s et al., 1976, 1977; Gunstone et al., 1977) have quantified the effects of the double bonds. Average values are included in Table 1, which also indicates the effect of other functional groups. The largest difference is apparent at the a α position (allylic groups) with a very large difference between cis and trans isomers. The changes at the γ position, though smaller, are also useful and despite the very small difference between cis and trans isomers shown here, it has been exploited in the distinction between Δ12c and Δ12t octadecenoates in hydrogenated oil (Gunstone et al., 1977; Mazzola et al., 1997; Miyake, et al., 1998).
Knothe and Bagby (1995) report that the chemical shifts of unsaturated carbon atoms are proportional or inversely proportional to the 1st, 2nd, 3rd, and 4th powers of the position of unsaturation. They depend on other functional groups in the molecule and on the nature of the unsaturation. Bianchi et al. (1995) and Howarth et al. (1995) argue for the importance of through-bond rather than through-space interactions.
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