From Kekules Four-Valent Carbon to Five- and Higher-Coordinate Hypercarbon Chemistry

From Kekule s Four-Valent Carbon to Five- and Higher-Coordinate Hypercarbon Chemistry 

One of the cornerstones of the chemistry of carbon compounds (organic chemistry) is Kekule s concept, proposed in 1858, of the tetra-valence of carbon. It was independently proposed in the same year by Couper who, however, got little recognition (vide infra). Kekule realized that carbon can bind at the same time to not more than four other atoms or groups. It can, however, at the same time use one or more of its valences to form bonds to another carbon atom. In this way carbon can form chains or rings, as well as multiple-bonded compounds. 

Kekule claimed that the concept came to him during a late night ride on a London omnibus in 1854. 

One fine summer evening, I was returning by the last omnibus, outside as usual, through the deserted streets of the metropolis, which are at other times so full of life. I fell into a reverie and lo the atoms were gamboling before my eyes.. .. I saw how, frequently, two smaller atoms united to form a pair, how a larger one embraced two smaller ones how still larger ones kept hold of three or even four of the smaller whilst the whole kept whirling 

To what degree Kekule s reeollection was factual we don t know, but Couper and Butlerov independently had developed similar, more well-defined concepts of valenee bonding, whieh may have not been entirely unknown to Kekule. 

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