Article · Wikipedia archive · Last revised Jun 21, 2026

Cyclopentene

Cyclopentene is a chemical compound with the formula (CH2)3(CH)2. It is a colorless liquid with a petrol-like odor. It has few applications, and thus is mainly used as a minor component of gasoline, present in concentrations of less than 1%. It is one of the principal cycloalkenes.

Last revised
Jun 21, 2026
Read time
≈ 2 min
Length
471 w
Citations
8
Source
Wikipedia ↗
Cyclopentene
Cyclopentene
Cyclopentene source ↗
Ball-and-stick model of cyclopentene
Ball-and-stick model of cyclopentene source ↗
Space-filling model of cyclopentene
Space-filling model of cyclopentene source ↗
Names
Preferred IUPAC name
Cyclopentene
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.005.030
UNII
  • InChI=1S/C5H8/c1-2-4-5-3-1/h1-2H,3-5H2 checkY
    Key: LPIQUOYDBNQMRZ-UHFFFAOYSA-N checkY
  • InChI=1/C5H8/c1-2-4-5-3-1/h1-2H,3-5H2
    Key: LPIQUOYDBNQMRZ-UHFFFAOYAS
  • C1CC=CC1
Properties
C5H8
Molar mass 68.11 g/mol
Density 0.771 g/cm3
Melting point −135 °C (−211 °F; 138 K)
Boiling point 44 to 46 °C (111 to 115 °F; 317 to 319 K)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
source ↗
1
3
1
Flash point −29 °C (−20 °F; 244 K)
Related compounds
Related compounds
 Cyclopentadiene
Cyclobutene
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 ?)

Cyclopentene is a chemical compound with the formula (CH2)3(CH)2. It is a colorless liquid with a petrol-like odor. It has few applications, and thus is mainly used as a minor component of gasoline, present in concentrations of less than 1%.12 It is one of the principal cycloalkenes.

History and synthesis

Cyclopentene was first prepared by Carl Gärtner in 1893 from iodocyclopentane with potassium hydroxide. He named it pentamethenylene (German: Pentamethenylen).3

Cyclopentene is produced industrially in large amounts by steam cracking of naphtha. In the laboratory, it is prepared by dehydration of cyclopentanol.4 Substituted cyclopentenes are the product of the vinylcyclopropane-cyclopentene rearrangement.5

It can also be produced by the catalytic hydrogenation of cyclopentadiene.6

Reactions

The polymerization of cyclopentene by Ziegler-Natta catalysts yields 1,3-linkages, not the more typical 1,2-linked polymer.7

Palladium-catalyzed hydrocarboxylation of cyclopentene gives cyclopentanecarboxylic acid:8

C5H8 + CO + H2O → C5H9CO2H
References

References

  1. Dieter Hönicke; Ringo Födisch; Peter Claus; Michael Olson (2002). "Cyclopentadiene and Cyclopentene". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_227. ISBN 978-3-527-30673-2.
  2. "Hydrocarbon Composition of Gasoline Vapor Emissions from Enclosed Fuel Tanks". nepis.epa.gov. United States Environmental Protection Agency. 2011.
  3. Gärtner, Carl (January 1893). "Das Pentamethenylen und sein Dibromür". Justus Liebigs Annalen der Chemie. 275 (2–3): 331–332. doi:10.1002/jlac.18932750217. ISSN 0075-4617.
  4. B. B. Corson, V. N. Ipatieff (1939). "Cyclohexylbenzene". Organic Syntheses. 19: 36. doi:10.15227/orgsyn.019.0036.
  5. Baldwin, John E. (2003). "Thermal Rearrangements of Vinylcyclopropanes to Cyclopentenes". Chemical Reviews. 103 (4): 1197–212. doi:10.1021/cr010020z. PMID 12683781.
  6. D. Hönicke, R. Födisch, P. Claus, M. Olson: Cyclopentadiene and Cyclopentene, in: Ullmanns Enzyklopädie der Technischen Chemie 2002, Wiley-VCH, Weinheim.
  7. Collins, Scott; Kelly, W. Mark (1992). "The microstructure of poly(cyclopentene) produced by polymerization of cyclopentene with homogeneous Ziegler-Natta catalysts". Macromolecules. 25 (1): 233–7. Bibcode:1992MaMol..25..233C. doi:10.1021/ma00027a039.
  8. Sang, Rui; Kucmierczyk, Peter; Dühren, Ricarda; Razzaq, Rauf; Dong, Kaiwu; Liu, Jie; Franke, Robert; Jackstell, Ralf; Beller, Matthias (2019). "Synthesis of Carboxylic Acids by Palladium‐Catalyzed Hydroxycarbonylation". Angewandte Chemie International Edition. 58 (40): 14365–14373. doi:10.1002/anie.201908451. PMID 31390131. S2CID 199466915.
External links