13C nuclear magnetic resonance spectra of some bromo- and methyl-substituted cyclohexa-2,5-dienones

Abstract

The ¹³C n.m.r. spectra of cyclohexa-2,5-dienones produced by bromination or nitration of a variety of methyl-substituted phenols are reported. Most of the signals have been assigned with the assistance of selective decoupling. Correlations of chemical shifts resulting from replacement of hydrogen by methyl and by bromine in the positions originally ortho and meta to the hydroxy group have been attempted. The effects resulting from changing the substituents at the 4-position from Br, Br to Me, Br to Me, NO₂, and to Me, OH have also been analysed. Comparison is made with effects found in related systems. Single-resonance spectra have been used to determine coupling constants {J(¹H, ¹³C)}, and these also are compared with cognate results.