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
Systematic IUPAC name
Other names
3D model (JSmol)
ECHA InfoCard 100.003.539 Edit this at Wikidata
EC Number
  • 203-892-1
MeSH octane
RTECS number
  • RG8400000
UN number 1262
  • InChI=1S/C8H18/c1-3-5-7-8-6-4-2/h3-8H2,1-2H3 checkY
Molar mass 114.232 g·mol−1
Appearance Colourless liquid
Odor Gasoline-like[2]
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
0.007 mg/dm3 (at 20 °C)
log P 4.783
Vapor pressure 1.47 kPa (at 20.0 °C)
29 nmol/(Pa·kg)
Conjugate acid Octonium
−96.63·10−6 cm3/mol
  • 0.509 mPa·s (25 °C)[3]
  • 0.542 mPa·s (20 °C)
255.68 J/(K·mol)
361.20 J/(K·mol)
−252.1 to −248.5 kJ/mol
−5.53 to −5.33 MJ/mol
GHS labelling:
GHS02: Flammable GHS07: Exclamation mark GHS08: Health hazard GHS09: Environmental hazard
H225, H304, H315, H336, H410
P210, P261, P273, P301+P310, P331
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
Flash point 13.0 °C (55.4 °F; 286.1 K)
220.0 °C (428.0 °F; 493.1 K)
Explosive limits 0.96 – 6.5%
Lethal dose or concentration (LD, LC):
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).
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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 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 and petroleum. Under standard temperature and pressure, octane is an odorless, colorless liquid. Like other short-chained alkanes with a low molecular weight, it is volatile, flammable, and toxic. For examples, as a neurotoxin with narcotic effects, n-octane is almost twice as toxic as n-heptane.[5]


N-octane has 23 constitutional isomers. 8 of these isomers have one stereocenter; 3 of them have two stereocenters.

(3S,4S)-3,4-Dimethylhexane (top left) and (3R,4R)-3,4-Dimethylhexane (top right) are non-superimposable mirror images, so they are chiral enantiomers. (meso)-3,4-Dimethylhexane (bottom) has a superimposable mirror image, so it is an achiral meso compound.

Achiral Isomers:

Chiral Isomers:

Production and Use

In petrochemistry, octanes are not typically differentiated or purified as specific compounds. Octanes are components of particular boiling fractions.[6]

A common route to such fractions is the alkylation reaction between iso-butane and 1-butene, which forms iso-octane.[7]

Octane is commonly used as a solvent in paints and adhesives.

N-octane is the octane isomer that has the longest carbon skeleton. Unlike its constitutional isomers, it has a very low knock resistance.
The octane isomer, iso-octane, is used as one of the standards for octane ratings. It has a rating of 100 by definition.
The octane isomer 2,3,3-Trimethylpentane has an octane rating exceeding 100.


  1. ^ "octane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 6 January 2012.
  2. ^ a b c d 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. Bibcode:1994JPCRD..23...41D. doi:10.1063/1.555943. ISSN 0047-2689.
  4. ^ "Octane". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  5. ^ "1988 OSHA PEL Project - Octane | NIOSH | CDC". www.cdc.gov. 2020-02-27. Retrieved 2024-04-19.
  6. ^ "Fractionation". www.appliedcontrol.com. Retrieved 2024-04-19.
  7. ^ Ross, Julian (January 1986). "Ullmann's Encyclopedia of industrial chemistry". Applied Catalysis. 27 (2): 403–404. doi:10.1016/s0166-9834(00)82943-7. ISSN 0166-9834.