OVB analysis of symmetry allowed and symmetry forbidden chemical reactions

Abstract

When orthogonal orbitals are used to construct configuration state functions (CSF) the latter are orthogonal to each other. Such CSFs are either neutral or ionic, they never change their character along a reaction path. This is in contrast to conventional Valence Bond CSFs based on non-orthogonal orbitals. When orthogonal, delocalized molecular orbitals from CASSCF (complete active space SCF) calculations are localized to defined fragments using orthogonal transformations, the localized fragment orbitals retain their orthogonality, and the CASSCF configuration state functions constructed are of Valence Bond type describing the same state but in terms of orthogonal fragment orbitals. This analysis of the CASSCF state function reveals local properties and processes that are hidden by the use of delocalized orbitals but that are responsible for symmetry forbiddenness or symmetry allowedness of chemical reactions.