alkene hydrocarbon which contains a closed ring of carbon atoms, but has no aromatic character.

a tar formed from distillation of bituminous coal; coal tar can be further distilled to give various aromatic compounds

an organometallic compound with the formula Fe(C5H5)2; it is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom.