Electronic Distribution in Some Conjugated Ketones. Molecular Orbital Calculations Including Overlap

Abstract

Electronic charge distributions in 8 conjugated ketones were computed by the semiempirical molecular orbital method in Wheland's approximation, including overlap between adjacent atoms. It is found that inclusion of overlap leads to a clearer picture of charge distribution. It is shown that covalent and ionic contributions to bond energies may decrease or increase at the same time upon excitation, or a structural change in the π system. A new ``Coulombic bond order'' is defined, giving a measure of bond energies in terms of Coulombic interactions between local charges.