NMR of quadrupole nuclei in organic compounds

Abstract

General aspects of nuclear magnetic resonance (NMR) of quadrupole nuclei in organic solids, including theoretical background on quadrupole interactions and analysis of the characteristic line shapes that arise from quadrupole and/or chemical shift interactions, are described. Two theoretical approaches for spectral simulations, the perturbation method, and the direct diagonalization method, are discussed with examples of 17O (I = 5/2), 33S (I = 3/2), and 79/81Br (I = 3/2) solid-state NMR analysis of organic compounds, as well as some examples of inorganic compounds with larger quadrupole interactions. When the magnitude of the quadrupole interactions is smaller than that of the Zeeman interactions, the perturbation method, in which equations can be definitively obtained to express the first- and second-order quadrupole interactions under static or magic-angle spinning conditions, is applicable. Otherwise, the direct diagonalization method, in which the combined Zeeman and quadrupole Hamiltonian is numerically calculated to derive probabilities for each transition, must be applied for spectral simulations. Several experimental techniques used to obtain NMR spectra broadened by large quadrupole interactions are briefly described.