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, L37L40 (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.