NMR and DFT study on media effects on proton transfer in hydrogen bonding: concept of molecular probe with an application to ionic and super-polar liquids

Abstract

Media effects of ionic and super-polar liquids on the state of H-bonding were studied by NMR and DFT methods. The proton sharing (positioning) in the H-bond was monitored following the chemical shifts of picolinic acid N-oxide (PANO) used as the molecular probe. The relationships between PANO 1H and 13C chemical shifts and proton position in the O-H...O bridge were calibrated using traditional organic solvents and other H-bond complexes of pyridine N-oxide with acids to increase the H-bond strength. A reliable parameter for H-bond monitoring was proposed. The state of the H-bond in ionic liquid media is largely governed by the dielectric properties of the bulk media. A drastic fall-out of PANO/[BuMePyr][TfO] from the general dielectric scheme built using solvents with increasing dielectric constant (from chloroform to water and culminating with formamide) was observed. On a molecular level this effect indicates that the ionic liquid [BuMePyr][TfO] can act on H-bonded systems as a stimulant of proton transfer. In 'super-polar' media (formamide) the intramolecular H-bond system converts into an intermolecular one forming a neutral H-bond complex of PANO with the formamide molecule.

Protonation of Pyridine Monocarboxylate‐N‐Oxides – Determination of Thermodynamic, Absorbance and Ion Interaction Parameters

“…Most of the quantum chemical calculations reported in the literature focussed on evaluation of intra molecular hydrogen bonding, vibrational spectra and proton dynamics of picolinic acid‐N‐oxide . Nicotinic acid N‐oxide (NANO) and isonicotinic acid‐N‐oxide have been studied to determine the UV, NMR, IR and Raman spectra of their monomers and oligomers.…”

1H and13C NMR study of phase transition and molecular motion in ionic liquids forming lyotropic liquid-crystalline ionogels

“…However, the calculated values of chemical shift anisotropies δ aniso for 1 H as well as for 13 C are much higher than those observed experimentally. As mentioned above, the applied DFT level was checked in many cases [12][13][14] and found to be quite adequate for magnetic shielding calculations. Hence such discrepancies between measured and calculated values of chemical shift anisotropies cannot be attributed to the level of theory.…”

“…The applied approach was checked in various cases earlier [12][13][14] and found to be adequate for this purpose.…”

Cross‐polarization with magic‐angle spinning kinetics and impedance spectroscopy study of proton mobility, local disorder, and thermal equilibration in hydrogen‐bonded poly(methacrylic acid)

“…For the first step (hop), that is, a large amplitude displacement of proton along OH…O bridge, the H‐bond has to be short and strong enough [ 26–28 ] or at least the O…O distance should be short. [ 29 ] The isototactic configuration of PMAA is the most favorable realizing proton conductivity along H‐bond chains.…”