MOLECULAR REACTIVITY IN SOLUTION - MODELING OF THE EFFECTS OF THE SOLVENT AND OF ITS STOCHASTIC FLUCTUATION ON AN SN2 REACTION

The polarizable continuum model - used up to date to evaluate the effects of a solvent in equilibrium - has been modified to take into account the local fluctuations of the solvent. The elaborated modified model has been applied for the study of the S(N)2 type reaction F- + CH3 F --> FCH3 + F-. The reaction profiles and hypersurfaces have been calculated for this system being in equilibrium solvent as well as in solvent with various simulated fluctuations. It was found, that a fluctuation of the solvent occurring at the F- side can decrease the energy barrier up to 50% of its value in equilibrium solvent. The shape of the reaction hypersurface is also changed by solvent fluctuation - shifting the transition state towards reactants or products, according to the position at which the fluctuation occurs. The study was supplemented by the evaluation of trajectories for both cases, i.e. reaction in equilibrium as well as with a fluctuation in the solvent. The reaction dynamics is substantially altered by the presence of a fluctuation.