Structure and Protonation Study of the Imidazo[2.1-b]-1,3,4-thiadiazole System: 1H Nuclear Magnetic Resonance, Crystal and Molecular Structure of 5,6-Dimethylimidazo[2,1-b]-1,3,4-thiadiazole and its Hydrobrimide

Crystalstructure analysis of 5,6-dimethylimidazo[2,1-b ]-1,3,4-thiadiazole (3) and its corresponding hydrobromide has shown that protonation occurs at N(7). Molecular properties, mainly aromaticity and basicity, of this system were interpreted on the basis of semi-empirically calculated ring-current, whic show that this molecules has a lower aromatic character than that of other fused heterocycles of imidazole with pyrimidine and thiazole rings. From 1-H nmr measurements the protonation site in acidic solution coul not be determined, but N(7) was found to be the site available for complex formation in the presence of a lanthanide shut reagent.