Two-dimensional 13C exchange spectroscopy with off-magic angle spinning

Abstract

Two-dimensional (2D) exchange spectroscopy of solid samples is useful for characterizing ultraslow molecular reorientation. Structural selectivity has been obtained by selective deuteration or slow magic-angle spinning. The disadvantages of both methods, i.e. isotope labelling and poor readability of the sideband exchange spectra, can be avoided if the sample is rapidly spun at an angle different from the magic angle. In the corresponding 2D experiment scaled wideline exchange spectra are observed separately at different isotropic chemical shifts. The technique is illustrated with spectra of isotactic poly(propylene) and oriented poly(oxymethylene). Contributions to the exchange signals from spin diffusion are identified by cross-peaks in the 2D exchange spectrum.