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Skeletal formula of 2,2,4-trimethylpentane
Ball and stick model of 2,2,4-trimethylpentane
Spacefill model of 2,2,4-trimethylpentane
Preferred IUPAC name
3D model (JSmol)
ECHA InfoCard 100.007.964 Edit this at Wikidata
EC Number
  • 208-759-1
MeSH 2,2,4-trimethylpentane
RTECS number
  • SA3320000
UN number 1262
  • InChI=1S/C8H18/c1-7(2)6-8(3,4)5/h7H,6H2,1-5H3 checkY
  • CC(C)CC(C)(C)C
Molar mass 114.232 g·mol−1
Appearance Colorless liquid
Odor petroleum-like
Density 0.692 g cm−3
Melting point −107.38 °C; −161.28 °F; 165.77 K
Boiling point 99.30 °C; 210.74 °F; 372.45 K
log P 4.373
Vapor pressure 5.5 kPa (at 21 °C)
3.0 nmol Pa−1 kg−1
UV-vismax) 210 nm
-98.34·10−6 cm3/mol
242.49 J K−1 mol−1
328.03 J K−1 mol−1
−260.6 to −258.0 kJ mol−1
−5462.6 to −5460.0 kJ mol−1
GHS pictograms
GHS02: Flammable
GHS07: Harmful
GHS08: Health hazard
GHS09: Environmental hazard
GHS Signal word Danger
H225, H304, H315, H336, H410
P210, P261, P273, P301+310, P331
NFPA 704 (fire diamond)
Flash point −12 °C (10 °F; 261 K)
396 °C (745 °F; 669 K)
Explosive limits 1.1–6.0%
Related compounds
Related alkanes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)
Infobox references

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 (the zero point is n-heptane). It is an important component of gasoline, frequently used in relatively large proportions to increase the knock resistance of the fuel.[2]

Strictly speaking, if the standard meaning of ‘iso’ is followed, the name isooctane should be reserved for the isomer 2-methylheptane. However, 2,2,4-trimethylpentane is by far the most important isomer of octane and so, historically, it has been assigned this name.[3]


Isooctane is produced on a massive scale in the petroleum industry by alkylation of isobutene with isobutane. The process is conducted in alkylation units in the presence of acid catalysts.[4]

Route to 2,2,4-trimethylpentane from isobutene and isobutane
Route to 2,2,4-trimethylpentane from isobutene and isobutane

It can also be produced from isobutylene by dimerization using an Amberlyst catalyst to produce a mixture of iso-octenes. Hydrogenation of this mixture produces 2,2,4-trimethylpentane.[5]


Engine knocking is an unwanted process that can occur during high compression ratios in internal combustion engines. Graham Edgar in 1926 added different amounts of n-heptane and 2,2,4-trimethylpentane to gasoline, and discovered that the knocking stopped when 2,2,4-trimethylpentane was added. This work was the origin of the octane rating scale.[6] Test motors using 2,2,4-trimethylpentane gave a certain performance that was standardized as 100 octane. The same test motors, run in the same fashion, using heptane, gave a performance which was standardized as 0 octane. All other compounds and blends of compounds then were graded against these two standards and assigned octane numbers.


In common with all hydrocarbons, 2,2,4-trimethylpentane is flammable.[7]

See also


  1. ^ "2,2,4-trimethylpentane - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Identification and Related Records. Retrieved 11 March 2012.
  2. ^ Werner Dabelstein; Arno Reglitzky; Andrea Schütze; Klaus Reders (2007). "Automotive Fuels". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_719.pub2.
  3. ^ Clayden, Jonathan (2005). Organic chemistry (Reprinted (with corrections). ed.). Oxford [u.a.]: Oxford Univ. Press. pp. 315. ISBN 978-0-19-850346-0.
  4. ^ Bipin V. Vora; Joseph A. Kocal; Paul T. Barger; Robert J. Schmidt; James A. Johnson (2003). "Alkylation". Kirk‐Othmer Encyclopedia of Chemical Technology. doi:10.1002/0471238961.0112112508011313.a01.pub2.
  5. ^ Dimerization of isobutylene,
  6. ^ Fuels and lubricants handbook, Volume 1, George E. Totten, Steven R. Westbrook, Rajesh J. Shah, page 62
  7. ^ 2,2,4-Trimethylpentane, Integrated Risk Information System, United States Environmental Protection Agency

External links

This page was last edited on 17 April 2021, at 15:06
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