Core electrons as probes of the net-charge distribution in molecules: a case study

High-level self-consistent-field calculations have been performed on amines NH3−nRn (with R suitable substituent and n=1,2,3) to study the influence of the substituent on the N(1s) binding energy. The results have been interpreted, through the use of the pointlike-charge potential model, in terms of inductive and field effects of the substituent and of electron localization–delocalization. We have found that: the inductive effect plays a fundamental role only when one considers the nearest neighbors; the field effect may prevail for the second or higher order neighbors; and the Mulliken charge may provide an accurate description of the charge distribution along the molecule only in the absence of delocalized electrons.