Abstract
The infrared (IR) peak shift in benzoic acid-additive mixtures has been studied. Benzoic acid crystals, in which benzoic acid molecules form a stable dimeric structure, showed the carbonyl stretching (vC=O) band at 1688 cm-1.The vC=O band of benzoic acid was shifted to a higher wavenumber of 1720 cm-1 when IR measurement was carried out for a physical mixture of benzoic acid with heptakis-(2, 6-di-O-methyl)-β-cyclodextrin (DMβCD) by KBr compression method. The shifted peak reverted to the original position when measured again by Nujol method following pulverization of the KBr disk. These phenomena were observed only in the case of using methylated polysaccharides as additives. The results of X-ray diffraction and solid-state 13C-NMR spectroscopy indicated that the crystal structure of benzoic acid was not influenced by compression and the dimeric structure was maintained.From the results of IR spectra using deuterated benzoic acid, the peculiar phenomena could be explained in terms of the changes in the hydrogen bonding feature of benzoic acid in the compressed disk with DMβCD.
