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The Coupling Exercise

March 11, 2009

When presented with an NMR dataset, a highly-experienced elucidator can interpret the dataset without any direct need to do peak picking, integration and multiplet analysis through software. (This may not be the case every time as severe peak overlap can complicate matters.) In essence, this NMR interpretation skill equates to speed reading and can be learned with some practice.

The 1H NMR spectrum below displays 5 multiplets with the chemical shift and integration information removed. In this exercise, can you recognize which multiplets are coupled to each other?


The first step is to roughly estimate the integral values for each multiplet and thus eliminate any notion of overlapping peaks. From the 1H NMR spectrum, there are 5 multiplets roughly integrating to an equal area, i.e. the integral ratio is approximately 1:1:1:1:1.

The next step is to judge the coupling constants for each multiplet, i.e. the spacing between the peaks. Without getting too technical here, a good approach is to eyeball the coupling constants as small, medium and/or large. From this point, it becomes a simple task of matching up the same couplings: A to B (small coupling), A to E (large coupling), and C to D (medium coupling).




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