Proton attached to N or O in HNMR spectroscopy [duplicate]








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[Spin spin coupling in a proton NMR of an ester?](/questions/24601/spin-spin-coupling-in-a-proton-nmr-of-an-ester)

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I was wondering why a hydrogen attached to a nitrogen or oxygen is not able to couple with p+ on adjacent carbon atoms and hence why it always appeats as a singlet in HNMR spectroscopy?




It depends on the condition of your experiment if a coupling of a proton of an amino or hydroxyl group with a proton attached to the $\alpha{}$-carbon is observable, or not. As pointed out by the indicator set by @Mithoron, intermolecular exchange processes need to be taken into account.


* If your alcohol (or amine) to be analyzed is very pure, and the deuterated solvent you deploy is both very pure, and dry, and free of acids or bases *catalysing* proton exchange, than you may observe $^3J$-couplings you expect to see. For example a freshly opened sample of deuterated DMSO (used as solvent) may contribute to this observation. See the *peak data* of the 1H NMR spectrum of ethyl alcohol in DMSO [here](http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_disp.cgi?sdbsno=1300).
* If you aim to analyze an alcohol, not well dried, analyzed in deuterated chloroform or methanol that was frequently exposed to ambient (humid) air, then indeed instead of a triplet of an hydroxyl group ($\ce{-OH}$) attached to a methylene group ($\ce{-CH2-{}}$) all what may be spot is a broad singlet signal. The same reference, 90 MHz 1H NMR in deutero chloroform provides one example. (Note the chemical displacement of the hydroxyl protons altered, too.)


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