Equilibrium acidities of carbon acids

Abstract

A scale of absolute equilibrium acidities for organic acids in dimethyl sulfoxide solution is presented, and these acidities are compared with: (a) apparent acidities in solvents of low dielectric constant, (b) absolute acidities in water, and (c) relative acidities in the gas phase. In dimethyl sulfoxide the carbon acid acetophenone is weaker than its oxygen analog, benzoic acid, by almost fourteen orders of magnitude, but the Hammett p for acetophenones is only one order of magnitude greater than for benzoic acids. This shows that large changes in the stabilities of ions in side chains may be accompanied by relatively small changes in p, and that the success of the Hammett equation rests, in part, on its relative insensitivity to energy changes. © 1977, Walter de Gruyter. All rights reserved.