| Abstract |
Molecules in solids are not static but they can undergo a whole range of motions; e.g. vibrations, reorientation of functional groups, reorientation of entire molecules and diffusion. Dynamic processes in solids are extremely important for example in energy storing materials. Nuclear magnetic resonance (NMR) is a spectroscopic method, which is very sensitive to local structure in the vicinity of the measured nuclei, and dynamic processes can have an important effect on NMR spectra.
In the last decade a new method, NMR crystallography, emerged. It combines quantum-chemical calculations with experimental NMR spectra to solve the structure of solids. NMR crystallography relies mainly on density functional theory (DFT) calculations and the success of NMR crystallography is based on an incredible precision of NMR parameters calculations using modern computational methods.
The proposed dissertation thesis will study dynamic processes in solids using NMR crystallography. Selected organic and inorganic compounds with interesting dynamic behaviour in crystals will be studied. The student will acquire experimental NMR spectra and perform the quantum-chemical calculations. One example of the studied problems is 5-chlorouracil and 5-bromouracil. Both compounds have a very similar layered structure with a hydrogen bond network resembling the hydrogen bond network in nucleic acids. Both compounds are disordered in the crystal structure. Experimental NMR spectra acquired at variable temperatures will enable to distinguish between static and dynamic disorder (where the molecules undergo a rotation around an axes). The importance of hydrogen bonds and weak hydrogen bonds (with CH hydrogen atom as a donor) for the structure stability will be determined.
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