Concept:Boiling point depends on the strength of intermolecular forces.
Hydrogen bonding increases boiling point significantly.
Carboxylic acids show the strongest intermolecular hydrogen bonding among common organic compounds.
Explanation:All given compounds can form hydrogen bonds.
But carboxylic acids form very strong hydrogen-bonded dimers.
Dimer formation increases the effective molecular mass and intermolecular attraction.
In
C2H5COOH (propanoic acid), the
−COOH group has an
O−H⋯O hydrogen bond, which is stronger than
O−H bonding in alcohols or
N−H bonding in amines.
The alcohol
n−C4H9OH has only one
O−H bond per molecule.
Amines
(CH3)3C−NH2 and
C2H5N(CH3)2 have weaker
N−H hydrogen bonding.
Therefore, the carboxylic acid has the strongest intermolecular attraction and the highest boiling point.
Answer:Option D:
C2H5COOH