1987 Volume 60 Issue 3 Pages 851-855
Fast reactions of diethyl fumarate anion radical (DEF−) and fluorenone anion radical (Fl−) with various organic halides (RX) in hexamethylphosphoric triamide have been studied by means of ns pulse radiolysis at room temperature. Reactions of acetophenone anion radical were also studied for comparison. It was found that the reaction rate of Fl− was subject to the steric and resonance effects of R groups of RX in accord with the classical concept of SN2 reactions: the rate constant was reduced by 2 orders of magnitude by the steric effect when R was changed from ethyl to bulky isopropyl or t-butyl, and it was still large by the resonance effect of R even if R was changed from ethyl to an allyl or a benzyl group. While the reaction rate of DEF− was not much affected when R was changed to more bulky groups, the rate constant was correlated to the reduction potential of RX. The results were interpreted in terms of a VB correlation diagram approach or rate-equilibrium relationship within a framework of SN2 reactions.
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