Denison-Hackh structure symbols: a forgotten episode in the teaching of organic chemistry.

The history of chemical nomenclature and symbolism is resplendent not only with proposals that were once widely used in the chemical literature, but which have since been displaced by more modern developments, but also with those which, however logical, were doomed to oblivion almost from their inception and which now survive as historical relics to be found only in the papers and books of their originators (1). Some of these latter proposals (Fig. 1) (2), such as the geometric symbolism of Hassenfratz and Adet, which was designed to encode the nomenclature reforms of Lavoisier and his collaborators, or the circle symbols of Dalton and Loschmidt, have at least managed, despite having never been widely adopted, to make it into the history books, whereas others remain forgotten in the dusty back issues of unread journals (3). This latter scenario was unfortunately the fate of the Denison-Hackh proposals for organic symbolism, despite the fact that certain aspects of these symbols have since been independently rediscovered and are currently widely used in the chemical literature. It is this latter irony which provides both a philosophical and a sociological justification for indulging in a brief historical retrospect of this forgotten symbolism. DENISON-HACKH STRUCTURE SYMBOLS: A FORGOTTEN EPISODE IN THE TEACHING OF ORGANIC CHEMISTRY