Hydrogen-bond basicity of the sulfonyl group. The case of strongly basic sulfonamidates RSO2NNMe3

Abstract

The hydrogen-bond basicity scale pK_HB(logarithm of the formation constant of 4-fluorophenol–base complexes in CCl₄) has been determined for 13 sulfonyl bases, and correlated to the infrared shifts, on complexation, of the ν(OH) vibrations of 4-fluorophenol and methanol. In 1:1 complexes, oxygen complexation is observed, even for sulfonamides, sulfamides and sulfonamidates. Substitution on the sulfonyl group by NCHNMe₂, NSMe₂ or [graphic omitted]Me₃ gives the strongest sulfonyl bases known. Since sulfonamides are less basic than sulfones, the electron-donating mechanism of [graphic omitted]Me₃ to SO₂ in sulfonamidates is probably mainly inductive.