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Rotor Synchronized MAS Two‐Dimensional Exchange NMR in Solids. Principles and Applications

 

作者: Zeev Luz,   Hans W. Spiess,   Jeremy J. Titman,  

 

期刊: Israel Journal of Chemistry  (WILEY Available online 1992)
卷期: Volume 32, issue 2‐3  

页码: 145-160

 

ISSN:0021-2148

 

年代: 1992

 

DOI:10.1002/ijch.199200021

 

出版商: WILEY‐VCH Verlag

 

数据来源: WILEY

 

摘要:

AbstractThe principles of the rotor synchronized magic angle spinning (MAS) two‐dimensional exchange NMR, first proposed by Veeman and coworkers are reviewed, with particular emphasis on situations where chemical exchange in solids proceeds in concert with molecular reorientation. Calculations of cross peak intensities as function of the ratio between the chemical shift anisotropy and the spinning rate are presented for several cases. These calculations emphasize the advantage of using slow spinning rates (ωR<ωLΔσ) in such experiments when detailed information about mechanistic pathways in solids is sought. Three applications of the method to solid systems using carbon‐13 NMR are described. These include: (a) Trimethylsulfoxonium iodide, in which the molecules undergo 120°‐jumps about the molecular C3symmetry axis; (b) Tropolone, where the tautomeric hydrogen shift is found to be a consequence of the self diffusion within the crystal lattice, and in general accompanied by molecular reorientation. Here the two‐dimensional pattern is used to obtain information about the various mechanisms of the diffusion process; (c) Bullvalene, where a quantitative analysis of the cross peak intensities as function of the mixing time provides kinetic information on two independent processes, viz. symmetric threefold jumps and a concerted Cope rearrangement‐molecular reorient

 

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