CAIE A-Level Chemistry 30.1.2 Electrophilic Substitution in Arenes

Practise complete electrophilic-substitution mechanisms for nitration, bromination and related arene reactions.

Exam points

generate the electrophile and show a curly arrow from the aromatic π system to its electron-deficient atom
draw the positively charged arenium intermediate with the new carbon–electrophile bond and ring hydrogen
move the C–H bond pair back into the ring, release H+ and explain why substitution preserves aromatic stabilisation

[Maximum number: 3]

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

cumene

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

Fig. 5.2

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

Include all relevant curly arrows and charges.

Fig. 5.3

Figure for Answer to Question 30.1.2—Mechanism: electrophilic substitution in arenes question 1 — CAIE A-Level Chemistry A2

M1: curly arrow from inside the hexagon ring

AND towards positively charged carbon atom (in the electrophile $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}^{+}$ )

M2: structure of the intermediate

M3: curly arrow from C-H bond into the ring AND formation / loss of $\mathrm{H}^{+}$

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30.1.2—Mechanism: electrophilic substitution in arenes question 1