This thesis comprises three parts, Parts A, B and C. Part A commences with a very brief survey based on the chemical literature of the concept of aromaticity. A number of excellent reviews covering both the historical and theoretical aspects of this subject have appeared recently and, in view of this, a more detailed consideration of aromaticity was deemed unnecessary. This is followed by a discussion of the chemistry of the mulenes with particular emphasis on the theoretical aspects of the subject. The chemistry of perinaphthene and its derivatives is then reviewed in detail and this leads logically to a reasoned description of the aims of the experimental investigation. Part B is a discussion of the results achieved in the course of investigations centred on the perinaghtene nucleus. Part C is devoted entirely to a description of experimental details, and is the complement to part B.