Far infrared studies of the hydrogen bond of phenols

Abstract

By means of a novel sampling techniques which involves using a polyethylene matrix, the far infrared vibrations of the hydrogen bond (—OH ⋯ O—vibrations) of ten phenols have been assigned to the 187–98 cm −1 range. The —OH out-of-plane deformation (γOH) of these hydrogen bonded phenols and the —OH torsion for these phenol monomers have been assigned in the 690-280 cm −1 range. More than one γOH frequency has been found in every compound that has more than one strong —OH stretching frequency (νOH), indicating distinctive γOH frequencies for different hydrogen bonded species. This implies that the broadness of νOH is at least partly due to the existence of different polymeric species. Making use of the L ippincott-S chroeder potential function, the frequency of the hydrogen bond stretching vibration (νσ) of solid phenol has been calculated. Reasonable agreement with the observed frequency is obtained when a reduced mass of the entire phenol molecule is used. From this observed phenol frequency, the frequencies of νσ for the other solid phenols can be predicted indicating that the vibration is not localized in the —OH ⋯ O— group. For the same phenols in the liquid state the frequency of νσ could not be predicted and there was no direct relationship between the —OH stretching frequency (or hydrogen bond strength) and νσ.