Aldehydes and ketones have lower boiling points than alcohols of similar molar mass because
- A. they have smaller molecules
- B. they are non polar
- C. they are ionic
- D. they cannot hydrogen bond to one another, having no hydrogen attached to oxygen
Explanation
Carbonyl compounds are polar and attract one another by dipole to dipole forces, which lifts their boiling points above those of alkanes, but with no O-H bond they cannot form hydrogen bonds between their own molecules and so boil below the corresponding alcohols. They can still accept hydrogen bonds from water, which is why the smaller members are water soluble. Propanone dissolving in water while boiling at only 56 degrees illustrates both points.
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