The Collaborative International Dictionary of English v.0.48:

Valylene \Val"yl*ene\, n. [Valerian + -yl.] (Chem.)
   A volatile liquid hydrocarbon, C5H6, related to ethylene
   and acetylene, but possessing the property of unsaturation in
   the third degree. It is the only known member of a distinct
   series of compounds. It has a garlic odor.
   [1913 Webster]