JEE Main · 2020 · 05 Sep 2020 · Shift 1 · Compounds Containing Nitrogen

Turning the nitrile $\mathrm{C}{}_2\mathrm{H}{}_5\mathrm{CN}$ into the primary amine $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{NH}{}_2$ means reducing the $\mathrm{C}\equiv \mathrm{N}$ triple bond fully to $\mathrm{CH}{}_2-\mathrm{NH}{}_2$. $\mathrm{LiAlH}{}_4$ is a strong enough hydride donor to accomplish this, delivering hydride through an imine intermediate down to the amine. $\mathrm{NaBH}{}_4$ and $\mathrm{Na}(\mathrm{CN})\mathrm{BH}{}_3$ are too mild to touch a nitrile, and $\mathrm{CaH}{}_2$ serves only as a base and drying agent, so lithium aluminium hydride is the appropriate reagent.