Nucleophilic substitutions in five-membered rings. Primary steric effects in thiophen derivatives

Abstract
In order to study primary steric effects (p.s.e.) in nucleophilic substitutions of five-membered rings, the rate of piperidino and benzenethiolate substitution of some 2-L-5-nitrothiophens (Ia—d) and 2-L-3-methyl-5-nitrothiophens (IIa—d) have been measured in methanol. The rate ratios (kH/kMe) obtained show an absence of p.s.e. in piperidino substitutions when the leaving group is halogen but not when L = SO2Ph. Benzenethiolate substitution data show the presence of a large Reinheimer–Bunnett effect.

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