Five points for carbon

A collaboration between researchers in Germany and the USA has yielded a crystal structure for a puzzling non-classical carbocation that ends half a century of chemical debate. Paul von Rague Schleyer of the University of Georgia and colleagues in Freiberg and Erlangen have crystallized the 2-norbornyl cation and determined its structure beyond reasonable doubt showing that the charged carbon atom at its center has five bonds rather than the three anticipated for a carbocation. The structure of 2-norbornyl cations conflicts with the classical view of carbon bonds but its existence explains the mechanism of several chemical reactions that might proceed through this intermediate species.