C_nH_2n+1OH

You may also see the general formula of alcohols written as CH_2n+2O.

-OH 

-OH is called a hydroxyl group.

• Primary: -OH group attached to a carbon with one other alkyl group (or no alkyl groups).
• Secondary: -OH group attached to a carbon with two other alkyl groups.
• Tertiary: -OH group attached to a carbon with three other alkyl groups.

Alcohols are less volatile and more water-soluble than alkanes of similar size due to hydrogen bonding between the hydroxyl groups.

Alcohols are polar molecules because they contain a polar O-H bond. This polarity arises from the difference in electronegativity between oxygen and hydrogen atoms.

Volatile compounds have low boiling points; the more volatile a compound is, the lower its boiling point.

Volatility is the tendency to vapourise i.e. to turn from liquid into gas.

Hydrogen bonding exists between alcohol molecules in the liquid state. These hydrogen bonds are stronger than the induced dipole-dipole forces that exist between alkene molecules so they require more energy to overcome.

The hydrogen bonding between two ethanol molecules is shown below.

Hydrogen bonds form between the polar -OH group of the alcohol and the water molecules.

Alkanes are non-polar and cannot form hydrogen bonds with water.

Hydrogen bonding

Induced dipole-dipole forces and permanent dipole-dipole forces are also present in alcohols, but are weaker than hydrogen bonding.