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.
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.
Faculty of Physics, Vilnius University, Sauletekio, 9, LT-10222 Vilnius, Lithuania. vytautas.balevicius@ff.vu.lt
Vytautas
V
Balevicius
Zofia
Z
Gdaniec
Kestutis
K
Aidas
D003198:Computer Simulation; D006860:Hydrogen Bonding; D052578:Ionic Liquids / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D015335:Molecular Probes / Q000737:chemistry*; D011522:Protons; D012015:Reference Standards
D052578:Ionic Liquids; D015335:Molecular Probes; D011522:Protons