A-Level Chemistry: Aromatic Chemistry Syllabus

Overview

In A-level Chemistry, aromatic chemistry usually focuses on benzene and related arenes. Students learn the structure and bonding in benzene, why it is unusually stable because of delocalised electrons, and why aromatic compounds usually undergo substitution rather than addition.

        Key idea: benzene is stable because its electrons are delocalised across the ring, so it resists addition reactions that would disrupt this stability.
      

1. Structure and Bonding in Benzene

Benzene has a planar hexagonal ring.
All carbon-carbon bonds are the same length, intermediate between single and double bonds.
Each carbon is sp² hybridised.
The ring contains delocalised p electrons above and below the plane.
This delocalisation makes benzene more stable than the Kekulé model suggests.

2. Reactivity of Aromatic Compounds

Benzene is less reactive than alkenes toward addition reactions.
Aromatic compounds prefer electrophilic substitution.
This preserves the stability of the aromatic ring.

3. Electrophilic Substitution

Students are typically expected to know the general mechanism for electrophilic substitution in benzene, usually limited to monosubstitution.

Nitration

Learn the conditions, products, and the generation of the NO₂⁺ nitronium ion.

Halogenation

Study the substitution of hydrogen by a halogen using a catalyst.

Friedel–Crafts Reactions

Understand alkylation and/or acylation using catalysts such as AlCl₃.

4. Phenol and Other Aromatic Derivatives

Phenol reacts more readily than benzene in bromination.
Students may study the acidity of phenol.
Some specifications include phenol reactions with bromine and ethanoyl chloride.
Some boards also include tests such as the FeCl₃ test for phenols.

5. Aromatic Amines and Nitro Compounds

Some courses compare the basicity of aromatic amines with ammonia and aliphatic amines.
Aromatic nitro compounds may be studied through their reduction to amines.

Exam Skills Checklist

Explain why benzene is unusually stable.
Describe delocalised bonding in the benzene ring.
Compare benzene with alkenes in terms of reactivity.
Write electrophilic substitution mechanisms.
Recall reagents, conditions, and products for nitration, halogenation, and Friedel–Crafts reactions.
Apply ideas to phenol and aromatic amines where required by the exam board.