Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms. Those with at least one double bond are called alkenes and those with at least one triple bond are called alkynes. Each double bond is represented by a number preceding the name of the base chain, representing on which hydrocarbon in the chain the double or triple bond can be found. Alkenes and alkynes with more than one double or triple bond respectively are named with the appropriate numeric prefix preceding the -ene or -yne.
Examples of unsaturated hydrocarbon include 2,4-pentadiene and 2-butyne, among others.
Unsaturated hydrocarbons with both double and triple bonds have the suffix -enyne and are handled in a similar manner.
The physical properties of unsaturated hydrocarbons are very similar to those of the corresponding saturated compounds. They are slightly soluble in water.
Except for aromatic compounds, unsaturated hydrocarbons are highly reactive and undergo addition reactions to their multiple bonds. Typical reagents added are hydrogen halides, water, sulfuric acid, elemental halogens and alcohols.
To test whether the hydrocarbon is unsaturated you should add bromine water. If the bromine water becomes decolourised (Goes colorless) then it is unsaturated.