The effect of relative concentration of shift reagents, Eu (fod)
3 and Pr (fod)
3, on the proton chemical shifts of the methyl esters of saturated, oleic, petroselinic, erucic, linoleic, linolenic, and stearolic acids was represented as figures comparable with one another.
The shift reagent, Pr (fod)
3, was superior to Eu (fod)
3 in complete separation of the signals for olefinic and the neighporing methylene protons from those for the other methyl and methylene protons. Estimation of total unsaturated fatty acids in fatty acid mixtures was possible by calculation from the integrated areas of two peaks (methoxycarbonyl methyl and non-diallylic α-methylene to double bonds) isolated as the result of the Pr (fod)
3-induced shift.
Difference in the induced shift between the methoxycarbonyl methyl protons of methyl oleate and petroselinate was observed. By the use of the induced shift, methyl petroselinate in mixed methyl esters could also be determined from the integrated areas of the separated singlets for the methoxycarbonyl methyl protons, the isolated multiplet for C-6 olefinic proton, and a peak for methylene protons near ester linkage.
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