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77 |
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For the prediction of the idealized line spectrum of, e.g.,
R2CH-CH3, it is answer the following questions
based on the formula of the molecule (You can find a short summary
here):
- Number and type of groups of equivalent protons
(This has been covered here)
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in this example: |
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a) |
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>CH- |
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b) |
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-CH3 |
- relative position of the signals in the NMR spectrum
(chemical shifts have been covered here)
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in this example: |
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a) |
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d = 1.4 ... 2.1 ppm |
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b) |
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d = 0.9 ... 1.9 ppm |
- relative intensities of the signals
(That's been covered there)
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in this example: |
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a) |
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1 |
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b) |
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3 |
- Multiplicity of the line splitting and the intensities
of the individual lines (This line of thought has been pursued
starting on page 74)
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in this example: |
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a) |
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M = 4 (Quartet), I = 1 : 3 : 3 : 1 |
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b) |
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M = 2 (Doublet), I = 1 : 1 |
Please note:
Since the relative intensity of the entire quartet a) is
Irel = 1, (it is caused by a single proton!),
the ratios of the individual lines of the quartet are
1/8 : 3/8 :
3/8 : 1/8 (Sum of the
individual lines = 1!)
In the case of the doublet with the total intensity Irel = 3
(three protons!) the ratio of the relative intensities is
3/2 : 3/2!
Now draw the idealized line spectrum for
R2CH-CH3!
as well as for:
| R2CH-CH2R' |
R2CH-CHR2' , |
R2CH-CR3' . |
In the process make sure to write down all the intermediate results,
as shown for step 1 - 4 of our example.
When you are done, compare your answers with our
solution!
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