Аннотация:Data on acid–base equilibria in different media and in the gas phase have been analysed. Methods for determining the protonation centre in a gas have been discussed. The change in the electronic effects of substituents on going from the gas phase to solution have been examined. The relationships between the strength of ionic hydrogen bonds and the acid–base properties of compounds in the gas phase have been demonstrated, and the results obtained by modelling solvation effects in the gas phase have been examined. New data on the structure and stability of molecular H-complexes in the gas phase and on the increase in the strength of the H-bond on solvation are presented. The bibliography contains 130 references.