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Homework Help: H NMR Spectrum - Molecular Structure

  1. Oct 17, 2008 #1
    1. The problem statement, all variables and given/known data
    Give the structure of C8H8O3.

    2. Relevant 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

    3. 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.
  2. jcsd
  3. Oct 20, 2008 #2


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    Science Advisor
    Homework Helper
    Gold Member

    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 gotta 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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