Topic 31
Halogen
Compounds
Topic 31 covers the halogenoarenes: how chlorobenzene and bromobenzene are made by electrophilic substitution of an arene with Cl₂ or Br₂ and an AlCl₃, AlBr₃ or iron catalyst (31.1.1), and why a halogenoarene is so much less reactive towards nucleophiles than a halogenoalkane, exemplified by chlorobenzene and chloroethane: the shorter, stronger C–Cl bond with partial double-bond character from the lone pair delocalised into the ring, and the electron-rich ring that repels nucleophiles (31.1.2). The AS halogenoalkane chemistry is in Topic 15.
Revision Notes
2 revision notes, in the order the specification teaches them.
Making Halogenoarenes by Electrophilic Substitution
Preparing halogenoarenes from benzene and methylbenzene by electrophilic substitution with a halogen and an aluminium halide catalyst.
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Why Halogenoarenes Resist Substitution: Chlorobenzene versus Chloroethane
The difference in reactivity between chloroethane and chlorobenzene towards nucleophilic substitution.
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31.1.1
- a
recall the reaction by which halogenoarenes can be produced: substitution of an arene with Cl2 or Br2 in the presence of a catalyst, AlCl3 or AlBr3 to form a halogenoarene, exemplified by benzene to form chlorobenzene
Revise - b
recall the reaction by which halogenoarenes can be produced: substitution of an arene with Cl2 or Br2 in the presence of a catalyst, AlCl3 or AlBr3 to form a halogenoarene, exemplified by methylbenzene to form 2-chloromethylbenzene and 4-chloromethylbenzene
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31.1.2
- 31.1.2
explain the difference in reactivity between a halogenoalkane and a halogenoarene as exemplified by chloroethane and chlorobenzene
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