Absorption Spectra of 2,5-Dimercapto-1,3,4-Thiadiazole and Its Methyl Derivatives

The absorption spectra of the three tautomeric forms of 2,5-dimercapto-1,3,4-thiadiazole have been determined by using the N- and S-methyl derivatives. In the ultraviolet region, a hypsochromic shift in absorption maxima is shown in the change from the dithionic to the thionic–thiolic and to the dithiolic forms. Strong bands in the infrared at 1508–1475 cm−1 and 1435–1415 cm−1 have been assigned to [Formula: see text]respectively.