Tritium Nuclear Magnetic Resonance Spectroscopy

Abstract

Tritium has a spin quantum number I = 1/2 and so is a suitable nuclide for high resolution NMR observation. Its essential nuclear magnetic properties are discussed, as well as its sensitivity to NMR detection. Also discussed are the relaxation characteristics of the 3H nucleus, spectrometer operating conditions, the chemical shifts of 3H in compounds, referencing, isotope effects, and coupling constants. The quantitation of 3H NMR spectra is considered, along with the use of coupled spectra, of resolution enhancement, and of proton spin-decoupled spectra. The significance of nuclear Overhauser effects in these contexts is described. The wide applicability and usefulness of 3H NMR spectroscopy for the investigation of tritium-labeled compounds, reaction products, and metabolites is illustrated with examples. Tritium has a radioactive nucleus which is a β-emitter, so that precautions are necessary in handling and using tritium-labeled compounds, but these safety measures are not onerous and are easily reduced to a simple standard routine. With this routine, 3H NMR spectroscopy is a safe, convenient, and direct method for establishing the positions of tritium label in compounds and of giving the relative amounts in each position. The method will also provide stereochemical information. Being rapid and non-destructive, it compares extremely favourably with the tedious methods of stepwise chemical degradation and counting hitherto used.