Chemistry:Octane

Short description: Hydrocarbon compound with the formula C8H18

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

Octane

Names
Systematic IUPAC name Octane
Other names n-Octane Octacarbane
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
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
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	CH 3(CH 2) 6CH 3
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 law constant (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 molar entropy (So298)	361.20 J/(K·mol)
Std enthalpy of formation (ΔfH⦵298)	−252.1 to −248.5 kJ/mol
Std enthalpy of combustion (ΔcH⦵298)	−5.53 to −5.33 MJ/mol
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)
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) [15-minute]
IDLH (Immediate danger)	1000 ppm
Related compounds
Related alkanes	Methane Ethane Propane Butane Pentane Hexane Heptane Nonane Decane
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

Tracking categories (test):

• SizeSet

Octane is a hydrocarbon and an alkane with the chemical formula C
8H
18, and the condensed structural formula CH
3(CH
2)
6CH
3. 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 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

External links

• International Chemical Safety Card 0933
• NIOSH Pocket Guide to Chemical Hazards. "#0470". National Institute for Occupational Safety and Health (NIOSH). https://www.cdc.gov/niosh/npg/npgd0470.html. 
• Dr. Duke's Phytochemical and Ethnobotanical Databases, Octane, [1]