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Benzene: Introduction to Aromatic Compounds

Molecular Orbital Theory of Benzene

The structure and chemical behavior of benzene (as well as of other aromatic compounds) can be explaind by either the resonance theory or the molecular orbital theory.

The linear combination of benzene's six 2p orbitals, which are perpendicular to the ring plane, yields three bonding and three antibonding π molecular orbitals.

Fig.1
Benzene's π molecular orbitals.

As each 2p orbital formally contains one electron, six π electrons must be distributed among six π molecular orbitals. Therefore, according to Hund's rule, the three molecular orbitals that have the lowest energy level - that is, the three bonding molecular orbitals - are fully occupied, while the three antibonding molecular orbitals remain empty. The resulting electron configuration is considerably low in energy. Benzene's high stability can partially be explained by its molecular orbitals and its electron configuration.

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