APPLICATION OF THE HAMMETT EQUATION TO THE ELECTROCHEMICAL OXIDATION OF DIARYL CHALCOGENIDES AND ARYL METHYL CHALCOGENIDES

The electrochemical oxidation of symmetrical 4,4'-disubstituted diaryl selenides and tellurides and 4-substituted aryl methyl sulfides, selenides and tellurides has been studied. Peak oxidation potentials show good correlation with Hammett sigma(p)+-values for all series of compounds (diaryl selenides, R = 0.98, n = 10; diaryl tellurides, R = 0.98, n = 14; aryl methyl sulfides, R = 0.97, n = 5; aryl methyl selenides, R = 0.98, n = 5; aryl methyl tellurides, R = 0.98, n = 5). From the slope of the Hammett plots (methyl aryl chalcogenides) it was concluded that the degree of conjugation of a heteroatom with a para-substituent through an aromatic ring decreases in the following order: S > Se > Te. Results from the electrochemical oxidation of unsymmetrical diaryl selenides and tellurides indicate that the heteroatom is interacting with only one of the aromatic rings in diaryl chalcogenides. Te-125 chemical shifts of symmetrical 4,4'-disubstituted diaryl tellurides correlate well with Hammett sigma(p)-values (R = 0.98, n = 13).