Flat versus twisted rotamers of 2,4-disubstituted thiazoles: the effect of intermolecular hydrogen bonds

In the title compounds, 2-amino-4-(2-chLoro-4,5-dimethoxyphenyl)-1,3-thiazole, C11H11ClN2O2S, (I), and 4-(2-chLoro-4,5-dimethoxyphenyl)-2-methyl-1,3-thiazole, C12H12ClNO2S, (II), the dihedral angles between the thiazole moiety and the chLoroaryl group are 51.61 (10) and 8.44 (14)degrees, respectively. This difference is a consequence of intermolecular hydrogen bonds forcing the stabilization of a twisted rotamer in (I). Substitution of the amino function by a methyl group precludes these contacts, giving a flat rotamer in (II)