Ab initio and DFT molecular orbital calculations are used to determine singlet–triplet energy splits, Δ E s–t,X, as well as relative energies, in the carbenic reactive intermediates X–C 2N, at seven levels of theory: B3LYP/6-31G*, MP2/6-31G*, B3LYP/6-311++G**, MP2/6-311+G*, MP3/6-311G*, MP4(SDTQ)/6-311++G** and QCISD(T)/6-311++G**; for X=H, NH 2, CN and OMe. MP3 results are more consistent to the B3LYP and/or QCISD(T) rather than the MP2 or MP4 results. Three possible structures considered for each singlet (s) and/or triplet (t) carbenes are: 3-X-2-azacyclopropenylidene ( 1 s-X and 1 t-X), [(X-imino)methylene]carbene ( 2 s-X and 2 t-X), and X-cyanocarbene ( 3 s-X and 3 t-X). Species 1 t-H, 1 t-NH2, 1 t-OMe, 2 t-NH2, 3 t-NH2, 3 s-OMe and 3 t-OMe show imaginary frequencies, so their corresponding structures are not minima and appear as transition states on the potential energy surface of X–C 2N. Cyclic triplet 1 t-CN, upon optimization transforms to an acyclic carbenonitrene structure. For all X–C 2N species inspected, Δ E s–t,X appears the highest for X=NH 2, and the lowest for X=H. For the six H–C 2N species with X=H, the order of relative energy is: 1 t-H> 2 s-H> 2 t-H> 3 s-H> 1 s-H> 3 t-H. Likewise, for the six structures with X=CN, the order of relative energy is: 1 t-CN> 2 s-CN> 2 t-CN> 1 s-CN> 3 s-CN> 3 t-CN. Finally, the order of relative energy for 12 structures with X=NH 2 and/or OMe is: 2 t-X> 1 t-X> 2 s-X> 3 t-X> 1 s-X> 3 s-X. The lowest energy minima, among the 12 species with X=H and/or CN, are triplet 3 t-X; while the lowest energy minimum, among the six species with X=NH 2 is singlet 3 s-NH2. The discussion includes geometrical parameters, dipole moments, charges and bond orders of 1– 3.