# Electrophilic aromatic substitution

Benzene's ring is very stable because its electrons are spread around the ring (aromatic). It reacts by substitution, not addition, so the ring survives. An electrophile attacks, a cation forms, then H⁺ is lost to restore the ring.

Chemistry (university) · Part 10: Organic reactions and mechanisms · Card 7 of 10 · Last updated 2026-10-19

## Analogy

Swapping one tile in a mosaic while keeping the whole pattern.

## Example

**Nitration of benzene**

HNO₃ + H₂SO₄ → NO₂⁺ (electrophile)
NO₂⁺ attacks the ring
Lose H⁺, ring restored
Product: nitrobenzene

## In practice

Nitration of benzene, with a mixture of nitric and sulfuric acids, is the first step to making dyes and many medicines.

## Practice

### Flashcards

- **What is the product when benzene reacts with NO₂⁺?** Nitrobenzene (substitution, ring kept).

## Questions people ask

### Why doesn't benzene react like an alkene?

Addition to benzene would destroy the aromatic ring, losing its extra stability of about 150 kJ/mol. Substitution keeps the ring intact, so it is the favoured path. Benzene is also less reactive than alkenes, which is why it needs a strong electrophile and a catalyst.

### What does an activating or directing group do?

Groups on the ring change both the speed and the position of the next substitution. Electron-donating groups such as OH and CH₃ speed up the reaction and direct new groups to the ortho and para positions. Electron-withdrawing groups such as NO₂ slow it and direct to meta.

Web page: https://studyvisually.com/learn/science/chemistry-university/chemistry-university-part-10/chemistry-university-part-10-concept-7
Study this card in the app: https://studyvisually.com/app/learn?category=chemistry-university&card=chemistry-university-part-10-concept-7