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

Abstract

The conformational stabilities of the a-and b-substituted enamines and vinyl ethers were predicted by orbital phase theory and con®rmed by ab initio molecular orbital calculations. Cyclic interaction significantly occurs among the nonbonding orbital n Y for the lone pair on the hetero atom Y (N in the enamines or O in the ethers), the p and p* orbitals of the C¸C bond, and the r C-H or r* C-X orbitals on the substituent CH 2 X. The cyclic -n Y -p-r C-H -p*-interaction is favored by the orbital phase continuity in the a-substituted molecules, while the cyclic -n Y -p-r* C-X -p*-interaction is favored in the b-substituted molecules. The most stable conformation was then predicted to be synperiplanar or (pseudo)equatorial in the a-substituted molecules and anticlinical or (pseudo)axial in the b-substituted molecules.

Structures and Stabilities of Heteroatom-Substituted Disilenes and Related Compounds: Four-Center π Systems

“…The total energies of the cis (or cisoid) isomers relative to those of the trans (or transoid) isomers are listed in Table . Generally, the orbital-phase continuity of terminal atoms in the highest occupied molecular orbital (HOMO) determines the relative stability of the isomers . The orbitals in phase stabilize and those out of phase destabilize the cis isomers via through-space interaction.…”