Recoupling of heteronuclear dipolar interactions in solid-state NMR using symmetry-based pulse sequences

We apply symmetry theorems to the problem of heteronuclear dipolar recoupling in the presence of magic-angle spinning in solid-state NMR. Examples are shown in which the 13C NMR signal is acquired while rotor-synchronized pulse sequences with the symmetry R1817 or R1825 are applied to the 1H spins. This allows recoupling of heteronuclear dipolar interactions combined with homonuclear decoupling of the irradiated 1H spins. The structure of the 13C NMR spectrum is sensitive to bond lengths and bond angles. A two-dimensional procedure is described for applications to multiply isotopically labelled systems.