This article describes an upper-level instrumental laboratory for undergraduates that explores the complementary nature of IR and NMR spectroscopy for analysis of several edible fats and oils that are structurally similar but differ in physical properties and health implications. Five different fats and oils are analyzed for average chain length, degree of unsaturation, and trans fat content. Careful interpretation of peak areas in 1H NMR spectra provides the extent of unsaturation and the average chain length. IR spectroscopy can easily identify the presence of trans fat. Instruction on acquisition, processing, and interpretation of spectra goes beyond what is typically taught in an organic undergraduate laboratory. This includes specifics on acquisition and digital filtering, examples of complex coupling, and introduction to 2D NMR experiments. After analysis, students must correlate each oil or fat to a given fatty acid distribution. Students can then reconcile the structural composition to the physical properties and health implications. Students work independently, are guided by literature, and get good results on a challenging problem.
Supplement
A student handout with instructions and background material for the experiment; notes for students (and instructor) regarding the acquisition and processing of NMR spectra; the IR SOP; and a two-dimensional proton COSY spectrum with notes that explains the peak assignments by connectivity
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