关键词: 脂肪酸, 酸盐, 氢键, 红外光谱, 拉曼光谱

Abstract: Fatty acid and their alkali soaps were well known as biosurfactants in living system, however, very few works had been published before on the fatty acid-soap complexes, which were revealed here possessing unusual structures and properties. The acid sodium salts and acid potassium salts in molar ratio of 1:1 of both capric acid and lauric acid were investigated by FTIR and FT-Raman spectroscopies. Two dominant features were determined. One was that the very strong and broad ν(OH) modes of fatty acids was absent above 1800 cm^-1 in the infrared spectra, and the other was the characteristic ν_as(COO^-) vibrations of alkali soaps could not be observed in both infrared and Raman spectra. The spectral results showed that a very strong hydrogen bond formed between carboxylate groups. In the infrared spectra of acid salts, a diffuse weak absorption in the region of 1500-800 cm^-1 was found and ascribed to the ν(OH) mode. In order to explain the unusual weakness of ν(OH)vibrations, the possibility of proton motions was discussed depending on the structural features of acid salts of fatty acids. The weak bands at 200cm^-1in the Raman spectra of acid salts other than the acids or salts showed that there may be some a defect conformation in the alkyl chains of the acid salts.

Key words: fatty acid, acid salt, hydrogen bond, infrared spectra, Raman spectra