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I did an $^1\ce{H}$-NMR sample to my salt p-carboxybenzyl triphenylphosphonium bromide. I got a doublet at 5.26, and according to every article it belongs to the $\ce{CH_2}$ next to $\ce{P^+}$. But I wonder how comes I didn't get a singlet for that?

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Phosphorous exists entirely as $\ce{^31P}$, and $\ce{^31P}$ has a magnetic moment of 1/2 (just like a proton). Therefore, a single phosphorous will split any protons coupled to it into a doublet - as you observed. If you looked at the corresponding $\ce{^31P}$ NMR spectrum you would see that the phosphorous signal would be split into a triplet by the two protons.

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  • $\begingroup$ and another question if i may, i got a very large peak at 3.38 in dmso, could it be water? $\endgroup$
    – danielle
    Commented Nov 23, 2014 at 16:48
  • $\begingroup$ The water impurity signal can move around a bit depending on the water concentration, but I'd bet your signal is due to water. This reference says the water impurity in dmso absorbs at 3.3. If the above answer was helpful, please mark it as accepted. Thanks! $\endgroup$
    – ron
    Commented Nov 23, 2014 at 17:01
  • $\begingroup$ im having trouble finiding out another two multiplets in 7.08 and another in 7.56 at the same reaction ,my solvent was tolouene.. $\endgroup$
    – danielle
    Commented Nov 26, 2014 at 12:41
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    $\begingroup$ For peak identification it would probably be best if you opened a new question and included a copy of the nmr spectrum along with your experimental procedure. $\endgroup$
    – ron
    Commented Nov 26, 2014 at 14:39

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