# A chemist compares the stability of benzene with that of a theoretical compound called 'cyclohexatriene', which would have three separate C=C double bonds arranged in a six-membered ring. Explain why benzene is more stable than this theoretical cyclohexatriene, and describe one piece of experimental evidence that supports this greater stability.

> WJEC A-Level Chemistry (Wales) — 4.2 Aromaticity · Explain · 5 marks

> Benzene has the molecular formula C₆H₆ and is described as an aromatic compound. A theoretical structure called cyclohexatriene is sometimes used as a comparison. Unlike benzene, cyclohexatriene would have alternating single and double carbon–carbon bonds with no delocalisation.

## Mark scheme (5 marks)

1. In benzene, the electrons from the p-orbitals are delocalised / spread across all six carbon atoms (forming a delocalised electron cloud / pi system)
2. This delocalisation makes benzene more stable than if the electrons were localised in three separate double bonds (as in cyclohexatriene)
3. All carbon–carbon bonds in benzene are identical / the same length, intermediate between a single and double bond
4. Experimental evidence: benzene resists addition reactions / does not readily react with bromine (bromine water remains orange/brown / is not decolourised)
5. This lack of addition reaction shows benzene is more stable than cyclohexatriene would be, since a compound with three real double bonds would readily decolourise bromine water

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-chemist-compares-the-stability-of-72400fed) · Published by Druglandscape Ltd.