Structure of 1(5)-aryl-3-phenyl-5(1)-(2-benzothiazolyl)formazanes

1,3-Diphenyl-5-(2-benzothiazolyl)formazane exists in its crystalline state (based on x-ray crystal structure data) in the E ^1,2 Z ^2,3 Z ^3,4-conformation, which is stabilized by intramolecular hydrogen bonding (IMHB); the proton is localized on the nitrogen atom which is bound to the heterocycle. In chloroform solutions 1(5)-aryl-3-phenyl-5(1)-(2-benzothiazolyl)formazanes exist in the form of equilibrium mixtures of their chelate and open E ^1,2 Z ^2,3 Z ^3,4-forms, in which the first of these forms predominates. Based on their ¹³ C-NMR spectral data the tautomeric equilibrium involving these forms is shifted in favor of the benzothiazolylhydrazone form. The amount of tautomer containing the benzothiazolidene fragment structure increases in DMSO solution.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1268–1274, September, 1991.