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alkane (ălˈkān), any of a group of aliphatic hydrocarbons whose molecules contain only single bonds (see chemical bond). Alkanes have the general chemical formula CnH2n+2. An alkane is said to have a continuous chain if each carbon atom in its molecule is joined to at most two other carbon atoms; it is said to have a branched chain if any of its carbon atoms is joined to more than two other carbon atoms. The first four continuous-chain alkanes are methane, CH4; ethane, C2H6; propane, C3H8; and butane, C4H10. Names of continuous-chain alkanes whose molecules contain more than five carbon atoms are formed from a root that indicates the number of carbon atoms and the suffix -ane to indicate that the compound is an alkane; e.g., alkanes with 5, 6, 7, 8, 9, and 10 carbon atoms in their molecules are pentane, hexane, heptane, octane, nonane, and decane, respectively. The name of a branched-chain alkane is formed by adding prefixes to the name of the continuous-chain alkane from which it is considered to be derived; e.g., 2-methylpropane (called also isobutane) is thought of as being derived by replacing one of the hydrogen atoms bonded to the second (2-) carbon atom of a propane molecule with a methyl (CH3) group, forming CH3CH(CH3)2. Chemically, the alkanes are relatively unreactive. They are obtained by fractional distillation from petroleum and are used extensively as fuels. The alkanes are sometimes referred to as the methane series (after the simplest alkane) or as paraffins.