heteronuclear multiple bond coherence gradient-selected heteronuclear multiple bond coherence CHMO:0000602 gradient-selected HMBC A type of heteronuclear NMR spectroscopy where pulsed-field gradients are used and a second frequency dimension is employed to disperse the signals and reveal correlations between protons and nuclei which are 2–3 bonds removed. GHMBC gradient heteronuclear multiple bond coherence gHMBC