Magic angle, spin exchange

As a consequence of restricted internal mobility in molecules in the crystalline state, nuclei in different conformation environments, but identical in other respects, can produce different signals in 13C cross polarization, magic angle spinning (CPMAS) solid-state NMR. This analysis is not necessarily limited to crystalline regions, since signals of different conformations are resolved if the exchange is slow with respect to the time scale of the NMR experiment. 

In summary, for this area to move forward, methods need to be introduced to provide information additional to 2H lineshapes when studying more complex systems. Calculations such as those just described are one real possibility experimental possibilities include use of magic-angle spinning 2H NMR, and using the full anisotropy of 2H 7j measurements and 13C NMR. A very nice illustration of the use of several different techniques in a motional study examined the slow alkane motions in a urea/alkane inclusion compound via 2H relaxation measurements, selective inversion experiments and two-dimensional 2H exchange.125... 

B. E. Hanson, M. J. Sullivan, R. J. Davis, Direct Evidence for Bridge Terminal Carbonyl Exchange in Solid Dicobalt Octacarbonyl by Variable-Temperature Magic Angle Spinning C-13 NMR-Spectroscopy. J. Am. Chem. Soc. 1984, 106, 251-253. 

Szeverenyi, N. M., Sullivan, M. J. and Maciel, G. E. (1982). Observation of spin exchange by two-dimensional Fourier transform carbon-13 cross- polarization— magic angle spinning. / Magn. Reson., 47,462-75. [141]... 

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