A combination of quantum and statistical mechanics is being used to probe the origins of solvent effects on the kinetics of organic reactions. Ab initio molecular orbital calculations provide gas-phase reaction paths and partial charges for the reacting systems. The reaction paths are then followed by Monte Carlo simulations in periodic cells containing hundreds of solvent molecules, and the changes in Gibbs free energies of solvation are obtained. Results are provided for several prototypical pericyclic reactions : Diels–Alder cycloadditions for methyl vinyl ketone with cyclopentadiene and the dimerization of cyclopentadiene, the Claisen rearrangement of allyl vinyl ether, and the electrocyclic ring opening of cyclopropanones to oxyallyls. Detailed insights are obtained on issues such as the acceleration of the Diels–Alder reactions and Claisen rearrangement in water, and the electronic nature of oxyallyls.
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