Ring–chain tautomerism. Part I. 2-Acyl- and 2-aroyl-benzoic acids

Abstract

The equilibrium constants for ring–chain tautomerism in a series of 2-acyl- and 2-aroyl-benzoic acids have been determined by an i.r. method (for solutions in dioxan) and by a ¹H n.m.r. method (for solutions in dioxan, methanol, and 80% 2-methoxyethanol–water). The observed pK_a values, which have been measured for solutions in 80% w/w 2-methoxyethanol–water, have been corrected for the tautomeric equilibria to give the true pK_a(pK_a^T). The results are related to the polar, resonance, and steric effects of the substituents.