When one nucleus is influenced by another nucleus with spin quantum number I
0, the two nuclei are said to be coupled, both will show 2 lines instead of 1 line for each nucleus.
0, the two nuclei are said to be coupled, both will show 2 lines instead of 1 line for each nucleus.
The reason is that the field caused by Hx can be parallel or antiparallel so the Ha can experience not only the applied field but also combination of both fields. One signal absorbs at higher field (if Hx is parallel) and one signal absorbs at lower field (if Hx is antiparallel). The two lines are observed for each nucleus. This is called spin-spin splitting. The signal of Ha is split into 2 peaks (doublet) because there is spin-spin coupling between nonequivalent protons (Ha and Hx).
In order to obtain the signals, the B0 will be adjusted to maintain the resonance conditions, either lower or higher field than without Hx. Each peak of the doublet has nearly equal area and is half in the absence of Hx because the population of Ha in the two spin states are nearly equal according to the Boltzmann Distribution. - Since Ha and Hx is split by each other, the distance between 2 lines of both Ha and Hx signals is equal. - If the two nuclei are only neighbors, then their signals are 2 lines (doublet).
The number of line splitting can be depicted by using the following equation;
multiplicity = 2nI + 1, where n is no. of neighboring protons.
nuclei
|
I
|
multiplicity
|
1H
|
1/2
|
n + 1
|
2H and 14N
|
1
|
2n + 1
|
35Cl
|
3/2
|
3n + 1
|
Since the spin quantum no. (I) of 1H is 1/2, therefore,
multiplicity = 2n + 1
Consider these examples,
Splitting patterns for a proton with 0, 1, 2, and 3 equivalent neighboring protons
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