November 2013

Cyanoethynyl anion

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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