Polarized Infrared Spectral Studies of Crystalline,Hydrogen-Bonded Organic Acids.

摘要

Polarized infrared spectra of oriented samples has been shown to be very useful in the study of the structures and properties of crystals. In principle, this method can be used to elucidate crystal structures. It has not been clear how this method can be utilized with hydrogen-bonded materials, however. This is due to the fact that hydrogen bonds are much weaker than chemical bonds. The method in which such substances should be treated (the size of the unit to be chosen as the molecule, whether to treat the hydrogen-bond differently than chemical bonds, etc.) has not been clear. This report gives the results of two studies of polarized crystal infrared spectra of hydrogen-bonded organic acids. Acrylic acid exists as a hydrogen-bonded dimer in the crystal and acetic acid exists as a hydrogen-bonded polymer in the crystal. The results are compared with the x-ray data and the theoretical treatment is carried out considering the hydrogen bonding in detail. It is shown that the correlation method is theoretically satisfactory for these hydrogen-bonded materials provided they crystallize in an orderly fashion. (Author)