Propynal (HC₂CHO) was detected in 1988 by Irvine and co-workers toward Taurus Molecular Cloud 1 (TMC-1), where many complex organic molecules have been detected. The observations were collected with the 43m telescope at NRAO and also with the 45m telescope at Nobeyama Radio Observatory. In 1991, Turner reported a very tentative detection of propynal toward Sgr B2 (and its absence toward Orion-KL). Cernicharo and co-workers solidly confirmed the detection of propynal in 2012 toward the b1 core in Barnard 1. In 2016, Loison and co-workers reported multiple observations of propynal toward seven starless cores and clouds.

Propynal is an unsaturated aldehyde with an acetylenic CC triple bond along its CCCO backbone (HC≡C–CHO).