Photoelectron spectra and electronic structure of derivatives of imidazoline

Abstract

We have obtained for the first time the photoelectron spectra (PES) of 20 diamagnetic and paramagnetic derivatives of imidazole. On the basis of calculations in the MNDO approximation, analysis of the vibrational structure, and comparisons in a series we have interpreted the bands in the range 7–11 eV. In the nitroxyl radicals of 3-imidazoline the highest occupied molecular orbital is the πNO* orbital, having also a contribution on the C4 atom. On introducing N-oxide groups there is a considerable rearrangement of the electronic structure of the radicals. In the PES of the nitroxyl radicals of 3-imidazoline-3-oxide there is multiplet splitting of the ionization band of the no·MO, amounting to 0.3–0.4 eV. Replacement of the methyl groups on the C2 atom by methoxyl groups leads to an increase in the interactions of the unshared pairs of the O atoms of the nitronium and nitroxyl groups, while the same replacement on the C5 atoms leads to a considerable decrease in this interaction. When the substituent on the N1 atom in derivatives of 3-imidazoline-3-oxide is varied the energy of ionization of the πC-NO MO decreases in the series: CH3 < H ≤ OH < O < NO.