13C nuclear magnetic resonance spectral confirmation of Δ6-and Δ7- trans -18:1 fatty acid methyl ester positional isomers

Abstract   Trans octadecenoic acid methyl ester isomers were obtained from a partially hydrognated soybean oil and isolated by silver-ion high-performance liquid chromatography. Recently, the double-bond positions for nine individual trans octadecenoic acid positional isomers (Δ8 through Δ16) were confirmed by gas chromatography-electron ionization mass spectrometry after derivatization to 2-alkenyl-4,4-dimethyloxazoline. In this communication, the presence of two additional trans-18:1 fatty acid methyl ester positional isomers (Δ6 and Δ7) in the same mixture is confirmed by 13C nuclear magnetic resonance spectroscopy. The identity of the Δ5-trans-18:1 fatty acid methyl ester positional isomer is inferred.