How would you rank the following compounds from highest to lowest vapor pressure: CH3CH2CH2OH, CH3OH, CH4, and CH3CH2OH?
From most to least volatile: methane; methanol; ethanol; propanol.
The alkane has very weak intermolecular forces operating, and is thus the most volatile. Alcohols have hydrogen bonding available, and are therefore much more involatile than the analogous alkanes. As the unbranched alcohol chain lengthens, dispersion forces can operate between the alkyl chains so that the boiling points (and involatility) increases.