16 past paper MCQs on Chemical Reactions of Benzene, from the Chemistry of Hydrocarbons unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.
1.Alkylbenzene is formed when benzene is treated with an alkyl halide in the presence of anhydrous aluminium chloride. Identify the type of reaction. (MDCAT 2022)
Correct answer: (c) Friedel-Crafts alkylation
An alkyl group substitutes for a ring hydrogen with the Lewis acid as catalyst.
2.Alkylbenzene is formed when benzene is treated with an alkyl halide in the presence of anhydrous aluminium chloride. Identify the type of reaction. (MDCAT 2023)
Correct answer: (c) Friedel-Crafts alkylation
The Lewis acid makes a carbocation from the halide, which substitutes into the ring: Friedel-Crafts alkylation.
3.In Friedel-Crafts acylation an acyl group is introduced into the benzene ring in the presence of the catalyst: (MDCAT 2024)
Correct answer: (a) $\mathrm{AlCl_3}$
Anhydrous aluminium chloride is the Lewis acid that generates the acylium electrophile.
4.Chlorination of benzene in the presence of Iron (III) chloride involves mechanism of: (UHS MDCAT 2025)
Correct answer: (b) Electrophilic Substitution
Iron(III) chloride polarizes the chlorine into an electrophile, which then substitutes into the ring.
5.Which of the following is an electrophile in sulphonation? (NUMS MDCAT 2025)
Correct answer: (b) SO3
Sulphur trioxide is itself electron poor at sulphur, so it attacks the ring without needing a catalyst.
6.Which reagent and condition are used to bring about the reaction shown? Toluene --> p-chloro toluene (SIBA MDCAT 2025)
Correct answer: (b) Cl2 in the presence of AlCl3
Aluminium chloride polarizes the chlorine into an electrophile for ring substitution; light would attack the side chain instead.
7.In Friedel Craft acylation an acyl group is introduced in benzene ring in the presence of catalyst: (UHS MDCAT 2024)
Correct answer: (a) AlCl3
Anhydrous aluminium chloride generates the acylium ion that attacks the ring.
8.Alkylbenzene is formed when benzene is treated with an alkyl halide in the presence of anhydrous aluminum chloride. Identify the type of reaction. (UHS MDCAT 2023)
Correct answer: (c) Friedel-Crafts alkylation reaction
An alkyl group is put on the ring with an alkyl halide and aluminium chloride, which is Friedel-Crafts alkylation.
9.Acetophenone can be formed by which of the following reaction of benzene? (NUMS MDCAT 2023)
Correct answer: (b) Acylation
Friedel-Crafts acylation with acetyl chloride puts the acetyl group on the ring.
10.A new C-C bond formation is possible with: (PMC MDCAT 2022)
Correct answer: (c) Friedel craft reaction
Friedel-Crafts alkylation and acylation both make a new bond from the ring carbon to carbon.
11.Which of the following process gives Benzenesulfonic acid from benzene? (PMC MDCAT 2022)
Correct answer: (b) Sulphonation
Fuming sulphuric acid substitutes a sulphonic acid group into the ring.
12.What is the Catalyst in Friedel-Crafts Alkylation? (PMC MDCAT 2022)
Correct answer: (a) AlCl3
Anhydrous aluminium chloride generates the carbocation that attacks the ring.
13.Electrophile in sulphonation of benzene is: (PMC MDCAT 2020)
Correct answer: (c) SO3
Sulphur trioxide is electron poor at sulphur and attacks the ring directly.
14.Acetophenone can be formed by which of the following reaction for benzene? (PMC MDCAT 2020)
Correct answer: (b) Acylation
Friedel-Crafts acylation with acetyl chloride gives acetophenone.
15.Which of the following acts as an electrophile in the electrophilic substitution of benzene with bromine? (UHS MDCAT 2018)
Correct answer: (a) Br+
The catalyst polarizes the bromine molecule into $\mathrm{Br^+}$, which attacks the ring.
16.For halogenation of benzene, which reagent is used: (UHS MDCAT 2017)
Correct answer: (b) AlCl3
Anhydrous aluminium chloride polarizes the halogen into an electrophile.