The boiling points of methoxyethane and propan-1-ol are 281 K and 370 K respectively. Which of the following is the most likely boiling point of propanal?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 322 K
Methoxyethane, propanal and propan-1-ol have nearly the same molar mass (58–60 g mol−1), so their boiling points depend on the forces between their molecules.
Methoxyethane (281 K): an ether, only weakly polar.
Propanal: the polar C=O group gives dipole–dipole attractions, stronger than in the ether, so it boils above 281 K. It has no O–H bond, so there is no intermolecular hydrogen bonding, and it boils below 370 K.
Propan-1-ol (370 K): its molecules are held by intermolecular hydrogen bonds.
Of the options, only 322 K lies between 281 K and 370 K.
NCERT (2026-27 edition):
8.3 Physical Properties – “… 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. The following compounds of molecular masses 58 and 60 are ranked in order of increasing boiling points.”
