癸酸和月桂酸酸盐体系的振动光谱研究

Vibrational Spectroscopic Studies on the Acid Salts of Capric Acid and Lauric Acid

对癸酸和月桂酸固体酸盐体系的红外和拉曼光谱进行了研究。在脂肪酸酸盐的红外光谱中４０００～１８００ｃｍ￣（－１）区间完全看不到脂肪酸的非常强且宽的ν（ＯＨ）振动，而代之以在１５００～８００ｃｍ￣（－１）区间出现一个弥漫的弱吸收。同时红外和拉曼光谱中也观察不到脂肪酸盐所特有的ν＿（ａｓ）（ＣＯＯ－）强谱带。光谱结果表明脂肪酸与其碱金属盐之间通过分子间氢键和羧基配位结合形成了酸盐络合物。文中结合光谱性质讨论了酸盐体系中强氢键的生成和质子活动的可能性。比较钠系酸盐与钾系酸盐的光谱，发现前者有比后者更弥散的氢键振动谱带。另外，对拉曼光谱ＬＡＭ－３谱带的调查指出，脂肪酸酸盐的烷基链可能存在不同于脂肪酸和皂类全反式构象的缺陷结构。

Fatty acid and their aklali soaps were well known as biosurfactants inliving 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 1 800 cm￣(-1) in the in-frared 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 1 500～800 cm￣(-1) was found and ascribed to the ν(OH) mode, In order to explain he 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 200 cm￣(-1) in 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.