Electrophilic Substitution

Edexcel A-level ChemistryArenesLesson 6 of 13

Benzene has a high electron density in its ring of delocalised π electrons, so it is attacked by electrophiles: electron-pair acceptors, usually positive ions such as NO₂⁺ or Br⁺. Unlike alkenes, however, benzene reacts by substitution, not addition: the electrophile replaces one hydrogen atom on the ring. Substitution keeps the stable delocalised system, whereas addition would destroy it.

Because benzene is so stable, a strong electrophile is needed, and it usually has to be generated using a catalyst.

General mechanism (electrophile E⁺):

More in Arenes

• The Kekulé Model
• The Delocalised Model of Benzene
• Evidence for Delocalisation
• Combustion of Benzene
• Bromination of Benzene
• Nitration of Benzene
• Friedel-Crafts Alkylation
• Friedel-Crafts Acylation

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