ABSTRACT
This chapter presents a minimum basic introduction into nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies. The basic physical principles of EPR spectroscopy and NMR spectroscopy are similar. Both methods allow probing with electromagnetic irradiation the energy levels emerging in the molecules when the latter are subjected to an external stationary magnetic field. The EPR spectra of frozen solutions are similar to the EPR spectra of polycrystalline materials. EPR spectroscopy of both liquid and frozen solutions is widely used for mechanistic studies in homogeneous catalysis. The application of NMR spectroscopy to homogeneous catalysis is restricted to measurements in liquid solutions since the NMR spectra of frozen solutions are extremely broad due to chemical shifts anisotropy and direct dipole-dipole and quadrupolar interactions. In liquids, the effect of quadrupolar interactions on the position of NMR resonances is averaged due to diffusional motions, but these interactions effectively induce spin relaxation.
