Which of the following molecules exhibits optical isomerism: ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2{\text{CH}}_3$, ${\text{CH}}_3{\text{CH(OH)CH}}_2{\text{CH}}_3$, ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_2\text{OH}$, or ${\text{CH}}_3{\text{COCH}}_3$?

Solution

1. Identify the presence of a chiral carbon atom in each molecule.
2. Butane, propan-1-ol, and acetone lack a carbon atom bonded to four distinct groups.
3. In butan-2-ol, the second carbon is bonded to a hydrogen atom, a hydroxyl group, a methyl group, and an ethyl group.
4. Since all four groups are different, the carbon is chiral.
5. Hence the answer is (B).