Octane is a hydrocarbon and an alkane with the chemical formula C 8 H 18, and the condensed structural formula CH 3 (CH 2) 6 CH 3. Octane has many structural isomers that differ by the amount and location of branching in the carbon chain.One of these isomers, 2,2,4-trimethylpentane (isooctane) is used as one of the standard values in the octane rating scale. Octane is a component of gasoline (petrol).As with all low molecular weight hydrocarbons, octane is volatile and very flammable.ctane has many structural isomers that differ by the amount and location of branching in the carbon chain. One of these isomers, 2,2,4-trimethylpentane (isooctane) is used as one of the standard values in the octane rating scale.