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In 2008, the cyanoethynyl anion, C3N–, became only the fourth anion to be
identified in an extraterrestrial environment. It was discovered by
Thaddeus et al. in the circumstellar shell of the late
carbon star CW Leo, also known as
IRC +10216. The detection was made with the
Green Bank Telescope
(which is having
budgetary
issues in spite of its immense value to the astronomy community).
Since C– is similar to N—both have three singly occupied p orbitals—the
bonding in C3N– is analogous to bonding two •CN radicals together. The molecular
orbitals shown below reflect this, with σ bonds between each of the three pairs of adjacent atoms and π bonds
between the terminal pairs, leaving the 2s pairs on the terminal C and N atoms to be pushed out along the molecular axis.
| σ2(C1-C2)
| σ2(C2-C3)
| σ2(C3-N)
|
| 
| 
|
| π2(C1-C2)
| π2(C3-N)
|
|
| 
|
|
| 2s2(C1)
| 2s2(N)
|
|
| 
|
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