Variational Flooding Study of a S N 2 Reaction.

We have studied the reaction dynamics of a prototypical organic reaction using a variationally optimized truncated bias to accelerate transitions between educt and product reactant states. The asymmetric SN 2 nucleophilic substitution reaction of fluoromethane and chloromethane CH3 F + Cl- ⇌ CH3 Cl + F- is considered, and many independent biased molecular dynamics simulations have been performed at 600, 900, and 1200 K, collecting several hundred transitions at each temperature. The transition times and relative rate constants have been obtained for both reaction directions. The activation energies extracted from an Arrhenius plot compare well with standard static calculations.