Balevicius, Vytautas ; Maršalka, Aru̅nas ; Klimavičius, Vytautas ; Dagys, Laurynas ; Gdaniec, Maria ; Svoboda, Ingrid ; Fuess, Hartmut (2018)
NMR and XRD Study of Hydrogen Bonding in Picolinic Acid N-Oxide in Crystalline State and Solutions: Media and Temperature Effects on Potential Energy Surface.
In: The Journal of Physical Chemistry A, 122 (34)
doi: 10.1021/acs.jpca.8b05421
Artikel, Bibliographie

Kurzbeschreibung (Abstract)

Solvent and temperature effects on H-bonding in crystalline picolinic acid N-oxide (PANO) and in solutions were studied by NMR (H-1 MAS and H-1-C-13 CP/MAS) and X-ray diffraction (XRD) methods. The single-crystal XRD experiments on beta-polymorph were carried out at 105 and 299 K. C-13 chemical shifts of PANO pyridine ring carbons were chosen as an effective diagnostic tool for the H-bond sensing. The crystal field in PANO forces the proton displacement from donor to acceptor atoms much stronger than the solvent reaction field, including that created by the most polar solvents. NMR and XRD data for crystalline PANO do not confirm any H-bond geometry changes in the studied temperature range. On the contrary, a considerable contraction of r(O-H) bond was observed for PANO in acetonitrile (ACN) solution upon heating. The relative contraction of r(O-H) bond with respect to R(O center dot center dot center dot O) perfectly fits the global dielectric scheme deduced for a vast set of common solvents and the dependence of the dielectric permittivity of ACN on temperature. The subtle H-bond changes can be explained by the temperature dependence of the shape of potential energy surface in the liquid state. Both factors, temperature and dielectric permittivity, are comparable in triggering this effect.

Frage zum Eintrag

Redaktionelle Details anzeigen