Calculation on pK_a Values of Carboxylic Acids in Aqueous Solution Using Relative Gibbs Free Energy

The 97 pKa values of 86 carboxylic acids in aqueous solution were calculated with density functional theory method at the level of B3LYP/6-31+G(d,p) and the polarizable continuum model(PCM) was used to describe the solvent.The pKa values were directly calculated employing the relative Gibbs free energies of the carboxylic acid dissociations in aqueous solution.In this way we obtained an approach in which pKa values of carboxylic acids in aqueous solution can be predicted with the standard deviation of 0.36 in pKa unit.