MPS(FC)6-311+ +G(d,p) calculations were carried out for S-ylide and S-ylide-like radical reaction paths. The geometry structures of the intermediates, the transition states and the products were optimized and IRC calculations were employed. We emphasize on the investigation of the topological properties of the two reactions. The changing trends of the chemical bonds were discussed. The energy transition states (ETS) and the structure transition states (STS) of the two reactions were found. The △ type topological structure were formed in the STS, not in the ETS.

Key words: REACTION MECHANISM, TOPOLOGY, TRANSITION STATE THEORY