Tautomerism in some Acetamido Derivatives of Nitrogen-containing Heterocycles: X-ray Structural Analysis of 2-Amino and 2-Imino Forms of Benzothiazole Derivatives

Amide and acylimine derivatives of nitrogen-containing heterocycles have been investigated by X-ray diffraction and IR and UV-VIS spectroscopy. X-Ray crystal diffraction indicated that the product of the reaction between 2-aminobenzothiazole and alpha-chloropropionyl chloride is in the amide form, whereas the product of the reaction between 2-aminobenzothiazole and trichloroacetyl chloride is in the acylimine form. The UV-VIS spectroscopic data define the position of the tautomeric equilibrium; the previously reported quantitative method to evaluate the position of the tautomeric equilibrium without the direct use of parameters arising from fixed parents is suitable for the compounds considered. Medium polarity, electron-withdrawing power of the acyl group, acidity of the exocyclic N-H bond, and ring size and aromaticity of the heterocyclic moiety were the main starting points for investigating the tautomeric properties in potential prototropic systems.