Conformation and photoelectron spectra of 2-(2-furyl)pyrrole and 2-(2-thienyl)pyrrole

Abstract

The electric dipole moments and He^I photoelectron spectra (p.e.s.) of 2-(2-furyl)pyrrole and 2-(2-thienyl)pyrrole have been measured and analysed. Dipole moment data, in conjunction with theoretical calculations of conformational energy at the ab initio STO–3G level, show that the most likely conformations for these molecules are the fully planar cis and trans, the former being more favourable. This conformational conclusion is supported by the p.e.s. evidence of strong mesomeric interaction between the two rings in both the molecules. Assignments of the p.e.s. bands have been made upon PMO analysis by comparison with those of the parent monocyclic compounds.