Question

Molecules whose mirror image is non-superimposable over them are known as chiral. Which of the following molecules is chiral in nature?

• A. \( \text{2-bromobutane} \)
• B. \( \text{1-bromobutane} \)
• C. \( \text{2-bromopropane} \)
• D. \( \text{2-bromopropan-2-ol} \)

Hint:

A chiral carbon is a carbon atom bonded to four different groups. Molecules containing such carbons are non-superimposable on their mirror images.

Answer 1

The Correct Option is A

A molecule is chiral if it contains at least one carbon atom (chiral carbon) bonded to four different substituents, making it non-superimposable on its mirror image. Step 1: Analyze each option.
Option (1): \( \text{2-bromobutane} \) The second carbon in \( \text{CH}_3\text{-CHBr-CH}_2\text{-CH}_3 \) is attached to: A bromine atom (\( \text{Br} \)), A methyl group (\( \text{CH}_3 \)), An ethyl group (\( \text{CH}_2\text{CH}_3 \)), A hydrogen atom (\( \text{H} \)). Since the second carbon is bonded to four different groups, \( \text{2-bromobutane} \) is chiral.
Option (2): \( \text{1-bromobutane} \) The first carbon in \( \text{CH}_3\text{-CH}_2\text{-CH}_2\text{-CH}_2\text{-Br} \) is bonded to: A bromine atom (\( \text{Br} \)), Two hydrogen atoms (\( \text{H} \)), An ethyl group (\( \text{CH}_2\text{CH}_2\text{CH}_3 \)). Since the first carbon is bonded to two identical substituents (\( \text{H} \)), \( \text{1-bromobutane} \) is not chiral.
Option (3): \( \text{2-bromopropane} \) The second carbon in \( \text{CH}_3\text{-CHBr-CH}_3 \) is bonded to: A bromine atom (\( \text{Br} \)), Two methyl groups (\( \text{CH}_3 \)), A hydrogen atom (\( \text{H} \)). Since this carbon is bonded to two identical methyl groups, \( \text{2-bromopropane} \) is not chiral.
Option (4): \( \text{2-bromopropan-2-ol} \) The second carbon in \( \text{CH}_3\text{-CBr(OH)-CH}_3 \) is bonded to: A bromine atom (\( \text{Br} \)), A hydroxyl group (\( \text{OH} \)), Two methyl groups (\( \text{CH}_3 \)). Since this carbon is bonded to two identical methyl groups, \( \text{2-bromopropan-2-ol} \) is not chiral. Step 2: Conclusion. Among the given options, only \( \text{2-bromobutane} \) contains a chiral carbon and is therefore chiral. Final Answer: \[ \boxed{\text{2-bromobutane}} \]