Structure explains the trend.

All molecules experience dispersion forces. Polar molecules also have dipole interactions, and suitable O–H or N–H groups can form hydrogen bonds. Stronger intermolecular attractions generally require more energy to separate molecules, increasing boiling point.

Within a homologous series, a longer chain generally increases dispersion forces and boiling point. Branching often lowers boiling point among comparable isomers by reducing surface contact. Melting points also depend on crystal packing, so their trends are less simple.

Short alcohols interact strongly with water through hydrogen bonding. As their non-polar carbon chain grows, water solubility tends to fall. Boiling does not normally break the covalent bonds inside molecules.