three-dimensional nuclear magnetic resonance spectroscopy heteronuclear three-dimensional nuclear magnetic resonance spectroscopy CHMO:0001072 heteronuclear 3D NMR Any type of nuclear magnetic resonance spectroscopy in which three independent frequency dimensions are employed for the correlation and dispersal of signals. Each signal is described by three frequencies, arising from a combination of protons and heteronuclei, thus effecting the distribution of signals within a cube.