Q4 / 120 · VITEEE 2012 · Chemistry
Consider the reactions
(i) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{CH}_{2} \mathrm{Br}\stackrel{\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}}{\longrightarrow}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{CH}_{2} \mathrm{OC}_{2} \mathrm{H}_{5}+\mathrm{HBr}$
(ii) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{CH}_{2} \mathrm{Br} \stackrel{\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}^{-}}{\longrightarrow}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{CH}_{2} \mathrm{OC}_{2} \mathrm{H}_{5}+\mathrm{Br}^{-}$
The mechanisms of reactions (i) and (ii) are respectively
- Correct answerA$\mathrm{S}_{\mathrm{N}} 1$ and $\mathrm{S}_{\mathrm{N}} 2$
- B$\mathrm{S}_{\mathrm{N}}$ 1 and $\mathrm{S}_{\mathrm{N}}$ 1
- C$\mathrm{S}_{\mathrm{N}} 2$ and $\mathrm{S}_{\mathrm{N}} 2$
- D$\mathrm{S}_{\mathrm{N}} 2$ and $\mathrm{S}_{\mathrm{N}} 1$
Solution
$\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O} \mathrm{H}$ being a weaker nucleopbile, when used as a solvent in case of hindered $1^{\circ}$ halide, favours $\mathrm{S}_{\mathrm{N}} 1$ mechanism while $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{O}^{-}$being a strong nucleophile in this reaction favours $\mathrm{S}_{\mathrm{N}} 2$ mechanism.
Hence, the correct answer is option: 'A'.