Unsaturated hydrocarbons are organic compounds that contain at least one double or triple bond between two adjacent carbon atoms/24%3A_Chemistry_of_Life-_Organic_and_Biological_Chemistry/24.04%3A_Unsaturated_Hydrocarbons). They are called "unsaturated" because they have fewer hydrogen atoms than saturated hydrocarbons, which have only single bonds between carbon atoms. The different types of unsaturated hydrocarbons are:

• Alkenes: Hydrocarbons that contain at least one double bond between two adjacent carbon atoms. The simplest alkene is ethylene (C2H4)/24%3A_Chemistry_of_Life-_Organic_and_Biological_Chemistry/24.04%3A_Unsaturated_Hydrocarbons).

• Alkynes: Hydrocarbons that contain at least one triple bond between two adjacent carbon atoms. The simplest alkyne is acetylene (C2H2).

• Aromatic hydrocarbons: Hydrocarbons that contain a ring of atoms with alternating double bonds, such as benzene (C6H6).

Unsaturated hydrocarbons are quite reactive and tend to undergo addition reactions with elemental halogens, hydrogen halides, alcohols, and many other compounds. They are used in a variety of applications, such as in the production of plastics, synthetic rubber, and solvents. To determine whether a hydrocarbon is unsaturated, bromine water can be added to it. If the bromine water becomes decolorized, the hydrocarbon is unsaturated.