Abstract
Structures of low-energy conformers of α-linolenic acid (ALA;18:3-cis-9,12,15 ω-3), eicosapentaenoic acid (EPA;20:5-cis 5,8,11,14,17 ω-3) and docosahexaenoic acid (DHA;22:6-cis 4,7,10,13,16,19 ω-3) in the liquid state, based on NMR and density functional theory calculations of 1H NMR chemical shifts, are provided. A critical discussion of the J. Mol. Liq. 314 (2020) 113,376 article is also presented on a number of issues related to: (i) the method of assignment of 1H and 13C chemical shifts of ALA, EPA and DHA; (ii) attribution of NMR signals of impurities to those of EPA and (iii) the conclusion of an unusually strong electron 13C and 1H shielding of HCCH2CH protons and carbons, due to an asymmetry in a twist between the two ends, which results in torque at the methylene site near the geometric center. The present data demonstrate that the folding effects of the chain as a function of the fragment number (CHCHCH2)n, were n = 3, 5 and 6 for ALA, EPA and DHA, do not result in unusually strong electron 1H and 13C shielding.
Published Version
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