Why do carboxylic acids have higher boiling points than similar alcohols or aldehydes?

• A. Carboxylic acids have lower molecular weights than alcohols or aldehydes, which increases their boiling points.
• B. Carboxylic acids form strong hydrogen-bonded dimers, increasing intermolecular forces and raising boiling points.
• C. Carboxylic acids contain only nonpolar bonds, leading to stronger London dispersion forces.
• D. Carboxylic acids cannot participate in hydrogen bonding, so their boiling points are higher.

Answer: (B)

Verified step by step guidance

1. Identify the key factor that influences boiling points: intermolecular forces. Stronger intermolecular forces lead to higher boiling points because more energy is required to separate the molecules.
2. Compare the types of intermolecular forces present in carboxylic acids, alcohols, and aldehydes. Alcohols and aldehydes can form hydrogen bonds, but carboxylic acids have a unique ability to form hydrogen-bonded dimers.
3. Understand what a hydrogen-bonded dimer is: two carboxylic acid molecules pair up through two hydrogen bonds, effectively doubling the size of the interacting unit and significantly increasing intermolecular attraction.
4. Recognize that this dimerization leads to stronger overall intermolecular forces in carboxylic acids compared to the single hydrogen bonds in alcohols or the weaker dipole interactions in aldehydes.
5. Conclude that the presence of these strong hydrogen-bonded dimers in carboxylic acids raises their boiling points above those of similar alcohols or aldehydes, despite having lower molecular weights.