EVB calculations of the thermodynamic activation parameters for the conversion of chorismate to prephenate were first performed on the uncatalyzed reference reaction in an aqueous environment. Reactions at 298K were fit to the experimental value of the activation free energy (24.5 kcal/mol), and the reaction free energy obtained from DFT (-13.2 kcal/mol), yielding the intrinsic gas-phase energy difference between the EVB resonance structures, Δα = -94.7, and the off-diagonal coupling element, H12 = 86.8 kcal/mol. Using these parameters, EVB/MD calculations were performed at 6 other temperatures to obtain an Arrhenius plot of the solution-phase reaction. From this plot, an activation free energy of ∆G ‡ = 24.4 kcal mol -1 was obtained, and a linear regression was performed, yielding activation enthalpies and entropies of ∆H ‡ = 20.9 kcal mol -1 and T∆S ‡ = -3.4 kcal mol -1 (at 298 K), respectively. These parameters are in excellent agreement with values obtained from experiment (Table ).