The study of conformational changes in 4,5-disubstituted phenanthrenes by nuclear magnetic resonance spectroscopy

Abstract

The 4,5-disubstituted phenanthrenes exist in chiral non-planar conformations; for substituents containing prochiral protons or groups of protons, the interconversion of enantiomeric conformations may be studied by nuclear magnetic resonance spectroscopy. Suitable substituents for this type of study are shown to include –CO₂Et, –CO₂·CHMe₂, –CO₂·CH₂Ph, and –CH₂·O·CO·CH₃ groups. Activation parameters for conformational inversion have been obtained. These results show that the acetoxymethyl group is more effective than the alkoxycarbonyl group in preventing planarity of the phenanthrene system. The relationship between these results and those results obtained by other workers, using polarimetric methods, is discussed.