A computational study of methyl alpha-D-arabinofuranoside: Effect of ring conformation on structural parameters and energy-profile

Ab initio molecular orbital calculations at the HF/6-31G* level of theory a nd density functional theory calculations at the B3LYP/6-31G* level have be en carried out on methyl alpha-D-arabinofuranoside (1). All 10 possible env elope forms were constructed and minimized, providing a partial energy surf ace which identified E-3 as the lowest energy north conformer and, dependin g on the level of theory used, either E-2 or E-1 as the southern hemisphere minimum. The southern conformation was the global minimum regardless of th e level of theory. The energy profile identifies pseudorotation through the eastern pathway as the mast favorable. Pseudorotation through the west is higher in energy and similar to inversion through the planar species. The d ependence of structural parameters (i.e., bond distances, bond angles, dihe dral angles, and interatomic distances) on the ring conformation have been determined. Energy profiles based on additional electron correlation and ex tended basis sets with the HF/6-31G* geometries are presented and provide q ualitatively similar results to the B3LYP/6-31G* profile.