ELECTRONIC-STRUCTURE OF A STABLE NUCLEOPHILIC CARBENE

The electronic and physical structure of a nucleophilic carbene in the imidazol-2-ylidene series was investigated by extended basis set ab initio SCF molecular orbital theory. Both singlet and triplet structures are considered. The calculated structure for the singlet (1A1) is in excellent agreement with that determined from a X-ray crystallographic study of 1,3-di-1-adamantylimidazol-2-ylidene. Configuration mixing coefficients and orbital populations at the carbene centers in imidazol-2-ylidene and :CF2 indicate similar carbene character for the two molecules. The proton affinity of imidazol-2-ylidene is calculated and found to be one of the highest known for neutral organic molecules.