Why do alcohols generally have higher boiling points than similar-sized alkanes?

Alcohols generally have significantly higher boiling points than alkanes of similar molecular weight because of their ability to form intermolecular hydrogen bonds.1

In an alcohol molecule, the oxygen atom of the strongly polarized O–H bond pulls electron density away from the hydrogen atom. This creates a partial positive charge on the hydrogen, allowing it to form a hydrogen bond with a pair of nonbonding electrons on the oxygen atom of another alcohol molecule.1

These intermolecular attractions are much stronger than the forces present in nonpolar hydrocarbons like alkanes. Consequently, more energy is required to separate alcohol molecules during the phase change from liquid to gas, resulting in higher boiling points. For instance, ethanol (molecular weight 46) boils at 78 °C, whereas propane (molecular weight 44) boils at −42 °C.1