ROLE OF GEOMETRICAL RELAXATION IN SOLUTION OF SIMPLE MOLECULES EXHIBITING ANOMERIC EFFECTS

The conformational equilibria in the gas phase and in solution of dime thoxymethane (DMM), MeO-C(H-2)-OMe, and dimethoxyethane (DME), MeO-C(H Me)-OMe, have been studied by means of quantum-chemical calculations. The influence of the anomeric effect on these equilibria and their int erconversion processes has been investigated. Solvent effects have bee n described using the continuum cavity model of Nancy's group. Geometr y optimizations have been performed in both gas-phase and solution med ia (water permittivity was used). For DMM, three stable conformers exi st, but for DME the potential energy surface in solution shows a new m inimum which corresponds to a fourth stable conformer. Energy profiles corresponding to rotation around the C-OMe bond, for interconversion of alpha- and beta-anomers, have been calculated for processes in the gas phase and in solution. One-electron and polyelectron population an alyses in terms of the natural hybrid orbitals of Weinhold have been p erformed to understand the evolution of the electronic structure with torsion about the C-O bonds.