CAIE A-Level Chemistry A2 30.1.1 Chemistry of Arenes Topic Practice

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Question 1

[Maximum number: 2]

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

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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}.

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Question (ii)

(ii)

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.

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