Structural elucidation of peanut, sunflower and gingelly oils by using FTIR and 1H NMR spectroscopy

Abstract

Aims: The present study focused on FTIR and1H-NMR spectroscopic methods to assign structural connectivity and purity of the oils. Methods: Non-destructive Fourier Transform Infrared (FTIR) and1H nuclear magnetic resonance (1H-NMR) spectroscopy techniques are used to assign the structural confirmation of the triacylglyceride (TAG) functional component in three different oils namely Sunflower, Peanut, and Gingelly oils respectively. Results: FTIR spectrum shows a very high intense band at 1744 cm-1 associated with the existence of the ester carbonyl functional group (O-C=O) and very weak shoulder peak of cis double-bond (C=C) stretching was noticed at ∼1655 cm-1. In1H-NMR spectrum shows well resolved chemical shift values in the range 5.3-0.8 ppm corresponding to characteristic group in aliphatic region. Conclusion: Each distinct peak was determined based on chemical shift as well as splitting pattern values. For olefin signal as triplet, tertiary methine protons as singlet, well separated oxymethylene seen as triplet at ~4.2 ppm owing to presence of high electronegative oxygen atom connected to methylene chain gives more deshielding effect. As for bis-allylic, α-carbonyl methylene, β-carbonyl methylene, allylic, saturated methylene along with terminal methyl proton signals are noticed in the span of 2.3-0.8 ppm. A remarkable feature of the spectra is well resolved chemical shift values is clearly support presence of longer hydrocarbon chains. Absence of multiplet coupling peaks and disappearance of signals in down shield region > 5.4 ppm confirms the absence of trans stereoisomer (E-conformation), aromatic and heterocyclic epoxide compounds.