Mid- and near-infrared study of hydrogen bond complexes between phenols and N,N-dimethylformamide

The mid- and near-infrared spectra of hydrogen bond complexes between phenol derivatives and N,N-dimethylformamide are investigated. The enthalpies of complex formation determined in carbon tetrachloride range from 23 to 26.6 kJ mol(-1). Some spectroscopic features observed in the mid- and near-infrared region are discussed. The first overtone of the nu(OH ... O) vibration is very broad and characterized by several submaxima which are tentatively assigned to a coupling between high and low frequency modes. The anharmonicities of the nu(OH ... O) vibration determined from the experimental frequencies observed in the mid-infrared and near-infrared region range between 117 and 150 cm(-1). The correlation between the enthalpies and experimental or harmonic frequency shifts is discussed. Comparison with complexes involving the same proton donors and N-methyldiacetamide shows that the anharmonicity roughly increases with the hydrogen bond strength. (C) 1998 Elsevier Science B.V. All rights reserved.