C3H6

from 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]

from 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.

from 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]

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