H NMR of unknown sample (organic chem)

[chops369]

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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[Ygggdrasil]

Chloroform gives an H-NMR signal around 7.2 ppm. Was your sample dissolved in CDCl3?

 

[chops369]

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?

 

[Ygggdrasil]

Yes, it's likely contamination from the solvent. A very common occurrence in NMR.

 

[DeeNos]

As a scientist, it is important to always consider all possibilities when analyzing data. In this case, the unknown compound has been identified as 4-nitrobenzaldehyde, but there is a small signal at approximately 7.2 ppm that does not fit with any of the known chemical shifts for aromatic, conjugated vinylic, or phenolic protons. One possibility that could explain this signal is the presence of the enol form of the aldehyde. However, it is important to consider other factors such as the concentration and stability of the enol form in the sample. It is also possible that the signal could be due to impurities or experimental error. Further analysis and experimentation may be necessary to accurately determine the cause of this signal. As a scientist, it is important to always critically evaluate data and consider all possibilities before drawing conclusions.