NMRactive

NMRactive refers to nuclei that are detectable by nuclear magnetic resonance (NMR) spectroscopy. In this context, a nucleus is NMR-active if it possesses a nonzero nuclear spin and a nonzero magnetic moment, allowing transitions between spin states in a magnetic field to be induced and observed. The observed resonance depends on the nucleus’s gyromagnetic ratio and the strength of the applied magnetic field.

Key features of NMR-active nuclei include their spin quantum number (I) and natural abundance. NMR-active nuclei with spin 1/2, such as 1H, 13C, 15N, 19F, and 31P, typically produce sharp, easily detectable signals. Nuclei with higher spins (I > 1/2), like 14N or 2H, can exhibit broader resonances due to quadrupolar interactions, often complicating spectra. Natural abundance strongly influences sensitivity; for example, 1H is nearly 100% abundant, whereas 13C is about 1.1%, and 15N around 0.37%. Some nuclei, like 17O, are NMR-active but extremely low in natural abundance, requiring enrichment for practical measurements.

Common NMR experiments exploit different NMR-active nuclei. Proton (1H) NMR is widely used for organic structure analysis, while 13C NMR provides carbon framework information. Other nuclei such as 15N, 19F, and 31P appear in specialized experiments for biomolecules, materials science, and phosphorus or fluorine-containing compounds. NMR-active isotopes can be further studied with multinuclear, two-dimensional, or dynamic techniques, and may be enhanced by methods like isotopic labeling or hyperpolarization to improve sensitivity.

In summary, NMRactive nuclei are those with nonzero spin and magnetic moment that enable NMR detection, driving the broad use of NMR spectroscopy across chemistry, biology, and materials science.