1H NMR question Watch

MMMargiela
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Why are not all protons observed in a1H NMR spectrum (that is obtained experimentally) for some molecules? Does anyone have an idea?
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Infraspecies
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As in, not all hydrogens, or not all the protons in every nucleus of every atom?
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MMMargiela
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(Original post by Infraspecies)
As in, not all hydrogens, or not all the protons in every nucleus of every atom?
As in not all protons present in the structure will produce a peak therefore wont show up on the experimental spectra but if the spectra is calculated mathematically it will. I think its due to the solvents being present experimentally but i don't know how that would affect it
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OpinionsForLife
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Maybe cos they are in the same environment :yes:

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Infraspecies
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(Original post by MMMargiela)
As in not all protons present in the structure will produce a peak therefore wont show up on the experimental spectra but if the spectra is calculated mathematically it will. I think its due to the solvents being present experimentally but i don't know how that would affect it
Oh, I see. Sometimes you can get exchange of protons with a solvent. If the solvent is deuterated, the proton can exchange with a deuteron, then it will not produce a peak, as they do not resonate within the shift range in which you measure proton NMR spectra.
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username913907
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(Original post by MMMargiela)
Why are not all protons observed in a1H NMR spectrum (that is obtained experimentally) for some molecules? Does anyone have an idea?
2 main things I can think of....

1. If the proton is acidic it can usually exchange with NMR inactive Deuteriums in most NMR solvents.
2. Proton decoupling in some spectral modes, e.g. 13C NMR. You are intentionally stopping the protons from coupling with outer nuclei but I guess they would still strictly have a peak if the spectrum showed those chemical shifts.
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MMMargiela
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(Original post by Infraspecies)
Oh, I see. Sometimes you can get exchange of protons with a solvent. If the solvent is deuterated, the proton can exchange with a deuteron, then it will not produce a peak, as they do not resonate within the shift range in which you measure proton NMR spectra.
(Original post by JMaydom)
2 main things I can think of....

1. If the proton is acidic it can usually exchange with NMR inactive Deuteriums in most NMR solvents.
2. Proton decoupling in some spectral modes, e.g. 13C NMR. You are intentionally stopping the protons from coupling with outer nuclei but I guess they would still strictly have a peak if the spectrum showed those chemical shifts.
Ah yes guys just what i was looking for, thanks!
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