Hydrocarbons are compounds composed solely of carbon and hydrogen. Despite their simple composition, hydrocarbons include a large number of different compounds with a variety of chemical properties. Hydrocarbons are derived from oil deposits, and are the source of gasoline, heating oil, and other "fossil fuels." They also provide the carbon skeletons required for the thousands of chemicals produced by the chemical industry.

Hydrocarbons are classified on the basis of their structure and bonding. The three major classes are aliphatics, alicyclics, and aromatics. Aliphatics have carbon backbones that form straight or branched chains, with no rings. Alicyclics are ring compounds that, while they may have one or more double bonds, do not form conjugated sets of double bonds around the ring like benzene. Aromatics are compounds with at least one benzene ring. Aliphatic means fatty, and aromatic refers to odor, but these terms no longer have significance for the...