CORE IONIZATION ENERGIES OF AMIDES AS A PROBE OF STRUCTURE AND BONDING

Core orbital energies are computed for planar ground-state and rotatio nal transition-state structures for formamide and N,N-dimethylacetamid e using ab initio molecular orbital calculations at the 6-31G level. Distortion of the amide linkage decreases the core ionization energy o f nitrogen and increases the core ionization energies of oxygen and th e carbonyl carbon. Similar trends are observed for bridgehead bicyclic lactams and are corroborated by the limited experimental data availab le. A simple interpretation can be made in the language of resonance t heories through reference to contributions of three canonical structur es (1A-1C) and in particular, the reduced contribution of 1B in distor ted amides. (C) 1997 Elsevier Science B.V.