Pearson's hard–soft acid–base principle and the heterolytic dissociative version of Pauling's bond-energy equation

Abstract

A correspondence between the γ parameter recently developed, which characterises the binding site of an ion, and Klopman's frontier-orbital energy has been established to show that γ does represent the hardness of an ion. It is shown that γ can be used to describe the polarity of an A–B bond where A is an acid and B a base. Also that Pearson's hard–soft acid–base principle means that acids and bases interact selectively in an exchange reaction of the type AB + CD ⇄ AC + BD so as to form bonds of similar, to the extent possible, polarity between themselves.