Question: Which of the following molecules is chiral in nature?

Step 1 (Governing Principle & Definition): [0.25 Mark]

A molecule is defined as chiral if it contains at least one chiral carbon atom (also known as a stereocenter). A chiral carbon is a carbon atom that is bonded to four different groups or atoms, represented as $C^*abcd$, where $a \neq b \neq c \neq d$.

Step 2 (Step-by-Step Structural Analysis): [0.5 Mark]

We analyze the structures of the given options to identify the presence of a chiral carbon:

• (A) 1-chloropropane: $CH_3-CH_2-CH_2-Cl$. The $C_1$ is bonded to two identical $H$ atoms. Not chiral.
• (B) 2-chloropropane: $CH_3-CH(Cl)-CH_3$. The $C_2$ is bonded to two identical $CH_3$ groups. Not chiral.
• (C) 1-chlorobutane: $CH_3-CH_2-CH_2-CH_2-Cl$. The $C_1$ is bonded to two identical $H$ atoms. Not chiral.
• (D) 2-chlorobutane: $CH_3-CH(Cl)-CH_2-CH_3$. The $C_2$ atom is bonded to four distinct groups: $$ -H, \quad -Cl, \quad -CH_3, \quad -CH_2CH_3 $$ Since all four groups are different, the $C_2$ atom is a chiral center.

Step 3 (Final Concluded Answer): [0.25 Mark]

Based on the structural analysis, 2-chlorobutane possesses a chiral center and is therefore chiral in nature. The correct option is (D).

💡 EL10 Concept Insight: Think of a chiral carbon like a hand; just as your left hand is a mirror image of your right hand but can't perfectly overlap, a chiral molecule has a "handedness" because its central carbon is holding four completely different things, making it impossible to superimpose on its mirror image.