Natural reaction orbitals

Natural reaction orbital (NRO) for analyzing chemical reactions from the viewpoint of the electronic theory is presented. The pair of the occupied and virtual NROs that drives chemical reaction are automatically extracted from the solutions of the coupled-perturbed self-consistent-field (CPSCF) equation for the perturbation of the nuclear displacement along the reaction path. Applying the NRO-based reaction analysis method to the H2CO– + H3CCl reaction, it was found that the sum of squared singular values of the solutions of the CPSCF equation gives the maximum peak at the transition state structure and the shoulder of the potential energy curve, which clearly explains the process of electron transfer and bond formation in this reaction. The NRO-based reaction analysis method has been demonstrated to be universal and robust for describing sophisticated reaction mechanisms.