Quantum Chemical Studies on the Double Proton Transfer in Benzoic and o-Chlorobenzoic Acid Dimers

The double proton transfer process has been studied for the benzoic (BAC) and o-chlorobenzoic acid (o-Cl-BAC) dimers in the gaseous state and for crystalline form at the non-empirical level. The correlation energy corrections have been taken into account at the MP2 level and zero-point energy as well as crystal field effects were considered. The results of calculations enable a reasonable interpretation of low potential barriers observed by NMR for some molecular crystals involving carboxylic dimers. The role of substituents and a possible mechanism of the double proton transfer are considered.