ChemistryCode 9701
Arenes
What this topic asks you to be able to do
- describe the chemistry of arenes, illustrated through these processes involving benzene and methylbenzene: substitution by Cl₂ and by Br₂, with AlCl₃ or AlBr₃ acting as catalyst, to produce halogenoarenes (aryl halides); nitration by a mixture of the concentrated acids HNO₃ and H₂SO₄ at 25°C to 60°C; Friedel–Crafts alkylation with CH₃Cl and AlCl₃ under heating; Friedel–Crafts acylation with CH₃COCl and AlCl₃ under heating; complete oxidation of the side-chain with hot alkaline KMnO₄, followed by dilute acid, yielding a benzoic acid; hydrogenation, with H₂ and a Pt/Ni catalyst while heating, of the benzene ring to form a cyclohexane ring
- describe the mechanism of electrophilic substitution in arenes, taking the formation of nitrobenzene and of bromobenzene as examples, and use the effect of electron delocalisation in arenes (aromatic stabilisation) to explain why substitution predominates over addition
- predict, from the reaction conditions, whether an arene is halogenated in its side-chain or in its aromatic ring
- describe how, during electrophilic substitution of arenes, distinct substituent groups steer incoming groups to different positions on the ring (limited to the directing effects exerted by –NH₂, –OH, –R, –NO₂, –COOH and –COR)