th  - 1987 - 51st ENC Conference

WF54 - POSTERS
2D EXCHANGE NMR IN NON-SPINNING POWDERS
C. Schmidt~ S. Kaufmann~ S. Wefing~ D. Theimer,
B. Bl~mich" and H. W. Spiess~
Max-Planck-Institut f~r Polymerforschung~
Postfach 3148, D-6500 Mainz
Information about molecular motions in isotropic
solids is typically derived from lineshape analyses of
wideline NMR spectra~ Nhile in liquid samples 2D exchange
NMR has become an accepted method. In 2D exchange spectra
some of the information hidden in the lineshapes of 1D
spectra is reencoded into frequency coordinates of
exchange signals, where it is accessible more accurately
and in a model-independent fashion.
We have studied deuteron and C-13 2D exchange NMR
for the characterization of molecular motions in powders
and amorphous solid samples. The deuteron quadrupole
coupling tensor is axially symmetric, so that particu-
larly simple exchange signals result. Discrete jumps are
characterized by elliptical exchange singularities, where
the excentricity of the ellipse is a direct measure of
the jump angle. Diffusive motions result in homogeneous
broadening with.characteristic 2D lineshapes discrimina-
ting different stages of partial diffusion towards the
full diffusion limit. For short mixing times pure
diffusion~ diffusion in connection with discrete jumps,
and pure jump motions can be distinguished.
The 2D exchange experiment can also be performed in
C-13 NMR on selectively labelled compounds. The asymmetry
of the chemical shielding tensor, however~ leads to more
complicated 2D exchange patterns. Experimental and theo-
retical data demonstrate that the wideline 2D exchange
experiment produces a direct image of the jump angle
distribution.
Ref erences:
1) C. Schmidt, S. Wefing~ B. Bl~mich and H.'W. Spiess,
Chem. Phys. Lett. 130, 84 (198b).
2) M. Linder, A. Hbhener and R. R. Ernst~ J. Chem. Phys.
73, 4959 ~1980).