ELECTRONIC ABSORPTION-SPECTRA OF PROTONATED 2-(2-FURYL)PYRROLES, 2-(2-THIENYL)PYRROLES, AND 2-ARYLPYRROLES

Protonation of 2-(2-furyl)-, 2-(2-thienyl)-, and 2-arylpyrroles by sul furic acid in ethanol was studied using electronic absorption spectros copy in the UV and visible regions. Pyrroles with heteroaromatic subst ituents are protonated at the alpha-positions of pyrrole and the heter ocycle, resulting in the appearance of additional long-wave spectral b ands. In the series of 2-arylpyrroles protonation capability is determ ined by the electronic effect of the phenyl ring substituents.