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cyclopropane,C3H6, a gaseous hydrocarbon. It is a cyclic alkane, its three carbon atoms being joined together in a ring. The angle between successive carbon-carbon bonds in the ring is only 60°, much less than that between successive carbon-carbon bonds in a normal open-chain alkane; the cyclopropane molecule is thus said to be "strained." Many reactions of cyclopropane involve breaking one of the carbon-carbon bonds in the ring, which opens the ring and relieves the strain. Cyclopropane is prepared commercially by the reaction of 1,3-dichloropropane with zinc. It is a potent inhalation anesthetic, that once enjoyed wide use, but has been replaced by less combustible gases. Cyclopropane allowed the transport of more oxygen to the tissues than did other common anesthetics and also produced greater skeletal muscle relaxation. It is not irritating to the respiratory tract. Because of the low solubility of cyclopropane in the blood, postoperative recovery was usually rapid but nausea and vomiting were common. See anesthesiaanesthesia
[Gr.,=insensibility], loss of sensation, especially that of pain, induced by drugs, especially as a means of facilitating safe surgical procedures. Early modern medical anesthesia dates to experiments with nitrous oxide (laughing gas) by Sir Humphry Davy of England
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(also trimethylene), an alicyclic hydrocarbon having the structural formula
Cyclopropane is a colorless gas with a boiling point of –32.8°C and a density of 0.720 g/cm3 at –79°C. Insoluble in water, it is soluble in alcohol and ether.
Cyclopropane is the first member of the homologous series of cycloparaffins. Its trimethylene ring, however, is characterized by reactions of the C═C double bond; for example, it forms 1,3-dibromopropane (BrCH2CH2CH2Br) in its reaction with bromine. The cyclopropane ring is easily broken because it is strained. Nevertheless, in contrast to olefins, cyclopropane does not react with potassium permanganate and ozone at 20°C. Cyclopropane and hydrocarbons containing the cyclopropane ring may be obtained by reacting zinc dust with derivatives that have two halogens attached at the 1 and 3 positions. They may also be obtained by other methods, including the joining of carbenes to olefins.
Cyclopropane and its derivatives are of great theoretical interest; for example, it has been discovered that compounds containing the cyclopropenyl cation have aromatic properties. The cyclopropane ring is found in biologically important natural compounds (seePYRETHRINS). Cyclopropane itself is used as an anesthetic.