Octane

Octane is a hydrocarbon and an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. 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. For examples, as a neurotoxin with narcotic effects, n-octane is almost twice as toxic as n-heptane.

Isomers
N-octane has 23 constitutional isomers. 8 of these isomers have one stereocenter; 3 of them have two stereocenters. Achiral Isomers:


 * 2-Methylheptane
 * 4-Methylheptane
 * 3-Ethylhexane
 * 2,2-Dimethylhexane
 * 2,5-Dimethylhexane
 * (meso)-3,4-Dimethylhexane
 * 3,3-Dimethylhexane
 * 3-Ethyl-2-methylpentane
 * 3-Ethyl-3-methylpentane
 * 2,2,4-Trimethylpentane (i.e. iso-octane)
 * 2,3,3-Trimethylpentane
 * 2,3,4-Trimethylpentane
 * 2,2,3,3-Tetramethylbutane

Chiral Isomers:


 * (3R)-3-Methylheptane
 * (3S)-3-Methylheptane
 * (3R)-2,3-Dimethylhexane
 * (3S)-2,3-Dimethylhexane
 * (4R)-2,4-Dimethylhexane
 * (4S)-2,4-Dimethylhexane
 * (3R,4R)-3,4-Dimethylhexane
 * (3S,4S)-3,4-Dimethylhexane
 * (3R)-2,2,3-Trimethylpentane
 * (3S)-2,2,3-Trimethylpentane

Production and Use
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.