Quantum-mechanical study of the resonances of the SN2 reaction Cl-+CH3Cl→ClCH3+Cl-

Abstract

The nucleophilic substitution reaction Cl^-+CH₃Cl→ClCH₃+Cl^- has been studied quantum mechanically by means of stabilisation and scattering calculations. A reduced dimensionality Hamiltonian model has been employed in which the bonds that are broken and formed during reaction, Cl–C and C–Cl, are explicitly treated. The reaction is driven by many narrow scattering resonances, which are analysed by means of the stabilisation method. It is found that part of the quasibound states are assignable by quantum numbers v and n, describing excitations in the intramolecular, C–Cl, and intermolecular, Cl^-···C, stretching modes of the Cl^-···CH₃Cl complex, respectively. The connection between reactivity and the splitting of resonance states of different symmetry at the reaction barrier region is discussed. Interestingly, it is found that the density of states in the transition state region directly correlates with the resonance structure of the cumulative reaction probability.