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
IUPAC name
Octane[1]
Identifiers
CAS Number
3D model (JSmol)
3DMet
Beilstein Reference
 1696875
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.003.539
EC Number
  • 203-892-1
Gmelin Reference
 82412
KEGG
MeSH octane
PubChem CID
RTECS number
  • RG8400000
UNII
UN number 1262
CompTox Dashboard (EPA)
Properties
Chemical formula
 C8H18
Molar mass 114.232 g·mol−1
Appearance colourless 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
Solubility in water
 0.007 mg dm−3 (at 20 °C)
log P 4.783
Vapor pressure 1.47 kPa (at 20.0 °C)
Henry's law
constant (kH)
 29 nmol Pa−1 kg−1
Conjugate acid Octonium
Magnetic susceptibility (χ)
 -96.63·10−6 cm3/mol
Refractive index (nD)
 1.398
Viscosity
  • 0.509 mPa·s (25 °C)[3]
  • 0.542 mPa·s (20 °C)
Thermochemistry
Heat capacity (C)
 255.68 J K−1 mol−1
Std molar
entropy (So298)
 361.20 J K−1 mol−1
Std enthalpy of
formation (ΔfH⦵298)
 −252.1–−248.5 kJ mol−1
Std enthalpy of
combustion (ΔcH⦵298)
 −5.53–−5.33 MJ mol−1
Hazards
GHS pictograms
GHS Signal word Danger
GHS hazard statements
 H225, H304, H315, H336, H410
GHS precautionary statements
 P210, P261, P273, P301+310, P331
NFPA 704 (fire diamond)
3
1
0
Flash point 13.0 °C (55.4 °F; 286.1 K)
Autoignition
temperature
 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)[4]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 500 ppm (2350 mg/m3)[2]
REL (Recommended)
 TWA 75 ppm (350 mg/m3) C 385 ppm (1800 mg/m3) [15-minute][2]
IDLH (Immediate danger)
 1000 ppm[2]
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 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" (an index of a fuel's ability to resist engine knock at high compression, which is a characteristic of octane's branched-chain isomers, especially iso-octane), particularly in the expression "high octane".

The octane rating was originally determined by mixing fuels from only heptane and 2,2,4-trimethylpentane (a highly branched octane), 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 (the straight chain of 8 carbon atoms with no branching) has a -20 (negative) 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.[5] 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 (24 including stereoisomers):

References
  1. "octane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 6 January 2012.
  2. NIOSH Pocket Guide to Chemical Hazards. "#0470". National Institute for Occupational Safety and Health (NIOSH).
  3. Dymond, J. H.; Oye, H. A. (1994). "Viscosity of Selected Liquid n‐Alkanes". Journal of Physical and Chemical Reference Data. 23 (1): 41–53. doi:10.1063/1.555943. ISSN 0047-2689.
  4. "Octane". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5. Oxford English Dictionary.