Correlations between molecular electrostatic potentials and some experimentally-based indices of reactivity

Abstract

The key role that electrostatics plays in molecular reactive behavior is demonstrated in this work, which surveys and further explores correlations that we found between the molecular electrostatic potential V(r) calculated by an ab initio SCF-MO approach (a gas-phase property) and experimentally-based indices of reactivity (derived from solution studies). In our relationships involving negative V(r), we find in all cases that spatial minima ( V min) provide correlations of higher quality than surface minima ( V S, min ). Relationships between V min and the hydrogenbond-acceptor parameter β, and V S,max and the hydrogen-bond-donor parameter α, confirm the physical validity of the empirically-derived solvatochromic parameters α and β. Correlations between the V min of NH 2-X molecules and the substituent constants σ I, and σ I + σ R (when σ R>0) for the substituents X show how electrostatic properties reflect the electron-attracting tendencies of substituent groups. Whereas good relationships exist between the p K a, values of some limited groups of molecules and their conjugate base V min, we find that the average local ionization energy Ī(r) is better suited as a general measure of aqueous acidity.