Nature of the π-Electronic Spectra of Aromatic Compounds I. Aromatic Hydrocarbons and Their Hydroxyl Derivatives

Abstract

Abstract The π-electronic spectra of a number of aromatic hydrocarbons and their hydroxyl derivatives have been theoretically studied by the ASMO-CI method within the framework of a limited LCMO approximation. The calculated singlet frequencies are in satisfactory agreement with the experimental findings. The experimental Clar relation is obtained theoretically. The present theory suggests that the substitution of a hydroxyl group at the α-position of the parent hydrocarbon has effects of a substantial red shift in the 1La band and a rather small shift in the 1Lb band, but the band characteristics are practically the same as those of the parent hydrocarbon. On the other hand, the substitution at the β-position has the effect of mixing the 1La species with the 1Lb species to a considerable extent, so that the band characteristics of the parent hydrocarbon should be considerably modified by this type of substitution. In the light of the present theory, it is better to regard the spectra of phenanthrene and pyrene as modified biphenyl spectra. A plot of the calculated frequency against the corresponding Hückel energy gives a rather good correlation.