The Bakerian Lecture: The structure of benzene

The structure of the parent of the aromatic series has long been one of the foremost unsolved problems of chemistry. The following formulae will be a sufficient reminder of the long, complicated period of historical development, which extended from 1865 until the present decade: Kekulé Dewar Claus Ladenburg Thiele Baeyer The fundamental difficulty for chemists has always been tha t of reconciling the stability of the benzene nucleus with its chemical transformations. If one considers only the transformations, Kekulé’s expression is undoubtedly the best single representation. Dewar’s is a possible addition if a dynamical system be postulated. But neither structure interprets the stability of the ring; nor do the saturated, but highly strained alternatives of Claus and Ladenburg. Formulae which employ imperfectly defined symbols leave us with the problem of more exactly defining the significance of symbols.