Question

Identify the reason for the highest boiling point of R-COOH as compared to alkanes, ethers, alcohols and aldehydes.

• A. Formation of carboxylate ion
• B. Van der waals force of attraction
• C. Formation of intramolecular hydrogen bonding
• D. Formation of intermolecular hydrogen bonding

Hint:

Carboxylic acid molecules join in pairs through two hydrogen bonds between molecules.

Answer 1

The Correct Option is D

Step 1: Approach
Rank the forces in the compared families.

Step 2: Ranking
Alkanes: weak dispersion forces. Ethers and aldehydes: dipole-dipole. Alcohols: one hydrogen bond per OH. Carboxylic acids: two hydrogen bonds between a pair, giving a stable dimer.

Step 3: Conclusion
The extra strong hydrogen bonding between molecules raises the boiling point the most, option (D).

Final Answer:
Intermolecular hydrogen bonding, which forms dimers, gives carboxylic acids the highest boiling points, option (D). \[ \boxed{\text{Intermolecular hydrogen bonding}} \]