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H NMR coupling constants

  1. Jul 28, 2009 #1
    background:

    I have a HNMR spectra and I am trying to figure out what is coupled to what. There is a set of 4 doublets where it is know that there 2 sets of coupled doublets. the doublets have j-values of 8.8 @ 8.04ppm, 8.8@ 7.58ppm, 8.4@7.39ppm and 8.4@7.00ppm. While I may have assumed that the 8.04/7.58 and the 7.39/7.00 are the coupled sets due to j-values, the peaks do not lean towards each other. on the other hand, the 8.04/7.0 and the 7.58/7.39 set do lean towards each other. In addition appears as though the chemical shift of the 7.00ppm H's is near what i would expect for the H's next to the 8.04ppm H's

    Question:

    If trying to predict whats coupled to what, is it more important that the j-values match or that the peaks lean towards each other? In addition since the chemical shifts of the 7.0 h's seem's to be near the 8.04 H's on the molecule and the fact that they lean towards each other enough to assume they are coupled, or since thier j-values are a little different would that negate them being coupled?
     
  2. jcsd
  3. Jul 31, 2009 #2

    chemisttree

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    The j-couplings are the more important ones here.
     
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