Abstract
Published data on the acid–base properties of organic substances in the gaseous phase have been reviewed. The proton affinity (PA) of bases is taken as the enthalpy of the gaseous reaction M + H+ → MH+, with the opposite sign, and the basic strength of the bases (GB) is taken as the change in the standard free energy of this reaction (again with opposite sign). Correspondingly, the acidity in the gaseous phase is taken to be the enthalpy of the reaction AH → A− + H+ or the change in the standard free energy of this reaction. The dependence of the acid strength and base strength in the gaseous phase on the structures of the molecules of the acids and bases has been examined, and the lack of agreement between the observed facts and the classical electronic interpretation based on the inductive and mesomeric effects of the groups has been discussed. Attention has been drawn to the change in the acid–base properties of organic molecules on going from the gaseous to the liquid phase, and the energetic effects of the solvation of the molecules and ions have been examined. The bibliography contains 78 references.