A series of new alkyl N,N-disubstituted 2-aminothiazole-5-carboxylates was prepared by condensing α-bromo-β-oxo-esters with N,N-disubstituted thioureas. The products exhibit i.r. carbonyl doublets, the higher and lower wavenumber components arising from the carbonyl O,S-syn-s-trans and anti-s-trans rotamers respectively. Variable temperature ¹H n.m.r. examination showed that the barriers to rotation of the 2-amino-groups are in the range 41â 47 kJ mol^{â 1}. Further evidence for rotational isomerism of the carboxylate group was provided by ¹³C n.m.r. study, but the size of its rotational barrier could not be assessed.The spectrometric work shows that there is strong mesomeric interaction between the carboxylate and amine groups.