Orientation of the unshared electron pair of the nitrogen atom in N-substituted 2,5-dimethyl-4-piperidinones

The axial orientation of the unshared electron pair of the nitrogen atom in cis isomers of N-substituted [R=H, CH3, CH2C6H5, or C(CH3)3] 2,5-dimethyl-4-piperidinones was proven by using the stereospecificity of the direct 13C-13C spin-spin coupling constants, vicinal 13C-1H spin-spin coupling constants, and two-dimensional nuclear-Overhauser-effect spectroscopy (NOESY). © 1989 Plenum Publishing Corporation.