Orbital phase control of the conformations of α- and β-substituted enamines and vinyl ethers

Abstract

The conformational stabilities of the α- and β-substituted enamines and vinyl ethers were predicted by orbital phase theory and confirmed by ab initio molecular orbital calculations. Cyclic interaction significantly occurs among the nonbonding orbital nY for the lone pair on the hetero atom Y (N in the enamines or O in the ethers), the π and π* orbitals of the CC bond, and the σC-H or σ*C-X orbitals on the substituent CH2X. The cyclic -nY-π-σC-H-π*- interaction is favored by the orbital phase continuity in the α-substituted molecules, while the cyclic -nY-π-σ*C-X-π*- interaction is favored in the β-substituted molecules. The most stable conformation was then predicted to be synperiplanar or (pseudo)equatorial in the α-substituted molecules and anticlinical or (pseudo)axial in the β-substituted molecules.