THEORETICAL-ANALYSIS OF THE ROLE OF THE SOLVENT ON THE REACTION-MECHANISMS - ONE-STEP VERSUS 2-STEP KETENE-IMINE CYCLOADDITION

The effect of correlation energy, basis set size, zero-point energy (Z PE) 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 metho d in which the solvation energy is obtained using a multipole expansio n of the molecular charge distribution. The ab initio results have bee n 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 th e performance of the configuration analysis. In gas phase, due to the correlation energy and/or the ZPE corrections, the reaction is predict ed to be a one-step process. In solution, the stabilization of the cha rge-transferred configurations results in the occurrence of a very sta ble, Zwitterionic intermediate giving a two-step mechanism. (C) 1994 b y John Wiley & Sons, Inc.