ABSTRACT
Hydrocarbons (HC) are composed of carbon and hydrogen molecules whose carbon–carbon bonds are composed of either all single bonds or combinations of single and multiple bonds. Aliphatic HCs, the term usually pertaining to fats or oils, applies to straight, open chains of carbon atoms, rather than ring structures, the simplest of which are the saturated HCs. Aromatic HCs are a special class of unsaturated HCs that contain one or more planar rings, such as a benzene ring. Benzene is the simplest aromatic molecule that can exist alone, attached as a substituent to other HCs, or as a substituted benzene. Aliphatic and alicyclic HC gases and liquids are generally nontoxic or of low acute toxicity, with the majority of effects described being similar to those for simple asphyxiants or pulmonary irritants. Petroleum and petroleum distillates represent an extremely valuable natural resource consisting of a complex mixture of thousands of aliphatic and aromatic compounds.
