Determination of the energy differences between the rotameric forms of furan and thiophen esters in carbon tetrachloride solution by infrared spectrometry

Abstract

Practical and theoretical aspects of the Title subject are discussed. Study of the temperature variation of the rotamers' carbonyl bands gives reliable enthalpy differences. The variation of the dielectric constant of the solvent with temperature does not significantly affect these values. Entropy differences are more difficult to assess: an attempt to allow for possible differences in the absorption coefficients of the rotamers gives results which are appreciably different from, and less acceptable than, those obtained by assuming the coefficients to be equal. The values based on this assumption lead to the tentative conclusion that the thermochemically less stable forms of several of the esters predominate in carbon tetrachloride at room temperature.