Orbital phase control of the conformations of alpha- and beta-substituted enamines and vinyl ethers

The conformational stabilities of the alpha- and beta-substituted enamines and vinyl ethers were predicted by orbital phase theory and confirmed by ab initio molecular orbital calculations. Cyclic interaction significantly oc curs among the nonbonding orbital ny for the lone pair on the hetero atom Y (N in the enamines or O in the ethers), the pi and pi* orbitals of the C=C bond, and the sigma(C-H) Or sigma*(C-X) orbitals on the substituent CH2X. The cyclic -n(Y)-pi-sigma(C-H)-pi*- interaction is favored by the orbital p hase continuity in the a-substituted molecules, while the cyclic -n(Y)-pi-s igma*(C-X)-pi*- interaction is favored in the beta-substituted molecules. T he most stable conformation was then predicted to be synperiplanar or (pseu do)equatorial in the alpha-substituted molecules and anticlinical or (pseud o)axial in the beta-substituted molecules.