Ring–chain tautomerism. Part 7. Substituted benzil-2-carboxylic and 2-phenylacetylbenzoic acids and their methyl esters

Abstract

The equilibrium constants. K_e, for ring–chain tautomerism in a series of substituted benzil-2-carboxylic and 2-phenylacetylbenzoic acids, as well as for the methyl esters of the latter series, have been determined by IR and NMR spectroscopic methods. 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 effects of substitution on both log K_e and pK_a, values have been assessed by means of the Hammett equation. The results are discussed.