AskDefine | Define cyclopropane

Dictionary Definition

cyclopropane n : a colorless flammable gas sometimes used as an inhalation anesthetic

User Contributed Dictionary

English

Noun

  1. organic compound pharmaceutical drug The simplest alicyclic hydrocarbon, C3H6, an inflammable gas, sometimes used as an anaesthetic.

Translations

the simplest alicyclic hydrocarbon, C3H6
  • Finnish: syklopropaani
  • Greek: κυκλοπροπάνιο
  • Italian: ciclopropano

Extensive Definition

Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms. The bonds between the carbon atoms are a great deal weaker than in a typical carbon-carbon bond. This is the result of the 60° angle between the carbon atoms, which is far less than the normal angle of 109.5° for bonds between atoms with sp3 hybridised orbitals. This angle strain has to be subtracted from the normal C-C bond energy, making the resultant compound more reactive than acyclic alkanes and other cycloalkanes such as cyclohexane and cyclopentane. This is the banana bond description of cycloalkanes.
There is also torsional strain because the hydrogen atoms are held in the eclipsed conformation.
However, cyclopropanes are more stable than a simple angle strain analysis would suggest. Cyclopropane can also be modeled as a three-center-bonded orbital combination of methylene carbenes. This results in the Walsh orbital description of cyclopropane, where the C-C bonds have mostly pi character. This is also why cyclopropanes often have reactivity similar to alkenes. This is also why carbenes can easily add into alkenes to produce cyclopropanes. Cyclopropanes taken to the extreme are tetrahedranes and propellanes.
Cyclopropane is an anaesthetic when inhaled, but has been superseded by other agents in modern anaesthetic practice. This is due to its extreme reactivity under normal conditions: when the gas is mixed with oxygen there is a significant risk of explosion.

History

Cyclopropane was discovered in 1881 by August Freund, who also proposed the right structure for the new substance in his first paper. Freund reacted 1,3-dibromopropane with sodium, the reaction is a intramolecular Wurtz reaction leading directly to cyclopropane. The yield of the reaction can be improved by the use of zinc instead of sodium. Cyclopropane had no commercial application until Henderson and Lucas discovered its anaesthetic properties in 1929. The industrial scale production started not before 1930.

Safety

Because of the strain in the carbon-carbon bonds of cyclopropane, the molecule has an enormous amount of potential energy. In pure form, it will break down to form linear hydrocarbons, including "normal", non-cyclic propene. This decomposition is potentially explosive, especially if the cyclopropane is liquified, pressurized, or contained within tanks. Explosions of cyclopropane and oxygen are even more powerful, because the energy released by the formation of normal propane is compounded by the energy released via the oxidation of the carbon and hydrogen present. At room temperature, sufficient volumes of liquified cyclopropane will self-detonate. To guard against this, the liquid is shipped in cylinders filled with tungsten wool, which prevents high-speed collisions between molecules and vastly improves stability. Pipes to carry cyclopropane must likewise be of small diameter, or else filled with unreactive metal or glass wool, to prevent explosions. Even if these precautions are followed, cyclopropane is dangerous to handle and manufacture, and is no longer used for anaesthesia.

Cyclopropanes

Cyclopropanes are a class of organic compounds sharing the common cyclopropane ring, in which one or more hydrogens may be substituted. These compounds are found in biomolecules; for instance, the pyrethrum insecticides (found in certain Chrysanthemum species) contain a cyclopropane ring.

Organic synthesis

Cyclopropanes can be prepared in the laboratory by organic synthesis in various ways and many methods are simply called cyclopropanation:
a possible reaction mechanism for this cyclopropanation was proposed:

Organic reactions

Although cyclopropanes are formally cycloalkanes, they are very reactive due to considerable strain energy and due to double bond character.
  • Cyclopropyl groups participate in cycloaddition reaction such as the formal [5+2]cycloaddition shown below:
This asymmetric synthesis is catalyzed by a rhodium BINAP system with 96% enantiomeric excess.
This reaction is catalyzed by platinum(II) chloride in a carbon monoxide environment. The proposed reaction mechanism is supported by deuterium labeling.
In another version of the same reaction the catalyst is PdBr2 is prepared in situ from palladium(II) acetate and copper(II) bromide and the solvent is toluene.
cyclopropane in German: Cyclopropan
cyclopropane in Modern Greek (1453-): Κυκλοπροπάνιο
cyclopropane in Spanish: Ciclopropano
cyclopropane in French: Cyclopropane
cyclopropane in Italian: Ciclopropano
cyclopropane in Hebrew: ציקלופרופאן
cyclopropane in Hungarian: Ciklopropán
cyclopropane in Dutch: Cyclopropaan
cyclopropane in Japanese: シクロプロパン
cyclopropane in Polish: Cyklopropan
cyclopropane in Portuguese: Ciclopropano
cyclopropane in Russian: Циклопропан
cyclopropane in Finnish: Syklopropaani
cyclopropane in Swedish: Cyklopropan
cyclopropane in Vietnamese: Cycloprôpan
cyclopropane in Turkish: Siklopropan
cyclopropane in Chinese: 環丙烷
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