Octane


Octane is a hydrocarbon and an alkane with the chemical formula C8H18, and the condensed structural formula CH36CH3. 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 is used as one of the standard values in the octane rating scale.
Octane is a component of gasoline. As with all low-molecular-weight hydrocarbons, octane is volatile and very flammable.

Use of the term in gasoline

"Octane" is colloquially used as a short form of "octane rating", particularly in the expression "high octane".
The octane rating was originally determined by mixing fuels from only heptane and 2,2,4-trimethylpentane, and assigning anti-knock ratings of zero for pure heptane and 100 for pure 2,2,4-trimethylpentane. The anti-knock rating of this mixture would be the same as the percentage of the latter in the mix. Different isomers of octane can contribute to a lower or higher octane rating. For example, n-octane has a -20 Research Octane Rating, whereas pure 2,2,4-trimethylpentane has an RON rating of 100. Some fuels have an octane rating higher than 100, notably those containing methanol or ethanol.

Metaphorical use

Octane became well known in American popular culture in the mid- and late 1960s, when gasoline companies boasted of "high octane" levels in their gasoline advertisements.
The compound adjective "high-octane", meaning powerful or dynamic, is recorded in a figurative sense from 1944. By the mid-1990s, the phrase was commonly being used as an intensifier and has found a place in modern English vernacular.

Isomers

Octane has 18 structural isomers :