An MO-theoretical Interpretation of the Nature of Chemical Reactions. I. Partitioning Analysis of the Interaction Energy

The molecular interaction energy, without considering the nuclear configuration change, is discussed by partitioning it into the Coulomb, exchange, delocalization, and polarization terms. A succinct approximate expression for each term is derived, and its magnitude is discussed. The expressions obtained as the second-order perturbation terms for the delocalization and the polarization energies are in accord with those of the well-established reactivity indices, the delocalizability, and the self-atom polarizability respectively. The chemical reactivity can thus be measured by the combined sum of these four terms. In usual ionic reactions the Coulomb and the delocalization terms are more important than the exchange and the polarization terms respectively.