Hypercarbon chemistry

Article By:

Olah, George A. Formerly, Loker Hydrocarbon Research Institute, University of Southern California, Los Angeles, California. Nobelist.

Prakash, G. K. Surya Loker Hydrocarbon Research Institute, University of Southern California, Los Angeles, California.

Last reviewed:2000

DOI:https://doi.org/10.1036/1097-8542.YB000790

One of the foundations of organic chemistry is A. Kekulé's concept of the tetravalency of carbon (also suggested by A. S. Couper). This led to the octet rule, proposed by G. N. Lewis in 1916, that only a maximum of four ligands can be bound to carbon by two-electron two-center sigma bonds, for a total of eight electrons around carbon. Violations of the octet rule in the compounds of the second and higher rows of the periodic table are recognized, but carbon, being a first-row element, cannot extend its valence shell. Through quantum theory, it is understood that the idea of bonding pairs of electrons always being between two atomic centers is, at best, only an approximation. Many organic molecules require a description that involves the electrons in the bond being distributed over two or more atoms. The majority of these molecules are conjugated unsaturated π systems that are described in terms of delocalized bonds, as in benzene [structure (1),

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