MOLECULAR AND ELECTRONIC STRUCTURE OF 1,2,5-THIADIAZOLE 1,1-DIOXIDE DERIVATIVES. E.E. Castellano,¹ O.E. Piro,² J.A. Caram,³ M.V. Mirífico,³ S.L. Aimone,³ E.J. Vasini³ and M.D. Glossman^{4, 1}Instituto de Física de São Carlos, Univ. de São Paulo, C.P. 369, 13560 São Carlos (SP), Brazil, ²Dept. Física, Ftad. de C. Exactas, Univ. Nacional de La Plata, La Plata, Argentina, ³INIFTA (CONICET), UNLP, La Plata, Argentina., ⁴QUINOR (CONICET), Dept. Química, FCE, UNLP, La Plata, Argentina.

Thiadiazoles are at the basis of some polymeric organic heterocycles of interest in Material Science. Furthermore, 1,2,5-thiadiazole derivatives have pharmacological applications. As part of physical chemistry studies on several 3,4 substituted 1,1-dioxide derivatives of 1,2,5-thiadiazole, we report here a single crystal X-ray diffraction study on the molecular structure of the following derivatives: 3,4-dimethyl (I), 3-methyl-4-phenyl (II) and 3,4-diphenyl (III). We shall also report ab initio Molecular Orbital (MO) calculations of the electronic structure, conformation and reactivity of I and II, as well as results of semiempirical MO calculations on the electronic structure and conformation of III. The theoretical molecular conformations will be compared with the experimental X-ray diffraction results.