Medium effects on the ionization of the acidic sites of bifunctional organic molecules: the case of 4-hydroxybenzoic acid

A theoretical ab initio and DFT study on the ionization of the acidic sites of 4-hydroxybenzoic acid, in the gas phase and in aqueous solution, has be en carried out. In aqueous solution, the studied compound behaves as a benz oic acid, the deprotonation occurring in the carboxylic group, while in the gas phase, deprotonation takes place in the phenolic group, i.e. the studi ed compound behaves as a phenol in the gas phase. (C) 2000 Elsevier Science B.V. All rights reserved.