Which of the following molecules is chiral?

• A. $2-\mathrm{butanol}$
• B. $\mathrm{ethanol}$
• C. $2-\mathrm{propanol}$
• D. $\mathrm{acetone}$

Answer: (A)

Verified step by step guidance

1. Understand the concept of chirality: A molecule is chiral if it has a non-superimposable mirror image, often due to the presence of an asymmetric carbon atom (a carbon atom bonded to four different groups).
2. Examine each molecule to identify any asymmetric carbon atoms. Start with ethanol (C₂H₅OH): Ethanol has two carbon atoms, but neither is bonded to four different groups, so it is not chiral.
3. Next, consider 2-propanol (C₃H₇OH): The central carbon atom is bonded to a hydroxyl group (OH), a hydrogen atom (H), and two methyl groups (CH₃), which are identical. Therefore, 2-propanol is not chiral.
4. Now, analyze acetone (C₃H₆O): Acetone has a central carbon atom double-bonded to an oxygen atom and bonded to two identical methyl groups (CH₃). It lacks an asymmetric carbon atom, so it is not chiral.
5. Finally, evaluate 2-butanol (C₄H₉OH): The second carbon atom is bonded to a hydroxyl group (OH), a hydrogen atom (H), a methyl group (CH₃), and an ethyl group (C₂H₅). These four different groups make the carbon atom asymmetric, indicating that 2-butanol is chiral.