Cyclopentane (also called C pentane) is a highly flammable alicyclic hydrocarbon with chemical formula C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It occurs as a colorless liquid with a petrol-like odor. Its melting point is −94 °C and its boiling point is 49 °C. Cyclopentane is in the class of cycloalkanes, being alkanes that have one or more rings of carbon atoms. It is formed by cracking cyclohexane in the presence of alumina at a high temperature and pressure.

Skeletal formula
Space-filling model
Preferred IUPAC name
Other names
  • 287-92-3 checkY
3D model (JSmol)
  • Interactive image
  • CHEBI:23492 checkY
  • 8896 checkY
ECHA InfoCard 100.005.470 Edit this at Wikidata
EC Number
  • 206-016-6
  • 9253
RTECS number
  • GY2390000
  • T86PB90RNU checkY
  • DTXSID6024886 Edit this at Wikidata
  • InChI=1S/C5H10/c1-2-4-5-3-1/h1-5H2 checkY
  • InChI=1/C5H10/c1-2-4-5-3-1/h1-5H2
  • C1CCCC1
Molar mass 70.1 g/mol
Appearance clear, colorless liquid
Odor mild, sweet
Density 0.751 g/cm3
Melting point −93.9 °C (−137.0 °F; 179.2 K)
Boiling point 49.2 °C (120.6 °F; 322.3 K)
156 mg·l−1 (25 °C)[1]
Solubility soluble in ethanol, acetone, ether
Vapor pressure 45 kPa (20 °C) [2]
Acidity (pKa) ~45
-59.18·10−6 cm3/mol
Occupational safety and health (OHS/OSH):
Main hazards
NFPA 704 (fire diamond)
Flash point −37.2 °C (−35.0 °F; 236.0 K)
361 °C (682 °F; 634 K)
Explosive limits 1.1%-8.7%[3]
NIOSH (US health exposure limits):
PEL (Permissible)
REL (Recommended)
TWA 600 ppm (1720 mg/m3)[3]
IDLH (Immediate danger)
Related compounds
Related compounds
cyclopropane, cyclobutane, cyclohexane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

It was first prepared in 1893 by the German chemist Johannes Wislicenus.[4]

Industrial usageEdit

Cyclopentane is used in the manufacture of synthetic resins and rubber adhesives and also as a blowing agent in the manufacture of polyurethane insulating foam, and is found in many domestic appliances such as refrigerators and freezers, replacing alternatives such as CFC-11 and HCFC-141b.[5]

Multiply alkylated cyclopentane (MAC) lubricants have low volatility and are used in some specialty applications.[6]

Formulation of cycloalkanesEdit

Cycloalkanes can be formulated via a process known as catalytic reforming.

For example, 2-methylbutane can be reformed into cyclopentane, by use of a platinum catalyst. This is particularly well known in automobiles, as branched alkanes will burn much more readily.

Fluorinated versionsEdit

This hydrocarbon has also been fluorinated into compounds ranging from C5H9F to perflorocyclopenane C5F10 by passing either cyclopentane or cyclopentadiene over TaF2.[7] Heptafluorocyclopentane has been studied as an alternative to linear HCFCs as a solvent having reduced ozone depletion.[8]


In a regular pentagon the angles at the vertices are all 108°, slightly less than the bond angle in perfectly tetrahedrally bonded carbon, which is about 109.47°. But cyclopentane is not planar in its normal conformations. It puckers in order to increase the distances between the hydrogen atoms (something which does not happen in the planar cyclopentadienyl anion C5H5 because it doesn't have as many hydrogen atoms). This means that the average C-C-C angle is less than 108°. There are two conformations that give local minima of the energy, the "envelope" and the "half-chair". The envelope has mirror symmetry (Cs), while the half chair has two-fold rotational symmetry (C2). In both cases the symmetry implies that there are two pairs of equal C-C-C angles and one C-C-C angle that has no pair. In fact for cyclopentane, unlike for cyclohexane (C6H12, see cyclohexane conformation) and higher cycloalkanes, it is not possible geometrically for all the angles and bond lengths to be equal except if it is in the form of a flat regular pentagon.


  1. ^ Record of cyclopentane in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 28 February 2015.
  2. ^ "ICSC 0353 - CYCLOPENTANE".
  3. ^ a b c d e NIOSH Pocket Guide to Chemical Hazards. "#0171". National Institute for Occupational Safety and Health (NIOSH).
  4. ^ J. Wislicenus and W. Hentschel (1893) "Der Pentamethenylalkohol und seine Derivate" (Cyclopentanol and its derivatives), Annalen der Chemie, 275 : 322-330; see especially pages 327-330. Wislicenus prepared cyclopentane from cyclopentanone ("Ketopentamethen"), which is prepared by heating calcium adipate.
  5. ^ Greenpeace - Appliance Insulation Archived 2008-10-30 at the Wayback Machine
  6. ^ "Pennzoil Products: High Tech Products". 12 April 2004. Archived from the original on 12 April 2004. Retrieved 15 July 2022.
  7. ^ Tatlow, John Colin (1995). "Cyclic and bicyclic polyfluoro-alkanes and -alkenes". Journal of Fluorine Chemistry. 75 (1): 7–34. doi:10.1016/0022-1139(95)03293-m. ISSN 0022-1139.
  8. ^ Zhang, Chengping; Qing, Feiyao; Quan, Hengdao; Sekiya, Akira (January 2016). "Synthesis of 1,1,2,2,3,3,4-heptafluorocyclopentane as a new generation of green solvent". Journal of Fluorine Chemistry. 181: 11–16. doi:10.1016/j.jfluchem.2015.10.012.

External linksEdit

  •   Media related to Cyclopentane at Wikimedia Commons