Consider the NMR of Brominated Pyridine shown below:

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When I looked at the NMR data, I was confused because I thought that H2 would also be split in the meta position by H6 but the data says that this is not present in the overall NMR Spectra, although from previous NMR lessons I thought that this would be observed.

Why does H2 not couple to H6 in the NMR shown above?

  • $\begingroup$ Can you speculate why that coupling constant is quite different from the 4J coupling in the other direction? $\endgroup$ – Karl Dec 23 '19 at 14:19
  • $\begingroup$ @Karl i'm not too sure what you mean. can you explain your question because I'm unsure $\endgroup$ – vik1245 Dec 23 '19 at 14:25
  • $\begingroup$ Of course there is a 4J coupling from H2 to H6, but it seems to be much smaller than the 2.5 Hz from H2 to H4. Agreed? $\endgroup$ – Karl Dec 23 '19 at 14:29
  • $\begingroup$ @Karl yes. I was wondering though if that was due to the presence of the Heteroatom present (N) on the pyridine ring? $\endgroup$ – vik1245 Dec 23 '19 at 14:32
  • $\begingroup$ Yes, of course. Hint: J coupling works through electrons. ;) N is more .... than C. $\endgroup$ – Karl Dec 23 '19 at 14:38

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