Carbon tetravalence

Kekule s formulas. In 1857 the German chemist A. Ke-kule deduced that oxygen was bivalent, nitrogen and phosphorus trivalent, and, what is most important, carbon tetravalent. He regarded valence as the number of... 

Unlike carbon, tetravalent silicon displays a pronounced acceptor ability and is capable of extending its valence shell to contain 10 or even 12 electrons. Such penta- or hexacoordinated species may either be anions or neutral coordination complexes in which the valence shell expansion is achieved by either intra- or intermolecular interaction with donor atoms belonging, as a rule, to the first (N, O and F) and second (P, S and Cl) rows. However, the Lewis acid strength of tetravalent silicon is weaker than that of the heavier members of Group 14, as dramatically illustrated by a comparison of the solid... 

The last formula—a stable compound, not a radical—is that of marsh gas, today known as methane. Some, following Anschutz, have imder-standably seen in this paper the proposal of a fifth chemical "type" to add to Gerhardt s four, namely the "marsh gas type," and a modern chemical eye sees an implicit suggestion of carbon tetravalence here. 

At a public celebration in his honor in 1890, in "highly indiscrete revelations of my intellectual life," Kekule spoke of the origin of his ideas on carbon tetravalence and self-linking. 

The first point that Kekule wanted to make is that his was the earliest such hypothesis for the aromatic nucleus that followed the rules of atomicity, especially carbon tetravalence, and that could not immediately be rejected for obvious predictive (or retrodictive) failures, ft is true that Couper and Loschmidt had each tentatively suggested structures for benzene, but Kekule was right that this was the first time that anyone had made a serious, competent, and sustained attempt to develop such a structural aromatic theory and to explore its consequences empirically. It was also the first time that anyone had proposed the CHT structure as the essence of aromaticity. 

A primer on organic-chemical nomenclature "cyclo" indicates a ring structure "hexa indicates six carbon atoms in the formula and "tri-ene" indicates that there are three carbon-carbon double bonds. Since the unnamed "default" is always the carbon-carbon single bond there must be three of them as well. Hydrogen atoms are assumed to fill in otherwise unspecified valences and are not normally named to maintain carbon tetravalence there must be six in this case. 

The two courses represented in Holzmann s notebook covered most of the new ideas that Kekule introduced in his two theoretical publications of 1857-58 and the first installment of his textbook published in 1859, including carbon tetravalence and self-linking. Consistent with Kussmaul s testimony, the names of Gerhardt and Williamson appear often, and Holzmann s notes show that Kekule gave clear preference to Williamson s realist theory of atomic linkages rather than to Gerhardt s... 

Convert by writing in all carbons, and then adding hydrogen atoms to make the carbons tetravalent. 

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