Analytical13C NMR: A rapid, nondestructive method for determining the cis,trans composition of catalytically treated unsaturated lipid mixtures

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Abstract
And Summary: High resolution natural abundance 13C Fourier transform nuclear magnetic resonance (NMR) has been found to be an effective tool for the rapid and direct determination of the cis/trans composition in partially hydrogenated and isomerized unsaturated lipids. With the eis and trans allylic carbon resonances as representative probes for double bond stereo‐chemistry. Evaluation of the cis/trans composition of complex, positionally isomerized mixtures can be made without the necessity of carrying out detailed analyses of multishift olefinic carbon resonances. Migration of double bonds in monoenes and polyenes and formation of conjugated unsaturation in cata‐lytically treated fats are discussed and assessed as possible sources of error in the evaluation of cis/trans isomer ratios. Carbon spin lattice relaxation times T1 were measured for both cis and trans allylic reson‐ances in isomeric mixtures of varying composition to assure quantitative intensity relationships. 13C NMR compositional analysis of complex mixtures is demonstrated.