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Topic: Help interpreting NMR and IR spectrum  (Read 3036 times)

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Offline ASensation

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Help interpreting NMR and IR spectrum
« on: April 24, 2022, 10:38:59 AM »
Hi, first time posting, I need some help trying to interpret and relate between these 2 spectra
1H NMR


IR
« Last Edit: April 24, 2022, 02:07:14 PM by sjb »

Offline Borek

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Re: Help interpreting NMR and IR spectrum
« Reply #1 on: April 24, 2022, 01:52:26 PM »
Please read the forum rules. You have to show your attempts at answering the question/solving the problem to receive help, it is a forum policy.
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Offline mjc123

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Re: Help interpreting NMR and IR spectrum
« Reply #2 on: April 24, 2022, 03:30:17 PM »
The IR is massively saturated; is it possible you could run it again with less sample?

Offline ASensation

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Re: Help interpreting NMR and IR spectrum
« Reply #3 on: April 24, 2022, 08:40:50 PM »
Please read the forum rules. You have to show your attempts at answering the question/solving the problem to receive help, it is a forum policy.
Ah my bad, I am very sorry. Mr. Admin.

My Attempts so far
This homework of mine in particular is to identify a given unknown compound supplied by my instructor and I would need to run multiple qualitative analysis before obtaining the IR and NMR spectrum to verify my qualitative analysis results as well as determining possible structures. The results for my qualitative analysis has been:

Alcohol (-OH) group: Present
Carboxylic acid group: Not present
Ester group: Not present
Any nitrogen group: Not present
Carboxyl group: Not present

NMR
My interpretations for the NMR spectra has been consistent with the results of qualitative analysis with the peaks appearing at chemical shift region of <2 ppm and a signal appearing >3 ppm for the presence of the -OH group. However the integration of the peaks seem to me to be quite odd to make out the structure of as it is shown to be 2 high signals of triplets and 1 medium sized triplet signal. What is more confusing is the lack of a quartet or maybe multiplet signal and the quartet shape for what I deemed to be the -OH group's signal, I have yet to find a possible structure that would explain such a signal shape while also falling in line with the rest of the spectra.

IR
For the IR Spectra, the shape of the spectrum itself is quite worrying to me. My interpretations so far has left me with:
Broad peak at 3368: -OH stretch
Peak at 2934: alkyl C-H stretch
sharp peak at 1651: possible Amide stretch or alkenyl C-C stretch

The rest of the spectrum seem quite hard to interpret as said here:
The IR is massively saturated; is it possible you could run it again with less sample?
However the IR was simply given to me by the instructor and was generated even before this assignment was given out.

I hope this satisfies the forum rules as well as some relevant information on my predicament.
Thank you.



Offline Babcock_Hall

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Re: Help interpreting NMR and IR spectrum
« Reply #4 on: April 25, 2022, 09:08:42 AM »
The behavior of -OH groups in NMR is a complex subject.  Only sometimes do they show coupling to other hydrogen atoms.  I seem to recall that this is because of their ability to exchange with small and variable amounts of H2O that are almost always present (there is also exchange between one hydroxyl group and another to consider).
EDT
You should express your integrals as ratios; this might help in their quantitative interpretation.  I would also apply the n+1 rule to each NMR signal.
« Last Edit: April 25, 2022, 11:25:31 AM by Babcock_Hall »

Offline ironman2538

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Re: Help interpreting NMR and IR spectrum
« Reply #5 on: June 24, 2022, 07:31:43 AM »
Is it possible that you give some more information on the same as to what exactly are you trying to do? NMR and FTIR are not standalone interpretation tools. You need some basic data as to how you got this NMR/IR, what were the raw materials and what are your expectations etc.
Secondly, you would also need to integrate the NMR properly. If possible use ratio of 1 or 2.

Offline wildfyr

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Re: Help interpreting NMR and IR spectrum
« Reply #6 on: June 26, 2022, 07:13:15 PM »
That might be an FTIR of mostly water.

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