FTIR STUDY OF THE SOLVENT INFLUENCE ON THE CARBONYL ABSORPTION PEAK OF ETHYL-ACETATE

The symmetric vibrational band for the carbonyl in ethyl acetate exhibits a solvent shift of as much as 31 cm-1 in aprotic solvents compared to its spectral position for the gas phase. This C=O band shift has been assigned to van der Waals and Lewis acid-base effects in previous investigations; however, new measurements in 24 aprotic solvents by using FTIR techniques do not support the former interpretation. An alternative model for the solvent influence is proposed that incorporates reaction field functions and a molecular orbital treatment of polar solvent effects upon the carbonyl in ethyl acetate as the solute. Additional evidence consistent with the new model has been derived from linear solvation energy relationships correlating the DELTA-nu(max)BAR(C=O) shift with solvatochromic behavior in the UV-visible region.