Chemistry - Halogen Derivative Question with Solution | TestHub

Racemization during an ${\mathrm{S}}_{\mathrm{N}}1$ reaction occurs when the reactant is an optically active (chiral) alkyl halide. For a molecule to be chiral, it must contain an asymmetric carbon atom, which is a carbon bonded to four different groups.

Let us analyze the given options:
1. $\mathrm{C}{\mathrm{H}}_3-\mathrm{CH}(\mathrm{Cl})-\mathrm{C}{\mathrm{H}}_3$ (2-chloropropane): The carbon atom bonded to chlorine is attached to two identical methyl ($-\mathrm{C}{\mathrm{H}}_3$) groups. It is achiral.
2. $\mathrm{C}{\mathrm{H}}_3-\mathrm{C}{\mathrm{H}}_2-\mathrm{CH}(\mathrm{Cl})-\mathrm{C}{\mathrm{H}}_3$ (2-chlorobutane): The carbon atom bonded to chlorine is attached to four different groups: a hydrogen atom ($-\mathrm{H}$), a chlorine atom ($-\mathrm{Cl}$), a methyl group ($-\mathrm{C}{\mathrm{H}}_3$), and an ethyl group ($-\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$). It is chiral.
3. $\mathrm{C}{\mathrm{H}}_3-\mathrm{C}{\mathrm{H}}_2-\mathrm{CH}(\mathrm{Cl})-\mathrm{C}{\mathrm{H}}_2-\mathrm{C}{\mathrm{H}}_3$ (3-chloropentane): The carbon atom bonded to chlorine is attached to two identical ethyl ($-\mathrm{C}{\mathrm{H}}_2\mathrm{C}{\mathrm{H}}_3$) groups. It is achiral.
4. $(\mathrm{C}{\mathrm{H}}_3{)}_3\mathrm{C}-\mathrm{C}{\mathrm{H}}_2-\mathrm{Cl}$ (1-chloro-2,2-dimethylpropane): The carbon atom bonded to chlorine is attached to two identical hydrogen atoms. It is achiral.

Since 2-chlorobutane is the only chiral compound among the choices, its planar carbocation intermediate can be attacked by the nucleophile from either side, leading to a racemic mixture. Therefore, it undergoes racemization during alkaline hydrolysis by the ${\mathrm{S}}_{\mathrm{N}}1$ mechanism.

Answer: