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.
|Preferred IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||70.1 g/mol|
|Appearance||clear, colorless liquid|
|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)|
|Solubility||soluble in ethanol, acetone, ether|
|Vapor pressure||45 kPa (20 °C) |
Refractive index (nD)
|Occupational safety and health (OHS/OSH):|
|NFPA 704 (fire diamond)|
|Flash point||−37.2 °C (−35.0 °F; 236.0 K)|
|361 °C (682 °F; 634 K)|
|NIOSH (US health exposure limits):|
|TWA 600 ppm (1720 mg/m3)|
IDLH (Immediate danger)
|cyclopropane, cyclobutane, cyclohexane|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
(what is ?)
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.
Multiply alkylated cyclopentane (MAC) lubricants have low volatility and are used in some specialty applications.
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.
This hydrocarbon has also been fluorinated into compounds ranging from C5H9F to perflorocyclopenane C5F10 by passing either cyclopentane or cyclopentadiene over TaF2. Heptafluorocyclopentane has been studied as an alternative to linear HCFCs as a solvent having reduced ozone depletion.
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 C5H−5 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.