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 respectively.
