Tautomerism and dimerization of acetamidothiazole derivatives - UV/Vis andNMR spectroscopic investigation

Amido (A)/imido (B) tautomerism has been investigated by UV/Vis and NMR spe ctroscopic methods for a number of 2-acetamidothiazoles and 2-acetamidobenz othiazoles, without the use of the physical properties of "fixed parents". The addition of polar substances to solutions of selected compounds in apol ar solvents (carbon tetrachloride, dichloromethane) strongly affects the [B ]/[A] ratios. Data show that the shift of the tautomeric equilibrium A/B to wards the B form has two main causes: (i) increase of the polarity of the m edium, and (ii) a base effect on the stabilization of the B form. The exper imental DeltaH and DeltaS values indicate (in agreement with H-1 NMR spectr oscopic data) that the self-assembly of 2-acetamido derivatives is a very i mportant factor in determining the position of the tautomeric equilibrium.