Theoretical and spectroscopic studies on the conformational equilibrium of 9-oxabispidines in solution

► DFT calculations on the conformational behavior of 2-endo-substituted bispidines and 9-oxabispidines were done. ► In both substance classes, double chair conformers are energetically strongly favored. ► This effect is even more pronounced in the 9-oxabispidines. ► 1H NMR investigations on several 9-oxabispidines confirm the dominance of the double chair conformers in solution. ► No evidence for noticeable populations of boat-chair conformers was found.