19F Single-Quantum and 19F−33S Heteronuclear Multiple-Quantum Coherence NMR of SF6 in Thermotropic Nematogens and in the Gas Phase
| Autor: | Henri Tervonen, Jani Saunavaara, Jukka Jokisaari, L. Petri Ingman |
|---|---|
| Rok vydání: | 2006 |
| Předmět: |
Analytical chemistry
Nuclear magnetic resonance spectroscopy Thermotropic crystal Surfaces Coatings and Films Sulfur hexafluoride NMR spectra database chemistry.chemical_compound chemistry Heteronuclear molecule Residual dipolar coupling Liquid crystal Kinetic isotope effect Materials Chemistry Physical and Theoretical Chemistry |
| Zdroj: | The Journal of Physical Chemistry B. 110:16232-16238 |
| ISSN: | 1520-5207 1520-6106 |
| Popis: | (19)F single-quantum (SQC) and (19)F-(33)S heteronuclear multiple-quantum coherence (HMQC) NMR spectroscopy of sulfur hexafluoride (SF(6)) dissolved in thermotropic liquid crystals (TLCs) were used to investigate the properties of TLCs. On one hand, environmental effects on the NMR parameters of SF(6), (19)F nuclear shielding, (19)F-(33)S spin-spin coupling, secondary isotope effects of sulfur on (19)F shielding, and the self-diffusion coefficient in the direction of the external magnetic field were studied as well. The temperature dependence of the (19)F shielding of SF(6) in TLCs was modeled with a function that takes into account the properties of both TLC and SF(6). It appears that the TLC environment deforms the electronic system of SF(6) so that the (19)F shielding tensor becomes slightly anisotropic, with the anisotropy being from -0.5 to -1.4 ppm, depending upon the TLC solvent. On the contrary, no sign of residual dipolar coupling between (19)F and (33)S was found, meaning that the so-called deformational effects, which arise from the interaction between vibrational and reorientational motions of the molecule, on the geometry of the molecule are insignificant. Diffusion activation energies, E(a), were determined from the temperature dependence of the self-diffusion coefficients. In each TLC, E(a) increases when moving from an isotropic phase to a nematic phase. The spin-spin coupling constant, J((19)F,(33)S), increases by ca. 10 Hz when moving from the gas phase to TLC solutions. The secondary isotope shifts of (19)F shielding are practically independent of TLC solvent and temperature. For the first time, (19)F-(33)S heteronuclear multiple-quantum NMR spectra were recorded for SF(6) in the gas phase and in a liquid-crystalline solution. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|