Parameter free evaluation of S2 reaction rates for halide substitution in halomethane

• Published in: Physical chemistry chemical physics : PCCP Vol. 24; no. 12; pp. 7474 - 748
• Main Authors: Bortoli, Marco, Campeggio, Jonatan, Orian, Laura, Zerbetto, Mirco, Polimeno, Antonino
• Format: Journal Article
• Published: 23.03.2022
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d1cp05220a

We estimate the kinetic constants of a series of archetypal S N 2 reactions, i.e. , the nucleophilic substitutions of halides in halomethane. A parameter free, multiscale approach recently developed [Campeggio et al. , Phys. Chem. Chem. Phys. , 2020, 22 , 3455] is employed. The protocol relies on quantum mechanical calculations for the description of the energy profile along the intrinsic reaction coordinate, which is then mapped onto a reaction coordinate conveniently built for the reactive process. A Kramers-Klein equation is used to describe the stochastic time evolution of the reaction coordinate and its velocity; friction is parameterized using a hydrodynamic model and Kramers theory is used to derive the rate constant of the reaction. The method is here applied to six S N 2 reactions in water at 295.15 K, which differ in the nucleophile and the leaving group. The computed reaction rates are in good agreement with the experimental data and correlate well with the trends observed for the activation energies. We present a multiscale, parameter-free approach to the estimation of a series of archetypal S N 2 substitutions of halides in halomethane.