Substituent effects on the chemical shift of the hydroxy-proton of 2,6-dimethylphenols and 1-naphthols in dimethyl sulphoxide

Abstract

The chemical shifts of the hydroxy-proton of 2,6-dimethylphenol and ten 4-substituted 2,6-dimethylphenols and of 1-naphthol and nine 4-substituted 1-naphthols have been measured for dimethyl sulphoxide solutions. Analysis of published data on the chemical shifts of phenols in dimethyl sulphoxide reveals that +M as well as –M 4-substituents exhibit enhanced resonance effects. Substituent effects in 2,6-dimethylphenols and in 1-naphthols parallel these effects in phenols. The Hammett ρ values for the three series are –1·49, –1·43, and –1·55 respectively. In naphthols –M 4-substituents do not exhibit enhanced resonance effects over and above those observed in the correspondingly substituted phenols.