SOLVENT EFFECTS ON THE RING-OPENING OF CYCLOPROPANONES TO OXYALLYLS -A COMBINED AB-INITIO AND MONTE-CARLO STUDY

Solvent effects on the disrotatory ring opening of cyclopropanone and 2,2-dimethylcyclopropanone have been computed by Monte Carlo simulatio ns at 25 degrees C, Geometries for the cyclopropanones, the transition state for the rearrangement of cyclopropanone, and the oxyallyls were obtained from ab initio (4/4) CASSCF calculations with the 6-31G bas is set. For each geometry, CHELPG and Mulliken charges were determined for use in the fluid simulations. Statistical perturbation theory yie lded the changes in free energies of solvation in four solvents for th e ring openings. The modest computed solvent effects are in good accor d with experimental data of Greene and coworkers. Our results support the intermediacy of oxyallyls in cyclopropanone stereomutations, indic ate the proximity of the oxyallyls to the transition states for the ri ng openings, and confirm the principally diradical rather than zwitter ionic nature of the oxyallyls.