May 26, 2020, 08:36:09 PM
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Topic: find molecular structure given H-NMR C-NMR and COSY  (Read 102 times)

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Offline Maxim_

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find molecular structure given H-NMR C-NMR and COSY
« on: May 23, 2020, 03:53:19 PM »
Hi,

For our exam we need to be able to identify a molecular structure given certain spectra. Doing this when only a single Hnmr spectra is given is usually doable as the structures are not overly complex, but I find that generally the more information the professor gives, the more complicated the structure is.

 I have attached the spectra for this particular problem as .png files.

Some of the questions I have that prevent me from puzzling this together are:

- Is the signal in the HNMR at 1.5 ppm a doublet of multiplets? when looking at the hnmr i would say no but the cosy spectrum shows it as a single signal?

- There are significantly more C signals (11) compared to H signals (4/5) and i struggle to find a way to connect these together. Am I  supposed to just add a bunch of Cl or something  instead of H on carbons?

- When looking at the C Spectrum the 5 signals at 70-90 ppm make me suspect i have a ringstructute substiture (cyclopentane/cyclobutane?) but i dont have a reason why the shift is so far downfield.

thank you very much for taking your time to respond,

kind regards,

Maxim
 

Offline Babcock_Hall

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Re: find molecular structure given H-NMR C-NMR and COSY
« Reply #1 on: May 24, 2020, 10:14:12 AM »
Any carbon bonded to four other carbons or any carbonyl (C=O) carbon (with the exception of an aldehyde) will not have a directly attached proton.  Is the NMR solvent CDCl3?  If so, you will see evidence of the solvent in both the H-1 and C-13 spectrum, and you may recall that deuterium is a spin-1 nucleus.  Not all compounds will follow first-order rules of coupling, and you may have a compound that does not.
« Last Edit: May 24, 2020, 10:28:19 AM by Babcock_Hall »

Offline Babcock_Hall

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Re: find molecular structure given H-NMR C-NMR and COSY
« Reply #2 on: Today at 07:09:32 AM »
The three closely spaced lines in the vicinity 77-78 ppm in the C-13 spectrum are from the solvent and may be ignored.

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