JEE PYQ: Haloalkanes And Haloarenes Question 17
Question 17 - 2019 (10 Apr Shift 1)
Increasing rate of $\text{S}_\text{N}1$ reaction in the following compounds is:
(A) Benzyl iodide ($\text{C}_6\text{H}_5\text{CHI}\text{CH}_3$) (B) $p$-MeO-benzyl iodide (with $\text{CH}(\text{CH}_3)$ and I) (C) $m$-Me-benzyl iodide (with $\text{CH}(\text{CH}_3)$ and I) (D) $p$-$\text{H}_3\text{CO}$-benzyl iodide (with extended chain)
(1) (A) < (B) < (C) < (4)
(2) (B) < (A) < (C) < (D)
(3) (B) < (A) < (D) < (3)
(4) (A) < (B) < (D) < (C)
Show Answer
Answer: (2)
Solution
The rate of $\text{S}_\text{N}1$ is decided by the stability of carbocation formed in the rate determining step. Carbocation (D) is most stable due to +R effect of $\text{CH}_3\text{O}$ group, (C) is stabilised by +I and +H effects of the $\text{CH}3$ group; (B) is least stable due to $-\text{I}$ effect of MeO group at meta. So increasing order of rate of $\text{S}\text{N}1$ is (B) < (A) < (C) < (D).
BETA
