High-Level-Optimized Stationary Points for the F-(H2O) + CH3I System: Proposing a New Water-Induced Double-Inversion Pathway.

We report 29 stationary points for the F-(H2O) + CH3I reaction obtained by using the high-level explicitly correlated CCSD(T)-F12b method with the aug-cc-pVDZ basis set for the determination of the benchmark structures and frequencies and the aug-cc-pVQZ basis for energy computations. The stationary points characterize the monohydrated F-- and OH--induced Walden-inversion pathways and, for the first time, the front-side attack and F--induced double-inversion mechanisms leading to CH3F with retention as well as the novel H2O-induced double-inversion retention pathway producing CH3OH. Hydration effectively increases the relative energies of the stationary points, but the monohydrated inversion pathways are still barrierless, whereas the front-side attack and double-inversion barrier heights are around 30 and 20 kcal/mol, respectively.