Octane is a hydrocarbon and also an alkane with the chemical formula C<sub>8</sub>H<sub>18</sub>, and the condensed structural formula CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>CH<sub>3</sub>. Octane has many structural isomers that differ by the location of branching in the carbon chain. One of these isomers, 2,2,4-trimethylpentane (commonly called iso-octane), is used as one of the standard values in the octane rating scale.
Octane is a component of gasoline and petroleum. Under standard temperature and pressure, octane is an odorless, colorless liquid. Like other short-chained alkanes with a low molecular weight, it is volatile, flammable, and toxic. Octane is 1.2 to 2 times more toxic than heptane.
N-octane has 23 constitutional isomers. 8 of these isomers have one stereocenter; 3 of them have two stereocenters.
Achiral isomers:
Chiral isomers:
In petrochemistry, octanes are not typically differentiated or purified as specific compounds. Octanes are components of particular boiling fractions.
A common route to such fractions is the alkylation reaction between iso-butane and 1-butene, which forms iso-octane.
Octane is commonly used as a solvent in paints and adhesives.