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Solid-State NMR Studies of the Guest Molecules in Urea Inclusion Compounds

Xiaorong Yang

ISBN 978-3-8325-1533-1
197 pages, year of publication: 2007
price: 40.50 €
This thesis work deals with the investigation of the structural and dynamic properties of various guest species in urea inclusion compounds. Urea inclusion compounds are widely used in chemical analyses and syntheses. Studies of the molecular properties of the guest and host components are therefore of intrinsic scientific interest. Solid-state NMR spectroscopy is particularly suitable for the evaluation of the guest dynamics as well as the structural properties in such materials.

The molecular behavior (dynamics, molecular order) of ?, ?-dibromoalkanes/urea inclusion compounds (CnH2nBr2, n = 6, 10, 11) with different selectively deuterated guest components was studied via solid-state 2H NMR spectroscopy, comprising variable-temperature line shape studies, spin-lattice and spin-spin relaxation experiments. In addition, the conformational properties were probed by high resolution solid-state 13C and 1H NMR experiments. For the long-chain guest systems (n = 10, 11), the guest dynamics at best can be described by the presence of overall reorientations around the channel axis (modeled by a non-degenerate jump motion) along with chain fluctuations. For the dibromohexane/urea inclusion compound, the guest species exclusively exist in distinct gauche conformations, which undergo exchange with rate constants that match the NMR time-scale. For comparison, the molecular properties of 1-bromodecane in urea have been studied as well. Both the molecular order and dynamics can be described in quite the same way as found for 1, 10-dibromodecane or 1, 11-dibromo- undecane in urea.

Furthermore, this work reports on 1H and 13C CP/MAS NMR studies on urea inclusion compounds with various types of guest species (n-alkanes, alkane derivatives of different chain lengths). These studies include high-speed MAS experiments as well as T1? and T1 relaxation experiments. High resolution 1H and 13C spectra manifest that the guests in urea channels are of high mobility. From the T1? data, the motion of the guest on the microsecond time scale might be explained by chain fluctuations and lateral motion and the interaction between the guest and host is confirmed.

Keywords:
  • Solid-State NMR
  • Inclusion Compounds
  • Dynamic NMR
  • Guest-Host System
  • Relaxation

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