Carbon‐13 NMR studies of olefins having nitrile and methoxycarbonyl substituents. Additivity relationships

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Abstract
Carbon‐13 NMR chemical shifts are reported for a series of seventeen olefins with tetra‐, tri‐, di‐ and mono‐substitution by nitrile and methoxycarbonyl groups. Analyses of the data for the nitrile, methoxy and carbonyl chemical shifts by multiple linear regression provide a good correlation with the pattern of geminal, cisoid and transoid substitution. The olefinic shielding data are more complicated, and the analysis requires the introduction of pairwise additivity parameters. It scems likely that the greater complexity arises from steric effects associated with cisoid and geminal methoxycarbonyl substituents, which produce deviations from planarity. The empirical relationships, which are reported here, are useful in removing several ambiguities in the spectral assignments. In this series of compounds it is also observed that substituents which are cis to the nitrile, shift the nitrile resonance 1–2 ppm to high field of those for the trans substituents.

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