CONFORMATION ANALYSIS OF GLYCERIDES BY NUCLEAR-MAGNETIC-RESONANCE

The conformation of the glycerol moiety of five glycerides, tri-, 1,3-di-, 1,2-di-, 1-mono-, 2-monopalmitin, was studied by using proton nuclear magnetic resonance (H-1-NMR) method. The spectra of 2-monopalmitin in chloroform-d(1) and in tetrahydrofuran-d(8) solutions showed the existence of the conformer, in which the O-C-alpha-C-beta-C-gamma, O-C-alpha-C-beta-O, O-C-beta-C-gamma-O and C-alpha-C-beta-C-gamma-O angle have gauche configuration. The increase in the polarity of the solution decreased the population of this gauche conformer. The activation energy for the rotational barriers for the C-alpha-C-beta and C-beta-C-gamma were large enough to separate the spectra of this conformer from other conformers by H-1-NMR. This gauche conformation of 2-monopalmitin may possibly be stabilized by the intramolecular hydrogen bonds in low polarity solutions. In the case of the other glycerides, this conformer was not observed. The fractional populations of the conformers of each glyceride were also analyzed by comparing the coupling constants of the proton in the glycerol moiety in several solutions.