Infrared Intensity Study on Molecular Interactions in Quinhydrone

Abstract The infrared intensities of the triclinic and monoclinic crystal modifications of quinhydrone (QH) have been measured, along with those of the parent molecules of p-hydroquinone (HQ) and p-benzoquinone (BQ) in solutions and in crystal form. The infrared spectra calculated by the density functional theory indicate that the hydrogen bond between HQ and BQ gives large changes in the infrared intensities of some bands of HQ, but gives rather small changes in the bands of BQ, even in ν(C=O). Charge-transfer interaction in QH is suggested to play an important role for the change in the infrared intensities of ν19a at 1520 cm−1 and τ(C–H) at 530 cm−1 in HQ. In the two crystal modifications of QH, the hydrogen bond is stronger in triclinic QH than in monoclinic QH, whereas the electrostatic interaction is stronger in monoclinic QH than in triclinic QH. The intensity differences of BQ between the CCl4 solution and the crystal are analyzed on the basis of the electrostatic model.