Theoretical study of carboxylic acids with explicit water molecules

Formic, acetic. trichloroacetic, benzoic and salicylic acids were studied with density functional theory in the explicit presence of six or seven water molecules. comparing the relative energies of the solvated acid and dissociated forms. Six water molecules are found to be sufficient to stabilize the dissociated ion pair of these weak acids at the B3LYP/6-31 + +G** level of theory. The H13O6+ ion appears as a common (six water molecule) structural unit for the dissociated carboxylic acids as studied here. The relative energy differences between the non-dissociated and dissociated clusters for each acid are in accordance with pK(a) data. (c) 2006 Elsevier B.V. All rights reserved.