Solvent effects on relative acidities for a series of substituted organic acids

Plots of relative acidities for a series of substituted benzoic acids as well as substituted phenols Delta pK(a) = pK(a)(unsubst) - pk(a)(subst) in a number of solvents against Delta pK(a) in the gas phase give for both series two linear sections, separately for electron withdrawing and releasing substituents (relatively to hydrogen in the unsubstituted acid). For benzoic acids slopes of the correlation lines for releasing substituents in all solvents and for the withdrawing substituents in protic solvents decrease with the solvent Lewis acidity indicating a dominant role of the anion solvation.