Reactive flux calculations of methyl vinyl ketone reacting with cyclopentadiene in water

Molecular dynamics and reactive flux simulations of the Diels-Alder reaction of methyl vinyl ketone (MVK) reacting with cyclopentadiene (CPD) in water have been carried out to calculate the activation free energy and transmission coefficient for the reaction. For this purpose, an empirical potential energy surface (PES) of the reaction was developed by first constructing an intramolecular PES of MVK + CPD using the B3LYP/6-31+g* level of ab initio theory. This calculation predicts that the reaction barrier height of MVK + CPD in the gas phase is 16 kcal/mol. The MVK + CPD complex was then surrounded by 215 SPC/F2 water molecules, and the activation free energy is seen to be reduced by 2.2 kcal/mol compared to that of the gas phase. The initial conditions for the reactive flux calculations were obtained at T = 300 K by a Nose-Hoover chain dynamics algorithm that was recently developed for this purpose. These calculations show that the transmission coefficient for the reaction in water is 0.67 and therefore that the dominant solvent effect is the static reduction in the activation free energy barrier.