Which of the following alcohols has the highest boiling point?

Solution

Chemistry ma’am · 3 steps

Every option has one -OH, so the hydrogen bonding ties; the longest unbranched chain wins.

1. Hydrogen bonding ties. Each of these alcohols has exactly one -OH group, so each molecule forms about the same hydrogen bonds. That factor cannot separate them.
2. Chain length decides. A longer carbon chain has more electrons and more surface area, so the van der Waals forces between molecules are stronger. Branching makes a molecule more compact, which reduces surface contact and lowers the boiling point.

   Alcohol	Carbons	Chain	Boiling point
   Ethanol, CH₃CH₂OH	2	straight	78 °C
   Propan-2-ol, (CH₃)₂CHOH	3	branched	82 °C
   Propan-1-ol, CH₃CH₂CH₂OH	3	straight	97 °C
   Butan-1-ol, CH₃CH₂CH₂CH₂OH	4	straight	118 °C

3. So. Butan-1-ol has the most carbons and no branching, so it has the strongest intermolecular forces and the highest boiling point. The answer is (c).

The idea to keep. When alcohols have the same number of -OH groups, compare size first: more carbons means a higher boiling point. For the same size, branching lowers it.

Answer from the NTA final answer key. Solution by PrepWiser.