Question
Asked 14 April 2017

Can anyone help me with H-NMR data interpretation?

Hey,
I had done the NMR analysis of a crystal that i suppose is Typtanthrin ( C15H8N2O2). The crystal was dissolved in CDCl3 for the analysis. I am given a plot as the results and i can not make any progress with its interpretation. Can anyone help me make progress with its interpretation. I dont have any expertise with NMR data and any help is highly appreciated. 
I have attached the plots for perusal.
Thank you

Most recent answer

Meenu Mridula
Mar Ivanios College
Thank you all for the detailed replies. Based on the suggestions the technician agreed upon re-running the samples overnight to detect the two missing peaks; since running a HSQC and HMBC was beyond our scope. And sincere gratitude to Anthony Foris for the PDF attachment :), that put things in a better light thanks again..... 

Popular answers (1)

Anthony Foris
Dupont, Retired
Dear Meenu,
I also looked at your spectra, and agree with Dr. Anklin. Attached please find more detailed analysis, additional references, as well as actual 1H and 13C NMR spectra of
tryptanthrin. Also included is a detailed comparison of your 13C spectrum with that of the one from reference 3. Other than for the missing 182 ketone carbonyl peak, and the 144 ppm resonance, they are a very good match. I suspect that the reason for the missing (undetected) peaks is that your 13C spectrum has poor S/N, and these weak signals were lost in the noise. If you do not have access to 2D NMR, you might reacquire the carbon spectrum with lots more NS (overnight?) to build up the signals.
Good luck in your research! AF
3 Recommendations

All Answers (4)

Rémy Bertrand Teponno
University of Dschang
Dear Meenu,
Please compare your NMR data to those of tryptanthrin present in the attached paper.
With regards,
Clemens Anklin
Bruker Corporation
Meenu,
the 1H spectrum is very nice and matches the description int he paper. The paper does lumps many signals together in the region 7.3 - 8.0 ppm. Your spectrum shows all signals nicely resolved. There are 8 signals for the 8 protons, 4 on each 1,2 substituted ring. In first approximation you will see d, dxd,dxd and d for each ring. There are long range couplings too. My interpretation is that the signals at 8.65 (d), 8.45 (d), 7.85 (dxd) and 7.8 (dxd) belong to one ring and the signals at 8.05 (d), 7.95 (d), 7.68 (dxd) and 7.43 (dxd) belong to the other. The latter 4 signals go together I think because of the stronger roofing effect. A detailed analysis of couplings or a COSY will make it unambiguous. Which signal belongs to what proton is harder just from the 1D spectrum. In the carbon spectrum you are missing two signals. You have all the protonated carbons but compared to the literature you miss the signal at 182 ppm and at 144 ppm. For assignment you will need a HSQC and HMBC
Best regards
2 Recommendations
Anthony Foris
Dupont, Retired
Dear Meenu,
I also looked at your spectra, and agree with Dr. Anklin. Attached please find more detailed analysis, additional references, as well as actual 1H and 13C NMR spectra of
tryptanthrin. Also included is a detailed comparison of your 13C spectrum with that of the one from reference 3. Other than for the missing 182 ketone carbonyl peak, and the 144 ppm resonance, they are a very good match. I suspect that the reason for the missing (undetected) peaks is that your 13C spectrum has poor S/N, and these weak signals were lost in the noise. If you do not have access to 2D NMR, you might reacquire the carbon spectrum with lots more NS (overnight?) to build up the signals.
Good luck in your research! AF
3 Recommendations
Meenu Mridula
Mar Ivanios College
Thank you all for the detailed replies. Based on the suggestions the technician agreed upon re-running the samples overnight to detect the two missing peaks; since running a HSQC and HMBC was beyond our scope. And sincere gratitude to Anthony Foris for the PDF attachment :), that put things in a better light thanks again..... 

Similar questions and discussions

Absence of some signals on 1H and 13C spectra of polyaromatic carboximidates?
Question
5 answers
  • Deleted profile
Hi,
I have encountered a strange behaviour of some signals (they are absent) in a series of polycyclic aromatic carboximidates spectra. We have X-Ray or mass spectroscopy data for these compounds, so we know how they look like. All signals in 1H and 13C spectra match up to structures, but some protons and carbons don't produce peaks at all.
(Picture 1) Here we have this problematic fragment. Red atoms are not visible on corresponding spectra. Imine proton can be found near 14 ppm (CDCl3), but its intensity is like 0,05 in comparison to single aromatic proton's signal.
Red carbon signal is absent in 13C spectrum.
(Picture 2) Analogical Coumarin was synthesised. In case of this compound all signals can be found and described on respective spectra.
(Picture 3) Trifluoromethanesulfonyl amide of compund (1) behaves like Coumarin (2). All signals can be found and described.
(Picture 4) This compound is similar to (1) but instead of phenyl ring (twisted 90o in relation to the rest of molecular plane) we used here the ferrocenyl as an off-planar substituent (it's twisted approximately 40o). The second ferrocenyl is also incorporated in this structure, but its position is distant from this problematic region of molecule.
1H Spectrum: Imine proton is visible at 14 ppm with proper intensity (integral = 1). Ferrocenyl (red one on illustration) signals are not visible at all. Signals from the second ferrocenyl (not included on ilustration) are present with proper intensities.
13C Spectrum: Imine carbon can be found at 189 ppm (CDCl3). 1st ferrocenyl signals (all of them!) are absent, 2nd ferrocenyl signals are present.
Does anyone know what is going here? Maybe this is an effect of strongly quadrupolar (14N) vicinity and/or CSA of C=N bond? Any idea, suggestion, hint or literature signpost would be a great help.
Best regards,
Arkadiusz

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