Determination of the nitrogen N1s and oxygen O1s core energies in planar and distorted lactams and amides: relationships with the concept of resonance

The core ionization energies of three strained lactams have been measured and compared with those of model lactams, amides, amines, and ketones. In general, the high values for N1s and the low values for O1s in planar amide (lactam) linkages compared to those in model amines and ketones are consistent with traditional resonance arguments. The N1s and O1s data for the distorted lactams 1,3-di-tert-butylaziridinone and 1-azabicyclo-[3.3.1]nonan-2-one are consistent with a reduced positive charge on nitrogen and a reduced negative charge on oxygen in accord with the classical resonance viewpoint