Konfigurations- und Konformationsanalyse mit Hilfe der Protonenspinresonanz – dargelegt am Beispiel der Steroide

Abstract

Among the physical means for the determination of the configuration and conformation of molecules proton magnetic resonance spectroscopy takes a prominent place. Steroids of known structure are in many respects ideal substances for finding the dependence of the two most important quantities in NMR spectroscopy – the chemical shift and the nuclear spin-spin coupling constant – upon the structure and geometry of a molecule. With the help of empirically determined correlations between these quantities the configuration and conformation of steroids and non-steroidal compounds of unknown structure may be determined.
The physical causes of the additional chemical shifts of the angular methyl protons due to substituents are discussed and it is shown how these shifts may be used for the elucidation of the configuration and even conformation of the steroids.
A careful determination of spin-spin coupling constants allows the evaluation of the dihedral angle between vicinal hydrogen atoms. This relationship is one of the most powerful aids in a conformational study. As an application the analysis of 11α- and 11β-bromo-12-ketocholanic acid is given.