13C spin diffusion of adamantane

Two-dimensional exchange spectroscopy of natural abundance 13C–13C spin diffusion in solid adamantane illustrates the influence that 13C–1H dipole–dipole coupling exerts on 13C spin diffusion by determining spectral overlap in the 13C system. 2D 13C spectra were obtained for several values of mixing time τm and compared with spectra calculated in the limit of nearest-neighbor coupling. Good agreement is obtained for short τm, during which the equilibration of neighboring spins dominates. For longer τm, slower spin diffusion that is not acounted for by the simple model is seen; after nearest-neighbor spins equilibrate, communication over larger distances produces further mixing. It is possible to modify spin diffusion rates by altering experimental conditions, e.g., magic-angle spinning, low-power 1H decoupling, or spin locking 13C in the rotating frame during τm.