Correlation of aqueous pKa values of carbon acids with theoretical descriptors:: A DFT study

Theoretical calculations are carried out to predict gas- and aqueous-phase acidities of a series of 21 carbon acids with pK(a) values varying from -6.20 to 50. Acceptable linear correlations (R-2 > 0.93, SD < 4) are obtained between calculated deprotonation Gibbs free energy changes and experimental pK(a) values (measured in water). Solvent effects are taken into account by means of the polarizable continuum model (PCM). Our calculations also show that the high acidity of alpha-proton carbonyl compounds and electron-withdrawing substituted methanes can be related to the strong increase in the vicinal charge interactions n(c) ->-pi(*) in anion species. Calculations are perfomed at the B3LYP/6-311++G(d,p) level of theory. (c) 2007 Elsevier B.V. All rights reserved.