The Collaborative International Dictionary of English v.0.48:

Propylene \Pro"pyl*ene\, n. [Cf. F. propyl[`e]ne.] (Chem.)
   A colorless gaseous hydrocarbon (C3H6) of the ethylene
   series, having a garlic odor. It occurs in coal gas, and is
   produced artificially in various ways. Called also propene.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Trimethylene \Tri*meth"yl*ene\, n. (Chem.)
   A gaseous hydrocarbon, C3H6, isomeric with propylene and
   obtained from it indirectly. It is the base of a series of
   compounds analogous to the aromatic hydrocarbons.

The Collaborative International Dictionary of English v.0.48:

cyclopropane \cyclopropane\ n.
   a colorless flammable gas (C3H6) with a three-carbon ring,
   sometimes used as an anesthetic.
   [WordNet 1.5]