Octane

For the gasoline rating system, see octane rating. For other uses, see Octane (disambiguation).

Octane

Names
IUPAC name Octane
Identifiers
CAS Number	111-65-9 Y
3DMet	B00281
Beilstein Reference	1696875
ChEBI	CHEBI:17590 N
ChEMBL	ChEMBL134886 Y
ChemSpider	349 Y
DrugBank	DB02440 N
EC Number	203-892-1
Gmelin Reference	82412
Jmol 3D model	Interactive image
KEGG	C01387 Y
MeSH	octane
PubChem	356
RTECS number	RG8400000
UN number	1262
InChI InChI=1S/C8H18/c1-3-5-7-8-6-4-2/h3-8H2,1-2H3 Y Key: TVMXDCGIABBOFY-UHFFFAOYSA-N Y
SMILES CCCCCCCC
Properties
Chemical formula	C8H18
Molar mass	114.23 g·mol−1
Appearance	Colorless liquid
Odor	Gasoline-like
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
Refractive index (nD)	1.398
Viscosity	542 μPa s (at 20 °C)
Thermochemistry
Specific 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 (ΔfHo298)	−252.1–−248.5 kJ mol−1
Std enthalpy of combustion (ΔcHo298)	−5.53–−5.33 MJ mol−1
Vapor pressure	{{{value}}}
Related compounds
Related alkanes	Heptane Nonane
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 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.

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. 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):

• 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

External links

• International Chemical Safety Card 0933
• Dr. Duke's Phytochemical and Ethnobotanical Databases, Octane, http://www.ars-grin.gov/cgi-bin/duke/chemical.pl?OCTANE