All the molecules have Van der Waals forces between them but propanol has the addition of having hydrogen bonding, which is barely stronger.
The improved forces between molecules capability that extra energy is required to destroy apart the molecules and therefore the substance has a greater boiling point.
Large molecules have extra electrons and nuclei that create van der Waals pleasing forces, so their compounds usually have greater boiling factors than similar compounds made up of smaller molecules.
Because 1-propanol has its hydroxyl to one side, the hydrogen bonds it forms can pack collectively greater densely than with 2-propanol, requiring extra kinetic electricity (temperature) to wreck them apart, which interprets to a greater boiling point
Learn more about boiling points of compounds here:
