The 13C n.m.r. spectra of a wide variety of flavonoids and related compounds and vanillin isomers are reported. Particular attention is directed towards features of the spectra which are most useful for structure elucidation, and the principle of additivity of substituent effects in such systems is critically examined. It is shown that the acetylation of phenolic hydroxy-group can be used to identify the positions of the hydroxy-groups on an aromatic ring, a technique which is particularly useful when both hydroxy- and methoxy-groups are present.
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Pelter et al. (1976) studied this question.