The exotic carbene compound tricarbonimine (HNCCC) was discovered in 1992 by Kawaguchi and co-workers toward TMC-1 using the Nobeyama 45m telescope. HNCCC is a less stable isomer of two well-known astromolecules, cyanoacetylene (HCCCN) and isocyanoacetylene (HCCNC). Additional details about the experimental measurement of the HNCCC rotational spectrum were reported in 1993 by Hirahara et al.; they also reported the spectrum of DNCCC, which was detected in 2020 by Cernicharo et al. toward TMC-1. Tricarbonimine was subsequently detected toward IRC +10216 by Gensheimer in 1997 and confirmed to be present there by Pardo et al. in 2022.

HNCCC has also been detected toward the pre-stellar core L1544 by Vastel et al. (2018) but was not detected toward Sgr B2(N) by Willis et al. (2020).

The IR spectrum of HNCCC was reported by Kołos & Sobolewski in 2001. Computational work by Osamura et al. from 1999 indicated that HNCCC and HCCNC can form from the dissociative recombination of HC₃NH⁺—first detected in 1994—with an electron.

Imines involve NH double-bonded to a carbon atom. Other detected imines include methanimine (CH₂NH), ethanimine (CH₃CHNH), E-cyanomethanimine (E-NHCHCN), Z-cyanomethanimine (Z-NHCHCN), Z-propargylimine (Z-HNCHCCH), and ketenimine (H₂CCNH).