Festkörper-NMR-spektroskopische Untersuchungen an Quadrupolkernen : der Kern Lithium-7 als Struktursonde

In this thesis several organolithium compounds were investigated by Solid-State-NMR-Spectroscopy. The systems were charactericed by 6-Li-CP/MAS-NMR-, 13C-CP/MAS-NMR- and 29-Si-CP/MAS-NMR-spectra.
The focus was on the interpretation of the 7-Li-MAS-NMR-spectra from which the quadrupolar parameters can be determined.
An empirical linear correlation was found between the quadrupolar coupling constant and the C-Li-C-angle present in all investigated systems. This is in good aggreement with former results for lithium amids. By simple
considerations about the electronegativity of the involved atoms and ab-initio-calculations it was shown that the magnitude of the quadrupolar coupling constant can be attributed to the different charge separation between
lithium and its bonding partners. The charge separation between lithium and nitrogen is larger than that between lithium and carbon. This will lead to a larger value for the electric field gradient and the quadrupolar coupling
constant in the case of the N-Li-bond. The fact that the carbon and the nitrogen systems display the same slope is due to the fact that the angular dependence is governed by purely geometrical factors.
The influence of electronical effects on the C-Li-bond was discussed for alkylsubstituated phenyllithium derivates. There was also found a systematic relationship between the asymmetry parameter and the structural angle X-Li-X (1+cos(alpha)).
Further parameters that can be derived from 7-Li-MAS-NMR-spectra are the anisotropy of the chemical shift and the dipolar coupling constant. They allow conclusions about periodical arrangements in the cristall lattice of the compounds.
Finally experimentally derived values of the quadrupolar parameters were confirmed by ab-initio-calculations on the measured organolithium systems.