Hydrocarbon, << `hy` droh KAHR buhn, >> refers to the most important class of organic compounds. Hydrocarbons contain only the elements hydrogen and carbon. They occur in petroleum and natural gas. Commercial petroleum products, such as gasoline, kerosene, airplane fuel, lubricating oils, and paraffin, are mixtures of hydrocarbons. Some hydrocarbons are found in coal tar and coal gas. Many others are synthesized (made artificially) from hydrocarbons found in nature.
Hydrocarbons are starting materials for the petrochemical industry. Petrochemical companies use hydrocarbons from crude oil and natural gas to manufacture solvents, plastics, and synthetic fibers and rubbers.
Organic chemistry is sometimes called the “chemistry of hydrocarbons and their derivatives,” because all organic compounds are essentially related to the hydrocarbons. Hydrocarbons can be divided into three large classes. These classes are: (1) aliphatics, (2) alicyclics, and (3) aromatics.
Aliphatic hydrocarbons
have the principal carbon atoms arranged in chains. They are further divided into the paraffin, olefin, and acetylenic series.
Paraffins,
or alkanes, include the greatest number of hydrocarbon compounds. Methane is the first member of the series. Others include ethane and propane. Paraffins react by substitution. Hydrogen atoms are replaced by other atoms or groups of atoms, such as halogens or hydroxyls.
Olefins,
or alkenes, have at least one double bond between two carbon atoms. Ethylene is the first member. Olefins react primarily by addition of molecules such as water, oxygen, and halogens. They can also react with themselves to form polymers (large chain molecules) such as polyethylene, which is used in plastics.
Acetylenes,
or alkynes, have at least one triple bond between two carbon atoms. Acetylene is the first and most important member of the series. Acetylenic hydrocarbons have reactions similar to the olefins.
Alicyclics
have their carbon atoms arranged in a ring. These atoms may have single or double bonds between them. Triple bonds in alicyclics are rare, but they can occur in sufficiently large rings. Many naturally occurring organic compounds fall into this class. The reactions of alicyclics are similar to those of the aliphatics.
Aromatics
are a small but highly important class of hydrocarbons. They are characterized by a six-carbon ring. This ring differs from the alicyclics in that it contains three double bonds. Benzene, is the most important aromatic. Others in the benzene series include toluene and the xylenes. Other aromatic series include the naphthalenes and the anthracenes.
