PROTONATION OF 2-(2-THIENYL)PYRROLE AND 2-(2-THIENYL)-1-VINYLPYRROLES

2-(2-Thienyl)pyrrole and its 3-alkyl-1-vinyl derivatives have been sho wn (H-1 NMR) to be protonated by HSO3F, CF3COOH, HCl and HBr at the py rrole C-5 atom. Reaction with the superacid system HSO3F-SbF5-SO2 resu lts in the equilibrium between pyrrolium and thiophenium ions. The hea ts of formation (DELTAH), charges and HOMO partial electron densities for 2-(2-thienyl)pyrrole and its protonated forms have been calculated by the MNDO method. The calculated DELTAH values of thienylpyrrolium and pyrrolylthiophenium ions are in agreement with the experimentally observed ratio.