PHOTOELECTRON SPECTROSCOPIC STUDY OF N-ARYL-PYRROLE AND N-HETEROARYL-PYRROLE

HeI photoelectron (PE) spectra of 13 N-aryl- and N-heteroaryl-pyrroles have been measured. The low energy region of the spectra has been ana lysed using semiempirical MNDO SCF MO calculations [assuming the valid ity of Koopmans' theorem (Physica, 1934, 1, 104)] and the composite mo lecule method (CMM) which has proven to be particularly useful for ele ctronic structure elucidation of complex molecules. Electronic structu re, especially in terms of the distribution of the outer valence elect rons over the molecule, has been shown previously to be mostly respons ible for their chemical properties. Attention has been paid to the eff ect which particular constituents, i.e. either pyrrole or N-aryl- and N-heteroaryl-pyrrole, respectively, may play in the pharmacological ac tivity of arylpyrroles. In all these compounds, the highest occupied M O is of pyrrole-type character, (a(2) symmetry, with a node on the N-a tom). Consequently, the same ionisation process yields the lowest ener gy band in all PE spectra.