Six pi electrons delocalize above and below a planar sp2 ring, giving equal carbon-carbon bond lengths.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Benzene consists of six sp2 carbon atoms forming a planar hexagonal ring held together by sigma bonds. Each carbon also has one unhybridized p orbital, and these six p orbitals overlap to form three bonding pi molecular orbitals that hold six delocalized electrons. All six carbon-carbon bonds are equal, about 139 pm, which lies between typical single and double bond lengths. The stabilization from delocalization, called resonance energy, is about 150 kJ/mol. This delocalized structure gives benzene its unusual stability and its characteristic reactions.
Key ideas: Count: six sigma C-C bonds, six C-H sigma bonds, and six pi electrons in three MOs delocalized over the ring. C-C is 139 pm, between 154 (single) and 134 (double). Enthalpy of hydrogenation is about -208 kJ/mol rather than three times -120 expected for cyclohexene, so benzene is about 150 kJ/mol more stable. All carbons are sp2, and the molecule is planar.
Common mistakes and connections: A major misconception is that benzene alternates between two Kekule forms, or that it has three isolated double bonds, so it should add bromine readily. It does not. Also, do not draw only one Kekule structure when predicting reactivity. Links to resonance, aromaticity, Huckel's rule and electrophilic substitution.
Six sp2 carbons form a flat ring of sigma bonds, with six p orbitals overlapping above and below to make a delocalized pi cloud and equal 140 pm bonds. The interactive lesson shows this as a live animation or chart.
Benzene undergoes substitution rather than addition, because addition would destroy the stable delocalized ring.
Six pi electrons delocalize above and below a planar sp2 ring, giving equal carbon-carbon bond lengths.
Benzene Bonding is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Bonding & Molecular Structure first: Paramagnetism, Heteronuclear Diatomic MOs, Delocalization.
The next topics in Bonding & Molecular Structure are Aromaticity and Huckel's Rule and Intermolecular Forces.
Yes. The interactive lesson includes a self-check question on Benzene Bonding, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Benzene Bonding is topic 68 of 104 in Bonding & Molecular Structure.