# Chemists once proposed that benzene had a ring structure containing alternating single and double carbon-carbon bonds, known as the Kekulé structure. Explain why experimental evidence does not support the Kekulé structure for benzene, and describe the accepted model of bonding in benzene that accounts for this evidence.

> Eduqas A-Level Chemistry — 4.2 Aromaticity · Explain · 5 marks

## Mark scheme (5 marks)

1. The Kekulé structure predicts that benzene should readily undergo addition reactions (like an alkene), but benzene undergoes substitution reactions instead
2. The Kekulé structure predicts two different C–C bond lengths (single and double), but all six carbon-carbon bonds in benzene are the same / equal length
3. Each carbon atom in the benzene ring contributes one electron to form a delocalised system / pi system
4. The delocalised electrons are spread above and below the plane of the ring / over all six carbon atoms
5. This delocalisation makes all six C–C bonds identical / gives extra stability (delocalisation energy / stabilisation) to benzene

## Key terms

- [Kekulé structure](https://www.gradenine.co.uk/glossary/kekul-structure)

## Related

- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/chemists-once-proposed-that-benzene-had-9fb39b57) · Published by Druglandscape Ltd.