octane 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 amount and 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 names systematic iupac name octane other names n-octaneoctacarbane identifiers cas number 111-65-9 y 3d model (jsmol) interactive image 3dmet b00281 beilstein reference 1696875 chebi chebi:17590 n chembl chembl134886 y chemspider 349 y drugbank db02440 n echa infocard 100.003.539 ec number 203-892-1 gmelin reference 82412 kegg c01387 y mesh octane pubchem cid 356 rtecs number rg8400000 unii x1rv0b2fjv y un number 1262 comptox dashboard (epa) dtxsid0026882 inchi inchi=1s/c8h18/c1-3-5-7-8-6-4-2/h3-8h2,1-2h3 ykey: tvmxdcgiabbofy-uhfffaoysa-n y smiles cccccccc properties chemical formula ch3(ch2)6ch3 molar mass 114.232 g·mol−1 appearance colourless liquid odor gasoline-like density 0.703 g/cm3 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 solubility in water 0.007 mg/dm3 (at 20 °c) log p 4.783 vapor pressure 1.47 kpa (at 20.0 °c) henry's lawconstant (kh) 29 nmol/(pa·kg) conjugate acid octonium magnetic susceptibility (χ) −96.63·10−6 cm3/mol refractive index (nd) 1.398 viscosity thermochemistry heat capacity (c) 255.68 j/(k·mol) std molarentropy (s⦵298) 361.20 j/(k·mol) std enthalpy offormation (δfh⦵298) −252.1 to −248.5 kj/mol std enthalpy ofcombustion (δch⦵298) −5.53 to −5.33 mj/mol hazards ghs labelling: pictograms signal word danger hazard statements h225, h304, h315, h336, h410 precautionary statements p210, p261, p273, p301+p310, p331 nfpa 704 (fire diamond) 1 3 0 flash point 13.0 °c (55.4 °f; 286.1 k) autoignitiontemperature 220.0 °c (428.0 °f; 493.1 k) explosive limits 0.96 – 6.5% lethal dose or concentration (ld, lc): ldlo (lowest published) 428 mg/kg (mouse, intravenous) niosh (us health exposure limits): pel (permissible) twa 500 ppm (2350 mg/m3) rel (recommended) twa 75 ppm (350 mg/m3) c 385 ppm (1800 mg/m3) idlh (immediate danger) 1000 ppm related compounds related alkanes methaneethanepropanebutanepentanehexaneheptanenonanedecane except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). n verify (what is yn ?) infobox references 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", particularly in the expression "high octane". "octane rating" is an index of a fuel's ability to resist engine knock in engines having different compression ratios, which is a characteristic of octane's branched-chain isomers, especially iso-octane. the octane rating of gasoline is not directly related to the power output of an engine. using gasoline of a higher octane than an engine is designed for cannot increase power output. the octane rating was originally determined by mixing fuels from only normal heptane and iso-octane (2,2,4-trimethylpentane, a highly branched octane), and assigning anti-knock ratings of zero for normal heptane and 100 for pure iso-octane. the anti-knock rating of this mixture would be the same as the percentage of iso-octane in the mix. different isomers of octane can contribute to a lower or higher octane rating. for example, n-octane (the straight chain of 8 carbon atoms with no branching) has a -20 (negative) research octane rating, whereas pure iso-octane 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 karter j. bokulich. by the mid-1990s, the phrase was commonly being used as an intensifier and it has found a place in modern english vernacular. isomers octane has 18 structural isomers (24 including stereoisomers): octane (n-octane) 2-methylheptane 3-methylheptane (2 enantiomers) 4-methylheptane 3-ethylhexane 2,2-dimethylhexane 2,3-dimethylhexane (2 enantiomers) 2,4-dimethylhexane (2 enantiomers) 2,5-dimethylhexane 3,3-dimethylhexane 3,4-dimethylhexane (2 enantiomers + 1 meso compound) 3-ethyl-2-methylpentane 3-ethyl-3-methylpentane 2,2,3-trimethylpentane (2 enantiomers) 2,2,4-trimethylpentane (isooctane) 2,3,3-trimethylpentane 2,3,4-trimethylpentane 2,2,3,3-tetramethylbutane