Theoretical study of charge distribution in the benzoyl and alkynoyl cations

Abstract

SCF-MO calculations, in the lNDO approximation, have been carried out on benzoyl (1), propynoyl (2), but-2-ynoyl (3), 3-phenylpropynoyl (4), and 3-fluoropropynoyl cations (5). In each case the geometries were optimized to minimum energy. In aggreement with ¹³C n.m.r. observations, significant charge delocalization into the phenyl rings occurs in (1) and (4). From an examination of the charge distributions, π-bond orders, and π- and σ-electron distributions it is shown that extensive delocalization of charge occurs in (2), (3), and (5), contrary to previous interpretations of ¹³C spectra. Thus all the mesomeric forms RCC–CO⁺↔RCC–[graphic omitted]O↔R[graphic omitted]z.dbd6;CCO contribute significantly in (2), (3), and (5) as well as in (4), and the charge is not substantially localized on oxygen as previously claimed.