Topic 30
Hydrocarbons
Topic 30 at A Level is the chemistry of arenes. These pages also cover the shape and bonding of benzene with sp² hybridisation and the delocalised π system (29.3.1) and the naming of aromatic compounds (29.1.4). They cover the substitution reactions of benzene and methylbenzene with chlorine and bromine, nitration, Friedel–Crafts alkylation and acylation, oxidation of the side chain to benzoic acid and hydrogenation of the ring (30.1.1); the mechanism of electrophilic substitution and aromatic stabilisation (30.1.2); side-chain versus ring halogenation (30.1.3); and the directing effects of substituents (30.1.4), with the halogenoarene preparation from Topic 31.
Revision Notes
9 revision notes, in the order the specification teaches them.
Structure and Bonding in Benzene
The structure and bonding of benzene: the Kekulé and delocalised models, p-orbital overlap, the π system and how benzene is represented.
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Evidence for the Structure of Benzene
The evidence for the structure of benzene: hydrogenation enthalpies, delocalisation energy, bond lengths and resistance to addition.
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Naming Aromatic Compounds
Naming substituted aromatic compounds: IUPAC rules, ring numbering, the phenyl group and worked examples.
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Electrophilic Substitution in Benzene
Electrophilic substitution in benzene: substitution versus addition, the general mechanism and the delocalised intermediate.
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Nitration of Benzene
The nitration of benzene: reagents and conditions, generation of NO₂⁺, the mechanism and the role of sulfuric acid.
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Halogenation of Benzene
The halogenation of benzene: the catalyst, generation of the halogen electrophile and the electrophilic substitution mechanism.
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Friedel–Crafts Alkylation and Acylation
Friedel–Crafts alkylation and acylation of benzene: AlCl₃ catalyst, the electrophile and the mechanism.
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Other Reactions of Benzene and Methylbenzene
The hydrogenation of benzene and side-chain oxidation of methylbenzene, with a reaction map of the arene chemistry.
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Directing Effects in Electrophilic Substitution
Directing effects in aromatic substitution: 2,4-directing and 3-directing groups, predicting products and planning synthesis.
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Summary maps
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Benzene Map
Cambridge International AS & A Level Chemistry · Topic 30 Hydrocarbons
Every reaction on one A4 page: reagents, conditions and reaction type for each arrow, colour coded, with the key tests.
Methylbenzene Map
Cambridge International AS & A Level Chemistry · Topic 30 Hydrocarbons
Every reaction on one A4 page: reagents, conditions and reaction type for each arrow, colour coded, with the key tests.
Benzene Structure Map
Cambridge International A Level Chemistry · 30 Benzene
All of the benzene section on one A4 page: the models, the evidence, stability and naming.
Reactions of Arenes Map
Cambridge International A Level Chemistry · 30 Reactions of arenes
All of the arenes section on one A4 page: substitution, hydrogenation, ring or side chain, oxidation and directing.
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30.1.1
- a i
describe the chemistry of arenes as exemplified by the substitution reactions of benzene and methylbenzene with Cl2 in the presence of a catalyst, AlCl3, to form halogenoarenes (aryl halides)
Revise - a ii
describe the chemistry of arenes as exemplified by the substitution reactions of benzene and methylbenzene with Br2 in the presence of a catalyst, AlBr3, to form halogenoarenes (aryl halides)
Revise - b
describe the chemistry of arenes as exemplified by the nitration of benzene and methylbenzene with a mixture of concentrated HNO3 and concentrated H2SO4 at a temperature between 25 °C and 60 °C
Revise - c
describe the chemistry of arenes as exemplified by the Friedel–Crafts alkylation of benzene and methylbenzene by CH3Cl and AlCl3 and heat
Revise - d
describe the chemistry of arenes as exemplified by the Friedel–Crafts acylation of benzene and methylbenzene by CH3COCl and AlCl3 and heat
Revise - e
describe the chemistry of arenes as exemplified by the complete oxidation of the side-chain of methylbenzene using hot alkaline KMnO4 and then dilute acid to give a benzoic acid
Revise - f
describe the chemistry of arenes as exemplified by the hydrogenation of the benzene ring using H2 and Pt/Ni catalyst and heat to form a cyclohexane ring
Revise
30.1.2
- a i
describe the mechanism of electrophilic substitution in arenes as exemplified by the formation of nitrobenzene
Revise - a ii
describe the mechanism of electrophilic substitution in arenes as exemplified by the formation of bromobenzene
Revise - b
describe the mechanism of electrophilic substitution in arenes with regards to the effect of delocalisation (aromatic stabilisation) of electrons in arenes to explain the predomination of substitution over addition
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30.1.3
- 30.1.3
predict whether halogenation will occur in the side-chain or in the aromatic ring in arenes depending on reaction conditions
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30.1.4
- a
describe that in the electrophilic substitution of arenes, the –NH2 substituent directs to particular ring positions
Revise - b
describe that in the electrophilic substitution of arenes, the –OH substituent directs to particular ring positions
Revise - c
describe that in the electrophilic substitution of arenes, the –R substituent directs to particular ring positions
Revise - d
describe that in the electrophilic substitution of arenes, the –NO2 substituent directs to particular ring positions
Revise - e
describe that in the electrophilic substitution of arenes, the –COOH substituent directs to particular ring positions
Revise - f
describe that in the electrophilic substitution of arenes, the –COR substituent directs to particular ring positions
Revise
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