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I am trying to interpret an $\ce{^1H}$-$\mathrm{NMR}$ spectrum on the molecule 4-amino-N-(2-chlorophenyl)benzenesulfonamide that I produced in a lab session. I have managed to assign all the hydrogen atoms to their peaks with reasoning but one, the 4-amino-group. The only peak left is a triplet, which has to be signal due to the 4-amino but this should be a singlet as there are no neighbouring hydrogen atoms. I have used software to generate a $\ce{^1H}$-$\mathrm{NMR}$ spectrum and it is coming up with the peak at the same position as my lab generated $\ce{^1H}$-$\mathrm{NMR}$, but as a singlet. Why is this triplet present in my lab $\mathrm{NMR}$ spectrum?

Is this to do with possible hydrogen bonding between the $\ce{NH2}$ and water? I do have a slight broad peak at $\pu{4.1 ppm}$.


Edit (02/04/22)

ChemDraw predictive NMR:

ChemDraw predictive NMR

Lab generated NMR:

[Lab generated NMR

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    $\begingroup$ Er, I'm not sure if there's enough info in your question to properly answer it. It would be really, really helpful if you could attach the spectrum (an image of it) and your assignments, or if you can't, at least provide the shifts and couplings you extracted. Please specify the solvent as well. I will assure you, though, that you are not observing coupling between NH2 and water (observing intermolecular J-coupling is, for all intents and purposes, not possible, and I expect it's extra impossible if you have something which is exchanging rapidly, as is the case for NH and OH groups). $\endgroup$ Apr 2, 2022 at 0:57
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    $\begingroup$ [...shifts, couplings, and integrals too, please. Also, how did you assign this? Did you use 2D NMR or are you just looking at the 1D multiplet structure? Lastly, how certain are you of your compound's purity? Sorry there are so many questions - but this is what I mean - I don't think it's possible to give a definitive answer without more details.] $\endgroup$ Apr 2, 2022 at 1:02
  • $\begingroup$ I added some NMR spectra: 1) NMR generated from ChemDraw which shows a singlet at 6.06 ppm for the NH2 2) NMR generated from the lab shows a triplet at 6.6 ppm for the NH2. The solvent used was d6-DMSO. The shifts, couplings and integrals can be found on the second spectrum. I did not use 2D NMR. Purity could be a major factor, this analysis was part of a two-step synthesis and the intermediate is also shown in the second spectrum. My initial thoughts was that this triplet came from the intermediate CH3, but I'm assuming this would produce a peak much more upfield, not at 6.6? $\endgroup$ Apr 2, 2022 at 20:21
  • $\begingroup$ Looks more like a minor product... how did you integrate the spectrum? $\endgroup$ Apr 2, 2022 at 20:25
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    $\begingroup$ Sorry, just updated the second spectrum and I've added the integration trace on. $\endgroup$ Apr 2, 2022 at 20:40

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To understanding the OP's problem of corresponding $\ce{^1H}$-$\mathrm{NMR}$, it was nice exchange of comments between OP and orthocresol. I agreed of all advices given by orthocresol. Yet I'm bothered by the large and significant signal at about $\pu{2.0 ppm}$, which was assigned as $\mathrm{DMSO}$-$d_5$ signal by OP. However, it is known fact that $\mathrm{DMSO}$-$d_5$ signal appeares around $\pu{2.5 ppm}$, which is exactly in the spectrum but errouniously assigned as signal of $\ce{CH3}$-group of intermediate with a question mark by OP. I donn't agree with these assignment of OP and my thoughts are given as follows:

I think OP's deacetylation experiment didn't work at all (only a trace of product appears). My reasoning is due to the appearence of two-proton doublet at around $\pu{7.7 ppm}$ due to the $\ce{H}$-7 and $\ce{H}$-7'. If acetamide group is removed, the lone pair of free $\ce{NH2}$-group is available and mesomeric effect would sheilded $\ce{H}$-7 and $\ce{H}$-7' positions (increasing electron density) more than that in phenyl nucleus. I'd expect that signal to be more at around $6.5$-$\pu{7.0 ppm}$. Therefore, I think the $\ce{^1H}$-$\mathrm{NMR}$ spectrum provided by OP is simply the unreacted starting material (acetamide intermediate) as I assigned the peak as follows:

Suggested peak of NMR

I think the $\mathrm{NMR}$ signal due to acetamide proton $(\ce{CH3CONH}-)$ should be burried in $7.0$-$\pu{7.5 ppm}$ reagion. It is probably the sharp singlet around $\pu{7.25 ppm}$ to my best guess (comparision of integrations at $7.0$-$\pu{7.5 ppm}$ reagion and $7.5$-$\pu{8.0 ppm}$ reagion would give the confirmation).

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    $\begingroup$ Yup seems very sensible! I didn’t look too closely at the aromatic region, bit of a mess, but the DMSO peak is definitely off & I didn’t spot that. $\endgroup$ Apr 3, 2022 at 10:03

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