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NMR doesn't match up with Molecule?

Discussion in 'MCAT Study Question Q&A' started by rockyDoctora, Jul 31, 2011.

  1. rockyDoctora

    2+ Year Member

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    Methyl Benzoate:


    [​IMG]

    According to Kaplan, this NMR spectrum is for methyl benzoate:

    [​IMG]

    I dont understand this. From the structure of methyl benzoate, there should be four groups:

    1) hydrogen at para (int = 1)
    2) hydrogens a bit closer to ester on benzene ring (int = 2)
    3) hydrogens again, a bit closer to the ester on benzene ring (int = 2)
    4) hydrogens on the methyl group (int 3)

    However, the number of peaks and the integration values on the NMR are 3, 3, 2... Is this right?

    Thanks for you help!
     
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  3. mohad

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    My ochem teacher said that sometimes the meta and para hydrogens can be considered "the same chemical environment" and therefore they're often grouped together as 3 hydrogens instead of 1 and 2. He also told us to not be surprised if we see that again on other sources. Really good NMR machines will distinguish them as 2 and 1, but they can be a group of 3.

    Sorry, I meant para and meta. Not Ortho.
     
    #2 mohad, Jul 31, 2011
    Last edited: Jul 31, 2011
  4. rockyDoctora

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    Sweeeeeet. Thanks a lot for the info!
     
  5. MD Odyssey

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    Kaplan is completely wrong here - there is a lot more going on. The H-NMR spectrum from SDBS for methyl benzoate is this:

    Edit: I suspect that the link to SDBS I posted was disallowed for some reason. If you go to SDBS and look it up, you'll find that there are additional signals that Kaplan hasn't showed you.
     
    #4 MD Odyssey, Jul 31, 2011
    Last edited: Aug 1, 2011
  6. collegestud2013

    collegestud2013 Probationary Status
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  7. axo86

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    lol @ singlets @ 7 and 8 ppm :D
     

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