On the importance of intramolecular hydrogen bond cooperativity in d‐glucose – an NMR and QTAIM approach

Abstract

The idea that hydrogen bond cooperativity is responsible for the structure and reactivity of carbohydrates is examined. Density functional theory and gauge-including atomic orbital calculations on the known conformers of the α and β anomers of d-glucopyranose in the gas phase are used to compute proton NMR chemical shifts and interatomic distances, which are taken as criteria for probing intramolecular interactions. Atom-atom interaction energies are calculated by the interacting quantum atoms approach in the framework of the quantum theory of atoms in molecules. Association of OH1 in the counterclockwise conformers with a strong acceptor, pyridine, is accompanied by cooperative participation from OH2, but there is no significant change in the bonding of the two following 1,2-diol motifs. The OH6 O5 (G-g+/cc/t and G+g-/cc/t conformers) or OH6 O4 (Tg+/cc/t conformer) distance is reduced, and the OH6 proton is slightly deshielded. In the latter case, this shortening and the associated increase in the OH6-O4 interaction energy may be interpreted as a small cooperative effect, but intermolecular interaction energies are practically the same for all three conformers. In most of the pyridine complexes, one ortho proton interacts with the endocyclic oxygen O5. Analogous results are obtained when the clockwise conformer, G-g+/cl/g-, detected for the α anomer, and a hypothetical conformer, Tt/cl/g-, are complexed with pyridine through OH6. Generally, the cooperative effect does not go beyond the first two OH groups of a chain. Copyright © 2017 John Wiley & Sons, Ltd.

Intramolecular O―H⋯O and C―H⋯O hydrogen bond cooperativity in D‐glucopyranose and D‐galactopyranose—A DFT/GIAO, QTAIM/IQA, and NCI approach

“…The interaction energy for the latter, O5–H2py, is unusually low, −7.7 kcal mol −1 , whereas the O5–H6 energy is enhanced and the interatomic distance is reduced (Table ). In contrast, the increase in the O5–H1 interaction energy is associated with a slightly greater distance and is probably due to the higher charge on H1 …”

“…The effect of pyridine complexation of OH1 on the interaction energies in the known conformers of the α and β anomers of GL has been discussed elsewhere . For the fragments, the increase in the O1–H2 energy (about 8 kcal mol −1 ) is much greater than that of O2–H3 (0–0.6 kcal mol −1 ) whereas that for O3–H4 is negligible.…”

“…The results of the complexation of OH1 of the fragments with pyridine follow the same pattern as was observed for the complete conformers of GL (Tables and ) . The increase in the shift of OH1 goes from about 6.5 ppm for GLα‐cc‐1 to 7.3 ppm for GLα‐cc‐4, regardless of the anomer.…”

“…The contributions of additional OH groups on their immediate precursors are always greater than those on more remote OH groups. This amounts to a cooperative effect on the free GL itself, but it has the same characteristics as that seen when the OH1 proton of the counterclockwise GL conformers is complexed with pyridine: the neighbouring group, OH2, participates but more remote groups are hardly affected. Charge distributions in the Tg+/cc/t conformers of both GL anomers, as well as three of the four conformers of α‐GA, reflect 1,3‐diol‐type intramolecular hydrogen bonding (Tables S6, S7, S9, and S10).…”

“…Hydrogen‐bond distances, nuclear magnetic resonance (NMR) shifts, and atom–atom interaction energies for hydrogen‐bonded conformers of 1,2‐diols and 1,3‐diols and their pyridine complexes evidence a cooperative effect on the OH ⋯ OH bond . However, for the most important conformers of GL, there appears to be no cooperativity beyond the anomeric OH group and its nearest neighbour, except in one case where there is a weak interaction with the hydroxymethyl group …”