cyclopropene

Cyclopropene is an organic compound with the formula C3H4. It is the smallest member of the cycloalkenes, consisting of a three-membered ring that contains a carbon–carbon double bond. The two carbons of the double bond are sp2-hybridized, and the ring's small size imposes substantial angle strain, giving cyclopropene markedly higher reactivity than larger alkenes.

The molecule is typically described as planar, with the ring enforcing severe geometric constraints. The high ring strain influences both its stability and its chemical behavior, making cyclopropene relatively unstable and prone to quick reactions that relieve strain. It is volatile and is usually handled as a reactive intermediate rather than a isolable, long-lived commodity.

Synthesis and handling of cyclopropene are confined to specialized laboratory settings. It is commonly generated in situ from cyclopropyl precursors via controlled elimination or rearrangement reactions to minimize polymerization or premature reactions. Due to its strain energy and reactivity, cyclopropene is often used as a building block in organic synthesis to access more complex, strained ring systems or as an intermediate in cycloaddition and ring-opening reactions.

Reactivity is dominated by the strained double bond, which readily participates in electrophilic addition and various cycloaddition processes. These characteristics make cyclopropene a useful, though challenging, tool in synthetic chemistry, where its controlled use enables access to diverse cyclic structures.

See also: cyclopropane, cycloalkenes, strained ring compounds.

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