An extended Hückel molecular orbital approach to the study of the electronic structures and barriers toSyn-Antiinterconversion inSynpurine nucleosides

The total energy and the electronic properties of some syn purine nucleosides have been determined as a function of the rotation angle around the C–N glycosidic linkage. Invariably, the crystallographic coordinates provide a state lying at or very near the minimum on the potential energy curve according to the extended Huckel parametrization here employed. The ribose moiety always carries a net positive charge whereas the base is always negatively charged. Changes in dipole moment magnitudes for the overall structure as well as in net atomic charges are noted upon rotation around the glycosidic linkage indicating that potential functions for polynucleotides may be in error if such changes are ignored.