CORRELATIONS BETWEEN MOLECULAR ELECTROSTATIC POTENTIALS AND SOME EXPERIMENTALLY-BASED INDEXES OF REACTIVITY

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 hydrogen-bond-acceptor parameter-beta, and V(S,max) and the hydrogen-bond-donor parameter-alpha, confirm the physical validity of the empirically-derived solvatochromic parameters-alpha and beta. Correlations between the V(min) of NH2-X molecules and the substituent constants sigma(I), and sigma(I) + sigma(R) (when sigma(R) > 0) for the substituents X show how electrostatic properties reflect the electron-attracting tendencies of substituent groups. Whereas good relationships exist between the pK(a) values of some limited groups of molecules and their conjugate base V(min), we find that the average local ionization energy IBAR-(r) is better suited as a general measure of aqueous acidity.