The photoelectron spectra and electronic structure of 2-carbonyl furans

The He(I), λ = 58.4 nm, photoelectron spectra of a series of six 2-carbonyl furans and 2-furonitrile have been measured in the gas phase. The low ionization energy bands are assigned to photoionizations from π orbitals of the furan ring, orbitals localized on the carbonyl group, and orbitals of the carbonyl substituents. Changes in ionization energies within the series can be rationalized in terms of the relative conjugative and inductive effects of the substituents. Substituent inductive effects were found to be dominant. The relatively broad vibrational fine structure on the low IE bands of the carbonyl furans could result from the presence of rotational isomers of the species. Keywords: photoelectron spectra, 2-carbonyl furans, molecular orbitals.