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H1 NMR Explanation

  1. Feb 3, 2014 #1
    Hi everybody,

    1. The problem statement, all variables and given/known data

    I am working on the spectra from the following link:
    http://www.chem.ucla.edu/cgi-bin/webspectra.cgi?Problem=bp2


    2. Relevant factors and first attempt

    For the most part, I understand how the spectra available contribute to the answer, but the left (upfield) side of the proton NMR is proving confusing. I see how the methyl group around 4ppm and the lone aldehyde hydrogen around 10.5 ppm produce their respective patterns, but the remaining 4 hydrogens on the left side of the benzene ring mystify me. To be more specific in my confusion:

    3. The confusion

    1. Why does the 7.0 ppm shift have a multiplicity of two? Given that each hydrogen is a different distance from the either and aldehyde, shouldn't each hydrogen have a different peak?

    2. What could account for the two-multiplicty 4-peak split between 6.9-7.0 ppm? Since this is a benzene ring, each hydrogen should be adjacent to a maximum of two hydrogens, no? One on each carbon on each side of the bond?

    I understand the other two shifts within the 7-8 ppm range, but not how they might fit in with the one above. What am I not seeing?

    Thanks for your help.
     
  2. jcsd
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