Conformational analysis. Part 17. An NMR and theoretical investigation of the conformation of bicyclo[5.2.1]decane-2,6-dione

Abstract

The conformation of bicyclo[5.2.1]decane-2,6-dione in solution has been investigated by molecular modelling and the lanthanide-induced shift (LlS) technique. Of the five possible conformers two were eliminated due to their large calculated steric energy and a third ‘twist’ conformer due to the observed symmetry in the ¹³C NMR and the ¹H NMR spectra. The remaining exo and endo conformers were calculated as having an energy difference of 1.5 kcal mol^–1. However, MNDO calculated the endo form as the more stable in contrast to MM2 and COSMIC which gave the reverse order. The LIS investigation was in agreement with a lanthanide monodentate complex bound to the exo form only confirming the MM2 and COSMIC calculations.