Propylene (IUPAC name propene) is an unsaturated hydrocarbon with a double bond, the second alkene after ethylene. It is a gas at standard ambient temperature and pressure. It can polymerize (polypropylene). It has been detected in the interstellar medium.
Propylene was not specifically searched for in the interstellar medium, as its rotational lines were expected to be weak, due to its low electric dipole moment. It has, however, been detected serendipitously in a spectral survey toward the dark cloud TMC-1 (Marcelino et al. 2007).