Organic Chemistry Multiple Choice Questions on “Reaction Intermediates”.
1. Which carbocation is the most stable?
a) 
b) 
c) 
d)
Answer: b
Clarification: 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) 
Answer: a
Clarification: 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
Answer: a
Clarification: (II) Here, Mesomeric effect stabilizes carbocation. So, it is highly stabilized.
(I) It is stabilized by hyperconjugation.
(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) 
Answer: c
Clarification: 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
Answer: d
Clarification: As we can see, in first step in presence to light carbene is formed.
