Octane is a

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

and an alkane with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

, and the condensed structural formula . Octane has many structural isomers that differ by the amount and location of branching in the

carbon chain In chemistry, catenation is the bonding of atoms of the same element into a series, called a ''chain''. A chain or a ring shape may be ''open'' if its ends are not bonded to each other (an open-chain compound), or ''closed'' if they are bonde ...

. 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 scale. Octane is a component of

gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...

(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 spark ignition internal combustion engines, knocking (also knock, detonation, spark knock, pinging or pinking) occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignite ...

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

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 and it has found a place in modern English vernacular.

Isomers

Octane has 18 structural isomers (24 including

stereoisomer In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in ...

s): *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 dimen ...

(2 enantiomers) * 4-Methylheptane * 3-Ethylhexane * 2,2-Dimethylhexane *

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 liq ...

* 3,3-Dimethylhexane * 3,4-Dimethylhexane (2 enantiomers + 1

meso compound A meso compound or meso isomer is a non-optically active member of a set of stereoisomers, at least two of which are optically active. This means that despite containing two or more stereocenters, the molecule is not chiral. A meso compound is "su ...

) * 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 (t ...

(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. References

{{DEFAULTSORT:Trimethylpentane, 2,3,3- Alkanes ...

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

References

External links

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

{{Hydrides by group Alkanes Hydrocarbons