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CAIE A-Level Chemistry A2 30.1 Arenes Questions

Practise selecting arene reagents, drawing electrophilic-substitution mechanisms and predicting substitution sites.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • select reagents and conditions for halogenation, nitration, Friedel–Crafts reactions and hydrogenation
  • draw electrophile formation, the arenium intermediate and restoration of the delocalised ring
  • predict ring or side-chain products from conditions and explain substituent effects on reactivity and position

Covered syllabus points

30.1.1—Chemistry of arenes30.1.2—Mechanism: electrophilic substitution in arenes30.1.3—Whether halogenation will occur30.1.4—In the electrophilic substitution of arenes,

Question 1

[Maximum number: 5]

Cumene is an aromatic hydrocarbon used in the synthesis of other useful chemicals.

cumene

cumene

Question (a)

(a)

Cumene can be synthesised via a Friedel-Crafts alkylation reaction, as shown in Fig. 5.2.

Fig. 5.2

Fig. 5.2

[ 5 ]

Question (i)

(i)

The first step of the reaction forms the (CH3)2CH+\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}^{+} cation.

Identify a suitable reagent for the formation of this cation from 2-bromopropane, (CH3)2CHBr\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHBr}.

[ 1 ]

Question (ii)

(ii)

Complete Fig. 5.3 to show the mechanism for the reaction of benzene with the (CH3)2CH+\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}^{+} cation.

Include all relevant curly arrows and charges.

Fig. 5.3

Fig. 5.3

[ 3 ]

Question (iii)

(iii)

The Friedel-Crafts alkylation of benzene by 1-bromopropane, CH3CH2CH2Br\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}, also produces cumene as the major product.

The CH3CH2CH2+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2}{ }^{+} cation formed in the first step quickly rearranges to form the (CH3)2CH+\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}^{+} cation.

Suggest why this is the case. Explain your answer.

[ 1 ]

Question 2

[Maximum number: 6]

Benzene can be used to make benzoic acid in the two-step process shown in Fig. 7.1.

Fig. 7.1

Fig. 7.1

Question (a)

(a)

Give the reagents and conditions for step 1 and step 2.
step 1
step 2

[ 2 ]

Question (b)

(b)

When treated with Cl2\mathrm{Cl}_{2} under suitable conditions, methylbenzene forms compound J .

When treated with Cl2\mathrm{Cl}_{2} under different conditions with different reagents, methylbenzene forms compound K.

Suggest and draw structures of compounds J and K in the boxes. The molecular formula of each compound is given.

Figure for Question (b) — CAIE A-Level Chemistry A2

State the reagents and conditions required to form each product.
to form compound J
to form compound K

[ 4 ]

Question 3

[Maximum number: 2]

Draw the major products from the nitration of benzoic acid and phenol in the boxes in Fig. 7.1. The molecular formula for each major product is given in the boxes.
major product from benzoic acid, C7H5NO4\mathrm{C}_{7} \mathrm{H}_{5} \mathrm{NO}_{4}
major product from phenol, C6H5NO3\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}_{3}

Question 4

[Maximum number: 3]

Cumene is an aromatic hydrocarbon used in the synthesis of other useful chemicals.

cumene

cumene

Cumene can be synthesised via a Friedel-Crafts alkylation reaction, as shown in Fig. 5.2.

Fig. 5.2

Fig. 5.2

Complete Fig. 5.3 to show the mechanism for the reaction of benzene with the (CH3)2CH+\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}^{+} cation.

Include all relevant curly arrows and charges.

Fig. 5.3

Fig. 5.3

Question 5

[Maximum number: 4]

Benzene can be used to make benzoic acid in the two-step process shown in Fig. 7.1.

Fig. 7.1

Fig. 7.1

When treated with Cl2\mathrm{Cl}_{2} under suitable conditions, methylbenzene forms compound J .

When treated with Cl2\mathrm{Cl}_{2} under different conditions with different reagents, methylbenzene forms compound K.

Suggest and draw structures of compounds J and K in the boxes. The molecular formula of each compound is given.

Figure for Question 5 — CAIE A-Level Chemistry A2

State the reagents and conditions required to form each product.
to form compound J
to form compound K

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