Engineering Chemistry MCQ (Electrophillic Substitution Reaction – 1)

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Engineering Chemistry MCQ (Electrophillic Substitution Reaction – 1)

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
Answer: b
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 catalysis in the nitration of benzene?
a) Conc. HCl
b) Dil. HCl
c) Conc. H2SO4
d) Dil. H2SO4
Answer: c
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.
a) 10
b) 9
c) 8
d) 7
Answer: d
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
Answer: a
Explanation: The necessary condition for desulphonation is to 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
Answer: c
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
Answer: a
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 the presence of a lewis acid as a catalyst to produce alkylbenzene is known as ___________
a) Nitration
b) Halogenation
c) Friedel-Crafts Acylation
d) Friedel-Crafts Alkylation
Answer: d
Explanation: The reaction in which benzene reacts with alkyl halide in the 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?
a) Toulene
b) Isopropyl benzene
c) O-xylene
d) P-xylene
Answer: b
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 ___________
a) Alkylbenzene
b) Alkylamine
c) Arylketone
d) Halobenzene
Answer: c
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
Answer: d
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.