Probing furanose ring conformation by gas-phase computational methods: Energy profile and structural parameters in methyl beta-D-arabinofuranoside asa function of ring conformation

The potential energy surface of methyl beta-D-arabinofuranoside (3) has bee n studied by ab initio molecular orbital (HF/6-31G*) and density functional theory (B3LYP/6-31G*) calculations via minimization of the 10 possible env elope conformers. The partial potential energy surface identified that the global minimum and lowest energy northern conformer was E-2. In the HF calc ulations, E-2 was the most stable southern conformer, while the density fun ctional theory methods identified E-4 as the local minimum in this hemisphe re. Additional calculations at higher levels of theory showed that the B3LY P-derived energies of many of the envelope conformers of 3 are dependent up on the basis set used. It has also been demonstrated that B3LYP/G-31+G**//B 3LYP/6-31G* single point energies are essentially the same as those obtaine d from full geometry optimizations at the B3LYP/6-31+G** level. The norther n and southern minima of the B3LYP/6-31+G** surface are, respectively, the E-2 and E-2 conformers. The B3LYP/6-31G* geometries were used to study the relationship between ring conformation and various structural parameters in cluding bond angles, dihedral angles, bond lengths, and interatomic distanc es.