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Start a new discussion about the current wiki pageComparison of HN and CH coupings (1)
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One bond HN coupling of 90 Hz was incorrectly mentioned as stronger then one bond CH coupling. CH couplings range from ~120 to ~200 Hz (aromatic).
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I'm not telling about the absolute value, but for a given gyromagnetic ratio of N vs the one of C, the coupling to the proton is stronger is the case of NH than the one of CH, if N had the same gyromagnetic ratio as the carbon.
2.5*gC=gN
the JCH should be 220 Hz, and not less that 200 Hz, if the electronic configuration of the carbon was the same as the one of nitrogen.
thanks for the aromatic 1JCH coupling constant, I didn't know that it change that's much ( but hybridization state change from sp3 to sp2 ). In which case we get 120 Hz ?
According to table in "Spin dynamics" by M. Levitt, γ(15N)=-27.126 rad s-1T-1 and γ(13C)=67.283 rad s-1T-1 Gyromagnetic ratio article here also lists those values, but they are divided by a factor of 2π
so it's γN *2.5 ~ γC and J coupling values are coming in the same order JHN < JCH.
As for hybridization of carbon, smaller coupling is with sp3, larger coupling with sp2. >200 Hz for aromatics. I guess variation in coupling value with hybridization makes sense since J coupling is mediated by the electron orbitals.
Yeah, but if the gyromagnetic ratio of nitrogen was the same than the one of carbon the coupling would be stronger, so if we consider only a electronic point of view the coupling between carbon, the coupling from proton to nitrogen is strong as the one from proton to carbon. Of course this is not the order we will give on a experimental point of view.
On the other hand the coupling between proton on a electronic point of view is very weak, because despite their scalar coupling constant that is in not that's weak, their is their high gyromagnetic ratio, so the electronic state of proton is not very favorable to J-coupling.
