Arrange the following compounds in the increasing order of their boiling points
- \(CH_3CH_2CH_2COOH\)
- \(CH_3CH_2CH_2CH_2OH\)
- \(CH_3CH_2OCH_2CH_3\)
- \(CH_3CH_2CH_2CH_3\)
- \(CH_3CH_2CH_2CHO\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → D < C < E < B < A
For compounds of comparable molecular mass (about 72–88 g mol−1) the boiling point depends on the intermolecular forces.
D. CH3CH2CH2CH3 (butane) — non-polar; only weak van der Waals forces, so it boils lowest.
C. CH3CH2OCH2CH3 (ethoxyethane) — weakly polar; no O–H, so no hydrogen bonding between molecules.
E. CH3CH2CH2CHO (butanal) — the polar C=O group gives stronger dipole–dipole attraction than in the ether.
B. CH3CH2CH2CH2OH (butan-1-ol) — molecules are linked by hydrogen bonds.
A. CH3CH2CH2COOH (butanoic acid) — carboxylic acids form hydrogen-bonded dimers, stronger than in alcohols, so it boils highest.
NCERT (2026-27 edition):
Physical Properties – “Methanal is a gas at room temperature. Ethanal is a volatile liquid. Other aldehydes and ketones are liquid or solid at room temperature. The boiling points of aldehydes and ketones are higher than hydrocarbons and ethers of comparable molecular masses. It is due to weak molecular association in aldehydes and ketones arising out of the dipole-dipole interactions. Also, their boiling points are lower than those of alcohols of similar molecular masses due to absence of intermolecular hydrogen bonding.”
Physical Properties – “… Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to more extensive association of carboxylic acid molecules through intermolecular hydrogen bonding.”