Ab initio calculations and photoelectron spectra of cyclic oxamides

Abstract

Photoelectron spectra of five-, six-, and seven-membered cyclic oxamides in which the oxamide unit is forced to adopt an s-cis or twisted s-cis conformation have been recorded. The spectra have been interpreted using ab initio calculations. In comparisons with acyclic s-trans oxamides it is found that the influence of the s-trans–s-cis conformational change on the ionization energies is masked by the effects of the alkyl parts of the ring systems. Ionization energies of cyclic oxamides with different ring sizes show some effects due to twisting around the intercarbonyl bond, but also in this case the alkyl parts of the ring systems strongly influence the spectra.