Abstract: The structures and stabilities of the CHClFLi, as a model carbenoid substituted by two different halogenes, were first predicted by using ab initio theory. Four equilibrium geometries were optimized. Two σ-complexes(geometries 1 and 2), formed by interaction of HOMO of singlet carbene HFC∶ with Li of LiCl, is close in energy and the most stable one. The three-membered ring geometry(geometry 3), formed by interaction of HOMOand LU-MO of singlet carbene HClC∶ with Li and Fof LiF respectively, is “loose” in the structure and more unstable. Geometry 4 is a double three membered ring, and it is the most unstable one. The center carbon of those four geometries except 3 have positive charges, so the nuclophilic reaction of CHClFLi should be slower than that of CHCl₂ Li and CHBr 2Li. The transition states of geometries 2, 3 and 4 to 1 were given. The barriers of conversion are very little (1.76, 7.24, 1.53 kJ/mol). The four geometries are all more stable than their corresponding carbene(dissociation energies is 89.67, 87.11, 145.2, 50.11 kJ/mol respectively).

Key words: Halocarbenoid, Equilibrium geometry,