Röntgenkristallstrukturanalyse und Organische Chemie

An introduction into X-ray crystal structure analysis as method to determine the structure of organic compounds is given. In this connection two new methods for phase determination of X-ray reflections of macromolecules are reported. A few specially selected samples of structures are given to demonstrate the efficiency of X-ray crystal structure analysis with regard to the elucidation of stereochemical problems in the field of organic chemistry. The examples of application are heterocyclic organic compounds (cycloaddition products of nitrile-ylides, a stable azomethinimine, a cyanine dyestuff) and biologically relevant molecules (aminoacids of the amatoxins, the main poison of the green deathcup toadstool). The mentioned molecular structures determined by X-ray crystal structure analysis are discussed under the following aspects.

1. Elucidation of constitution, configuration and conformation.
2. Identification and verification of chemical pathways for new classes of compounds.
3. Bond relationships, influence of ring strain and other intramolecular interactions upon bond lengths and angles.
4. The attempt to find general stereochemical principles among related molecules or molecular parts points to the fundamental aspects of these experiments. Generally, the 1,4-diaza-s-trans-1,3-butadiene system, the steric influence of a free electron pair at a double bonded nitrogen and the CF₃-group are studied.
5. Obtaining of initial parameters for quantum mechanical calculations and comparison with theoretical results.
6. With regard to the structure analysis of two amino acid fragments of the amatoxins the configuration of the hydroxylated isoleucines of the amatoxins and the configuration at the chiral SO center of the natural amatoxins and of the synthetic phalloidin sulphoxides are fixed. The configuration at the SO center is decisive for the poisonous effect.