Unique and redundant spectral fingerprints of docosahexaenoic, alpha-linolenic and gamma-linolenic acids in binary mixtures

•In six carbon atom moiety [=C1-C2-C=C-C5-C6=], asymmetry at C1-C2 versus C5-C6 stretching perturbs 3D molecular symmetry.•From 3 + 1 mixtures of DHA with ALA (or γ-LN), sites of conformational changes relative to DHA can be distinguished.•ALA in DHA disrupts orientation of last double bond in DHA, γ-LN disrupt the first double bond (from carbonyl end).•Unequal twisting in two methylene moiety at C2 and C5 results in broad changes in curvature in any six carbon atoms set.•Torsion relative to cis H-C3=C4-H (cis C2-C3=C4-C5) is from carbon atom out-of-plane twisting at C1-C2H2 and/or C6-C5H2.