Question

Identify the correct increasing order of boiling points of the given compounds:

• A. Propan-1-ol $<$ butan-1-ol $<$ butan-2-ol $<$ pentan-1-ol
• B. Pentan-1-ol $<$ butan-1-ol $<$ butan-2-ol $<$ propan-1-ol
• C. Propan-1-ol $<$ butan-2-ol $<$ butan-1-ol $<$ pentan-1-ol
• D. Butan-1-ol $<$ butan-2-ol $<$ propan-1-ol $<$ pentan-1-ol

Hint:

Boiling point trends in alcohols: Longer chain $\uparrow$ BP More branching $\downarrow$ BP All alcohols have hydrogen bonding, so size and branching dominate comparisons.

Answer 1

The Correct Option is C

Concept: Boiling points of alcohols depend on:

• Hydrogen bonding (present in all alcohols)
• Molecular mass (higher mass $\Rightarrow$ higher boiling point)
• Branching (more branching $\Rightarrow$ lower boiling point due to less surface area)

Step 1: Compare carbon chain length. Higher carbon chain $\Rightarrow$ stronger van der Waals forces $\Rightarrow$ higher boiling point. So: \[ \text{propan-1-ol}<\text{butanol isomers}<\text{pentan-1-ol} \]
Step 2: Compare branching among butanol isomers. Butan-1-ol = primary alcohol (less branched) Butan-2-ol = secondary alcohol (more branched) More branching $\Rightarrow$ lower boiling point. So: \[ \text{butan-2-ol}<\text{butan-1-ol} \]
Step 3: Combine both trends. \[ \text{Propan-1-ol}<\text{butan-2-ol}<\text{butan-1-ol}<\text{pentan-1-ol} \]