Physical properties of aldehydes and ketones

Solubility in water

The water molecules can form hydrogen bonds to the O atom of the carbonyl group. This accounts for the solubility of small $C$ chain aldehydes and ketones in the water.

The solubility is however less than that of the corresponding alcohols which are both donor and acceptor of hydrogen bonds relative to water.


No hydrogen bond provides any strong mutual attraction between aldehydes or ketones (the polarity of the $C-H$ bond is too low!). These substances are more volatile than alcohols of comparable molecular weight. Lower dipole-dipole attraction than that of hydrogen bonds remains between carbonyl groups and provides higher boiling temperatures than those of the corresponding hydrocarbons which are associated only by weak Van der Waals forces . Inertia increases with the molar mass, so volatility decreases: Gradually, as the chain of $C$ atoms extends , the hydrophobicity of the hydrocarbon chain outweighs the hydrophilicity of the carboxyl group and the volatility of aldehydes and ketones approximates more and more that of the alkanes with comparable molar masses: