The Molecular Orbital Picture of Benzene

FIGURE 13.11 A comparison of the total 71 energy of benzene, 1,3,5-hexatriene, and three ethylenes. The calculations are based on the number of electrons and the energy of each n electron. 

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The molecular orbital picture of benzene proposes that the six jt electrons are no longer associated with particular bonds, but are effectively delocalized over the whole molecule, spread out via orbitals that span all six carbons. This picture allows us to appreciate the enhanced stability of an aromatic ring, and also, in due course, to understand the reactivity of aromatic systems. There is an alternative approach based on Lewis structures that is also of particular value in helping us to understand chemical behaviour. Because this method is simple and easy to apply, it is an approach we shall use frequently. This approach is based on what we term resonance structures. 

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