Photoelectron Spectra of Substituted Benzenes

Photoelectron spectra were measured in the region between 6 and 21 eV for aniline, N,N-dimethylaniline, phenol, anisole, benzonitrile, acetophenone, nitrobenzene, and their methyl derivatives. The observed spectra were interpreted in terms of their MO’s obtained by the CNDO/2 and EHMO methods, the methyl-substituent effect and the steric hindrance effect being considered. Both effects are essential for the reliable assignment of the observed photoelectron spectra. We found a general tendency that the interaction of the doubly degenerate highest occupied orbitals (e1g) of the benzene ring with the highest occupied orbital of a substituent group is important for the interpretation of the observed lower energy (7∼12 eV) bands. The only exceptional case is the nitrobenzenes in which the lowest vacant orbital of the substituent group is rather close to the highest occupied orbitals of the benzene ring and the interaction between them is important. The effects of the substituent groups upon the observed photoelectron spectra are classified into four types.