Semi-empirical MO-calculations on the electronic spectra of benzoquinonechlorimides

Article abstract of DOI:10.1016/0584-8539(80)80064-X

The electronic spectra of chloro p-benzoquinone(4)-chlorimides have been studied and the energy levels have been calculated using PPP-CI procedure, on the basis of which, the spectral bands have been assigned.The results show that the p-benzoquinone(4)-chlorimide possesses a n-?* transition at 23.25 kk and three ?-?* transitions, one strongly allowed at 35.46 kk and two weakly allowed at 44.44 and 30.30 kk.Substitution by chlorine atom in the quinonoid ring does not change the spectral pattern appreciably.A comparison of the spectrum of p-benzoquinone with those of its mono and dichlorimide clearly reveals that the strongly allowed ?-?* transition and the lowest weakly allowed ?-?* transition shift bathochromically and the ?-?* transition hypsochromically as the oxygen atoms in p-benzoquinone are replaced progressively by chlorimino groups.An additional weakly allowed ?-?* transition is found around 44.44 kk in quinonechlorimides.Inversion is shown to result in allowedness of transition from HOMO to LVMO in quinonechlorimides whereas it is forbidden in the case of quinones.