(A Level) Arenes and halogenoarenes

Learning objectives

Describe the shape of benzene using sp² hybridisation, a σ-bond framework and a delocalised π system, and explain why arenes undergo substitution rather than addition

Describe the reactions of benzene and methylbenzene: halogenation with an AlCl₃ or AlBr₃ catalyst, nitration with concentrated HNO₃ and H₂SO₄ at 25–60 °C, Friedel–Crafts alkylation and acylation, side-chain oxidation by hot alkaline KMnO₄ and hydrogenation over Pt or Ni

Describe the mechanism of electrophilic substitution, including how the electrophile is generated, for the nitration and bromination of benzene

Predict whether methylbenzene is halogenated in the side chain (UV light) or in the ring (halogen carrier), and predict substitution positions from the directing effects of –NH₂, –OH and –R (2- and 4-) and –NO₂, –COOH and –COR (3-)

Explain why chlorobenzene resists nucleophilic substitution that chloroethane undergoes readily, using the overlap of a chlorine lone pair with the ring π system to strengthen the C–Cl bond