Abstract
Recoupling strategies for anisotropic interactions enable the investigation of molecular structure, order and dynamics in a sensitive and site‐specific fashion by solid‐state NMR spectroscopy. Whereas magic‐angle spinning (MAS) efficiently averages anisotropic interactions and enhances spectral resolution, recoupling pulse sequences selectively restore certain parts of rotor‐modulated dipole–dipole couplings or chemical shift anisotropies (CSA). More specifically, it is possible to recouple either the ω~R~‐ or the 2ω~R~‐modulated terms of an interaction Hamiltonian, which exhibit different orientation dependencies and, in this way, provide a means of distinguishing whether the observed NMR spectra are affected by molecular motion or by molecular orientation. Sideband patterns generated by reconversion rotor encoding allow for a precise and selective determination of coupling constants and anisotropies, which contain site‐specific information on structure, orientation and/or dynamics of individual molecular segments. Corresponding recoupling schemes are presented in a common context, and the possibilities of exploiting these effects for the determination of order parameters of oriented materials, such as oriented polymer chains or extruded fibres of a discotic mesogen, are discussed. The obtained orientational order parameters are compared to results from two‐dimensional wide angle X‐ray scattering (WAXS).