Relationship between the electronic chemical potential and proton transfer barriers

Gas phase proton transfer (PT) reactions in an isoelectronic series of neutral, positively and negatively charged hydrogen-bonded systems are analyzed using density functional theory calculations. Based on an equation of state relating the difference in proton affinity of the Brِnsted bases involved, the ground state energy difference between the two H-bonded complexes and the corresponding dissociation energies, a general criterion for determining the intermolecular PT distance is discussed. The electronic chemical potential of transfer is introduced to account for the charge transfer during the PT reaction. Correlations between this new reactivity index and PT barriers are observed. Proton affinity differences appear as the driving force determining the PT energy barriers in the systems studied.