LONG-RANGE SIGMA-INDUCTIVE INTERACTIONS THROUGH SATURATED C-C BONDS IN POLYMETHYLENE CHAINS

Analysis of the NMR shifts of unsaturated carbon in monounsaturated li near long-chain esters, alcohols and acids, including data from jojoba oil; shows a highly linear dependence of the logarithm of the shift s eparation in the C=C bond upon the number of bonds separating this fro m the ester moiety. Both the linearity of this dependence, and the obs ervation that it does not change sign upon reversal of the ester group ing, rule but the 'electric field effect' as an explanation, but are s emi-quantitatively consistent with a remarkably simple, 'sigma-inducti ve' through-bond mechanism. Semi-empirical MO calculations' support th is conclusion. The attenuation factor is 1.75 per saturated C-C bond i n each class of compound, although the actual shift separations, for a given chain length, vary up to twofold with changes in the polarizing group and with; (Z)-(E) isomerism at the C=C bond. Other series of co mpounds show the same attenuation factor.