Current textbooks delay teaching NMR until discussing alkyl halides or alcohols when 1H spectra become amenable to first order analysis. However 1H NMR isn’t appropriate for teaching beginners as learning chemical shifts and coupling simultaneously can cause confusion with students. Proton decoupled 13C spectra deal with chemical shifts only and can be introduced early in the course prior to discussing alkanes with functional groups. Primary, secondary, tertiary and quaternary carbons are distinguished by DEPT experiments. Teaching 13C before 1H NMR has been recommended but textbooks have ignored it, most likely due to the limited access to 13C spectra in undergraduate institutions. Today 13C spectral acquisition is common even in labs with 60 MHz spectrometers thus resurrecting this idea seems appropriate now. After methane, heptane (C7H16) isomers are the simplest ones giving a signal for each C atom. Both 3-methylhexane and 2, 3-dimethylpentane are chiral so each C atom has a unique chemical shift. Students are surprised at this after previously learning that the methyl groups of an isopropyl moiety have identical shifts in pentanes and hexanes. Thus stereochemistry is introduced without reference to optical isomerism. Other examples will be discussed.

13C should precede 1H NMR in teaching organic chemistry

249th National Meeting (2015)

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