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3

 For the molecule CH3-CH2-CO-CH2-CH3 you should have found the following answers (If your answer was wrong click on the links for the correct explanations):

  1. Number of signals

    2. The compound has two groups of equivalent protons:
    • the protons of the -CH2-groups and
    • the protons of the CH3-groups.
    Therefore the spectrum contains two resonance signals.
    Wrong answer? Click here!

  2. Chemical shifts

    3. According to the table of expected chemical shift ranges, the signals should appear at:
    • d = 1,9 ... 3,2 ppm for the -CH2-CO-protons,
    • d = 0,6 ... l,9 ppm for the CH3-protons.
    Wrong answer? Click here!

  3. Relative Intensities

    4. In this ketone, there are
    • 4 equivalent -CH2-protons and
    • 6 equivalent CH3-protons.
    Therefore the ratio of the respective resonance signals should be 2 : 3.
    Wrong answer? Click here!

  4. Line splitting due to spin-spin couplings

    5. The spin-spin coupling between the methylene and the methyl protons causes a splitting of the
    • -CH2-signal into a quartett (Intensities 1: 3: 3: 1, or rather 1/4 : 3/4 : 3/4 : 1/4) and of the
    • CH3-signal into a triplett (Intensities 1: 2: 1, or rather 3/4 : 3/2 : 3/4 ).
    Wrong answer? Click here!

  5. Coupling constants of the multiplets

    6. The predicted value for the coupling constant between -CH2- und -CH3-protons is JCH2,CH3 = 6..8 Hz.
    Wrong answer? Click here!
Now try to draw the predicted spectrum of (CH3CH2)2CO!

Compare it to the correct solution!