---
title: "Benzene: Delocalisation and Electrophilic Substitution"
description: "Benzene's six electrons spread around the ring instead of sitting in three double bonds, which makes it much more stable than the alternative structure. That stability is why it substitutes rather tha"
canonical: https://lightmysky.com/learn/science/benzene-delocalisation-and-electrophilic-substitution-mt_jFqF7cZ0Ij
source: https://lightmysky.com/learn/science/benzene-delocalisation-and-electrophilic-substitution-mt_jFqF7cZ0Ij.md
retrieved: 2026-09-12
---

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# Benzene: Delocalisation and Electrophilic Substitution

Benzene's six electrons spread around the ring instead of sitting in three double bonds, which makes it much more stable than the alternative structure. That stability is why it substitutes rather than adds.

Subject: Science · Area: Chemistry · Ages 17 to 18
Page: https://lightmysky.com/learn/science/benzene-delocalisation-and-electrophilic-substitution-mt_jFqF7cZ0Ij

## Ready when they can

- Compares the enthalpy of hydrogenation of benzene with three times that of cyclohexene and says what the gap shows
- Gives two further pieces of evidence against alternating double bonds, such as equal bond lengths and the failure to decolourise bromine water
- Draws the mechanism for nitration, including how the electrophile is generated
- Explains why the ring is restored at the end of the mechanism

## Lesson: Benzene keeps its ring

Benzene spreads its six pi electrons around the whole ring instead of fixing them in three double bonds. Burning it with hydrogen releases clearly less energy than three cyclohexenes would, so the ring starts from a calmer, more stable place.

Two more clues agree. Every carbon to carbon bond in benzene shares one length, and benzene will not decolourise bromine water the way alkenes do.

**Example.** In nitration, concentrated nitric and sulfuric acids make the NO2+ electrophile, the ring offers its electrons to it, and then a proton drops off so the shared loop closes again as nitrobenzene.

**Tip.** Adding would smash the shared ring and its bonus stability, so benzene substitutes instead and keeps the ring intact. Whenever you write the mechanism, end it by restoring the loop.

**Recap.** Shared electrons bring bonus stability, tests deny fixed double bonds, and substitution protects the ring.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Electrophilic Addition to Alkenes](https://lightmysky.com/learn/science/electrophilic-addition-to-alkenes-mt_1RB5nj8zR8)
- [Hess's Law and Enthalpy Cycles](https://lightmysky.com/learn/science/hesss-law-and-enthalpy-cycles-mt_530V9czLOb)
- [Giant Covalent Structures: Diamond, Graphite and Graphene](https://lightmysky.com/learn/science/giant-covalent-structures-diamond-graphite-and-graphene-mt_YTEj9srwPG)

## Opens up

- [Aromaticity: Huckel's Rule and Antiaromatic Systems](https://lightmysky.com/learn/science/aromaticity-huckels-rule-and-antiaromatic-systems-mt_2UmZKQozyN)
- [Hybridisation, Conjugation and Delocalisation in Organic Molecules](https://lightmysky.com/learn/science/hybridisation-conjugation-and-delocalisation-in-organic-molecules-mt_Anv0MSQ4hq)