Definition of cyclopentadienyl in US English:

cyclopentadienyl

noun

Chemistry
  • A planar cyclic anion, C₅H₅ −, derived from cyclopentadiene, which has aromatic character and forms complexes with metal atoms, most notably sandwich compounds in which a metal atom is bonded between two parallel cyclopentadienyl rings. Abbreviated Cp.

Origin

Early 20th century; earliest use found in Journal of the American Chemical Society. From cyclopentadiene + -yl.