Origin of J-Coupling

Geminal. Two atoms or functional groups are geminal if they are both bound to the same atom. Geminal atoms or functional groups discussed in the context of NMR spectroscopy are usually but not always the same species. 

The can be measured directly from a given resonance in the H 1-D spectrum if other resonances do not obscure what are called the satellite peaks. Because is 1.1% abundant, 1.1% of the total integrated intensity from the resonance of a carbon-bound H will be split such that two peaks (each 0.55% of the total peak area) will occur approximately equidistant from and on either side of the H- C center peak. One peak will be from H s bound to C s in the a spin state, and the other from H s boimd to in the (3 spin state. The distance (in Hz) between the two satellite peaks is Jch- 

If a spin-VT nucleus is in the a spin state, it will slightly perturb the strength of the applied field felt by its nearby neighbors in the molecule. If the spin-VT nucleus is in the p spin state, there will also be a perturbation of the field felt by its neighbors, but the sign if the p perturbation will be opposite that of the a perturbation. Put another way, if spin A is J-coupled to spin X, then spin A rvill alter spin X s precession frequency such that spin X s near spin A s in the a spin state will be shifted in one direction, and spin X s near spin A s in the p spin state will be shifted in the other direction. Spin A is said to split the resonance arising from spin X because the resonance for spin X is now observed to be split into two equal peaks. 

In contrast to the chemical shift, which varies in direct proportion to the strength of the applied magnetic field, the J-coupling is independent of field. This invariance stems from the fact that the size of the nuclear dipole or quadrupole moment does not vary with the 

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