Modeling SN2 Reactions in Methanol Solution by ab Initio Calculation of Nucleophile Solvent−Substrate Clusters
journal contributionposted on 2005-11-11, 00:00 authored by Xufeng Lin, Cunyuan Zhao, David Lee Phillips
Ab initio calculations were used to study the SN2 reactions of the CH3OCH2I molecule with a methoxide ion (CH3O-) and a methanol molecule by systematically building up the reaction system with explicit incorporation of the methanol solvent molecules. For the reaction of CH3OCH2I with a methoxide ion, the explicit incorporation of the methanol molecules to better solvate the methoxide ion led to an increase in the barrier to reaction. For the reaction of CH3OCH2I with a methanol molecule, the explicit incorporation of the methanol molecules led to a decrease in the barrier to reaction because of an inclination of this reaction to proceed with the nucleophilic displacements accompanied by proton transfer through the H-bonding chain. The H-bonding chain served as both acid and base catalysts for the displacement reaction. A ca. 1015-fold acceleration of the methanol tetramer incorporated SN2 reaction was predicted relative to the corresponding methanol monomer reaction. The properties of the reactions examined are discussed briefly.