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Exchangeables Protons acquired in different Deuterated Solvents

A deuterated solvent can impact whether exchangeable protons, such as OH or NH, are visible on a 1H NMR spectrum. The advantage of eliminating any contribution from an exchangeable proton(s) is to simplify spectral interpretation. One disadvantage of not seeing exchangeable protons is the deficiency to the total proton count in establishing the molecular formula.

The diagram below compares two 1H NMR spectra for the same functional group in two different deuterated solvents. The 1H NMR spectrum in deuterated-DMSO shows two doublets whereas the spectrum acquired in deuterated-methanol shows only the singlet for the CH group.

ExchangeableProtonsAndSolvents_Jun42009

4 Replies to “Exchangeables Protons acquired in different Deuterated Solvents”

  1. Hello Arvin,
    Wish you a Merry Xmas and Happy New Year!!!
    1H NMR of my compound does not show NH2 peak and the NMR was taken in CDCL3. What could be the reason for the non appearance of NH2 peak? Are there any experiments to show the existence of NH2 peak? Mass spec/1H NMR corresponds to the structure.
    Thanks for the help.
    Marto

  2. What relative effect does H-bonding vs acidity have on the speed of proton exchange? My guess would be that H-bonding is more critical since an amide NH will exchange quite rapidly in a D2O shake, but would you expect the more acidic alpha-protons in a beta-diketone to exchange as readily?

  3. Hi Rita,
    The presence of an exchangeable peak varies on exchange rate with deuterium from the solvent. One good way to check for this is to collect an HSQC spectrum and look for a 1H-13C correlation.
    Regards,
    Arvin

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