17.5 : 苯的结构：分子轨道模型

The molecular orbital model describes benzene as a regular planar hexagon with six sp² hybridized carbons.

Adjacent carbon atoms form σ bonds via sp²–sp²  orbital overlap. Each carbon atom also forms a σ bond with hydrogen by sp²–1s orbital overlap. All the bond angles are 120°.

In addition, each carbon has a half-filled unhybridized 2p atomic orbital perpendicular to the plane of the ring.

These six 2p orbitals combine to form three bonding and three antibonding molecular orbitals.

The bonding orbitals are completely filled by the six π electrons, while the antibonding orbitals are empty, giving benzene a closed-shell configuration that confers stability.

Consequently, the π electron density is delocalized in the form of doughnut-shaped regions above and below the plane of the ring.

Delocalization also explains why just one carbon–carbon bond length is observed for benzene, with a value between typical carbon–carbon single and double bond lengths.