Question

Identify the chiral molecule from following.

• A. 2-Bromopropane
• B. 2-Bromo-2-methylbutane
• C. 2-Bromo-3-methylbutane
• D. 3-Bromopentane

Hint:

Logic Tip: Look for symmetry. If the left side of the molecule mirrors the right side around the substituted carbon (like in 2-bromopropane or 3-bromopentane), the molecule is achiral. If one side is a methyl group and the other is a branched isopropyl group, the symmetry is broken, creating chirality.

Answer 1

The Correct Option is C

Concept:
A chiral molecule must contain at least one chiral center (stereocenter). A carbon atom is a chiral center if it is $sp^3$ hybridized and bonded to four distinct and different atoms or groups.
Step 1: Examine the structure of each option.
Let's draw and analyze the central carbons for each molecule:

• (A) 2-Bromopropane: $CH_3-CH(Br)-CH_3$. The $C_2$ carbon is attached to $-H$, $-Br$, and two identical $-CH_3$ groups. Not chiral.
• (B) 2-Bromo-2-methylbutane: $CH_3-C(Br)(CH_3)-CH_2-CH_3$. The $C_2$ carbon is attached to $-Br$, an ethyl group ($-CH_2CH_3$), and two identical methyl groups ($-CH_3$). Not chiral.
• (D) 3-Bromopentane: $CH_3-CH_2-CH(Br)-CH_2-CH_3$. The $C_3$ carbon is attached to $-H$, $-Br$, and two identical ethyl groups. Not chiral.

Step 2: Analyze the correct option.
Consider (C) 2-Bromo-3-methylbutane: $CH_3-CH(Br)-CH(CH_3)_2$. The $C_2$ carbon is bonded to: 1. A Hydrogen atom ($-H$) 2. A Bromine atom ($-Br$) 3. A Methyl group ($-CH_3$) 4. An Isopropyl group ($-CH(CH_3)_2$) Since all four groups attached to $C_2$ are different, it is a chiral center.