29.3 Shapes of aromatic organic molecules; σ and π bonds

Each carbon in benzene is sp² hybridised and forms three σ bonds in a trigonal-planar arrangement. The remaining p orbital overlaps with neighbours to make one delocalised π system above and below the ring.

Delocalisation makes the ring planar and gives all six C–C bonds an intermediate character rather than three independent double bonds. The π electrons are spread around the ring.

Benzene has six equal C–C bond lengths, shorter than a single bond but longer than a local C=C double bond. This helps explain why addition would sacrifice aromatic stabilisation.

The circle in a benzene drawing is not an extra bond or atom, and the molecule is not a set of three isolated alkenes.