In Z and E stilbene, the methine protons are chemically equivalent, resulting in the same chemical shift with no coupling observed. Similarly, the methylene protons of ethanol show no coupling because they have the same chemical shift. A common misconception is that the coupling of these protons does not exist. However, if the methylene protons in ethanol are rendered diastereotopic by synthesizing ethyl camphorsulfonate, the protons no longer have the same shift and the geminal coupling constant can be determined. In such multispin systems, the spacing between the lines is the sums and differences of coupling constants. These spectra are too complicated for second year undergraduate students to analyze. Two and three spin systems are suitable. For example, it is possible to determine the coupling constants of the chemically equivalent methine protons in Z and E stilbene by measuring the 13C satellites in their 1H spectra. When undergraduate students apply such methods to characterizing compounds with chemically equivalent protons, fundamental introductory organic chemistry concepts such as structure, symmetry, and stereochemistry are reinforced. Support was provided by the NSF Division of Undergraduate Education through grant DUE #9650684 for purchase of a 300 MHz NMR spectrometer and a faculty research grant from the Fordham University Research Council.

There is more information in your proton NMR spectrum than you realized

251st National Meeting (2016)

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