Advanced Topic 782 of 1102 Organic Chemistry
Electrophilic Aromatic Substitution
Benzene reacts with electrophiles, replacing hydrogen while keeping aromaticity.
In-depth explanation of Electrophilic Aromatic Substitution
Electrophilic aromatic substitution is the reaction of an aromatic ring with an electrophile, in which one ring hydrogen is replaced by the electrophile. The electrophile first attacks the pi system to form a positively charged, non-aromatic intermediate called a sigma complex or arenium ion, which is stabilized by resonance. Loss of a proton from this intermediate restores aromaticity, which is the driving force for the reaction. Substituents already on the ring control the rate and the position of the new group. Common examples include nitration, halogenation, sulfonation and Friedel-Crafts reactions.
Going deeper: Electrophilic Aromatic Substitution
Key ideas: Mechanism: the ring attacks an electrophile, giving a sigma complex (arenium ion) in the slow step, then loss of H+ restores aromaticity. Reactions: nitration (HNO3 and H2SO4), sulfonation (SO3), halogenation (X2 with FeX3), Friedel-Crafts alkylation and acylation. The electrophile is generated first, such as NO2+ or Br+ polarised by a Lewis acid.
Common mistakes and connections: Students write an addition product that destroys aromaticity. Another common error is forgetting the catalyst (benzene does not react with Br2 alone). Sulfonation is reversible, which makes it useful as a blocking group. Links to directing effects, activation by -OH and -NH2, and why benzene prefers substitution over addition.
Visualization of Electrophilic Aromatic Substitution
The electrophile attacks the ring, forming a high-energy arenium ion; loss of H+ restores aromaticity to give substitution, not addition. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Benzene reacts with bromine in the presence of iron(III) bromide to give bromobenzene.
Frequently asked questions about Electrophilic Aromatic Substitution
What is Electrophilic Aromatic Substitution?
Benzene reacts with electrophiles, replacing hydrogen while keeping aromaticity.
Is Electrophilic Aromatic Substitution a beginner, intermediate or advanced topic?
Electrophilic Aromatic Substitution is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Electrophilic Aromatic Substitution?
Study these earlier topics in Organic Chemistry first: Hydration of Alkenes, Ozonolysis, Polymerization of Alkenes.
What comes after Electrophilic Aromatic Substitution?
The next topics in Organic Chemistry are Nitration of Benzene and Friedel-Crafts Reactions.
Can I practise Electrophilic Aromatic Substitution with quizzes?
Yes. The interactive lesson includes a self-check question on Electrophilic Aromatic Substitution, and the Organic Chemistry quiz draws on every topic in this area.
Where Electrophilic Aromatic Substitution fits in Organic Chemistry
Electrophilic Aromatic Substitution is topic 54 of 148 in Organic Chemistry.