High-Resolution1H Multiple-Quantum Spectra in Solids with Strong Dipolar Interactions

1996 ◽  
Vol 120 (2) ◽  
pp. 261-263 ◽  
Author(s):  
Shangwu Ding ◽  
Charles A. McDowell
Keyword(s):  
Multiple Quantum ◽  
Dipolar Interactions ◽  
Quantum Spectra

Introduction

1981 ◽  
Vol 299 (1452) ◽  
pp. 477-477
Keyword(s):  
Dipolar Coupling ◽  
Chemical Shifts ◽  
Exchange Interactions ◽  
Magic Angle ◽  
Multiple Quantum ◽  
Cross Polarization ◽  
Dipolar Interactions ◽  
Viscous Liquids ◽  
Full Interaction ◽  
Radio Frequency Pulses

N.m.r. spectra in solids and viscous liquids are often broadened by dipolar interactions, which are normally so strong that effects due to chemical shifts and the weak scalar couplings are obscured. Means have therefore been sought to obtain high-resolution n.m.r. spectra from solids in ways that remove the broadening effect of dipole-dipole coupling. One approach has been to use elaborate sequences of radio-frequency pulses designed to reduce the dipolar coupling, and a variety of methods have been demonstrated. These methods often reveal not only chemical shifts and exchange interactions, but also the full interaction tensor components of the crystalline state. Another approach has involved very rapid spinning of the sample about the ‘magic angle’, and of course this has also been combined with multiple pulse experiments. Another approach is to exploit multiple-quantum spectra by which the dipolar Hamiltonian is ‘avoided rather than eliminated’, in the words of A. Pines and his colleagues. Finally, there are elegant extensions and developments of the cross-polarization experiments of S. R. Hartmann and E. L. Hahn. All of these techniques can be combined in different ways to tease out the wealth of information in n.m.r. spectra of solid materials.

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