Reaction Intermediates - Organic Chemistry Questions and Answers

This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Reaction Intermediates”.

1. Which carbocation is the most stable?
a)
b)
c)
d)
View Answer

Answer: b
Explanation: This is stabilized by extended conjugation. The more adjacent methyl groups there are, the larger hyperconjugation stabilization is because of the increased number of adjacent C–H bonds.

2. Which one among the following carbocations has the longest half-life?
a)
b)
c)
d)
View Answer

Answer: a
Explanation: Higher the stability of cation more will be its half-life. As, in the carbocation, p orbital overlap with the compound, will be more stabilizing factor than aromaticity.

3. The order of decreasing stability of the following cations is?
(I) CH₃C⁺HCH₃ (II) CH₃C⁺HOCH₃ (III) CH₃C⁺HCOCH₃
a) III > II > I
b) I > II > III
c) II > I > III
d) I > III > II
View Answer

Answer: a
Explanation: (II) Here, Mesomeric effect stabilizes carbocation. So, it is highly stabilized.

Find the order of decreasing stability of the following cations

(I) It is stabilized by hyperconjugation.

Order of decreasing stability of cations is CH3C+HCH3 (II) CH3C+HOCH3 (III) CH3C+HCOCH3

(III) It is destabilized as because of carbonyl group; more electronegative Oxygen is present it will decrease electron density of C⁺.

4. Which of the following is most stable intermediate?
a)
b)
c)
d)
View Answer

Answer: c
Explanation: Stabilized by +M effect of OH and hyperconjugation effect (5αH).

5. Which intermediate is involved in the reaction given below?

a) free radical
b) carbocation
c) carbanion
d) carbene
View Answer

Answer: d
Explanation: As we can see, in first step in presence to light carbene is formed.

The intermediate is involved in the reaction

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6. Among the following which is most stabilized cation?
a)
b)
c)
d)
View Answer

Answer: c
Explanation: The positive charge of carbon will be stabalised by mesomeric effect of -NH₂ group.

7. Arrange the following intermediate into decreasing order of stability.

a) I > II > III > IV
b) II > IV > III > I
c) II > I > IV > III
d) II > I > III > IV
View Answer

Answer: d
Explanation: Mesomeric effect will stabilize carbocation is highly stable.
+M effect of –NH₂ > –OH

The following intermediate in decreasing order of stability is II greater than I greater than III greater than IV

8. Arrange the following intermediate into decreasing order of stability.

a) I > III > II > IV
b) II > III > IV > I
c) III > IV > II > I
d) I > III > IV > II
View Answer

Answer: a
Explanation: Mesomeric effect will stabilize carbocation is highly stable.

9. What is the correct decreasing order of stability of following cation?

a) II > III > I > IV
b) IV > II > III > I
c) IV > III > I > II
d) III > I > II > IV
View Answer

Answer: b
Explanation:
(I) It is destabilized by –M and high –I effect.

(II) It is destabilized by –I nature only at meta position –M effect.

(III) It is destabilized by –M and less –I effect.

(IV) There is no destabilisation by group.

10. What is the correct decreasing order of stability of following cation?

a) I > II > III > IV
b) I > IV > II > III
c) I > III > II > IV
d) IV > III > II > I
View Answer