Dewar benzene

• Bicyclo [ 2.2.0 ] hexa -2 ,5-diene
• Dewar benzene

Liquid

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Dewar benzene (also Dewar benzene) is the common name for the compound bicyclo [ 2.2.0 ] hexa -2 ,5-diene, a valence isomer of benzene. The name describes the proposed by James Dewar formula for benzene.

In 1962, the first time derivative of this basic structure are produced in the following year, the synthesis of pure Dewar benzene. It has because of the four-atom rings and double bonds in a high ring strain and is therefore much less stable than benzene. Moreover, it is non-aromatic as opposed to benzene and showing in the NMR spectrum of two instead of a signal.

Under normal conditions, it isomerizes with a half-life of 37 hours of benzene. The conversion is kinetically inhibited, as is thermally forbidden to benzene because of the conservation of orbital symmetry, the direct reaction. The thermal ring opening with a hike of four electrons leads to the Woodward -Hoffmann rules for conrotatory course ( same sense of rotation of the sp3 carbons of the Dewar benzene ), after which an exocyclic and an endocyclic proton and thus a trans double bond would arise. The geometry is obtained for reasons of ring strain energy is not desirable, which accounts for the comparatively long half-life of the dewar benzene.

Representation

It is produced by irradiation of cis -1 ,2- Dihydrophthalsäureanhydrid followed by oxidation with lead (IV ) acetate.

More valence isomers of benzene

• Prismane
• Benzvalene
• Bicyclopropenyl