Kekule benzene

Only left ring corresponds to Kekule benzene. 

It is wrong (but common) to see a reversible reaction written with a double-headed arrow, as A B. Such an arrow implies resonance, e.g. between the two extreme valence-bond structures of Kekule benzene. 

The sequential removal of H and H+ from isobutene-type structural units (so-called H2+ abstraction ) was also used to generate the radical anion of non-Kekule benzene , i.e. l,3-dimethylenecyclobutane-l,3-diyl (39) (Scheme 11). As shown by Hill and Squires161, this highly unusual, distonic C(,II(, isomer can be produced in pure form by reaction of O with 1,3-dimethylenecyclobutane (38). Working in a flowing afterglow mass spectrometer, subsequent reactions were again used to characterize this radical anion and differentiate it from other ( VdL, isomers. 

In the process )USt described we are actually considering not only the energy of delocalization but also the energy required to stretch and compress the C—C bonds in Kekule benzene from the lengths 1.54 and 1.34 A to the... 

The modem dye industry is built upon the coal tar industry as its source of material, and upon the Kekule benzene theory as its scientific basis. Without these foundations, the dye industry could not have been developed. 

Such oscillation of the double bonds of the benzene ring is one of the assumptions in connection with the Kekule benzene formula as referred to when we were discussing the constitution of benzene (p. 474). 

In this example, the repulsion between bulky substituents in a planar structure makes the Kekule benzene less stable than the Dewar isomer. 

An a-type reaction is the isomerization to the Kekule benzene which is accomplished thermally or catalyzed by silver ions (72) 43,68). 

In Figure 15 we show all 14 Kekule valence structures of benzo[ / i]perylene. A close look at the Kekule valence structures of benzo /2i]perylene shows that, while some are similar (and some are symmetry-related), others are visibly different. In particular, one can notice a difference between the first Kekule structure, in which five rings out of six, when looked at in isolation, have the Kekule valence structure of benzene, and the last structure, in which only one ring has the Kekule valence structure of benzene. The first structure (structure A in Figure 15), which is the Kekule valence structure with the maximal number of Kekule benzene rings, is known as the Fries structure. In the pre-quantum chem-... 

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