Abstract: Isomeric structures and energies of dimethyllithoflurosilylenoid and diethyl lithoflurosilylenoid were investigated by using ab initio molecular orbital theory. Alkyl groups increase the donor of σ electrons of silicon to lithium atom and it leads to an increase of the thermal stability of σ-complex. But alkyl groups decrease the donor of π electrons of fluorine atom to silicon, leading to a decrease of the thermal stability of p-complex. However, because of the joint action of that two effect, alkyl groups change little the thermal stability of the three-membered ring.

Key words: Ab initio calculation, Silylenoid, Substituted lithofluro-silylenoids