AB-INITIO STUDY OF THE RELATIVE ENERGIES OF THE METHYLSULFONYL AND METHOXYSULFINYL RADICALS

The geometries and relative energies of the methylsulfonyl and methoxysulfinyl radicals have been determined using ab initio calculations at the SCF and correlated levels of theory. The CH3OSO radical was found to be 10.3 kcal mol-1 more stable than the CH3SO2 isomer calculated at the spin-projected MP4 level (PMP4SDTQ). Both species have structures belonging to point group C(s) with the CH3OSO radical having a cis C arrangement. Rotation about the C-O bond was studied and found to have a barrier of 5.2 kcal mol-1 at the MP2/6-31 IG(d,p) level with the trans structure being a transition state. The rotation about the C-S bond in CH3SO2 was studied and found to have a barrier of 2.4 kcal mol-1. In addition, the reaction between the methyl radical and sulfur dioxide forming the CH3SO2 and CH3OSO radicals was studied and the transition states characterized. The activation energy for the formation of CH3SO2 was found to be 1.0 kcal mol-1 while that for the formation of CH3OSO was found to be 19.9 kcal mol-1 at the PMP4SDTQ level. The harmonic vibrational frequencies for each structure were determined characterizing each as a minimum or transition state.