Identify the major product in the following reaction.
(A)(see structure)
(B)(see structure)
(C)(see structure)✓ Correct
(D)(see structure)
Answer: (C)
Solution
The reaction involves a cyclopentyl bromide treated with alcoholic KOH (a strong base), which promotes E2 elimination (dehydrohalogenation).
In E2 elimination:
A β-hydrogen is abstracted by the base
The bromide leaves as Br⁻
A double bond forms between the α and β carbons
For cyclopentyl bromide, elimination of HBr gives cyclopentene (a five-membered ring with one double bond).
According to Zaitsev's rule, the more substituted alkene is the major product. In this cyclic system, the elimination leads to the formation of cyclopentene with the double bond in the ring.
Option (3) shows the correct structure of cyclopentene (methylcyclopentene if there's a methyl substituent), which is the major product.
Answer: (3)
JEE Main · 2024 · 05 Apr 2024 · Shift 2 · Single correct option
