A test of electrostatic and reaction-field theories: equilibria in isodesmic reactions of some chlorobenzenes

Abstract

The enthalpy of solvation of chlorobenzene and 1,2-, 1,3-, and 1,4-dichlorobenzene has been measured in two solvents of different polarity. The results have allowed us to construct several isodesmic reactions and to evaluate their reaction enthalpies in solution. These values agree at least semiquantitatively with the reaction-field theory but the results are very sensitive to the choice of parameter and modification of the basic equations. It follows that the success of the reaction-field theory has been essentially fortuitous and almost every experimental finding can be reproduced by choosing a suitable modification from a number of those recommended in the literature. The alternative electrostatic calculation (the ‘Kirkwood–Westheimer’ model) yields still worse results and cannot be extended outside ionic equilibria.