JEE PYQ: Haloalkanes And Haloarenes Question 21
Question 21 - 2019 (12 Apr Shift 2)
An ‘Assertion’ and a ‘Reason’ are given below. Choose the correct answer from the following options:
Assertion (A): Vinyl halides do not undergo nucleophilic substitution easily.
Reason (R): Even though the intermediate carbocation is stabilized by loosely held $\pi$-electrons, the cleavage is difficult because of strong bonding.
(1) Both (A) and (R) are wrong statements.
(2) Both (A) and (R) are correct statements and (R) is the correct explanation of (A).
(3) Both (A) and (R) are correct statements but (R) is not the correct explanation of (A).
(4) (A) is a correct statement but (R) is a wrong statement.
Show Answer
Answer: (4)
Solution
$\text{CH}_2=\text{CH}-\text{Cl} \leftrightarrow \text{CH}_2^–\text{CH}=\text{Cl}^+$. Due to partial double bond character of C-halogen bond, halogen leaves with great difficulty, if at all it does. Hence, vinyl halides do not undergo nucleophilic substitution easily. So, assertion is correct. Intermediate carbocation is not stabilised by loosely held $\pi$ electrons because empty orbital, being at 90$^\circ$, cannot overlap with $p$-orbitals of $\pi$ bond. So, reason is wrong.
BETA
