Arenes | CIE A Level Chemistry Exam 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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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