J13C—H coupling constants in monosubstituted ethylenes

J13C—H coupling constants in monosubstituted ethylenes

f3pectrochimicaActa,Vol. 26A,pp.663to 658.Pergamon PreaslQ69. PrintedinNorthem Ireland JIQ_= coupling constants in monosubstituted ethylenes L. LUNU...

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f3pectrochimicaActa,Vol. 26A,pp.663to 658.Pergamon PreaslQ69.

PrintedinNorthem Ireland

JIQ_= coupling constants in monosubstituted ethylenes L. LUNUZI and F. TADDEI Instituto di Chimica Organica e Chimica Industriale, Centro di Spettroscopie Molecolare de1 C.N.R., Universita’ di Bologna, Vi&, Risorgimento, 4-(40136) Bologna, Italy (Remiced 26 June 1968) Abstract-Coupling constants Jla+n in monosubstituted ethylenes containing as ilrst atom of the substituent group 0, S, C and N in divinyl ether, divinyl sulphide, methyl vinyl ketone and N vinyl 2-pyrrolidone were measured. The constants were found to be linearly correlatedwith those of the correspondingmonosubstituted methanes. Empirical expressionsare given which reproduce l*C-H spin-spin couplings for saturated and ethyl&c systems as a function of substituent electronegativity and C-substituent bond length. spin-spin coupling constants in hydrocarbons seem to be correlated with carbon hybridization. For saturated, ethylenic and acetylenic hydrocarbons the values of this constant are 120, 170 and 248 c/s respectively, which parallel the increase of s-character of the carbon hybrid orbital which enter into the description of the C-H bond [l]. On the other hand a quantitative rationalization of the changes in JlsCH of hydrocarbons due to substitution has yet to be achieved. In mono- and polysubstituted methanes changes in 13C-protoncoupling constants were attributed by several authors [2, 31 to changes of s-character in the hybrid carbon atom participating to the C-H bond caused by substituents. The inadequacy of this interpretation has been recently discussed [4-73. In monosubstituted methanes, CH,X, empirical correlations were proposed between JIaCH and both subst’t I uent electronegativity and the C-X bond distance [4, 73. This type of correlation not involving explicitly hybridization at the carbon atom was subsequently extended to polysubstituted methanes [S], for which very large changes in these constants are observed. Only a few experimental results are at the present available for ethylenio compounds [9-l 11.

W~R~T~N

[I] J. N. SHOOLERY, J. Chem. Phys. 31, 1427 (1969). [2] N. M~LER and D. E. PBITcm, J. Chem. Phya. 81, 768, 1471 (1959). [3] C. Julw, H. S. GUTOWSKY, J. Chmn. Phye. 37, 2198 (1902). [4] N. DEEESKAMIP~I-I~E.SACEI+UN, 2. Phyeik. Chma. 84, 273 (1962). [5] J. KAUBATSOS and C. E. ORZEUH JR.,J. Am. Chern.800.88, 3574 (1964). [6] D. M. GRBNTand W. M. LITCEYAN, J. Am. Chem. Sot. 87, 3994 (1966). [7] L. LUNAZZI and F. TADDEI, BoU. Sci. Fat. ChGm.Ied. Bologna %, 359 (1965). [S] L. Lu~Azzr and F. T~DDEI, Speotroohh.A&o HA, 841 (1967). [Q] D. M. G~AEAMand C. E. HAT,LOWAY, Can. J. Chmn.41, 2114 (1963). [IO] R. E. MAYO and J. H. GOLDSTEIN, J. Mol. Spctry 14, 173 (1964). [ll] R. T. HOB~OOD JR.,R. E. MAYO and J. H. GOLDSTEIN, J. Ohem. Phya. 89,2601

663

(1963).

664

L.

LUNUZIand F. T~DDEI

The purpose of the present investigation was to measure Y!-proton spin-spin coupling constants for a set of monosubstituted ethylenic compounds CH,=CHX, where X contains as fist atom 0, S, C and N, and from these data and those of other derivatives found in literature [9-l l] we intend to test the existence of a correlation similar to those [7] previously found for saturated compounds.

