Carbon-Oxygen Hydrogen Bonding in Dehydrohalogenation Reactions: PM3 Calculations on Polyhalogenated Phenylethane Derivatives

The dehydrohalogenation reactions of PhCH -CH Cl and PhCHCl-CX LG (X = H, F; LG = F, Cl) with methoxide have been studied using PM3 quantum chemical calculations in vacuo and within a dielectric medium. For PhCH -CH Cl and PhCHCl-CH Cl the loss of HCl is predicted to occur via an E2 mechanism, while for the other three compounds loss of hydrogen halide occurs via a two-step mechanism, with a hydrogen-bonded carbanion as an intermediate. The mechanistic implications of these calculations are discussed in comparison with experimental data. 2 2 2 2 2