Conformational Studies by Dynamic NMR. 97. Structure, Conformation, Stereodynamics and Enantioseparation of Aryl Substituted Norbornanes.

The structure of a 1,7,7-triaryl norbornane (compound 3) has been determined by X-ray diffraction and was found essentially equal to that predicted by Molecular Mechanics calculations. Restricted rotation of the aryl groups has been also observed by dynamic NMR spectroscopy in this compound and in a number of analogously substituted norbornanes. The aryl-norbornane bond rotation barriers were measured by line shape analysis of the 13C NMR spectra obtained at temperatures lower than -100 °C and were found to cover the range 6.0 to 7.9 kcal mol-1. An exception was the rotation involving the ortho-anisyl group in compound 5 which occurs near ambient temperature since the corresponding barrier is much higher (14.4 kcal mol-1). In one case (compound 4) configurational enantiomers could be separated by chiral HPLC and the corresponding CD spectra recorded.