What does cyclopropane mean?
Cyclopropane is a colourless, highly flammable gas with the formula C₃H₆, in which three carbon atoms join into a triangular ring — the smallest possible carbocycle. Because the natural bond angle of carbon (about 109 degrees) cannot be accommodated in such a tight triangle, the molecule carries considerable angle strain, making it markedly more reactive than ordinary alkanes despite containing only single bonds. This combination of simplicity and strain makes cyclopropane a staple topic in organic chemistry and a useful building block in synthesis, where ring-opening reactions convert it into other compounds. The name simply combines 'cyclo-', indicating a ring structure, with 'propane', reflecting its three-carbon composition. Historically, the compound enjoyed a distinguished second life as an inhalational general anaesthetic from the 1930s onward: it induced sleep quickly and was well tolerated by patients, though its explosiveness in air eventually led to its replacement by non-flammable agents. Today the word belongs firmly to the laboratory and the textbook rather than the operating theatre.
nounA colourless, highly flammable gaseous hydrocarbon (C₃H₆) consisting of a ring of three carbon atoms, used chiefly as a general anaesthetic and as an intermediate in organic synthesis.
- A colourless, flammable cyclic hydrocarbon (C₃H₆) whose three carbon atoms form a ring; notable for the severe angle strain that makes it unusually reactive for an alkane.
- A once widely used inhalational general anaesthetic, valued for rapid induction before being largely replaced by safer agents.
"Because its carbon atoms form a strained three-membered ring, cyclopropane is far more reactive than ordinary open-chain alkanes."
"The cyclopropane ring in the molecule imparts a reactivity quite unlike that of normal alkanes."
"Introduced clinically in the 1930s, cyclopropane anaesthesia was prized for its quick onset and easy reversal."
As a mass noun denoting the substance, 'cyclopropane' is usually uncountable; a plural appears mainly when referring to multiple substituted derivatives bearing the cyclopropane ring.
"Several halogenated cyclopropanes were prepared for the study."
Cyclopropane's three-carbon ring is so bent out of shape that it reacts like an alkene — yet for decades surgeons used this strained little molecule to put patients to sleep.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cyclopropane
The word cyclopropane was coined in the late nineteenth century by combining the prefix 'cyclo-' — derived from Greek kyklos, meaning circle or wheel, and already standard for ring-shaped compounds — with 'propane', the name of the three-carbon alkane, reflecting the compound's composition. It thus follows the transparent naming conventions of systematic chemical nomenclature rather than evolving through older languages. Its relatives include the alkane series names (methane, ethane, propane, butane) and the many scientific terms built on the cyclo- root, such as cyclone and bicycle.
How cyclopropane is actually used
Cyclopropane is a technical term encountered almost exclusively in chemistry, pharmacology, and medical contexts; it is never used figuratively in general speech. Its clinical role has declined sharply since the late twentieth century because the gas is flammable and explosive in mixtures with air, so modern readers are most likely to meet the word in organic chemistry discussions of ring strain rather than in accounts of anaesthesia.
Easily confused with cyclopropane
Propane is a straight-chain three-carbon gas (C₃H₈), whereas cyclopropane has the same number of carbons arranged in a closed ring and is much more chemically reactive.