NMR dipolar echoes in solids containing spin-12 pairs

A model of loosely-coupled spin-$\text{1}\text{2}$ pairs is used to explain the proton NMR dipolar echo behaviour observed in crystalline hydrates. This behaviour is distinctly different from that previously predicted and observed in solids containing single spin-$\text{1}\text{2}$ nuclei and is shown to originate in the differentiation of the intrapair from the interpair dipolar interactions.