Abstract: In order to explore the similarities and differences in their reactive sites, the structures of six fatty acids with different chain lengths and unsaturation degrees were optimized by software Gaussian 09 at the theoretical level of m06-2x/def2tvzp, and the single point energy was calculated using the ma-def2tzvp basis in this study. Afterward, the surface electrostatic potential, average local ionization energy, frontier molecular orbital and condensed Fukui function were analyzed and visualization results were obtained. The results suggested that the nucleophilic reaction site of saturated fatty acids was hydroxyl hydrogens, and the electrophilic reaction site of caprylic acid was near the oxygen atoms. The carboxyl groups of palmitic acid and stearic acid showed no electrophilic activity with the increase in chain length. The unsaturated fatty acid oleic acid exhibited higher nucleophilic electrophilic activity near the oxygen atoms, and higher electrophilic activity at the double bonds. As the number of double bonds increased, the reactive sites of linoleic acid and linolenic acid were both double bonds. The reactivity of fatty acids with the same chain length enhanced with increasing unsaturation degree. The results of this study can provide a theoretical basis for revealing the relationship between the structure and properties of fatty acids, and provide a reference for the selection of fatty acids in the edible oil industry.

Key words: fatty acid; reactive site; density functional theory