Theoretical investigation on stability and isomerizations of CH3SO isomers

The stability and isomerizations of CH3SO isomers have been investigated at B3LYP/6-311G(d,p), MP2/6-311G(d,p), QCISD/6-311G(d,p), and CCSD(T)/6-311G(d,p) levels. Geometries of isomers and transition states (TS) have been optimized at the B3LYP/6-311G(d, p) level. Vibration analysis and the intrinsic reaction coordinate (IRC) calculated at the same level have been applied to validate the connection of the stationary points. The four different methods give similar results: 11 isomers and 9 isomerization channels were found. CH3SO and CH2(S)OH are the most stable species among the 11 isomers. Furthermore, the breakage and formation of the chemical bonds in isomerization reactions have been discussed by the topological analysis method of electronic density. The "energy transition state (ETS)" and the "structure transition state (STS)" of all the isomerizations have been found. The topological analysis shows that the relative positions of ETS and STS are determined by reaction energy. The nonplanar four-member ring structure transition state (STS), which was first found in this paper, extended the concept of ring STS.