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Solid State NMR

Solution State NMR is now a well established technique used by Chemists worldwide for a variety of purposes. NMR of the solid state, however, is theoretically and practically more difficult and is still in its early years of development. One of the key problems to overcome in solid state NMR is peak broadening caused by both the Chemical Shift Anisotropy (CSA) of the molecule and the dipolar interactions between local spins.

Novel experimental methods have been implemented to imitate the fast molecular tumbling present in solutions (resulting in the averaging out of the dipolar and CSA Hamiltonians). These Include;

  • Magic Angle Spinning (MAS): The sample is spun at high frequencies (kHz range)whilst inclined at the “magic” angle of 54.74 degrees to the vertical.
  •  Combined Rotation And Multi Pulse Spectroscopy (CRAMPS): The physical rotation of the sample is combined with radiofrequency pulses.
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Hydrogen spectra for the Alpha polymorph demonstrating the resolution that can be achieved using 30kHz MAS (black line) and 12.5 kHz CRAMPS (red line).

 

Useful Solid state nmr links

General

Levitt textbook (see website)