An assessment of the electronic structure of alkylbenzenes

The nature and manifestations of the valence orbital interactions between benzene and selected alkyl groups are elucidated through correlations of the gas phase photoelectron spectra with the corresponding ground state orbital eigenvalues obtained according to the semiempirical CNDO/S–CI molecular orbital method. An important result is the finding that alkane orbitals strongly interact with the higher-lying occupied benzene σ orbitals of appropriate symmetry to yield several moderate charge-transfer excitations below 7.0 eV which are predominately of σ→π* character. The oscillator strength for these transitions is found to be strongly dependent on the relative orientation of the benzene and alkane moieties.