NMR chemical shift reagents in structural determination of lipid derivatives: II. Methyl petroselinate and methyl oleate

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Abstract
Whentris(1,1,1,2,2,3,3‐heptafluoro‐7,7‐dimethyl‐4,6‐octaneodionato)europium (III)—Eu(fod)3—forms a complex with a sufficiently basic functional group in a donor molecule, the change in the magnetic environment of protons near the coordination site causes their nuclear magnetic resonance (NMR) signals to shift to different positions. Consequently Eu(fod)3 and other compounds that similarly affect NMR signals have been designated chemical shift reagents (csr). Because of their ability to shift proton signals, csr substantially increase the amount of structural information that can be obtained from NMR spectroscopy, frequently converting complicated splitting patterns into first‐order spectra. Some generally useful experimental and interpretive csr techniques are described here using methyl petroselinate and methyl oleate as examples. Csr studies of methyl petroselinate reveal that the position of the double bond is at C‐6, and that there is no chain substitution or branching before C‐9. Csr studies of methyl oleate reveal that the position of the double bond is at or beyond C‐9, and that there is no chain substitution or branching before C‐6. Some suggestions are presented for expanding the amount of structural information that can be obtained by csr studies of unsaturated lipid derivatives.