Estimation of carbon-carbon bond lengths and medium-range internuclear: Distances by solid-state nuclear magnetic resonance

We describe magic-angle-spinning NMR methods for the accurate determination of internuclear dipole-dipole. couplings between homonuclear spins-1/2 in the solid state. The new sequences use symmetry principles to treat the eff ect of magic-angle sample-rotation and resonant radio frequency fields. The pulse-sequence symmetries generate selection rules which reduce the interf erence of undesirable interactions and improve the robustness of the pulse sequences with respect to chemical shift anisotropies. We show that the pul se sequences may be used to estimate distances between C-13 spins in organi c solids, including bond lengths in systems with large chemical shift aniso tropies, such as conjugated systems. For bond-length measurements, the prec ision of the method is +/-2 pm with a systematic overestimate of the intern uclear distance by 3 +/-1 pm. The method is expected to be a useful tool fo r investigating structural changes in macromolecules.