In proton-decoupled NMR, radiofrequency irradiation of proton spins averages selected couplings to the nuclei being observed. A common example is a carbon-13 spectrum measured while broadly decoupling hydrogen-1, which collapses carbon-proton multiplets and simplifies the spectrum.
Decoupling does not remove every interaction or make every carbon peak quantitatively comparable. Relaxation and nuclear Overhauser effects can change intensities, while couplings to other nuclei can remain. The notation states the observed and decoupled nuclei explicitly.
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