RESULTSAND DISCUSSION The proton magnetic resonance spectra of N vinyl 2-pyrrolidone, divinyl ether, X

H(3) \

P)H

C=C

/

/ \

H(2)

(I) methyl vinyl ketone and divinyl sulphide were recorded and analyzed with particular attention to the 13Csatellite bands of vinylic protons. Both low and high field side bands of each vinylic proton were not always observed, because of overlapping with the main proton spectrum. In Figs. l-3 spectral contour and assignment of W

I--

500

400

303 C/S

Fig. 1. ‘*C satellite spectrum of N vinyl 2-pymolidone.

satellites are shown for N vinyl 2-pyrrolidone, methyl vinyl ketone and divinyl ether respectively. The spectrum of divinyl sulphide is similar to that of the latter derivative. Only in the case of methyl vinyl ketone the complete laC satellite spectrum was observed. J 18~~ coupling constants for the other compounds were obtained by analysing the ABC group of the main protonic spectrum and the AK Y sets of satellite bands. The values obtained are reported in Table 1 together with the J H-H constants derived both from the main protonic spectrum and W satellites. The latter constants were used to test the correctness of the assignments.

Jq_u

450

coupling oonstants in monosubstituted ethylenes

665

400

Ch

Fig. 2. ‘*C satellite spectrum of methyl vinyl ketone at higher (a) and lower (b) field relatively to the main protonic spectrum.

400

3co

200

C/S

Fig. 3. “C satellite spwtrmn of divinyl ether.

In order to analyse changes in J IICH of vinyl derivatives caused by substitution coupliug constants relative to proton l(J~~u(~) were considered. Those relative to protons 2 and 3 are very little affected. The Jc18_= coupling constants in vinyl derivatives show a substituent dependence similar to that of derivatives CH,X, as shown in Fig. 4. The experimental values employed in this correlation are those reported in the first and last column of Table 2. The mean value of the ratio JlllDH(vinyl)/J IsoH(methyl) is l-28, approximately only

4

L. LTJNAZZI and F. TADDEI

556

Table 1. J~SC_H and JH__H in c/s of some monosubstituted vinyl derivatives derived from the satellite bands and main protonic spectrum. Estimated error for J13n~ constants is &h/s From main protonio spectrum*

From *‘C satellite bands Compound

J130-H(l) Jl3c-ma,

J~3c-Iicsl

J,_,

J,_,

Ja-3

Jl-3

J,s

J3-3

Divinyl ether

182

166

169

6.4

14.1

1.9,

6.1,

13.7,

1.7,

Divinyl sulphide

171

163

169

9.8,

16.8,

0

9.7,

16.4,

0.2,

N vinyl 2-pyrrolidone

172

162

164

8.9

16.8

0

9.00

16.0,

0.0,

Methyl vinyl ketone

162

161

169

10.7,

17.6

1-O

Tetravinyltin$

167

160

162

13.1

19.9

3.2

10.8,

IS-O,

(10.66)

(17.66)

13.9 (13.78)

* The relative sign of these constants wan not determined. Probable error fO.2

0.7, (O-96)t

20.9

3.4

(20.69)

(3.14s

o/s.

c0

Jp_,hhyl),

ds

Fig. 4. Correlation between JI~C_H in CHIX derivatives and JIS~H(~) monosubstituted ethylenes.

in

the same of the ratio of s-percentage in q&Jand q? hybrids at carbon (1.33). It is however slightly dependent on substituent electronegativity. This can be seen for silicon and fluorine, elements in the opposite side of electronegativity scale, where 1121 N. VANMEURS, Rec. Trav.Chim. 86, 1166 (1966). [13] L. LUNAZZI and F. TADDEI, Spectrochim. Acta %A, 611 (1969). [14] D. J. BLEARS, S. S. DANYLKJCK and S. CAWLEY, J. OrgawmetaZ. Chem. 6, 284 (1966).

