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Schlagwörter:
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Zusammenfassung:
Deuterium 2D exchange nuclear magnetic resonance (NMR) spectroscopy was
used to elucidate the detailed mechanisms of the dynamic processes in solid
bullvalene. The measurements were performed in the temperature range of −73
to 10 ˜ on a deuterated single crystal with the magnetic field parallel to the
monoclinic plane where the four molecules in the unit cell are magnetically
equivalent. In agreement with earlier carbon−13 and deuterium NMR studies,
two independent processes were identified: symmetric threefold jump and valence
bond isomerization (Cope rearrangement) combined with molecular reorientation.
The latter process can proceed in the crystal by nine different pathways,
characterized by specific cross peak patterns in the 2D spectrum. Due to the
low symmetry at the crystallographic sites of the bullvalene molecules the Cope
rearrangement/reorientation process may proceed with different rates along the
different pathways. Analyses of the experimental results show that only four
pathways are actually active with approximately equal rates
