Kekule ring structure

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... 

The ring systems are treated as branched chains and phenyl group is treated for the purpose of determining its priority as though it had one of the Kekule s structures... 

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. 

As we continue to larger rings, the results are not so clearcut. There is a tendency for the saddle points to alternate in and out somewhat, but the interaction energy appears to be a maximum at the ring of six atoms. These last more-or-less qualitative comments have been based upon just the two simple Kekule-like structures of the rings, and may not be able to show the proper behavior. The actual surface calculations of ( 2)2 and (H2)3 included many more structures and show strikingly different qualitative behavior. 

Look at the "Kekule" resonance structure shown in the center of Eq. 5-4. The two negative charges flanking the dissociable proton are sufficient to hold it firmly to the ring at low pH. The proton is half dissociated only when the pH is raised to 9.2. At still higher values of pH (pfCa -12.4) a proton dissociates from a ribose hydroxyl group. 

Based on these assumptions, Kekule postulated a structure that had six carbons forming a ring structure. The remaining three modes of unsaturation were the result of three double bonds alternating with three single bonds. This arrangement allowed all the carbon atoms to have four bonds as required by structural theory. 

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. 

In Fig. 23 we have illustrated several HH-Clar structures of smaller benzenoids and have indicated their vulnerable rings. Each of the Kekule valence structure having a single vulnerable ring will produce the corresponding O-Clar structure (i.e., a Kekule valence structure that qualifies as Clar structure). In Fig. 24 are shown additional HH-Clar structures having besides vulnerable ring additional ji-sextets. These structures will reduce to k-Clar structures when Ji-sextet of the vulnerable... 

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 ... 

The evidence from X-ray, spectroscopic, and thermochemical investigations considered in the previous sections shows clearly that the lower phosphonitrilic chlorides possess cyclic structures which exhibit a high degree of stability, suggestive of aromatic character. Such a view of their structure is compatible with their low reactivity compared with other acid chlorides, and with the maintenance of the ring structure in a variety of derivatives. It is easy to write Kekule-type structures for the trimeric chloride (III) such structures have also been suggested... 

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