Computational investigation of the peroxy radicals CH3S(O)nOO and the peroxynitrates CH3S(O)nOONO2 (n = 0, 1, 2)

The structural, energetic and thermochemical properties of the homologous peroxynitrates, CH3S(O)nOONO2, (n = 0,1,2), and their isomers, the decomposition peroxy radicals CH3S(O)nOO, the isomeric sulfonyl and sulfoxyl radicals, CH3S(O)2 and CH3S(O)3, and the isomerization transition states, TS1 = [CH3SOO ↔ CH3S(O)2] and TS2 = [CH3S(O)OO ↔ CH3S(O)3] are studied using ab initio and DFT computational methods. The results indicate the following stability order CH3S(O)2OO > CH3SOO > CH3S(O)OO, which underlines the stabilizing effect of the two sulfonic-type O atoms. The same order is obeyed by the association peroxynitrates, CH3S(O)nOONO2, (n = 0,1,2), which are located at a potential energy well ranging from 26 to 29 kcal mol−1 with regard to the peroxy radical and NO2 at the G3 and CBS-QB3 levels of theory, with the sulfinyl analog showing the shallowest well. The lowest stability found for the sulfinyl peroxy radical and the corresponding peroxynitrate, verifies the significant stabilization effect of the π nature of the sulfinyl radical, RSO, proposed by Yin et al. [12], which reduces the stability of its peroxy derivatives where this character is lost.