Tracking molecular charge distribution along reaction paths with atomic multipole moments

Abstract

We explore the idea of supplementing partial atomic charges with cumulative multipole moments for modeling electrostatic effects during chemical reactions. To this end, we investigate the first stage of alkaline hydrolysis of O,O-dimethyl phosphorofluoridate and show how changes in atomic moments provide a more detailed description of charge redistribution during the reaction than is possible using charges alone. Furthermore, the electrostatic potential on the solvent-excluded surface for this reaction roughly converges at the quadrupolar level, with a root-mean-square deviation of ~1 kcal/mol compared to the ab initio Hartree-Fock expectation value. We arrive at similar conclusions for four other reactions, namely the alkaline hydrolysis of demeton-S and phosalone, carbon dioxide hydration, and hydrogen cyanide isomerization. Employing multipole moments on atoms therefore appears to be a feasible and compact way to derive catalytic fields defining the optimal catalytic environment for chemical reactions.