A complete 1D and 2D NMR studies of variously substituted 3-azabicyclo[3.3.1]nonan-9-ones

► The 3-azabicycles 1-16 exist in a twin-chair conformation with an equatorial orientation of all substituents. ► Bulkier ethoxy substituents on the ortho position flattened the bonds between C-2/C-4 and C-1/C-5. ► The CO bond of ethoxy preferred to be syn to H-2a/H-4a to avoid the dipole-dipole interaction. ► The H-2a/H-4a are significantly deshielded than H-1/H-5 by their proximity with the ortho-ethoxy groups. ► In 1-methylated compounds, the α-effect is exploited due to methylation on the bridge-head.