Chemistry A2 · An introduction to A Level organic chemistry. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Benzene, C6H6, is a flat regular hexagon. Each carbon atom is sp2 hybridised. It uses its three sp2 orbitals to make three σ bonds: two to the carbon atoms on each side and one to a hydrogen atom. The bond angles are 120°.
Each carbon atom has one p orbital left, with one electron in it, at right angles to the ring. The six p orbitals overlap sideways all round the ring. This makes a delocalised π system of six electrons, with electron density above and below the plane of the ring.
Because the electrons are shared equally, all six carbon–carbon bonds are the same length, and benzene is more stable than a ring with three separate C=C bonds would be.
Drawing or describing benzene as three C=C double bonds and three C–C single bonds. There are no separate double bonds: the six π electrons are spread over all six carbon atoms.
Answer: 15 σ bonds and 6 delocalised π electrons
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