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item Knothe, Gerhard - Gary

Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2006
Publication Date: 2/19/2006
Citation: Knothe, G.H. 2006. NMR characterization of dihydrosterculic acid and its methyl ester. Lipids. 41:393-396.

Interpretive Summary: Vegetable oils and animal fats contain fatty acids with varying structures. The varying structures form the basis of their different chemical, biological and physical properties as well as potential applications. Different procedures have been developed for their analysis. A common and important analytical method in chemistry, which has also been applied to fatty acids, is nuclear magnetic resonance (NMR). This work describes the analysis of a certain kind of fatty acid and a derivative thereof by NMR. The results aid in analyzing and identifying these kinds of compounds in various situations. An important example is in mixtures with other fatty acids and their derivatives used in industrial applications, to which such compounds may impart improvement of physical properties.

Technical Abstract: Dihydrosterculic acid (2-octyl cyclopropaneoctanoic acid) and its methyl ester were selected for 1H- and 13C-NMR analysis as compounds representative of cyclopropane fatty acids. The 500 MHz 1H-NMR spectra acquired with CDCl3 as solvent show two individual peaks at -0.30 and 0.60 ppm for the methylene protons of the cyclopropane ring. Assignment were made with the aid of 2D correlations. In accordance with previous literature, the upfield signal is assigned to the cis proton and the downfield signal to the trans proton. This signal of the trans proton is resolved from the peak of the two methine protons of the cyclopropane ring, located at 0.68 ppm. The four protons attached to the two methylene carbons alpha to the cyclopropane ring also show a split signal. Two of these protons, one from each methylene moiety, display a distinct shift at 1.17 ppm, and the signal of the other two protons is observed at 1.40 ppm, within the broad methylene peak. The characteristic peaks in the 13C spectra are also assigned.