Protonated and methylated dimethyl sulfoxide cations and dications. DFT/GAO-MP2 MMR studies and comparison with experimental data

Energies, electronic structures, and thermodynamics of protonated and methy lated dimethyl sulfoxide (DMSO) cations and dications were calculated using the density functional theory (DFT) method. The O-protonated structure 2 w as found to be 37.0 kcal/mol more stable than the S-protonated 3. For dipro tonated DMSO dication, the O,O-diprotonated form 6 was found to be the glob al minimum, more stable by 20.8 kcal/mol than O,S-diprotonated 7. Interesti ngly, for dimethylated DMSO dication, O,O-dimethylated 11 and O,S-dimethyla ted 12 are isoenergetic. C-13, O-17, and S-33 NMR chemical shifts of the ca tions and dications were calculated using the GIAO-MP2 method and compared with the available experimental data.