Infrared spectroscopic investigation of the conformational properties of furan-2-carboxylates

Abstract As an extension of previous studies on furan-2-aldehyde, we have investigated methyl furan-2-carboxylate, ethyl furan-2-carboxylate and methyl furan-2-thiolcarboxylate in order to obtain detailed information on their conformational properties. The skeletal vibrations of the i.r. spectra in different solvents (carbon tetrachloride, acetonitrile, chloroform) and in one liquid phase show the existence of two conformers, the syn and anti forms. The conformational equilibria do not appear to be temperature-dependent, or to be altered by change of phase from liquid to solid. The relative enthalpy differences between the two conformers is indicated by the effect of solvent polarity on their ratios.