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

The equilibrium constants. Ke, 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 pKa 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 pKa(pKaT). The effects of substitution on both log Ke and pKa, values have been assessed by means of the Hammett equation. The results are discussed.