Reactions of Organic Halides in Solution

REACTIONS of organic halides in solution which involve substitution by a nucleophilic reagent at a saturated carbon atom have been extensively studied by Hughes, Ingold and co-workers1. These authors conclude that reactions of this type may occur by two possible mechanisms, a unimolecular mechanism SN1 or a bimolecular mechanism SN2. The increase in the unimolecular SN1 reaction-rate of the halide R – X as R varies along the series methyl, ethyl, sec.-propyl, tert.butyl, is attributed by these authors to the increase in electron accession to the reaction centre2. The decrease in the bimolecular SN2 reaction-rate along this series3 is also attributed to the increase in electron accession to the reaction centre; this electron accession is assumed to inhibit the approach of the nucleophilic reagent.