JEE PYQ: Haloalkanes And Haloarenes Question 10
Question 10 - 2020 (07 Jan Shift 2)
For the following reactions:
$\text{CH}_3\text{CH}_2\text{CH}_2\text{Br} + \text{Z} \xrightarrow{k_s(\text{Substitution})} \text{CH}_3\text{CH}_2\text{CH}_2\text{Z} + \text{Br}^-$
$\text{CH}_3\text{CH}_2\text{CH}_2\text{Br} + \text{Z} \xrightarrow{k_e(\text{Elimination})} \text{CH}_3\text{CH}=\text{CH}_2 + \text{HZ} + \text{Br}^-$
where $\text{Z} = \text{CH}_3\text{CH}_2\text{O}^-$ (A) or $\text{H}_3\text{C}-\text{C}(-\text{CH}_3)_2-\text{O}^-$ (B),
$k_s$ and $k_e$ are, respectively, the rate constants for substitution and elimination, and $\mu = \frac{k_s}{k_e}$, the correct option is:
(1) $\mu_\text{B} > \mu_\text{A}$ and $k_e(\text{A}) > k_e(\text{B})$
(2) $\mu_\text{A} > \mu_\text{B}$ and $k_e(\text{B}) > k_e(\text{A})$
(3) $\mu_\text{B} > \mu_\text{A}$ and $k_e(\text{B}) > k_e(\text{A})$
(4) $\mu_\text{A} > \mu_\text{B}$ and $k_e(\text{A}) > k_e(\text{B})$
Show Answer
Answer: (2)
Solution
Among the given bases (A) and (B), $t$-butoxide being bulky base favours elimination reaction and ethoxide favours substitution reaction. $\therefore$ when Z$\ominus$ = $\text{CH}_3\text{CH}_2\text{O}^-$, substitution reaction favoured. When Z$\ominus$ = $(\text{CH}3)3\text{CO}^-$, elimination reaction favoured. Hence, $\mu\text{A} > \mu\text{B}$ and $k_e(\text{B}) > k_e(\text{A})$.
BETA
