FT-IR of trichloroacetoimidates in different solvent systems

In this work, the solvent effect on some trichloroacetimidates was studied by FT-IR spectroscopy together with conformational and chemometric analysis. As confirmed also by conformational analysis, no intramolecular H-bond was detected; in fact no low energy conformers with intramolecular hydrogen bonding were found with significant populations. Among the various functional groups, the C=O bond results the best diagnostic vibrational mode for the analysis of solute-solvent interactions; a prevailing bulk dielectric effect of the solvent operates on the v(C=O) stretching mode at higher frequencies (unperturbed band), while solute-solvent intermolecular interactions are responsible for the position and the intensity of the band at lower frequencies. An isosbestic point was found, claiming for an equilibrium between free and bonded conformations of comparable energy. Among all solvent parameters, only the Acceptor Number shows a linear correlation with the v(CO) stretching modes. From the conformational analysis, all the compounds show two kinds of conformers of similar energy. (c) 2005 Elsevier B.V. All rights reserved.