Relationship between the Molecular Structures of 1, 2, 4-Thiadiazolidine Derivatives and Their PMR Solvent Effects

Abstract

The PMR solvent shifts (Peel, - vc6D6) of the methyl (or methylene) groups attached to the nitrogen atoms in 2, 4-dimethyl (or diethyl) -3, 5-bis (arylimino) -1, 2, 4-thiadiazolidines, 2-aryl3-arylimino-4-methyl (or ethyl) -5-methyl (or ethyl) -imino-1, 2, 4-thiadiazolidines, 2-methyl (or ethyl) -3-arylimino-4-aryl-5-methyl (or ethyl) imino-1, 2, 4-thiadiazolidines, and 2, 4-dimethy1-3, 5-bis (arylimino) -1, 2, 4-thiadiazolidine 1-oxides have been measured and related to the Hammett a constants or the Taft a constants (Table 1, Figs.1-7). From these experimental results, it was found that there was a reasonably good correlation between the solvent shifts (vcci, c6D6) for the methyl (or methylene) groups attached to the sp2-hybridized nitrogen atoms and the corresponding Hammett a constants (Table 2, Figs.1-7). On the other hand, the solvent shifts for the methyl (or methylene) groups attached to the spa-hybridized nitrogen atoms have been shown to be correlated with the corresponding Taft a constants (Table 2, Figs.1, 3, 4 and 6).
The results can best be explained in terms of the concept of the conjugated system between the nitrogen atoms and the benzene rings in the 1, 2, 4-thiadiazolidine derivatives. t Studies on 1, 2, 4-Thiadiazolidine Derivatives.