Effects of sulfenyl, sulfinyl and sulfonyl groups on acidities and homolytic bond dissociation energies of adjacent C?H and N?H bonds

Abstract

Acidities and bond dissociation energies (BDEs) of the N–H bond in two phenylsulfenylamides, PhSNHBz and PhSNH-t-Bu, and four phenylsulfenylanilides, 4-GC6H4NHSPh, where G = MeO, H, Br and CN, were measured in order to compare the effects of substituents on acidities and BDEs of N—H bonds with those of C—H bonds. The effects of PhS groups on acidities and BDEs in a series of C—H acids were found to be comparable to those on acidities and BDEs of PhS in a similar series of N—H acids. Comparisons were also made of the effects of changing the oxidation state of sulfur in the series PhS, PhSO and PhSO2 on the acidities and BDEs of adjacent N—H and C—H bonds in weak acids. Hammett-type plots of pKHA values for phenyl benzyl sulfones (4-GC6H4CH2SO2Ph) and phenylsulfenylanilides (4-GC6H4NHSPh) were linear vs σp− values. A linear plot was obtained and explained for a plot of BDE of the N—H bonds in remotely substituted phenylsulfonylanilides with σ+ values. Plots of BDEs vs Eox(A−) were also linear for 4-substituted phenylsulfenylanilides (4-GC6H4NHSPh), phenylsulfonylanilides (4-GC6H4NHSO2Ph) and phenyl benzyl sulfones (4-GC6H4CH2SO2Ph). © 1998 John Wiley & Sons, Ltd.