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For the gasoline rating system, see octane rating. For other uses, see Octane (disambiguation).
Skeletal formula of octane
Skeletal formula of octane with all implicit carbons shown, and all explicit hydrogens added
Ball-and-stick model of octane
Space-filling model of octane
IUPAC name
111-65-9 YesY
3DMet B00281
ChEMBL ChEMBL134886 YesY
ChemSpider 349 YesY
DrugBank DB02440 N
EC Number 203-892-1
Jmol 3D model Interactive image
KEGG C01387 YesY
MeSH octane
PubChem 356
RTECS number RG8400000
UN number 1262
Molar mass 114.23 g·mol−1
Appearance Colorless liquid
Odor Gasoline-like[2]
Density 0.703 g cm−3
Melting point −57.1 to −56.6 °C; −70.9 to −69.8 °F; 216.0 to 216.6 K
Boiling point 125.1 to 126.1 °C; 257.1 to 258.9 °F; 398.2 to 399.2 K
0.007 mg dm−3 (at 20 °C)
log P 4.783
Vapor pressure 1.47 kPa (at 20.0 °C)
29 nmol Pa−1 kg−1
Viscosity 542 μPa s (at 20 °C)
255.68 J K−1 mol−1
361.20 J K−1 mol−1
−252.1–−248.5 kJ mol−1
−5.53–−5.33 MJ mol−1
Vapor pressure {{{value}}}
Related compounds
Related alkanes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

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 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.

Use of the term in gasoline

"Octane" is colloquially used as a short form of "octane rating" (an index of a fuel's ability to resist engine knock at high compression ratios, which is a characteristic of octane's branched-chain isomers, especially isooctane), particularly in the expression "high octane." However, components of gasoline other than isomers of octane can also contribute to a high octane rating, while some isomers of octane can lower it, and n-octane itself has a negative octane rating.[3]

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" is recorded in a figurative sense from 1944.[4] By the mid-1990s, the phrase was commonly being used as an intensifier and has found a place in modern English vernacular.


Octane has 18 structural isomers (24 including stereoisomers):


  1. "octane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 6 January 2012. 
  2. Cite error: Invalid <ref> tag; no text was provided for refs named PGCH
  3. eejit's guides – Octane ratings explained
  4. Oxford English Dictionary. 

External links