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

Abstract

Density functional theory calculations are used to compute proton nuclear magnetic resonance (NMR) chemical shifts, interatomic distances, atom-atom interaction energies, and atomic charges for partial structures and conformers of α-D-glucopyranose, β-D-glucopyranose, and α-D-galactopyranose built up by introducing OH groups into 2-methyltetrahydropyran stepwisely. For the counterclockwise conformers, the most marked effects on the NMR shift and the charge on the OH1 proton are produced by OH2, those of OH3 and OH4 being somewhat smaller. This argues for a diminishing cooperative effect. The effect of OH6 depends on the configuration of the hydroxymethyl group and the position, axial or equatorial, of OH4, which controls hydrogen bonding in the 1,3-diol motif. Variations in the interaction energies reveal that a "new" hydrogen bond is sometimes formed at the expense of a preexisting one, probably due to geometrical constraints. Whereas previous work showed that complexing a conformer with pyridine affects only the nearest neighbour, successive OH groups increase the interaction energy of the N⋯H1 hydrogen bond and reduce its length. Analogous results are obtained for the clockwise conformers. The interaction energies for C-H⋯OH hydrogen bonding between axial CH protons and OH groups in certain conformers are much smaller than for O-H⋯OH bonds but they are largely covalent, whereas those of the latter are predominantly coulombic. These interactions are modified by complexation with pyridine in the same way as O-H⋯OH interactions: the computed NMR shifts of the CH protons increase, the atom-atom distances are shorter, and interaction energies are enhanced.

Cooperativity in alkane‐1,2‐ and 1,3‐polyols: NMR, QTAIM, and IQA study of O─H…OH and C─H…OH bonding interactions

“…The variations of NMR shifts, atom–atom distances, and interaction energies are less regular than for the 1,3‐polyols, no doubt because the arrays are not rectilinear. These results shed no light on the question of cooperativity between intramolecular C─H … OH interactions and intermolecular hydrogen bonding with pyridine in α‐ d ‐glucopyranose and α‐ d ‐galactopyranose 46 . In the present case, such interactions are small and reduced by intermolecular hydrogen bonding, whereas they are increased in the pyranoses.…”

“…Quasi‐linear alkane‐1,3‐polyols based on the tG'Gg' motif illustrate very clearly several features expected of O─H … OH hydrogen bond cooperativity and intermolecular hydrogen bonding with pyridine. Up until now, the only BCP for a 1,2‐diol motif was reported for the pyridine complex of the G–g+/cl/g– conformer of α‐ d ‐glucopyranose 46 . The present work establishes that BCPs, albeit unstable and basis set‐dependent, are common in acyclic alkane‐1,2‐polyols, from butane‐1,2,3,4‐tetrol, 10 , onwards, and their pyridine complexes, from propane‐1,2,3‐triol, 9 , onwards.…”

“…Spectroscopic studies and theoretical calculations confirm that structures with chains of potentially hydrogen‐bonded OH groups are the most stable 28–44 . However, cooperativity between O─H … OH hydrogen bonds in the 1,2‐diol and 1,3‐diol motifs of pyranoses is irregular and not necessarily reciprocal 45, 46 . Klein claims that there is negative cooperativity in glucopyranose, 47 and other authors consider that the driving forces for conformational preferences are steric effects, electrostatic repulsion, and hyperconjugation 48, 49 .…”

Relationships between NMR shifts and interaction energies in biphenyls, alkanes, aza‐alkanes, and oxa‐alkanes with X─H…H─Y and X─H…Z (X, Y = C or N; Z = N or O) hydrogen bonding

“…For the sake of consistency with previous work, gas‐phase energies were optimised by density functional theory calculations at the Becke, three‐parameter, Lee–Yang–Parr (B3LYP)/6‐311+G(d,p) level and proton NMR shifts were computed by the GIAO model with the Perdew, Burke, and Ernzerhof (PBE0) functional and the correlation‐consistent polarised valence‐only triple‐zeta (cc‐pVTZ) basis set. All structures were analysed in terms of the QTAIM, and noncovalent interaction (NCI) plots were used to highlight interactions between atoms .…”

“…The strength of a X─H … Z hydrogen bond depends on the acidity of the donor and the basicity of the acceptor, the strongest and, therefore, the most common, hydrogen bonds involving systems where X and/or Z are/is O and/or N. However, the bond strength depends on the hybridisation of these atoms, and other combinations of atoms are conceivable . The C─H … O hydrogen bond is common in the solid state and contributes to the 3D structure and reactivity of proteins and other biomolecules, as well as occurring in sugars and myo ‐inositol . Most of the literature on such hydrogen bonds involves a carbonyl group acceptor.…”