A free energy of hydration profile for the Claisen rearrangement of allyl vinyl ether (AVE) has been obtained from Monte Carlo statistical mechanics simulations at 25 °C. The gas-phase minimum energy reaction path through the chair transition state was determined from ab initio 6-31G(d) calculations and was followed in a periodic cell containing 838 water molecules. The transition state is computed to be 3.85 ± 0.16 kcal/mol better hydrated than the reactant, which corresponds to a rate increase by a factor of 664 over the gas-phase reaction. This large effect is shown to be consistent with available experimental data. The origin of the effect is analyzed. The energetic impact of multiple conformational states for the reactant has also been considered.
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