Cyanobutadiynyl, C5N, has been detected first toward TMC-1 and tentatively toward IRC+10216:
M. Guélin, N. Neininger, and J. Cernicharo,
Astronomical Detection of the Cyanobutadiynyl Radical C<sub>5</sub>N
Astron. Astrophys. 335, L1–L4 (1998).
Contributor(s): H. S. P. Müller; 12, 2003