H NMR Spectrum - Molecular Structure

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SUMMARY

The discussion centers on determining the molecular structure of C8H8O3 using H NMR spectrum analysis. Key findings include the identification of a meta-disubstituted benzene ring, indicated by peaks at ~7.8 ppm (doublet), ~7.45 ppm (triplet), ~7 ppm (doublet), and ~6.85 ppm (triplet), which correspond to the aromatic protons. The singlet at ~3.5 ppm, integrating for 4H, suggests the presence of an OH group, although the integration raises questions about the number of chemically identical hydrogens. The IR spectrum confirms the presence of both an OH and a C=O group, supporting the proposed structure.

PREREQUISITES
  • Understanding of H NMR spectroscopy
  • Knowledge of IR spectroscopy and functional groups
  • Familiarity with molecular structure and degree of saturation concepts
  • Experience with interpreting NMR peaks and integration
NEXT STEPS
  • Research the implications of meta-disubstitution in aromatic compounds
  • Explore the behavior of OH groups in NMR spectroscopy
  • Investigate the integration of NMR signals and potential for coincident peaks
  • Learn about the effects of solvent choice on NMR results
USEFUL FOR

Chemistry students, organic chemists, and anyone studying molecular structure determination through spectroscopy techniques.

edimeo25
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Homework Statement


Give the structure of C8H8O3.

Homework Equations


IR tells us that there is an OH group and a C=O group
Degree of saturation = 5 --> Benzene ring + C=O

H NMR spectrum shows:
Peak at ~7.8ppm integrating for 1H and is a doublet
Peak at ~7.45ppm integrating for 1H and is a triplet
Peak at ~7ppm integrating for 1H and is a doublet
Peak at ~6.85ppm integrating for 1H and is a triplet
Peak at ~3.5ppm integrating for 4H and is a singlet

The Attempt at a Solution


It's hard to show my attempt at a solution, but I believe it will be a meta-disubstituted benzene ring. I just can't figure out how to insert the 3rd oxygen atom and how exactly you can have 4 chemically identical hydrogens with no neighboring hydrogens in this type of molecule. The 3 peaks between 7.8 and 7ppm I believe account for the neighboring hydrogrens of the benzene ring if its substituents are in the meta orientation.

Any help would be greatly appreciated. Thanks for your time.
 
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Since you have an OH by IR given to you in this problem, start there. In NMR, the OH group usually shows up as a broad hump or a singlet depending on concentration and solvent. You only have one signal that you identified as a singlet at ~3.5 ppm so that's got to be it, however; it integrates to four protons. That's a problem...
Is it possible that you have two coincident singlets present that integerate to 4 protons? If so, what other functional group has an absorbance of ~3.5 ppm? What solvent is used in the NMR?
 

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