A Theoretical Study Of SN2′ Reactions of Allylic Halides: Role of Ion Pairs

Various disparate experimental results are explained by the hypothesis that reactions of anionic nucleophiles with allylic halides are generally S(N)2. The S(N)2' reactions that do Occur proceed generally with anti stereochemistry. Reactions with ion pair nucleophiles Occur preferentially LIS S(N)2' reactions with syn stereochemistry. This hypothesis is consistent with a variety Of computations at the HF, B3LYP, mPWIPW91 and MP2 levels with the 6-31+G(d) basis set of reactions of Li and Na fluoride and chloride with allyl halides and 4-halo-2-pentenes. Solvation is considered by a combination of coordination of dimethyl ether to the lithium and sodium cations and dielectric solvation with a polarized continuum model.