What is "cyclopentadiene"

n. (context organic compound English) an unsaturated alicyclic hydrocarbon, C₅H₆; it forms complexes with some transition elements

Cyclopentadiene is an organic compound with the formula CH. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction. This dimer can be restored by heating to give the monomer.

The compound is mainly used for the production of cyclopentene and its derivatives. It is popularly used as a precursor to the cyclopentadienyl ligand (Cp) in cyclopentadienyl complexes in organometallic chemistry.