Caveat Regarding the Use of Substituent Parameters in Statistical Analyses of Molecular Properties. I. The Interdependence of Field, Resonance, Electronegativity and Polarizability Effects

Abstract

lt is shown that several frequently employed electronegativity ( α₁₎, field ( σF) and resonance ( σR) parameters are substantially interdependent for most of the commonly used substituents. Substituents are shown to belong to two categories, In which the first atom of the group is a first row (FR) or non-first row (NFR) atom, The degree, of interdependence of the three parameters increases markedly when the two substituent types are treated separately, although it is found that, for NFR groups, σ_F and σ_x alone are highly correlated, in contrast to FR groups, where σR contributes significantly to the interdependence equations. The disparate behaviour of FR and NFR substituent types is partly reconciled by the inclusion of a polarizability parameter (σ_x). Evidence is presented which indicates that σ_F is the parameter which is constitutionally dependent on the other three, although the dependence seems not to be completely causative, but partially fortuitous. Implications for the quantitative analysis of molecular processes at positions close to the substituent where electronegativity and polarizability effects are believed to operate, are discussed.