AN AB-INITIO MC-SCF STUDY OF THE SOLVENT EFFECTS IN POLAR AND NONPOLAR [2+2]-CYCLOADDITIONS

Solvent effects in non-polar and polar [2 + 2] cycloadditions are examined with MC-SCF methods, using the dimerization of ethylene as a prototype of non-polar cycloaddition and the reaction between dicyanoethylene and hydroxyethylene as a prototype of polar cycloaddition, The effect of the solvent has been included via the continuum model of Rivail. Solvent effects stabilize the gauche transition state relative to the anti transition state in the two-step mechanism. The concerted transition state remains very high in energy, even when solvent effects are considered.