Abstract
The positions of p-bands of 20 aromatic polycyclic hydrocarbons have been calculated by the semiempirical limited configuration interaction method in a π-electron approximation using Hückel's molecular orbitals. The agreement with experimental values is very good. The effect of the extent of configuration interaction has been studied. It has been demonstrated that the contribution of electron repulsion integrals is nearly constant within this class of hydrocarbons. The failure of the approximation of Hückel in the studies of spectra of compounds with conjugated double bonds belonging to different classes of hydrocarbons, has been explained by the fact that the contribution of electron repulsion integrals is larger with polyenes and considerably smaller with tropylium and its benzoderivatives. The usefulness of the approximation of Hückel within one class of compounds is demonstrated by a comparison of the experimental and theoretical (according to Hückel) positions of the lowest energy absorption maximum of the aromatic hydrocarbon derivatives.
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