SCRF/Monte Carlo Study of Solvent Effects on a Polar [2+2] Cycloaddition

Solvent effects on the polar [2+2] cycloaddition of 1,1-dicyanoethylene (DCNE) and methyl vinyl ether (MVE) have been studied using ab initio self-consistent reaction field (SCRF) and Monte Carlo (MC) statistical mechanics calculations. Emphasis is placed on the dependence of transition-state structure and energetics on solvation and on the impact of using different charge sets and geometries from the SCRF calculations in the MC simulations. The ab initio calculations were performed with dielectric constants e of 1.0, 2.23 (CCl4), and 35.94 (CH3CN) with the 6-31G* basis set at the Hartree−Fock (HF) level and incorporating electron correlation through MP2 and Becke3LYP density functional methods. Computed dipole moments of 10−17 D for the transition structures overlap estimates based on the solvent effects observed by Steiner and Huisgen. However, the mechanistic picture that emerges is medium dependent. In the gas phase and nonpolar solvent, the results here indicate a concerted (single barrier) process w...