Octane is a hydrocarbon and an

alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which ...

with the chemical formula , and the condensed structural formula . Octane has many

structural isomer In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a chemical compound, compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct chemical bond, b ...

s that differ by the amount and location of branching in the carbon chain. One of these isomers,

2,2,4-trimethylpentane 2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH3)3CCH2CH(CH3)2. It is one of several isomers of octane (C8H18). This particular isomer is the standard 100 point on the octane rating scale ...

(commonly called iso-octane) is used as one of the standard values in the

octane rating An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonating ...

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 "

," 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 the mid-1990s, the phrase was commonly being used as an

intensifier In linguistics, an intensifier (abbreviated ) is a lexical category (but ''not'' a traditional part of speech) for a modifier that makes no contribution to the propositional meaning of a clause but serves to enhance and give additional emotional co ...

and it has found a place in modern English vernacular.

Isomers

Octane has 18

structural isomers In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct bonds between them. The term meta ...

(24 including stereoisomers): *Octane (''n''-octane) *

2-Methylheptane 2-Methylheptane is a branched alkane isomeric to octane. Its structural formula The structural formula of a chemical compound is a graphic representation of the molecular structure (determined by structural chemistry methods), showing how the at ...

3-Methylheptane 3-Methylheptane is a branched alkane isomeric to octane. Its structural formula is CH3CH2CH(CH3)CH2CH2CH2CH3. It has one stereocenter. Its refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensi ...

enantiomers In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical anti ...

) * 4-Methylheptane * 3-Ethylhexane *

2,2-Dimethylhexane The comma is a punctuation mark that appears in several variants in different languages. It has the same shape as an apostrophe or single closing quotation mark () in many typefaces, but it differs from them in being placed on the baseline o ...

2,3-Dimethylhexane 2,3-Dimethylhexane is a structural isomer of octane Octane is a hydrocarbon and an alkane with the chemical formula , and the condensed structural formula . Octane has many structural isomers that differ by the amount and location of branchin ...

(2 enantiomers) * 2,4-Dimethylhexane (2 enantiomers) *

2,5-Dimethylhexane 2,5-Dimethylhexane is a branched alkane used in the aviation industry in low revolutions per minute helicopters. As an isomer of octane, the boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liqu ...

3,3-Dimethylhexane 3,3-Dimethylhexane is a colourless, odourless liquid, chemical compound in the family of hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 ...

* 3,4-Dimethylhexane (2 enantiomers + 1 meso compound) * 3-Ethyl-2-methylpentane * 3-Ethyl-3-methylpentane *

2,2,3-Trimethylpentane The comma is a punctuation mark that appears in several variants in different languages. It has the same shape as an apostrophe or single closing quotation mark () in many typefaces, but it differs from them in being placed on the baseline o ...

(2 enantiomers) *

2,2,4-Trimethylpentane 2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH3)3CCH2CH(CH3)2. It is one of several isomers of octane (C8H18). This particular isomer is the standard 100 point on the octane rating scale ...

(isooctane) *

2,3,3-Trimethylpentane 2,3,3-Trimethylpentane is a chemical compound in the family of hydrocarbons which has a formula of C8H18. It is an isomer of octane Octane is a hydrocarbon and an alkane with the chemical formula , and the condensed structural formula . Octane ...

2,3,4-Trimethylpentane 2,3,4-Trimethylpentane is a branched alkane. It is one of the isomers of octane Octane is a hydrocarbon and an alkane with the chemical formula , and the condensed structural formula . Octane has many structural isomers that differ by the amo ...

2,2,3,3-Tetramethylbutane Tetramethylbutane, sometimes called hexamethylethane, is a hydrocarbon with formula C8H18 or (H3C-)3C-C(-CH3)3. It is the most heavily branched and most compact of the many octane isomers, the only one with a butane (C4) backbone. Because of its h ...

References

External links

* * * Dr. Duke's Phytochemical and Ethnobotanical Databases, Octane

{{Hydrides by group Alkanes Hydrocarbons