SEP 19 2014.
Web of Science Citations:
Four alpha- and three beta-isomers of the D-glucose were optimized in gas phase using ab initio (MP2) and DFT (omega B97X-D) methods, both using the aug-cc-pVDZ basis set. While earlier works suggest that the orientation of the hydroxyl groups is due to intramolecular hydrogen bonds (H-bonds), the present study reveals that most H-bonds forming five-membered rings are either weak or even do not exist. The quantum theory of atoms in molecules (QTAIM) analysis showed only a few cases of H-bond in D-glucose, particularly for those H-bonds forming six-membered rings, while the non-covalent interactions (NCI) analysis indicated that most intramolecular H-bonds are not strong enough to justify the counter-clockwise arrangement of the OH center dot center dot center dot O chains. Natural bond orbital analysis supported the findings obtained from QTAIM and NCI analyses and indicated that the anomeric effect for D-glucose in the gas phase is governed by a balance of steric, electrostatic, and hyperconjugative interactions. (C) 2014 Elsevier Ltd. All rights reserved. (AU)