th - 1987 - 51st ENC Conference
th - 1987 - 51st ENC Conference
th - 1987 - 51st ENC Conference
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Tuesday - PM<br />
WF54 - POSTERS<br />
2D EXCHANGE NMR IN NON-SPINNING POWDERS<br />
C. Schmidt, S. Kaufmann, S. Wefing~ D. Theimer~<br />
B. Bl~mich" and H. W. Spiess~<br />
Max-Planck-Institut f~r Polymerforschung~<br />
Postfach 31489 D-6500 Mainz<br />
Information about molecular motions in isotropic<br />
solids is typically derived from lineshape analyses of<br />
wideline NMR spectra~ while in liquid samples 2D exchange<br />
NMR has become an accepted me<strong>th</strong>od. In 2D exchange spectra<br />
some of <strong>th</strong>e information hidden in <strong>th</strong>e lineshapes of 1D<br />
spectra is reencoded into frequency coordinates of<br />
exchange signals~ where it is accessible more accurately<br />
and in a model-independent fashion.<br />
We have studied deuteron and C-13 2D exchange NMR<br />
for <strong>th</strong>e characterization of molecular motions in powders<br />
and amorphous solid samples. The deuteron quadrupole<br />
coupling tensor is axially symmetric~ so <strong>th</strong>at particu-<br />
larly simple exchange signals result. Discrete jumps are<br />
characterized by elliptical exchange singularitiesp where<br />
<strong>th</strong>e excentricity of <strong>th</strong>e ellipse is a direct measure of<br />
<strong>th</strong>e jump angle. Diffusive motions result in homogeneous<br />
broadening wi<strong>th</strong>.characteristic 2D lineshapes discrimina-<br />
ting different stages of partial diffusion towards <strong>th</strong>e<br />
full diffusion limit. For short mixing times pure<br />
diffusion~ diffusion in connection wi<strong>th</strong> discrete jumps,<br />
and pure jump motions can be distinguished.<br />
The 2D exchange experiment can also be performed in<br />
C-13 NMR on selectively labelled compounds. The asymmetry<br />
of <strong>th</strong>e chemical shielding tensor~ however, leads to more<br />
complicated 2D exchange patterns. Experimental and <strong>th</strong>eo-<br />
retical data demonstrate <strong>th</strong>at <strong>th</strong>e wideline 2D exchange<br />
experiment produces a direct image of <strong>th</strong>e jump angle<br />
distribution.<br />
References:<br />
1) C. Schmidt, S. Wefing~ B. Bl~mich and H.~W. Spiess~<br />
Chem. Phys. Left. 130, 84 (198b).<br />
2) M. Linder, A. H~hener and R. R. Ernst~ J. Chem. Phys.<br />
73~ 4959 (1980).