The detection of the Z isomer of propargylimine (Z-HNCHCCH) was reported in 2020 by Bizzocchi et al. The molecule was detected toward the molecular cloud G+0.693–0.027 located toward the galactic center in a survey that was performed in April and August 2019 with the IRAM 30m telescope. 18 rotational transitions were matched to new laboratory data measured at the Max Planck Institute for Extraterrestrial Physics. The experiments characterized both the Z and E isomers of propargylimine. E-propargylimine was not detected toward G+0.693–0.027 in the survey data.

Z-propargylimine (also known as 2-propyn-1-imine) is a cousin of Z-cyanomethanimine, with the –CN cyano group replaced by the –CCH ethynyl group. The kinetics study of García de la Concepción et al. modeled the E/Z ratio of propargylimine and two other interstellar imines.