Structures and stability of 1-methoxy-l-lithioethene H_2C=CLiOCH_3 have been determined by using DFT method at B3LYP/6-3lG(d,p) level. H_2C=CLiOCH_3 has four equilibrium geometries, with only one being stable, which is geometry 1. The transition-state of decomposition reaction of geometry 1 has been determined and the structure of TS of this reaction has been gained. According to Eyring' s classical transition-state theory, the rate coefficients of the decomposition reaction of H_2C = CLiOCH_3 at different temperatures have been calculated. The average life of H_2C = CLiOCH_3 at different temperatures has been obtained using the rate coefficients of decomposition reaction and the stability of the carbenoid of this type has been discussed according to the average life of H_2C = CLiOCH_3 at different temperatures.

Key words: LITHIUM COMPOUNDS, ETHYLENE P, DECOMPOSITION, TRANSITION STATE THEORY, STABILITY