Fatemeh Delshad - Department of Chemistry, Arak Branch, Isla mic Azad University, Arak, Iran

The saturated heterocyclic compounds comprise a large segment of organic and inorganic chemistry and are quite widespread in nature (e.g., in alkaloids, carbohydrates, plant growth regulators, etc.), the knowledge about the impacts of the stereoelectronic, steric and electr ostatic interactions on the conformational properties of heterocyclic compounds is of very general interest. In ۱۹۹۱, Renaued examined the reactivity of radicals derived from thiacyclohexane ۱ -oxide with the sulfinyl group in the axial and equatorial positions. While preferential radical reactionsyn to the S=O bond in the former was explained in steric terms, the high stereoselectivity observed for the deuteration of the latter was rationalized as the result of a stereoelectronic effect orienting the attack at the radical center anti to the lone pair of the S-atom (see Scheme ۱).۱Altho ugh the im portance of the hyperconjugative interactions in the reactivity of radicals derived from thiacyclohexane ۱-oxide (۱) has mentioned,۱ there is no published experim ental or quantitative theoretical data about the donor-acceptor delocalization effects on the structuraland configuration al properti es of radic als derived from thiacyclohexane ۱-oxide (۱) and selenacyclohexan e ۱-oxide (۲ ). In this w ork, the contributions of the total dipole mom ents, steric effects and the anomerc effect (AE ) associate d with the electron delo calization o n the configurational an d structural properties of radicalss ۱ and ۲ w ere investig ated by mea ns of molecular orbital (ROHF/۶ -۳۱G*) based method and natural bond orbital ( NBO) interpretation (see scheme ۱). ۲-۴