Chapter 10: Filters for Long-lived Spin Order

Nuclear magnetic equivalence symmetry is a key property in the ability of a molecule to sustain long-lived spin order. In addition, it is an important property in the ability to distinguish NMR signals of long-lived spin order from those due to other types of spin order. This chapter presents a general view of the symmetry properties of long-lived spin order including symmetry under rotations in three-dimensional space. Long-lived spin order is found to be a type of “scalar” spin order, invariant to global rotations of nuclear spin systems. Schemes for filtering scalar order of progressive complexity, and their applications in NMR of long-lived spin order, are then discussed.