HC_nN species with even n are triplet radicals. The first member of the series, HC₂N, was detected in 1991. It is bent rather than linear. No compounds with n>4 have been identified to date in the ISM. HC₄N has singly occupied orbitals in both the π_x and π_y systems, as shown below:

The 2π_x² orbital shows that there's pi bonding between C1 and C2, but there is also a small amount of pi bonding between C2 and C3. The bonding in HC₄N can thus be viewed as a resonance between the two configurations shown to the left. The top configration dominates, however. The singly occupied 3π orbitals are consistent with this: the largest amplitude is on C3, but there's some amplitude on C1 as well.