A semiempirical model for the description of solvent effects on chemical reactions

Abstract

An attempt is made to provide a more rigorous basis for the desc~ipon of solvent effects on chemical reactions by taking into accouht the various free energy contributions involved in the transfer of a substrate from the gas to the solution phase. It is shown that the solvent influence on various chemical and physical processes can be represented in a semiquantitative or even quantitative way by means of three parameters, namely the socalled acceptor number, which represents a measure of the electrophilic or acceptor properties of the solvent, the donor number, which represents a measure of the nucleophilic or donor properties of the solvent and the standard free enerj!y of vaporization of the solvent which is related to the free eneri!Y required to create holes in the solvent in which the substrates can be accomodated. Protic solvents usually do not obey the relationships obtained for aprotic media and this appears to be due to the varying basicity of the substrates under consideration.