Benzopyrones. Part 18. Carbon-13 nuclear magnetic resonance spectroscopy of chromones

Abstract

The carbon n.m.r. spectra of 29 substituted chromones have been measured and assigned. The data for these and 10 other chromone derivatives show that the chemical shifts of the six benzenoid carbon nuclei are affected to a relatively small extent (<±2 p.p.m.) by changes in the substituents on the pyrone ring. Similarly the pyrone ring carbons (C-2, C-3, and C-4) are relatively insensitive to changes in substituents at C-6 and C-7 of the benzene ring. Carbon n.m.r. data can be used to identify isomeric chromone derivatives which are otherwise difficult to differentiate.