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Answers:

  1. If the magnetic fields of two protons can interact via s- and p- electrons in bonds connecting the two protons directly, or indirectly over additional nuclei, then their energy levels in the external magnetic field of the spectrometer will show additional splittings. Because of that additional transitions with only small differences in energy become possible.
  2. Since these interactions are mediated by bond electrons, this phenomenon is referred to as through-bond spin-spin coupling.
  3. In the most basic case, when only n equivalent protons X are coupling to the proton A, the following relationship exists between the number of coupling protons and the multiplicity MA of the signal dA
    MA = nX + 1
  4. In this case the relative intensities of the lines in various multiplets follow characteristic patterns:
    Multiplicity Relative intensities
    2 1 : 1
    3 1 : 2 : 1
    4 1 : 3 : 3 : 1
    5 1 : 4 : 6 : 4 : 1
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Otherwise try to apply your knowledge in the next excercise.

Draw a schematic NMR spectrum of the molecule R2CH-CH3!

Compare your solution to the correct answer on page 75!