Benzene Kekule ring structure

Definition The local aromaticity is given by the quotient of the number of time a ring appears in all Kekule valence structures as a benzene Kekule ring and the number of Kekule valence structures. 

Structure. The representation of the benzene molecule has evolved from the Kekule ring formula (1) to the more electronically accurate (2), which iadicates all carbon—carbon bonds are identical. 

F, A. Kekule s structural formulae for organic compotmds ring structure of benzene 1865. 

Only four years after Kekule proposed the ring structure for benzene, and before the configuration of salicylic acid was established, Kraut concluded on the basis of sound chemical evidence that the products obtained on heating acetylsalicylic acid possess chain structures formed through intermolecular esterification. He assigned the dimeric and tetrameric formulas... 

Figure 11.16 The Kekule structures of benzene (C6H6) (upper structures), showing the two possible arrangements of the double bonds around the ring. Below is the aromatic resonance structure with the rotation of the double bonds symbolized by a ring, and the hydrogen atoms assumed to be present at each of the six corners .

Chemists proposed many structures for benzene. However, the facts didn t support any of the possibilities until Kekule proposed a ring structure in 1865. Some of the proposed structures, including Kekule s, are in Figure 6-1. 

The other contentious issue is what might be termed the Kekule/Loschmidt controversy. Here Kekule is said to have been anticipated by J. Loschmidt in his proposal of a ring structure for benzene.134,135 Indeed one of the authors has proceeded to repeat the charge and, on the strength of researches by Kekule s biographer,... 

Friedrich August Kekule von Stradonitz studied the chemistry of carbon in the 1850s and 1860s. He proposed the ring structure of benzene and that carbon was tetravalent. 

Attempts to localize the double bonds of the benzene ring in a Kekule-like structure have been made with some success by the groups of Vollhardt [57] and of Frank and Siegel [58]. This was reminiscent of the Mills-Nixon effect predicted in the 1930 s, although the partial localization has nothing to do with the tautomeric equilibrium in benzene argued by Kekule. 

Naphthalene Naphthalene (C10H8) is the simplest fused aromatic compound, con- Hydrocarbons sisting of two fused benzene rings. We represent naphthalene by using one of the three Kekule resonance structures or using the circle notation for the aromatic rings. 

Naden continued in verse to describe the presentation, then reported how a member of the audience in sad sepulchral tone 95 had disputed the speaker s view of molecules, particularly, it can be inferred, the cyclic structure of benzene first proposed by Kekule only 20 years earlier. Her Demonstrator, Thomas Turner, obviously contested the ring structure of benzene, as he replied in verse ... 

Kekule s structure, then, accounts satisfactorily for facts (a), ( ), and (c) in Sec. 10.3. But there are a number of facts that are still not accounted for by this structure most of these unexplained facts seem related to unusual stability of the benzene ring. The most striking evidence of this stability is found in the chemical reactions of benzene. 

Many rings and clusters, however, cannot be understood within the two-center two-electron bond framework. This is sometimes extended by assuming resonance, for example between the two Kekule-type structures for benzene (6). A more natural approach is to extend the molecular orbital (MO) approach (see Topic C6) to many atoms. The so-called Hiickel theory of ring systems makes important predictions relevant to inorganic molecules such as S2N2. Clusters such as boranes also... 

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