An infrared study of rotational isomerism in thiazole-2-carboxylates

Abstract

A series of alkyl thiazole-2-carboxylates containing a range of substituents at the 4- and 5-positions has been prepared. Solutions of these esters (mostly new compounds) show well resolved doublets in the i.r. CO region which arise from rotational isomers. The higher wavenumber components are assigned to the more polar carbonyl O,S-anti-s-trans-rotamers and the lower wavenumber components to the carbonyl O,S-syn-s-trans-forms. Small, but systematic, differences between the methyl esters are noted.