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 ex ...
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
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 symbols, ...
, 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
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 bonded ...
. 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
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 organic co ...
(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
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 ...
," 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
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 organic co ...
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
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 dimensi ...
(2
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
*
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
*
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
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 "sup ...
)
*
3-Ethyl-2-methylpentane
*
3-Ethyl-3-methylpentane
*
2,2,3-Trimethylpentane (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
*
2,3,4-Trimethylpentane
*
2,2,3,3-Tetramethylbutane
References
External links
*
*
* Dr. Duke's Phytochemical and Ethnobotanical Databases, Octane
{{Hydrides by group
Alkanes
Hydrocarbons