Following the oxidation state of organosulfur compounds with NMR: Experimental data versus DFT calculations and database-powered NMR prediction
The thioether-sulfoxide-sulfone oxidation ladder is a feature significant for drug synthesis and medicinal chemistry. The studies presented herein showed the suitability of various NMR prediction methods for following the oxidation state of sulfur. Method accuracy and the value of additional information were evaluated. As a model for the study, a small set of novel terminal alkynes containing a thioether, sulfoxide or sulfone fragment and an n-alkyl chain was used. The compounds have been synthesized and investigated using 1H and 13C NMR spectroscopy, with 2D-NMR spectra providing the certainty of assignment. The experimental NMR spectra were confronted to chemical shifts calculated using the DFT-GIAO method and two generally available database-powered NMR prediction algorithms. The ability to correctly determine the oxidation state of sulfur using experimental and predicted NMR data is discussed, as well as the predictive power and accuracy of the prediction methods used. Additionally, the structure and conformational dynamics of the synthesized compounds are discussed using the DFT-based calculations results.