Singlet-triplet Splitting and Stability of Saturated Acyclic and Cyclic Carbenes: DFT Calculations

DFT calculations were carried out on the singlet-triplet splitting for CnH2n+2C: (n = 0-7) and CnH2nC:  (n = 2-7) at B3LYP/6-311++G (3df,2p) level of theory. For the estimation of stabilization energies (SE), the isodesmic reactions were applied. The results of the isodesmic reaction show a high stability for singlet state relative to the corresponding triplet state by substitution of methyl or methylene groups at the both sides of methylenic center in CnH2n+2C:. Substitution of methylene groups at the both sides of cyclopropenylidene (CnH2nC:) leads to reduce the instability of triplet state; decreasing the singlet-triplet splitting.

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