coupling

Jq.._~

ethylenes

const8ntsin mon~u~titu~

657

Table 2. Comparisonbetweenexperimenhland csloulstedJI~c__H(~) for monosubstituted ethylenes.In the I& colnmn8f~ given the coupling con&a&~ of the corresponding rnon~b~itu~ methanes

Jw---a @PI

X

15&2(Q) 162 182 171 172 2~.2~10~ 194*9(10) 196+(10) lQO.Q(lO) 140*3(H) 157

E co 0 ET F CI Br I Si So.

Jlq_...~(care.)* 167.1 156.3 182.4 174.4 166*3 200.0 194.2 194.9 192-l 147.1 -

A

J%-E

40.9 -5.7 -j-o*4 -+3-P -&? -0.2 --0.7 -1.7 $1.2 j-7.0 -

125(15) 126(3) 140(7) 138(7) 132(7) I49(2) 160(7) 152(7) 151(7) llQ(l6) 128(16)

* From equation(2).

the ratios are 1.18 and l-38 respectively. The dependence of [Jla~,(vinyl)J/ [Jlro_,(methyl)] on substituent electronegativity can be expressed by means of equation ( 1). Jlsc_u(v;nyl)lJlsc_a(methyl) = [email protected], + 1.13, (11 where Ex is the substituent ele~~o~eg&tivity in the ~~~ken’s s&e [17]. Thus it seems that the substituent affects in &slightly different way JlsCH in the two se&s of substituted hydrocarbons. The ratio of s-percentage in spa rtnd ~9 hybrids (1.33) can be introduced in equation (1) yielding: J’w--HmY~)

= %[email protected]!? y&p)

[0*0123Bx + 0*854~~~~n(methyl)

Coupling constants o&uIauted for monosubstituted ethyl&c derivatives by means of equ&tion (2) are reported in the second column of Table 2. The low deviations A between c&&&ed md experimental vahms of coupling constants for vinyl derivatives show the empirical vaJidity of equation (2), taking in account that the experimental error is of the order of 2 c/s and that coupling constants relative to derivatives containing the Iess and the most electronegative heteroatom differ by 60 c/s. Since it W&Epreviously reported that J ls,u(methyl) correlate well with substituent ele~~~eg&tivity [7f rendC-X bond distance (d), & unified expression aan be written which reproduces empiriclalIy J 18~~ in monosubstituted methanes and ethylenes.

J %L-H

s= g6

[0*0123& $ 0*854]N(3.25dE,

+ 94.90)

[lb] L. W. ~Elm?liX3, J. C&em. f%.ys.&b, 2128 (1964). [lS] R. &mBECKE and W. G. Sc=mn El%, J. them. P&8. [email protected], 722 (1961). KINNER, C%en&. Rev. 56, 745(1956). [17] H. 0. mnsndH.A.S

658

L. LUXWXIand F. TADDEI

The exponent iV is zero and one for saturated and ethylenic derivatives respectively. The validity of this expression can be checked by the comparison of experimental data made previously for monosubstituted methanes [7] and in the present work for ethylenic derivatives. EXPEEIMENTU The compounds investigated were prepared by standard methods [l&20] while N vinyl 2 pyrrolidone, a commercial product, was purified by Gas Chromatography. PMR spectra were recorded on the neat samples with a Varian DP 60 spectrometer operating at 56.4 MC/S. Both the main protonic spectrum and the satellite bands were calibrated by the “side band” technique with respect to T.M.S. added as an internal standard. [18] L. BRANDSMAand J. F. ARENS, Rec. Trav. Ch&-n. 81, 33 (1962). [19] L. BRANDSMAand J. F. ARENS, Rec. Traw. Chim. 80, 237 (1961). [20] A. WOHL and A. PRILL, Ann. MO, 123 (1924).