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

Abstract

The ' 3C 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 t o 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,NO,, and to Me,OH have also been analysed. Comparison is made with effects found in related systems. Singleresonance spectra have been used to determine coupling constants {J(' H,13C)}, and these also are compared with cognate results.Phenols very commonly react with electrophiles to give cyclohexa-2,5-dien-1 -ones [equation (l)], which if suitably substituted are often isolable as crystalline compounds. The literature relating to such reactions, to which Zincke' and Auwers made extensive preparative contributions, has been revie wed. 3-' the 3C n.m.r. spectra of some substituted 6-bromo4methylcyclohexa-2,Sdienones