Substituent Effects in the Reactions of Some 2-Methoxy-3-nitro-5-X-thiophenes with Pyrrolidine and Piperidine in Methanol

Abstract

The kinetics of the title reactions have been studied as a function of amine and methoxide ion concentrations in buffered solutions. All the reactions studied are general base-catalysed. An examination of the catalytic coefficients obtained for each amine-substrate system has showed that the catalysis observed occurs through a SB-GA mechanism and that the general base-catalysed product forming step is controlled by the ring size of the cyclic amine. The Hammett ρ 1 values calculated are consistent with previous evidence concerning the interactions between the substituent at the C-5 para-like carbon atom and the leaving group. Moreover, the results confirm that a methyl group in such a position can behave as a weakly electron-attracting substituent