This set of Engineering Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Electrophillic Substitution Reaction – I”.
1. Which of the following is rate determining step in electrophilic substitution reaction?
a) Generation of electrophile
b) Attack by an electrophilic reagent on benzene ring
c) Formation of product
d) All of the mentioned
Explanation: Attack by an electrophilic reagent on benzene ring is a rate determining step in electrophilic substitution reaction. It is also the slowest step of the reaction.
2. Which of the following act as a catalysis in the nitration of benzene?
a) Conc. HCl
b) Dil. HCl
c) Conc. H2SO4
d) Dil. H2SO4
Explanation: Conc. H2SO4 act as a catalysis in the nitration of benzene. Benzene is treated with a mixture of concentrated nitric acid and concentrated sulphuric acid at a temperature not exceeding 50°C.
3. Fuming sulphuric acid is the solution of _________% SO3 in conc. H2SO4.
Explanation: Fuming sulphuric acid is the solution of 7% SO3 in conc. H2SO4. It is also called Oleum which is produced in the contact process, where sulphur is oxidized to sulphur trioxide which is subsequently dissolved in concentrated sulphuric acid.
4. Which of the following is the necessary condition for desulphonation?
a) Remove volatile hydrocarbon by steam distillation
b) Low concentration of water
c) High concentration of sulphonating agent
d) A large excess of fuming sulphuric acid
Explanation: The necessary condition for desulphonation is- Use dilute acid, high concentration of water and remove volatile hydrocarbon by steam distillation.
5. Which of the following act as electrophile in halogenation?
a) Nitronium ion
b) Sulphonium ion
c) Halonium ion
d) Acylium ion
Explanation: Halonium ion act as electrophile in halogenation. Nitronium ion is used in nitration. Sulphonium ion is used in sulphonation. Acylium ion is used in acylation.
6. Aromatic bromination catalyzed by the Lewis acid thalium acetate gives
a) Para isomer
b) Ortho isomer
c) Meta isomer
d) Para and ortho isomer
Explanation: Aromatic bromination catalyzed by the Lewis acid thalium acetate gives only para isomer. It is not Ortho and meta directing.
7. The reaction in which benzene reacts with alkyl halide in presence of a lewis acid as a catalyst to produce alkylbenzene is known as
c) Friedel-Crafts Acylation
d) Friedel-Crafts Alkylation
Explanation: The reaction in which benzene reacts with alkyl halide in presence of a lewis acid as a catalyst to produce alkylbenzene is known as Friedel-Crafts Alkylation. With anhydrous ferric chloride as a catalyst, the alkyl group attaches at the former site of the chloride ion.
8. Which of the following is not a product of the reaction of benzene with CH3Cl and AlCl3?
b) Isopropyl benzene
Explanation: p-xylene is not a product of reaction of benzene with CH3Cl and AlCl3. Toulene, isopropyl benzene and O-xylene are the products of such reaction.
9. The product of Friedel-Crafts Acylation reactions are
Explanation: The product of Friedel-Crafts Acylation reactions are Arylketone. The acylated products may easily be converted to the corresponding alkanes via Clemmensen Reduction or Wolff-Kishner Reduction.
10. How will you convert benzene into n-propyl benzene?
a) Friedel-Crafts Alkylation
b) Friedel-Crafts Acylation
c) Friedel-Crafts Alkylation followed by clemmensen reduction
d) Friedel-Crafts Acylation followed by clemmensen reduction
Explanation: Friedel-Crafts Acylation followed by clemmensen reduction of ketone will give n-propyl benzene. Clemmensen reduction is a chemical reaction described as a reduction of ketones (or aldehydes) to alkanes using zinc amalgam and hydrochloric acid.
Sanfoundry Global Education & Learning Series – Engineering Chemistry.
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