A comparison of sensitivities to substituent effects of five-membered heteroaromatic rings in gas phase ionization

Abstract

The molecular ionization potentials of a number of substituted furans, thiophens, selenophens, and pyrroles have been determined by the electron-impact technique. The ρ value for this reaction is more negative than that for the most selective electrophilic substitutions. The sensitivity to substituent effects appears to vary in the reverse order to that of the ‘ground-state aromaticity’ of the rings (furan > pyrrole > thiophen > benzene).