Cyclopentane (also called C pentane) is a highly

flammable A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...

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 A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...

with a petrol-like

odor An odor (American English) or odour (English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is caused by one or more volatilized chemical compounds ...

. Its melting point is −94 °C and its

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envir ...

is 49 °C. Cyclopentane is in the class of

cycloalkane In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing ...

s, being

alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which ...

s that have one or more rings of carbon atoms. It is formed by cracking

cyclohexane Cyclohexane is a cycloalkane with the molecular formula . Cyclohexane is non-polar. Cyclohexane is a colorless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cyclohexan ...

in the presence of alumina at a high temperature and pressure. It was first prepared in 1893 by the German chemist Johannes Wislicenus.

Production, occurrence and use

Cycloalkanes are formed by catalytic reforming. For example, when passed over a hot platinum surfact, 2-methylbutane converts into cyclopentane. Cyclopentane has no particular use. No commercial products are made from cyclopentane itself. As a volatile hydrocarbon it is an incidental component of some fuels and blowing agents. In principle, it could be used as a

refrigerant A refrigerant is a working fluid used in the heat pump and refrigeration cycle, refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Ref ...

except that it is rather flammable. Cyclopentane can be fluorinated to give compounds ranging from to perfluorocyclopentane . Such species are conceivable refrigerants and specialty solvents. The cyclopentane ring is pervasive in

natural product A natural product is a natural compound or substance produced by a living organism—that is, found in nature. In the broadest sense, natural products include any substance produced by life. Natural products can also be prepared by chemical syn ...

s including many useful drugs. Examples include most

steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...

s, prostaglandins, and some lipids.

Conformations

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 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 ( C), while the half chair has two-fold rotational symmetry ( C). 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

(C₆H₁₂, see cyclohexane conformation) and higher

s, 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. File:Cyclopentane envelope conformation.svg, Envelope File:Cyclopentane3D.png, 3D envelope File:Cyclopentane halfchair.svg, Half-chair

References

External links

* {{Authority control Cyclopentanes Hydrocarbon solvents Cycloalkanes