# Benzene is more stable than expected based on its molecular formula. This extra stability is explained by the delocalised model of bonding in benzene. Explain why the delocalised model of benzene predicts greater stability than a structure containing three isolated carbon–carbon double bonds, and describe the evidence from one reaction of benzene that supports this greater stability.

> Edexcel A-Level Chemistry (9CH0) — 18.1 Aromatic chemistry · Explain · 5 marks

## Mark scheme (5 marks)

1. In the delocalised model, the six pi electrons are spread over all six carbon atoms (rather than fixed between two carbons)
2. Delocalisation lowers the energy of the molecule / makes it more energetically stable than a localised (Kekulé) structure
3. All C–C bond lengths in benzene are equal / intermediate between a single and double bond length, consistent with delocalisation rather than alternating single and double bonds
4. Benzene preferentially undergoes electrophilic substitution rather than addition (accept: does not readily undergo addition reactions / does not react with bromine water under normal conditions)
5. Substitution preserves the delocalised pi system / ring is maintained because the extra stability would be lost if addition occurred

## Key terms

- [delocalised](https://www.gradenine.co.uk/glossary/delocalised)

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/benzene-is-more-stable-than-expected-2694f2ed) · Published by Druglandscape Ltd.