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 hydrobromide
Abstract
Crystal structure 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-currents, which show that this molecule has a lower aromatic character than that of other fused heterocycles of imidazole with pyrimidine and thiazole rings. From 1H n.m.r. measurements the protonation site in acidic solution could not be determined, but N(7) was found to be the site available for complex formation in the presence of a lanthanide shift reagent.