H NMR of unknown sample (organic chem)

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Discussion Overview

The discussion centers on the analysis of an H NMR spectrum for an unknown organic compound with the formula C7H5NO3, specifically focusing on a signal at approximately 7.2 ppm that is not integrated for any hydrogens. Participants explore the potential identity of this signal and its implications for the compound's structure.

Discussion Character

  • Homework-related, Technical explanation, Exploratory

Main Points Raised

  • One participant suggests that the signal at 7.2 ppm could represent an aromatic, conjugated vinylic, or phenolic proton, but expresses uncertainty about these interpretations.
  • Another participant points out that chloroform, a common solvent, produces a signal around 7.2 ppm, questioning whether the signal is related to the sample or the solvent.
  • A later reply confirms that the sample was indeed dissolved in CDCl3, implying that the observed signal may not be indicative of the sample's structure.
  • Participants discuss the likelihood of the signal being contamination from the solvent, which is noted as a common occurrence in NMR analysis.

Areas of Agreement / Disagreement

Participants generally agree that the signal at 7.2 ppm is likely due to the solvent, but there is some initial uncertainty regarding its potential relation to the sample's structure.

Contextual Notes

The discussion does not resolve the initial question about the identity of the signal, as it shifts towards the interpretation of solvent effects in NMR spectroscopy.

chops369
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Homework Statement


Last week in organic chem lab, we were provided with an H NMR spectrum of an unknown compound with the formula C7H5NO3. I'm not terribly good at analyzing these spectra, but I've managed to figure out that I'm looking at 4-nitrobenzaldehyde. The only thing that's bothering me is this tiny signal, which shows up at about 7.2 ppm and is not integrated for any hydrogens. Known chemical shift data gives three possibilities: (1) aromatic proton, (2) conjugated vinylic proton, and (3) phenolic proton. I don't really see how this signal could represent any of those. Would it be possible that the signal is representative of the tiny amount of the enol form of the aldehyde? If not, what do you think it might be?

Homework Equations


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The Attempt at a Solution


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Last edited:
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Chloroform gives an H-NMR signal around 7.2 ppm. Was your sample dissolved in CDCl3?
 
Ygggdrasil said:
Chloroform gives an H-NMR signal around 7.2 ppm. Was your sample dissolved in CDCl3?
Yes it was. I would assume that means the signal really has nothing to do with the structure of the sample?
 
Yes, it's likely contamination from the solvent. A very common occurrence in NMR.
 

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