Hydrocarbon compound with the formula C8H18
Octane
Names
Systematic IUPAC name
Other names
n -Octane
Identifiers
1696875
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard
100.003.539
EC Number
82412
KEGG
MeSH
octane
RTECS number
UNII
UN number
1262
InChI=1S/C8H18/c1-3-5-7-8-6-4-2/h3-8H2,1-2H3
Y Key: TVMXDCGIABBOFY-UHFFFAOYSA-N
Y
Properties
CH3 (CH2 )6 CH3
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
1.398
Viscosity
0.509 mPa·s (25 °C)[ 3]
0.542 mPa·s (20 °C)
Thermochemistry
255.68 J/(K·mol)
361.20 J/(K·mol)
−252.1 to −248.5 kJ/mol
−5.53 to −5.33 MJ/mol
Hazards
GHS labelling :
Danger
H225 , H304 , H315 , H336 , H410
P210 , P261 , P273 , P301+P310 , P331
NFPA 704 (fire diamond)
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):
TWA 500 ppm (2350 mg/m3 )[ 2]
TWA 75 ppm (350 mg/m3 ) C 385 ppm (1800 mg/m3 ) [15-minute][ 2]
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).
Chemical compound
Octane is a hydrocarbon and also an alkane with the chemical formula C8 H18 , and the condensed structural formula CH3 (CH2 )6 CH3 . 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. Octane is 1.2 to 2 times more toxic than heptane .[ 5]
Isomers
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:
2-Methylheptane
4-Methylheptane
3-Ethylhexane
2,2-Dimethylhexane
2,5-Dimethylhexane
(meso )-3,4-Dimethylhexane
3,3-Dimethylhexane
3-Ethyl-2-methylpentane
3-Ethyl-3-methylpentane
2,2,4-Trimethylpentane (i.e. iso-octane)
2,3,3-Trimethylpentane
2,3,4-Trimethylpentane
2,2,3,3-Tetramethylbutane
Chiral Isomers:
(3R )-3-Methylheptane
(3S )-3-Methylheptane
(3R )-2,3-Dimethylhexane
(3S )-2,3-Dimethylhexane
(4R )-2,4-Dimethylhexane
(4S )-2,4-Dimethylhexane
(3R ,4R )-3,4-Dimethylhexane
(3S ,4S )-3,4-Dimethylhexane
(3R )-2,2,3-Trimethylpentane
(3S )-2,2,3-Trimethylpentane
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.
References
External links