The detection of propylene (CH₂CHCH₃) was reported in 2007 by Marcelino and co-workers toward TMC-1, the Taurus Molecular Cloud 1, based on observations with the IRAM 30m telescope. Six doublet lines from the A and E torsional states were observed (plus an additional A-species line).

Propylene (or propene) is a simple, unsaturated alkene. One of its primary uses is as a feedstock for the production of polyproylene, a widely-used plastic, though it remains somewhat challenging to recycle it.