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Updated Mar 13, 2026

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Understanding Benzene and Electrophilic Substitution Reactions

Diah Diamond

@diahdiamond

Electrophilic substitution is one of the most important reaction types... Show more

Electrophilic Substitution
addition would disrupt, the Js system so substitution reactions are more.common...

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general equation

Electrophilic Substitution Reactions

Ever wondered why benzene doesn't just add groups like alkenes do? Electrophilic substitution happens because adding groups would destroy benzene's stable π electron system, so substitution (swapping hydrogen for something else) is much more favourable.

The basic mechanism is straightforward: an electrophile (E⁺) attacks the benzene ring, forming an unstable intermediate where a hydrogen temporarily disrupts the aromatic system. Then H⁺ is lost, restoring the stable benzene structure.

Nitration uses concentrated HNO₃ and concentrated H₂SO₄ as a catalyst. The acids react together to generate NO₂⁺ (the electrophile), which attacks benzene to form nitrobenzene. Keep the reaction cool to prevent multiple substitutions happening at once.

Halogenation needs a halogen carrier like FeCl₃ or AlBr₃ because halogens alone aren't electrophilic enough. The carrier polarises Br₂ to create Br⁺, which can then attack the benzene ring.

💡 Remember: These reactions substitute a hydrogen atom rather than adding across a double bond - that's what keeps the aromatic ring stable!

Friedel-Crafts reactions form new C-C bonds to aromatic rings and come in two types. Alkylation adds alkyl chains using haloalkanes and halogen carriers under reflux. Acylation adds acyl groups $C=O chains$ using acid chlorides, halogen carriers, and reflux conditions.

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Chemistry

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Updated Mar 13, 2026

•

1 page

Understanding Benzene and Electrophilic Substitution Reactions

Diah Diamond

@diahdiamond

Electrophilic substitution is one of the most important reaction types in organic chemistry, especially when it comes to benzene and aromatic compounds. These reactions allow you to add different groups onto benzene rings whilst keeping the stable aromatic structure intact.

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Electrophilic Substitution Reactions

💡 Remember: These reactions substitute a hydrogen atom rather than adding across a double bond - that's what keeps the aromatic ring stable!