Dewar structure

The Dewar structure (IV) has never been seriously considered since it suffers from the same defects, in an accentuated form, as the Kekule structure. Its advantage over the other structures is largely that it explains the intimate relationship that usually obtains between the para positions in the benzene ring. 

The Dewar-type structure for the central ring of the anthracene system in 19 is possible only because the 9,10 substituents prevent the system from being planar. From 19 is the actual structure of the molecule and is not in resonance with forms like 20, although in anthracene itself, Dewar structures and structures like 20 both contribute. This is a consequence of rule 2 (p. 41). In order for a 20-like stracture to contribute to resonance in 19, the nuclei would have to be in the same positions in both forms. 

The beauty of the Dewar structure, Ingold remarked, lay in the fact that it explains quinoid transformations and aromatic tautomerism as well-established principles of aliphatic and alicyclic chemistry, that is, it provided a rationale for the unification of aliphatic and aromatic chemistry. 

Ingold wrote Soddy that he was going to test the hypothesis by building up the Dewar structure by the methods used to obtain bridged-ring compounds, that is, by closing carbon rings separately.30... 

Dewar structure org chem A structural formula for benzene that contains a bond between opposite atoms. dii-or, str3k-ch3r dew point chem The temperature and pressure at which a gas begins to condense to a liquid. du, point ... 

They are estimated by calculation to account for about 75% of the resonance stabilization of benzene with Dewar structures accounting for most of the remaining stabilization. However, such resonance structures have no separate physical reality or independent existence. A dotted circle is often used to indicate the resonance-stabilized bonding of benzene. Nonetheless, the most frequently appearing structures of benzene are the two Kekule structures. 

DEWAR STRUCTURES KEKULE STRUCTURES c/s-Benzene dihydrodiol dehydrogenase,... 

Deuterium-hydrogen exchange in proteins, HYDROGEN EXCHANGE IN PROTEINS DEVIATION DEWAR STRUCTURES DFP,... 

DEWAR STRUCTURES KEKULE STRUCTURES RESONANCE RAMAN SPECTROSCOPY RAMAN SPECTROSCOPY Resonance stabilization,... 

The Rumer diagrams for benzene actually mirror the real spatial symmetry, and thus the Kekule and Dewar structures emerge. 

Plus less stable forms such as the Dewar structures... 

Pairing schemes 9 and 10 correspond to Kekule s structures, whereas 11,12, and 13 are called Dewar structures because J. Dewar suggested, in 1869, that benzene might have a structure such as 14 ... 

It is clear that the first diagrams, 1 and 2, correspond to the familiar Kekule structures, and the three remaining ones, 3—5, to the Dewar structures. 

One can further consider the refinement of the picture by mixing in the three Dewar structures, D, 3. The Dewar types remain unchanged under the i symmetry operation, and hence will have a g symmetry and form the Aig and E2g combinations, as shown in Fig. 7.4c here the Aig combination is the positive combination of all the Dewar structures, whereas, the E2g... 

FIGURE 7.4 (a) Kekule and Dewar structures of benzene, and their symmetry... 

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