JEE Main · 2024 · 30 Jan 2024 · Shift 1 · Haloalkanes and Haloarenes

Compound A formed in the following reaction reacts with B gives the product C. Find out A and B.

1. (A)$\mathrm{A}={\mathrm{CH}}_3-\mathrm{C}\equiv \overline{\mathrm{C}}\stackrel{+}{\mathrm{Na}},\mathrm{B}={\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{Br}$✓ Correct
2. (B)$\mathrm{A}={\mathrm{CH}}_3-\mathrm{CH}={\mathrm{CH}}_2,\mathrm{B}={\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\mathrm{Br}$
3. (C)$\mathrm{A}={\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_3,\mathrm{B}={\mathrm{CH}}_3-\mathrm{C}\equiv \mathrm{CH}$
4. (D)$\mathrm{A}={\mathrm{CH}}_3-\mathrm{C}\equiv \overline{\mathrm{C}}\stackrel{+}{\mathrm{Na}},\mathrm{B}={\mathrm{CH}}_3-{\mathrm{CH}}_2-{\mathrm{CH}}_3$

Answer: (A)

Solution

Propyne is deprotonated (e.g. by $\mathrm{NaN}{\mathrm{H}}_2$) to the sodium acetylide $\mathrm{C}{\mathrm{H}}_3-\mathrm{C}\equiv {\mathrm{C}}^{-}\mathrm{N}{\mathrm{a}}^{+}$ (A), which displaces bromide from 1-bromopropane (B, $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{Br}$) in an ${\mathrm{S}}_{\mathrm{N}}2$ reaction to give the higher alkyne $\mathrm{C}{\mathrm{H}}_3-\mathrm{C}\equiv \mathrm{C}-\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$ (C).

JEE Main · 2024 · 30 Jan 2024 · Shift 1 · Single correct option