in agreement with those that have been reported previously (19, 20). The CCH couplings given here for diethyl maleate and diethyl fumarat,e are considerably different’ from those reported in a previous study (‘2.2). DISCUSSION
In t,he vinyl compounds the largest substituent which varies over a range of 17 Hz. A corresponding
effects are found for J,,,, , trend has also been observed
in monosubstituted et)hyl derivatives (25) (assuming ./eCH is negative) and in the five-membered heterocycles ($6, 27). In the latter compounds JCBH. varies from 6.3 t,o 14 HZ while .IVan,, varies from 6.3 to 7.3 Hz as the hrt,eroatom changes from carbon to oxygen. As has been pointed out previously- (20, 28), tllth substit,uent effects on these couplings can be rat,ionalized in terms of the I’ople :u~(l Bothner-Bv theory of geminal coupling constams (29 ). The substituent effects on ./ oa~lZand Jc,ao observed llert, arc of opposite s&t. Similar observations were noted in the subst>ituted cvclopropanes (JO), but I Ilk” substituent effect’s in t,hese compounds are considerably less pronounced than irk t,he vinyl derivatives. Using molecular orbital iheory, Gil and Formosinllo Simoes (31 ) speculale that, the substit,uent effects on .ICnIly and .I,,rl:i in vinyl compounds are of opposite sign. Their prediction that, .I ontr3 would clecrtuscb and of the subatituent incrrasec: i> J CaH3would increase as t.he electronegntivity contrary to t,he experiment,allp observed changes. ‘I%(~ model of ,Jamesori rin(.l Gutowsky (32) has been used t,o calculate geminal ‘“C---H coupling const:uitS ( SS) and is successful in explaining many of the observed trends. In the C:I,Wof the couplings to C, in the vinyl compounds t’he observed change in ,~~.,rFiri.4 correctly predicted. However, because of both positjive and negative contributions to the couplings, predictions could not be m:& concerning the subst,itucwt, effects on J,,,,:, . In previous studies of long-range ‘“C-H couplings, relationships 11ave btltbii investigated between C-H and H-H coupling constants (26, SO, ,~4-~3i’). ; ‘l‘lre long-range ‘Y-H couplings in aromat,ic compounds have been correlated witli geometrically similar H-H couplings (26, 3i’ ). In the subst itutrd cycloprop:u~e:: it, was found that correlations existed between J ccl1 and a linear combinatioir of the geminal H-H coupling and a vicinal H-H coupling (30 ). In t,he present study correlations have been investigated bet,ween the 101ig. range ‘“C-H couplings and both the geminal and vicinal H---H couplings in 111tb vinyl compounds. Although general trends :w observed betlveen JCC, :~n(d .J,cH , much better correlations are found between J,2C:H and the vicinal H- H couplings. There is an inverse croportionality betwtn Jo,,, and both the I./,< and t,he tram vicinal H-H couplings. A plot of JcBII, iis tlicl reciprocal of th(a :IV~‘I’ implies ;I age of these two H-H couplings is shown in Fig. 1. This correlation linear relationship bet,ween e1 CcHand clcctronegativity since it has been noted 1~~ Schaefer and Hutton t,hat t,he prot,onproton couplings in vinyl compounds art’ linearly related to t,he inverse of t,he substituent, elcct,ronegat,ivit,~ (&s ). Figures 2 and 4 show plots of each of t’he long-range C’-H couplings to (‘, IL\ the average of t,he vicinal H-H couplings. Since .I,:,,, was found to correlate inversely wit811.JHCCH, correlations between JonN and the reciprocal of ?I,,,,:, \vere also investigated. There was esseruiully no difference bt%ween the con&t ioil coefficient, obtained for eit’her case. Figure 4 shows a plot of ‘JCaHa z’s the directly bonded coupling ./CnWI ‘l‘llip
. I\;
l3C NMR
6.0
JW
257
OF ETHYLENES
\
.
.
-\;
-^IL_.___l
I J HCCH
1.0
0.6
FIG. 1. Jcgnl us l/Jnccn. (-3.67)
are included.
The CCH coupling values for ethylene (-2.4) H-H couplings are from Refs. (I-8,6-8, 10,17).
and acrylonitrile
8.0 I
-2.01----II.0
I8.0
J
HCCH
FIG. 2. JCYH~us ~HCCH.The CCH coupling values for et,hylene (-2.4) (0.29) are included. H-H couplings are from Refs. (2-4, 6-8, 17).
and acrylonitrile
correlation is considerably better than t,hat between Jcaaa and JHCCH, alt,hough much better correlations are found with t’he proton-proton for JGH%and JGJCBH1 couplings. Both t,he geminal and vicinal 13C-H couplings to the carbonyl carbon in acrolein and acrylic acid were found to be positive. As is observed for vicinal H-H couplings in vinyl compounds, the trans CCCH couplings are larger than the cis CCCH couplings, Karabatsos et al. (3.9) have noted that the dependence
CRECELY,
258
CRECELY,
AND GOLDSTEIN
0.0
. /
Jw
,r’,’
?? /
/’
.
3
I
- 6.0
I
I
IO.
I 7.
J
HCCH
Fra. 3. .Jcan3 2’sJn,,,,n. The CCH coupling values for ethylene (-2.4) -4.42) are included. I3-H couplings are from Xefs. (&SP 6-8, f7).
\
and acrylouitrilr~
‘\\
- 8.0 -
FIG. 4. Jca~I vs. Jc~FI~.
(-4.42)
are included.
of CCCH couplings vicinal proton-proton
The CCH coupling values for ethylene (-2.4) and acrylonitrilr Directly bonded *3C-H couplings are from Refs. (6’~9, I7j.
in sp” compounds couplings.
on dihedral
angle
is similar
to tbat
of
ACKNOWLEDGMEST The authors are grateful RCA Spectra 70/46. RECEIVED:
to the Emory University
(‘ompufer
(lenter
for the use of the
July 22, 1970 REFERENCES
1. 2. 8. 4, 5.
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