Which one of the following compounds is achiral?

Propan-2-ol

The correct answer is Option (1) → Propan-2-ol

A compound is chiral if it contains at least one asymmetric (chiral) carbon attached to four different groups. If no such carbon exists — or if symmetry cancels chirality — the compound is achiral.

Option-wise Detailed Explanation

1. Propan-2-ol Structure: CH₃–CHOH–CH₃. The carbon bearing –OH is attached to two identical CH₃ groups. Because two substituents are the same, this carbon is not asymmetric. Since there is no chiral center in the molecule, Propan-2-ol is achiral.

2. Butan-2-ol Structure: CH₃–CH(OH)–CHâ‚‚CH₃. The second carbon is attached to four different groups: H, OH, CH₃, and Câ‚‚Hâ‚…. This makes it a chiral carbon. Therefore, Butan-2-ol exists as enantiomers and is chiral, not achiral.

3. 2-Chlorobutane Structure: CH₃–CH(Cl)–CHâ‚‚CH₃. The second carbon is attached to H, Cl, CH₃, and Câ‚‚Hâ‚… — four different groups. This creates a stereogenic center, so the compound is chiral.

4. 2,3-Dihydroxybutanal This molecule contains two carbons bearing –OH groups and different substituents, creating chiral centers. No internal symmetry removes chirality here. Hence, it is chiral and not achiral.