propadiene

Propadiene, also known as allene, is an organic compound with the formula C3H4. It consists of a central carbon atom double-bonded to two terminal carbons, giving the structure H2C=C=CH2. It is the simplest member of the cumulene family.

In propadiene, each terminal carbon is sp2-hybridized and the central carbon is sp-hybridized. The molecule contains two orthogonal π systems, resulting in a linear arrangement along the C=C=C axis. The unsubstituted molecule is achiral, but substitution on the terminal carbons can confer axial chirality.

Propadiene is a volatile, reactive hydrocarbon that is typically handled under controlled conditions. It is produced commercially by dehydrogenation of propylene derivatives and can also arise as a byproduct in various hydrocarbon processing streams; it can be generated in situ for use in synthesis.

In organic synthesis, propadiene behaves as a 1,3-diene equivalent in cycloaddition chemistry and can participate in metal-catalyzed reactions leading to cyclopropane and related products. Its reactivity as a cumulene makes it a versatile building block, and under certain conditions it can polymerize to form polyallenes.

Safety and handling: propadiene is flammable and should be used with appropriate ventilation and precautions to avoid ignition or containment hazards.

See also: allene, cumulene, polyallene.