December 04, 2021, 02:41:08 PM
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Topic: Combined spectroscopy problem  (Read 2598 times)

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Offline luscofusco

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Combined spectroscopy problem
« on: May 07, 2021, 12:23:04 PM »
I'm doing this problem and I don't know how to continue.

So far I managed to get from the 1H NMR 6 hydrogen atoms or a multiple of 6. From the 13C NMR 6 or 12 carbon atoms depending on symmetry.

Then with the IR spectra:
cm-1IntensityGroup
3100-3000weakH-C(sp2)
3000-2900weakH-C(sp3)
1600strongC=C(aromatic)

Can the 2500 cm-1 be a O-H from carboxylic acid and then 2000-1900 cm-1 the C=O from that carboxylic acid?

I'm not sure how to read the mass spectra, I get the [M]+ at 171 and [M+2]+ at 173. I'm not sure if the 172 peak is relevant or not.

Overall I guess that the compound might be some benzene acid or similar. Any help appreciated.

Offline Babcock_Hall

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Re: Combined spectroscopy problem
« Reply #1 on: May 07, 2021, 12:39:41 PM »
An aromatic ring often gives several signals in the general vicinity of 1450-1600 wavenumbers, but it depends upon the substitution pattern.  An aromatic ring may also produce several weak signals in the vicinity of 1600-2000, although some of these can be masked by a strong signal in the same region.  Offhand 1900-2000 wavenumbers is too high for the C=O stretch.

Offline luscofusco

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Re: Combined spectroscopy problem
« Reply #2 on: May 07, 2021, 01:42:23 PM »
Thank you.
Could the 2500 signal be produced by the aromatic ring?

Offline Babcock_Hall

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Re: Combined spectroscopy problem
« Reply #3 on: May 07, 2021, 03:32:44 PM »
I assume that you have access to a table of IR absorption frequencies.  In using such information one also needs to keep in mind the depth and breadth of the peaks.  That might help with deciding whether or not the 2500 wavenumber signal comes from an -OH group.

It would be good if you could provide some more of your own thinking, as per the Forum Rules.  There is quite a bit of information in the two NMR spectra and the mass spectrum.
« Last Edit: May 07, 2021, 03:57:34 PM by Babcock_Hall »

Offline luscofusco

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Re: Combined spectroscopy problem
« Reply #4 on: May 08, 2021, 07:23:49 AM »
Yes, I use the slides that the teacher gave us, but I don't understand them very well, and a book. I'll keep working on it, thank you.


Offline Babcock_Hall

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Re: Combined spectroscopy problem
« Reply #5 on: May 08, 2021, 09:38:53 AM »
I suggest starting with the M+2 peak at m/z 173.

Offline Babcock_Hall

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Re: Combined spectroscopy problem
« Reply #6 on: May 08, 2021, 02:32:19 PM »
The ratio of the M+2/M peak intensity is a useful piece of information.

Offline Babcock_Hall

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Re: Combined spectroscopy problem
« Reply #7 on: May 10, 2021, 03:41:14 PM »
Thank you.
Could the 2500 signal be produced by the aromatic ring?
I am not sure what is producing it.  However, you have other data that can lead to a structure.

Offline luscofusco

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Re: Combined spectroscopy problem
« Reply #8 on: May 17, 2021, 12:54:55 PM »
Sorry for the delay, this is what I've managed to do so far:

The M+2/M intensity is about 1/3 so Cl is present.
The M peak is odd so it contains N too (teacher said that if there's N it's only one for these exercises).
Then I divided 171 by 13 and I got C13H15 formula, then I needed to substract the Cl and the N so it is a CH2 for the N and C2H11 for the Cl.
This gives C10H2 remaining, so there should be more H than the initial guess. My guess was 6 or a multiple of 6 but I don't see how to "guess" it now. Do I just try 12, if it doesn't work 18 and so on? Or just add 6H to that formula? Maybe my initial guess is wrong but adding the H in the NMR spectra is 6 no matter what you do.

I'm stuck with the formula, I think if I manage to get it the remaining part should be easier.

Offline Babcock_Hall

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Re: Combined spectroscopy problem
« Reply #9 on: May 17, 2021, 05:23:11 PM »
If you can identify the functional group of which the nitrogen is a part, you should be all set.  The IR, NMR chemical shifts, and mass spectral fragmentation data can all be used.
« Last Edit: May 17, 2021, 07:00:45 PM by Babcock_Hall »

Offline MOTOBALL

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Re: Combined spectroscopy problem
« Reply #10 on: May 17, 2021, 07:33:39 PM »
For your MS data, you need to be aware of the  number of “Rings + Double Bonds” in the molecule; this can be calculated from the molecular formula.
You should google this.

Regards

Offline Babcock_Hall

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Re: Combined spectroscopy problem
« Reply #11 on: May 17, 2021, 08:36:27 PM »
The peaks at 125 m/z and 127 m/z are helpful.

Offline Orcio_Dojek

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Re: Combined spectroscopy problem
« Reply #12 on: June 06, 2021, 05:32:48 AM »
@luscofusco Did you considered one of the O2N-C6H4-CH2Cl ?

IR spectra fits for the para isomer, but does not fit with the H-NMR.

Meta isomer fits with H- and C-NMR but have some different IR spectra.

All isomers fit with yours MS spectrum.

Offline luscofusco

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Re: Combined spectroscopy problem
« Reply #13 on: June 10, 2021, 06:55:20 AM »
Hello @Orcio_Dojek I did consider a nitro group but my first option was a secondary amine. Yours makes a lot more sense, thank you for your feedback.

Offline MOTOBALL

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Re: Combined spectroscopy problem
« Reply #14 on: June 10, 2021, 01:10:31 PM »
@luscofusco Did you considered one of the O2N-C6H4-CH2Cl ?

IR spectra fits for the para isomer, but does not fit with the H-NMR.

Meta isomer fits with H- and C-NMR but have some different IR spectra.

All isomers fit with yours MS spectrum.

Orcio,

You do them no favours by spoon-feeding them the answer!!!!
We should steer them in the right direction with hints, to allow them to work out the answer themselves.

Regards,
Motoball

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