Octane

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For the gasoline rating system, see Octane rating, or for other uses, see Octane (disambiguation).
Thermodynamic data
Identifiers
CAS number 111-65-9
RTECS number RG8400000
SMILES CCCCCCCC
Properties
Molecular formula C8H18
Molar mass 114.2285 g/mol
Appearance colorless liquid
Density 0.703 g/ml, liquid
Melting point

−57 °C (216 K)
Boiling point

125.52 °C (398.7 K)
Solubility in water Immiscible
Viscosity 0.542 cP at 20 °C
Thermochemistry
Std enthalpy of
formation ΔfHo298		 −250 kJ/mol
Std enthalpy of
combustion ΔcHo298		 −5430 kJ/mol
Hazards
EU classification Flammable (F)
Harmful (Xn)
Dangerous for
the environment (N)
R-phrases R11, R38, R50/53,
R65, R67
S-phrases (S2), S9, S16, S29, S33,
S60, S61, S62
Flash point 13 °C
Autoignition
temperature		 220 °C
Related Compounds
Related alkanes Heptane
2,2,4-Trimethylpentane
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Octane is an alkane with the chemical formula CH3(CH2)6CH3. It has 18 isomers.

One of the isomers, 2,2,4-trimethylpentane or isooctane, is of major importance, as it has been selected as the 100 point on the octane rating scale, with n-heptane as the zero point. Octane ratings are ratings used to represent the anti-knock performance of petroleum-based fuels (octane is less likely to prematurely combust under pressure than heptane), given as the percentage of 2,2,4-trimethylpentane in an 2,2,4-trimethylpentane / n-heptane mixture that would have the same performance. It is an important constituent of gasoline.

Octane has 18 isomers :