Ch 12 Ppt 2

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  1. Mass spectrometry:
    __ can be obtained from a very small sample

    It does not involve __ or __.

    A beam of high-energy electrons __.

    The masses of the fragments and their relative abundance reveal information about the __ of the molecule.
    molecular weight

    • absorption
    • emission of light

    breaks the molecule apart

  2. A high-energy electron can do what, creating a what (a positive ion with an unpaired e-).
    dislodge an electron from a bond, creating a radical cation
  3. Only the __are deflected by the magnetic field.
    Amount of deflection depends on __.
    The detector signal is proportional to the __.
    By varying the magnetic field, ions of all masses are collected and counted. =>
    • cations 
    • m/z
    • number of ions hitting it
  4. The __: A mixture of compounds is separated by __, then identifiedby __.
    • GC-MS
    • gas chromatography
    • mass spectrometry
  5. Masses measured to 1 part in 20,000.
    A molecule with mass of 44 could be C3H8, C2H4O, CO2, or CN2H4.
    If a more exact mass is 44.029, do what?
    pick the correct structure from the table
  6. Molecules with heteroatoms

    1) __ are present in their usual abundance

    2) __ contain 1.1% C-13, so there will be a small __. 

    3) If Br is present, M+2 is __.

    4) If Cl is present, M+2 is __.
    • isotopes
    • hydrocarbons
    • M+1 peak
    • equal to M+
    • 1/3 M+
  7. If iodine is present, peak at __, __.
    If N is present, M+ will be an __.If S is present, M+2 will be __.
    • 127, large gap
    • odd number
    • 4% of M+
  8. More stable carbocations will be __.

    __ favored.

    Alcohols usually __. M+ may __.
    more abundant

    resonance-stabilized cations

    lose a water molecule

    not be visible
  9. A compound with no S, Cl, or Br has...
    an M+1 peak that is small and an M+2 peak that is even smaller
  10. If sulfur is presnet:
    M+2 is 4% M+ (and is larger than M+1)
  11. If Cl is present, what?
    M+2 peak is 1/3 as large as the M+ peak
  12. If Bromine is present, what?
    M2+ is equal to M+
  13. Explain iodine
    • recognized by the presence of an iodonium ion, I+ at m/z 127
    • This is combined with a characteristic 127-unit gap in the spectrum corresponding to loss of the iodine radical
  14. Nitrogen?
    gives an odd molecular weight, and usually gives some major even-numbered fragments
  15. Stable compounds containing only C, H and O have __ and most __.
    • even MW 
    • of their major fragments are odd-numbered
  16. m/z is hwat? But since what? We do what?
    • the mass to charge ratio
    • since they''re +1 
    • we just relate it to its mass
  17. Unlike nitrogen, explain other compounds not containing nitrogen?
    give even MW and odd numbered fragments
  18. The stability of the __ is apparently more important than the stability of the __.
    • cation
    • radical
  19. True or False:

    Both cation and radical are detected.
    False: only cation
  20. R-CH2-O-R can be stabilized into what?

    loss of an alkyl group
  21. Ketones and aldehydes will be cleaved where?
    between the R and the C=O
  22. Ethers will undergo alpha cleavage where?
    between R-CH2
  23. Amines undergo alpha cleavage to give stabilized cations how?
    R2N-CH2 and R
  24. Loss of a small, stable molecule is seen how?
    mass spectral peak; indicated by a fragment peak with an even mass number
  25. the radical cation may lose what?
    • water
    • CO
    • CO2
    • ethene or other alkenes
  26. When alcohols lose water, what isn't seen and why?
    the molecular ion (M+) because it loses water so quickly
  27. In addition to losing water, alcohols commonly fragment next to the __ to give a __. This fragnemntation is called __ because it breaks the bond next to the carbon bearing hte hydroxyl group.
    • carbinol cabon atom
    • resonance-stabilized carbocation
    • alpha cleavage
  28. ;
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Ch 12 Ppt 2
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