Homo-Nuclear Decoupling

During proton-proton homo-nuclear decoupling, a proton resonance is irradiated during acquisition.  If the irradiated proton has a coupling partner, the partner's multiplet collapses and removes the active coupling. The partner multiplet will still show couplings to other, non-irradiated protons. This allows one to identify the coupling network, i.e., to determine what protons are coupled. Since the partner multiplet is simplified, it can  allow one to measure the J value for any remaining couplings.

The proton spectrum of sucrose at 500 MHz is shown in the lower trace. In the upper spectrum, the 1 proton has been irradiated, collapsing the 2 proton (which is a doublet of doublets from J interactions with the 1 and 3 protons) into a doublet.