Theoretical analysis of the role of the solvent on the reaction mechanisms: One-step versus two-step ketene–imine cycloaddition

The effect of correlation energy, basis set size, zero-point energy (ZPE) correction, and solvation on the reaction mechanism of the ketene–imine cycloaddition reaction has been investigated. The electrostatic solvent effect was studied with a self-consistent reaction field method in which the solvation energy is obtained using a multipole expansion of the molecular charge distribution. The ab initio results have been analyzed by means of a theoretical method based on the expansion of the MOs of the supermolecule in terms of those of the reactants and the performance of the configuration analysis. In gas phase, due to the correlation energy and/or the ZPE corrections, the reaction is predicted to be a one-step process. In solution, the stabilization of the charge-transferred configurations results in the occurrence of a very stable, Zwitterionic intermediate giving a two-step mechanism. © 1994 by John Wiley & Sons, Inc.