Editing Octane rating (section)

== Misconceptions around octane rating ==
[[File:GasStationPump4.jpg|left|thumb|Gas stations have gasoline with different octane ratings. Higher numbers indicate that the fuel can better avoid unintended combustions within the cylinders of the engine.]]
Due to its name, the chemical "octane" is often misunderstood as the only substance that determines the octane rating (or octane number) of a fuel. This is an inaccurate description. In reality, the octane rating is defined as a number describing the stability and ability of a fuel to prevent an engine from unwanted combustions<ref>{{Cite web |title=Dictionary.com {{!}} Meanings & Definitions of English Words |url=https://www.dictionary.com/browse/octane-number |access-date=2024-04-03 |website=Dictionary.com |language=en}}</ref> that occur spontaneously in the other regions within a [[Cylinder (engine)|cylinder]] (i.e., delocalized explosions from the spark plug). This phenomenon of combustion is more commonly known as [[engine knocking]] or self-ignition, which causes damage to pistons over time and reduces the lifespan of engines.

In 1927, Graham Edgar<ref>{{cite journal |last1=Beatty |first1=Harold A. |title=Graham Edgar, Chemist of Parts |journal=Science |date=2 March 1956 |volume=123 |issue=3192 |pages=365 |doi=10.1126/science.123.3192.365 |pmid=17736435 |bibcode=1956Sci...123..365B }}</ref> devised the method of using [[2,2,4-Trimethylpentane|iso-octane]] and [[Heptane|n-heptane]] as reference chemicals, in order to rate the knock resistance of a fuel with respect to this isomer of octane,<ref name=":02">{{Cite web |title=A Brief History of Octane in Gasoline: From Lead to Ethanol {{!}} White Papers |publisher=EESI |url=https://www.eesi.org/papers/view/fact-sheet-a-brief-history-of-octane |access-date=2024-04-03 |website=www.eesi.org}}</ref> thus the name "octane rating". By definition, the isomers ''iso-octane'' and ''n-heptane'' have an octane rating of 100 and 0, respectively.<ref>{{Cite web |title=Octane |url=http://www.mckinseyenergyinsights.com/resources/refinery-reference-desk/octane/ |access-date=2024-04-03 |website=www.mckinseyenergyinsights.com |language=en}}</ref> Because of its more volatile nature, n-heptane ignites and knocks readily, which gives it a relatively low octane rating;<ref>{{Cite web |title=Chemical isomer – Energy Education |url=https://energyeducation.ca/encyclopedia/Chemical_isomer |access-date=2024-04-03 |website=energyeducation.ca |language=en}}</ref> the isomer iso-octane causes less knocking because it is more branched and combusts more smoothly. In general, branched compounds with a higher intermolecular force (e.g., London dispersion force for iso-octane) will have a higher octane rating, as they are harder to ignite.<ref>{{Cite web |title=Why do highly branched alkanes have higher octane numbers than their corresponding linear isomer? |url=https://chemistry.stackexchange.com/questions/99333/why-do-highly-branched-alkanes-have-higher-octane-numbers-than-their-correspondi |access-date=2024-04-15 |website=Chemistry Stack Exchange |language=en}}</ref>

=== Octane ratings of octane isomers ===
Octane isomers such as ''n-octane'' and ''[[2,3,3-Trimethylpentane|2,3,3-trimethylpentane]]'' have an octane rating of -20 and 106.1, respectively ('''RON''' measurement).<ref>{{cite journal |last1=Balaban |first1=A. T. |title=Topological indices based on topological distances in molecular graphs |journal=Pure and Applied Chemistry |date=1983 |volume=55 |issue=2 |pages=199–206 |doi=10.1351/pac198855020199 }}</ref> The large differences between the octane ratings for the isomers show that the compound octane itself is clearly not the only factor that determines octane ratings, especially for commercial fuels consist of a wide variety of compounds.