Association of symmetrical alkane diols with pyridine: DFT/GIAO calculation of 1 H NMR chemical shifts

2018

Self Cite

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.

Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

2018

Self Cite

“…Intramolecular OH ... OH bonds in carbohydrate derivatives (1,2‐diols, 1,3‐diols and amido‐alcohols) are strengthened by intermolecular complexation with pyridine, a strong hydrogen bond acceptor . The already enhanced NMR shift of the donor OH proton in hydrogen‐bonded conformers of 1,2‐diols and a 1,3‐diol is further increased if pyridine is complexed with the donor proton of the acceptor OH group: OH ... OH ... py . This enhancement is associated with a decrease in the distance between the intramolecular donor proton and the acceptor oxygen.…”

Section: Introductionmentioning

confidence: 99%

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

Joubert

2017

Self Cite

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.

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

2019

Self Cite

Hydrogen-hydrogen C─H … H─C bonding between the bay-area hydrogens in biphenyls, and more generally in congested alkanes, very strained polycyclic alkanes, and cis-2-butene, has been investigated by calculation of proton nuclear magnetic resonance (NMR) shifts and atom-atom interaction energies.Computed NMR shifts for all protons in the biphenyl derivatives correlate very well with experimental data, with zero intercept, unit slope, and a root mean square deviation of 0.06 ppm. For some congested alkanes, there is generally good agreement between computed values for a selected conformer and the experimental data, when it is available. In both cases, the shift of a given proton or pair of protons tends to increase with the corresponding interaction energy. Computed NMR shift differences for methylene protons in polycyclic alkanes, where one is involved in a very short contact ("in") and the other is not ("out"), show a rough correlation with the corresponding C─H … H─C exchange energies. The "in" and "in,in" isomers of selected aza-and diazacycloalkanes, respectively, are X─H … H─N hydrogen bonded, whereas the "out" and "in,out" isomers display X─H … N hydrogen bonds (X = C or N).Oxa-alkanes and the "in" isomers of aza-oxa-alkanes are X─H … O hydrogen bonded. There is a very good general correlation, including both N─H … H─Y (Y = C or N) and N─H … Z (Z = N or O) interactions, for NH proton shifts against the exchange energy. For "in" CH protons, the data for the different C─H … H─Y and C─H … Z interactions are much more dispersed and the overall shift/exchange energy correlation is less satisfactory.