Coulombic repulsion triplet carbenes

In a singlet state a or p carbene, the electron-electron coulomb repulsion would be severe, since two electrons are constrained to the same small MO. On the other hand, the triplet configuration is stabilized by relief of the coulomb repulsion and exchange repulsion however, the separation of electrons into different MOs does not come without a cost. Thus, the magnitude of the energy difference between the triplet and singlet states (the singlet-triplet split-... 

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