Structures of Cl-CH3Cl(H2O)n (n = 0, 1, 2) cluster at room temperature from Monte Carlo samplings using the ab initio MO method

Recently developed ab initio MO-MG samplings have been applied to investigate the solvation effects on the structure of the Cl-CH3Cl ion-dipole complex, which may be formed at the initial stage of the S(N)2 reaction in the Cl-CH3Cl(H2O)(n) (n = 0,1,2) clusters. Simulation results at room temperature indicate that most of the configurations appeared consist of the methyl chloride and the hydrated chloride ion; CH3Cl ... Cl-(H2O)(n). The hydrated chloride ion is weakly bounded to methyl chloride and widely distributed around the molecule. The distribution of the Cl- ion covers the CH3 group of methyl chloride in the n =1 cluster, which is similar to that observed in the n = 0 cluster. In the n = 2 cluster, the distribution of the Cl- ion distinctly covers almost whole methyl chloride. This implies that a chance for Cl- to attack the carbon atom of the CH3 group is reduced in the n = 2 cluster and the intracluster S(N)2 reaction may be hindered to a certain extent. (C) 1999 Elsevier Science B.V. All rights reserved.