The protonation of some 5-substituted 3-nitro- and 3-substituted 5-nitro-2-pyrrolidin-1-ylthiophenes

Abstract

The protonation of some 5-substituted 3-nitro-2-pyrrolidin-1-ylthiophenes 1C and 3-substituted 5-nitro-2-pyrrolidin-1-ylthiophenes 2C in aqueous perchloric acid has been studied. The modified Hammett, Bunnett–Olsen and Marziano–Cox–Yates methods have been used to calculate pK_BH⁺ values, which have been correlated with substituent effects. Furthermore, the protonation of pyrrolidin-1-ylthiophenes 1C and 2C has been compared with that of the corresponding N,N-di-methylamino-(1A and 2A) and piperidin-1-yl-thiophenes (1B and 2B). The results have been interpreted on the grounds of the different interactions occurring between the amino group at C-2 and the nitro group or variable substituent at C-3.