2,3-Butadienenitrile, CH₂CCHCN, aka cyanoallene, has been detected with the 100m Greenbank telescope toward TMC-1:
F. J. Lovas, A. J. Remijan, J. M. Hollis, P. R. Jewell, and L. E. Snyder,
Hyperfine Structure Identification of Interstellar Cyanoallene toward TMC-1
Astrophys. J. 637, L37–L40 (2006).
As the number of four observed rotational transitions is somewhat small, the (partial) resolution of the ¹⁴N hyperfine structure is a decisive aspect in securing the detection.

Contributor(s): H. S. P. Müller; 02, 2006