Dependence of Stereoelectronic and Charge Effects on pKa Values of 1,3-Dithiane-Derived Sulfides, Sulfoxides, and Sulfones: An Experimental and Computational Investigation

The pK(a) values of conformationally fixed 1,3-dithianes were investigated with experimental and theoretical methods to gain an insight into the influence of the relative orientation of the acidic proton and the stabilising S=O or S-C bonds. Experimental values were determined with a modification of the spectrophotometric method using overlapping indicators developed by Bordwell; theoretical values were obtained with the proton exchange methods using DFT calculations. It turned out that stereoelectronic stabilisation is important for sulfides and sulfoxides, whereas charge effects become dominant in sulfones. Deprotonation of the equatorial proton is favoured for most of the compounds except for the equatorial/axial bis-sulfoxide.