For the group of 86 catacondensed and pericondensed benzenoid hydrocarbons, the theoretical estimates of the excitation energy of the p band, calculated by the Hiickel method and by the semiempirical method of the limited configuration interaction, as well as the experimental values of the same quantity, are plotted against the number of atoms of the respective molecules. In the plots thus obtained, the influence of the topology and size of the molecules on the changes of the theoretical and experimental values of the p-band excitation energy may be traced. A surprising similarity of plots for the three quantities mentioned has been found, and the importance of the molecular topology as the molecule characteristics is shown. Approximate rules based on the distribution of the "nodal points" in the highest occupied molecular orbital of the parent hydrocarbon have been derived, predicting the direction of the p-band shift with benzene ring annelation.(3) (a) A. Streitweiser, Jr.

Character of transition in a series of linear p-quinones has been investigated on the basis of configuration analysis. Correlation graphs of the states have been constructed enabling interpretation of the spectra in the terms of local transitions in the fragments and charge-transfer transitions between the fragments. Influence of various types of annelation on the first ππ* absorption band in the spectra of the mentioned compound class has been investigated qualitatively from the viewpoint of interaction of the frontier MOs of the fragments.

Aromatic polynuclear pquinones and their derivatives have been studied using their electronic absorption and luminescence spectra and their basicity. The data were used to provide a basis for the study of the relationships between the structure and the spectral characteristics.

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