QUANTUM-CHEMICAL STUDY OF THE MOLECULAR AND ELECTRONIC-STRUCTURE OF YL-2,3-DIHYDRO-1,4-THIAZINO[2,3,4-I,J]QUINOLINIUM)

Conformational isomerism of yl-2,3-dihydro-1,4-thiazino[2,3,4-i,j]quin olinium) has been studied by semiempirical MNDO and AM1 methods. Six s ymmetrical and unsymmetrical stationary states have been found. Optimu m intramolecular rotations around single bonds have been considered. T he possibility of the inversion of the reaction centers in nucleophili c and electrophilic reactions depending on the conformational state of the molecule has been shown. The spatial structure of one of the conf ormers found is similar to that typical of (-)-cystine. The observed c onstancy of some geometric and electronic parameters makes it possible to study the principal physicochemical properties of dithiazinoquinol inium compounds by the most sophisticated ab initio methods using smal l model structures, which are constructed by taking into account the v ariability of other geometric parameters, as an example.