If the molecule is, however, photoexcited via a single electron HOMO-LUMO transition (light blue arrow in Fig. ), the resulting ππ * Slater determinant in the reactant, again, correlates with a corresponding ππ * Slater determinant in the product. It is, therefore, regarded as energetically feasible in the excited state, i.e., photochemically "allowed." More generally, the conrotatory pathway is thermally allowed and photochemically forbidden, and the disrotatory pathway is thermally forbidden and photochemically allowed in molecules with 4n electrons in the molecular orbitals involved in the reaction. The pattern inverts for molecules with 4n + 2 electrons in the involved orbitals.