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Homework Help: Chemistry: determing name of a compound.

  1. Oct 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A compound only contains C, H and O. An elemental analysis of the compound gives the result C: 40.00%; H: 6.71%. The 13C NMR, IR spectrum and mass spectrums are in the graph below.

    Graphs: http://s512.photobucket.com/albums/t323/antiuniverse/graphs.gif [Broken]

    I need to determine the name of the compound.

    2. Relevant equations

    3. The attempt at a solution
    I'm not entirely sure. From the elemental analysis:

    If we had 100g of compound, we'd have:
    40g C
    6.71g H
    53.29 O

    Work out the moles:
    40g / 12 = 3.3333 moles of C
    6.71g / 1 = 6.7100 moles of H
    53.29g / 16 = 3.3306 moles of O

    Divide by smallest ratio:
    2.8571 / 2.8571 = 1 atom of C
    6.7100 / 2.8571 = 2 atoms of H
    1.1652 / 2.8571 = 1 atom of O

    So the empirical formula would be H2CO (or C2H4O2?). I think the mass spectrum is telling me that the empirical formula must be H2CO (which has a molecular weight/mass of 30).

    From the 13C NMR spectra I believe it's either an aldehyde or ketone. I know that H2CO is formaldehyde (methanal) which is an aldehyde and correlates with what I found in the 13C NMR spectra.

    Could anybody look over this and let me know if it's correct?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Oct 16, 2008 #2
    I think you're solid; the IR spectrum spike between 1750/cm denotes a C=O bond. The NMR spectrum implies that all hydrogens in the molecule produce the same signal, and must have the same environments (symmetrical on the molecule); this spike is also pretty far from the starting point which would mean that the hydrogens are attached to something close to oxygen (like a carbonyl carbon). I don't know how to read mass spec (for some reason my organic teacher never went over this). Your calculations look good, and CH2O seems like it's probably the answer.
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