PECULIAR PEAK SHIFTS IN THE IR-SPECTRUM OF BENZOIC-ACID CRYSTALS BY COMPRESSION WITH METHYLATED ADDITIVES

The infrared (IR) peak shift in benzoic acid-additive mixtures has bee n studied, Benzoic acid crystals, in which benzoic acid molecules form a stable dimeric structure, showed the carbonyl stretching (v(c=o)) b and at 1688 cm(-1) The v(c=o) band of benzoic acid was shifted to a hi gher 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)-be ta-cyclodextrin (DM beta CD) by KBr compression method, The shifted pe ak reverted to the original position when measured again by Nujol meth od following pulverization of the KBr disk, These phenomena were obser ved only in the case of using methylated polysaccharides as additives, The results of X-ray diffraction and solid-state C-13-NMR spectroscop y indicated that the crystal structure of benzoic acid was not influen ced by compression and the dimeric structure was maintained, From the results of LR spectra using deuterated benzoic acid, the peculiar phen omena could be explained in terms of the changes in the hydrogen bondi ng feature of benzoic acid in the compressed disk with DM beta CD.