Proton nuclear magnetic resonance (proton NMR, hydrogen-1 NMR, or ¹H NMR) is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the structure of its molecules. In samples where natural hydrogen (H) is used, practically all the hydrogen consists of the isotope ¹H (hydrogen-1; i.e. having a proton for a nucleus). A full ¹H atom is called protium.