Achievements of multiple-pulse n.m.r

Abstract

A survey is given of the achievements of multiple-pulse n.m.r. with regard to measurements of shielding tensors of protons. The need to investigate single crystals rather than powder samples is stressed. It is useful to consider separately protons in hydrogen bonds and protons bonded directly to carbon atoms. While for the former group of protons there is now a wealth of experimental shielding data, measurements of shielding tensors of protons from the latter group are still difficult and scarce. Symmetry arguments applied to some available data show that the measurable shielding tensors are substantially influenced by the crystal lattice and do not directly reflect molecular properties. Several implications of this fact are discussed. It is pointed out that continuation of multiple-pulse n.m.r. calls for a new kind of motivation. The study of molecular motions in solids through site-specific spin relaxation measurements may become a new area of interest and activities for multiple-pulse n.m.r.