30.1 Arenes | CIE A Level Chemistry Topic Questions 2025

1a1 mark

Benzene can react with aluminium bromide, AlBr₃, and bromoethane, CH₃CH₂Br, to form ethylbenzene.

Write the equation for the formation of the CH₃CH₂⁺ species.

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1b1 mark

Name the mechanism for the formation of ethylbenzene from benzene and aluminium bromide.

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1c3 marks

Using the CH₃CH₂⁺ electrophile, draw the mechanism for the conversion of benzene into ethylbenzene. Include all necessary curly arrows and charges.

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1d1 mark

State the type of reaction that occurs in part (c).

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1a3 marks

The nitration of benzene is the first important step in manufacturing dyes and explosives.

i)

Write the equation for the generation of the electrophile.

[1]

ii)

State which reactant acting as a Brønsted-Lowry base and justify your answer.

[1]

iii)

Identify the conjugate acid in the reaction.

[1]

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1b5 marks

Compound B is produced in two steps as outlined in Fig. 1.1.

7-2-1b-h-benzene-pathway-1

Fig. 1.1

i)

Outline the reagents and conditions required for the production of compound A drawn in Fig. 1.1.

[2]

ii)

Using curly arrows, describe the mechanism for step 1.

[3]

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1c2 marks

Draw the dot-and-cross diagram for the structure of the catalyst, once the electrophile has been generated in part (b).

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1d4 marks

Explain why benzene can generally only undergo substitution reactions.

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1a5 marks

4-nitromethylbenzene can be prepared via an electrophilic substitution reaction as shown in Fig. 1.1.

Fig. 1.1

i)

This reaction also forms an isomer of 4-nitromethylbenzene as a by-product. Draw the structure of this by-product.

[1]

ii)

Write an equation for the reaction between HNO₃ and H₂SO₄ that forms the electrophile for this reaction.

[1]

iii)

Describe how the structure and bonding of the six-membered ring in intermediate T differ from those in methylbenzene. In your answer refer to the hybridisation, the π bonding and the bond angles in the ring system.

[3]

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1b6 marks

Benzocaine is used as a local anaesthetic. It can be synthesised from 4-nitromethylbenzene by the route shown in Fig. 1.2.

Fig. 1.2

i)

Give the systematic name of compound W.

[1]

ii)

Suggest the reagents and conditions for step 1.

step 1 .....................................................................................

[2]

ii)

Suggest the reagent for step 2.

step 2 ...................................................................................................

[1]

iii)

Suggest the reagents and conditions for step 3 and step 4.

step 3 ........................................................................................................

step 4 ........................................................................................................

[2]

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1c5 marks

A sample of benzocaine was analysed by carbon-13 NMR and proton NMR spectroscopy.

i)

Predict the number of peaks in the carbon-13 NMR spectrum of benzocaine.

[1]

Benzocaine was dissolved in CDCl₃ and the proton NMR spectrum of this solution was recorded as shown in Fig. 1.3.

fig-4-3-9701-y22-sp-4-cie-ial-chem

Fig. 1.3

ii)

The data in Table 1.2 should be used in answering this question.
Complete Table 1.1 for the chemical shifts δ 1.2 ppm, 3.5 ppm and 5.5 ppm.

Table 1.1

δ / ppm	environment of proton	number of ¹H atoms responsible for the peak	splitting pattern
1.2
3.5
5.5
7.1–7.4	attached to aromatic ring	4	two doublets

[3]

iii)

Explain the splitting pattern for the absorption at δ 1.2 ppm.

[1]

Table 1.2

Environment of proton	Example	chemcial shift range, δ / ppm
alkane	–CH₃, –CH₂–, >CH–	0.9–1.7
alkyl next to C=O	CH₃–C=O,–CH₂–C=O, >CH–C=O	2.2–3.0
alkyl next to aromatic ring	CH₃–Ar, –CH₂–Ar, >CH–Ar	2.3–3.0
alkyl next to electronegative atom	CH₃–O,–CH₂–O, –CH₂–Cl	3.2–4.0
attached to alkene	=CHR	4.5–6.0
attached to aromatic ring	H–Ar	6.0–9.0
aldehyde	HCOR	9.3–10.5
alcohol	ROH	0.5–6.0
phenol	Ar–OH	4.5–7.0
carboxylic acid	RCOOH	9.0–13.0
alkyl amine	R–NH–	1.0–5.0
aryl amine	Ar–NH2	3.0–6.0
amide	RCONHR	5.0–12.0

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1d3 marks

Benzocaine can also be used to synthesise the azo compound S by the following route.

Fig. 1.4

i)

Suggest the reagent(s) used for step 1.

[1]

ii)

Suggest structures for compounds R and S and draw them in the boxes in Fig. 1.4.

[2]

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Reagent	Product with compound A
Na
H⁺ / KMnO₄

Arenes (CIE A Level Chemistry)

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