Exocyclic Hydroxymethyl Rotational Conformers of β- and α-d-Glucopyranose in the Gas Phase and Aqueous Solution

Abstract

The intrinsic exocyclic hydroxymethyl rotational surface for β-d-glucopyranose as well as the β−α anomer energy difference for d-glucopyranose has been studied using ab initio quantum mechanical methods including continuum solvation. Relevant stationary points, including rotational transition states, have been characterized by full geometry optimization using the 6-31G(d) basis set for the most stable counterclockwise (cc) overall conformation. Effects of dynamic electron correlation on both the geometric structures and the relative energetics of this system are also explored using Moller−Plesset perturbation theory (MP2 through MP4(SDTQ)) and density functional methods (BLYP). A total of six stationary points, including three minima and three transition states, were identified along the exocyclic rotational surface. All three minima were found to be very close in energy with a final order of GG (0.0) < GT (2.84) < TG (3.05) based on the relative free energy, , determined at the MP4(SDTQ)/6-31G(d)//MP2/6-...