NMR chemical shift reagents in structural determination of lipid derivatives: III. Methyl ricinoleate and methyl 12‐hydroxystearate

Chemical shift reagents (CSR) can substantially increase the amount of structural information obtainable from NMR studies of saturated and unsaturated lipid derivatives. It is theoretically possible to obtain even more information from CSR studies of unsaturated lipid derivatives by introducing additional CSR‐active functional groups into those molecules through derivatization of their double bonds. However additional CSR coordination sites complicate spectral interpretation, because they increase the number of signals that overlap. Therefore two model compounds were investigated to test the feasibility of attempting other CSR analyses of polyfunctional molecules of unknown structure. This paper describes successful CSR studies of methyl ricinoleate and methyl 12‐hydroxystearate. A series of complementary interpretive techniques was used to assign proton signals in spectra obtained during incremental Eu(fod) 3 addition studies with these compounds. Individual proton signals can be observed and assigned for all the protons in methyl ricinoleate, except those on carbons 5, 6 and 7. Information obtained for methyl 12‐hydroxystearate is less specific. Signals are observed for all protons in methyl 12‐hydroxystearate, although in some cases several proton signals overlap.