Engineering Chemistry MCQ (Nucleophillic Substitution Reaction)

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Engineering Chemistry MCQ (Nucleophillic Substitution Reaction)

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1. The atom which defines the structure of a family of organic compounds and their properties is called ___________
a) Resonating structure
b) Homologous structure
c) Functional group
d) Nucleophile
Answer: c
Explanation: The atom which defines the structure of a family of organic
compounds and their properties is called a functional group. Functional groups are
specific groups of atoms or bonds within molecules that are responsible for the
characteristic chemical reactions of those molecules.

2. The functional group in alkyl halide is ___________
a) Hydroxyl group
b) Halogen atom
c) Inert gas
d) All of the mentioned
Answer: b
Explanation: The functional group in alkyl halide is a halogen atom. Halide refers to
halogen. Halogens are a group in the periodic table consisting of five chemically
related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).

3. The halide ion is an extremely ___________
a) Weak base
b) Weak acid
c) Strong base
d) Strong acid
Answer: a
Explanation: The halide ion is an extremely weak base because hydrogen halide are
acidic as they release a proton.

4. When the nucleophile :OR attacks the RX, the resultant product will be ___________
a) R – OH
b) ROR
c) R:CN
d) RNHR
Answer: b
Explanation: When the nucleophile :OR attacks the RX, the resultant product will be ROR. X will be separated.

5. Select the correct statement from the following option.
a) SN2 reaction follows second order kinetics
b) No intermediate is involved in SN2 mechanism
c) SN2 reactions are one-step reaction
d) All of the mentioned
Answer: d
Explanation: SN2 reaction follows second order kinetics and no intermediate is
involved in it. So, SN2 reactions are one-step reaction.

6. The reactivity order of alkyl halides in SN2 is ___________
a) CH3 X > 10 > 20 > 30
b) CH3 X > 20 > 10 > 30
c) CH3 X > 30 > 10 > 20
d) CH3 X > 30 > 20 > 10
Answer: a
Explanation: The correct order of reactivity in alkyl halide is- CH3 X > 10 > 20 > 30. CH3 X is most reactive whereas 30 is least reactive.

7. SN1 reaction involves heterolysis to form the carbocation as an intermediate.
a) True
b) False
Answer: a
Explanation: SN1 reaction involves heterolysis to form the carbocation as an intermediate.

8. Which step in SN1 reaction is a slow rate determining step?
a) Attack of nucleophile
b) Formation of a racemic mixture
c) Formation of a transition state
d) All of the mentioned
Answer: c
Explanation: The first step of formation of the transition state is a slow rate determining step in SN1 reaction.

9. A low concentration of nucleophile favours the ___________
a) SN2 reaction
b) SN1 reaction
c) Both SN1 and SN1 reaction
d) None of the mentioned
Answer: b
Explanation: A low concentration of nucleophile favours the SN1 reaction but high
concentration of nucleophile favours the SN2 reaction.

10. Which of the following reactions are favoured by polar aprotic solvent?
a) SN1 reactions
b) SN2 reactions
c) Both SN1 and SN1 reactions
d) None of the mentioned
Answer: b
Explanation: SN1 reactions are favoured by polar protic solvents whereas SN2
reactions are favoured by polar aprotic solvent.

11. Arrange the following in the decreasing order of leaving group in nucleophilic substitution reaction.
a) H– > Cl– > HO– > Br– > CH3COO–
b) Cl– > Br– > HO– > H– > CH3COO–
c) Cl– > Br– > CH3COO – > HO– > H–
d) HO– > CH3COO – > H– > Br– > Cl–
Answer: c
Explanation: The correct order is- Cl– > Br– > CH3COO – > HO– > H– .

12. Reaction of alcohol with SOCl2 is ___________
a) SN1
b) SN2
c) SNAr
d) SNi
Answer: d
Explanation: Reaction of alcohol with SOCl2 proceeds with retention of configuration
via substitution nucleophilic internal (SNi) mechanism.

13. The nucleophilic substitutions do not occur in haloarenes because ___________
a) The carbon-halogen bond is much shorter
b) The carbon-halogen bond is stronger compared to that in haloalkanes
c) The lone pair of electrons on the halogen participates in delocalisation with the πelectrons of benzene ring
d) All of the mentioned
Answer: d
Explanation: The nucleophilic substitutions do not occur in haloarenes because the
carbon-halogen bond is much shorter and stronger compared to that in haloalkanes
and the lone pair of electrons on the halogen participates in delocalisation with the π-electrons of benzene ring.

14. Which of the following drastic condition is required for the substitution in haloarenes?
a) High temperature
b) High pressure
c) Strong concentrated reagent
d) All of the mentioned
Answer: d
Explanation: Drastics conditions like high temperature, high pressure and strong concentrated reagents are used to carry substitution in haloarenes.

15. The rate of nucleophilic substitution reactions are higher in the presence of ___________
a) Electron withdrawing groups
b) Electron releasing groups
c) Both electron withdrawing and releasing groups
d) None of the mentioned
Answer: a
Explanation: The rate of nucleophilic substitution reactions are higher in the
presence of electron withdrawing groups.