Complexes of phosphine oxides with substituted phenols: hydrogen bond characterization based on shifts of PO stretching bands

Abstract

In this work IR spectral characteristics of PO groups are used to evaluate the strength of OHO hydrogen bonds. Three phosphine oxides: triphenylphosphine oxide, tributylphosphine oxide and hexamethylphosphoramide are investigated as proton acceptors. The results of the experimental IR study and DFT calculation of 30 complexes formed by phosphine oxides with various substituted phenols or CF₃CH₂OH in CCl₄ solution at room temperature are reported. We show that the PO vibrational frequency changes non-linearly upon hydrogen bond formation and strengthening and that the shift of the PO band could be used for the estimation of hydrogen bond strength in complexes with phosphine oxides. The accuracy of these estimations and the influence of solvation effects on the main characteristics of complexes are discussed.