Objective: The project is geared to providing fundamental information as to whether such structural modifications of polycyclic aromatic hydrocarbons as perturbed delocalization, three-dimensional characteristics, and other electronic features are crucial to maintenance of carcinogenic reactivity. Approach: Certain benzenoid hydrocarbons and heterocycles are known to be potent carcinogens. This proposal describes the synthesis of new types of potentially delocalized nonbenzenoid systems which have in common the size, shape, and reactivity conceivably necessary for carcinogenic reactivity. Knowledge of the reactivity and carcinogenicity of these inherently novel molecules is important because of the possible insight which may be gained into the chemical basis for carcinogenesis. Specifically, the target compounds are in certain cases expected to possess homoaromatic character, in other cases to exhibit rapid valence tautomerism, and in still other instances to possess fixed double bonds. Accordingly, a wide range of structural types are to be made available. All stable target compounds prepared in this work are to be evaluated for possible carcinogenicity.