Low-temperature NMR spectra of fluoride–acetic acid hydrogen-bonded complexes in aprotic polar environment
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- 作者：Golubev ; Nikolai S. ; Tolstoy ; Peter M. ; Smirnov ; Sergei N. ; Denisov ; Gleb S. ; Limbach ; Hans-Heinrich
- 关键词：Low-temperature NMR ; Hydrogen bond ; Isotope effect ; Acetic acid ; Fluoride anion
- 刊名：Journal of Molecular Structure
- 出版年：2004
- 出版时间：August 20, 2004
- 年：2004
- 卷：700
- 期：1-3
- 页码：3-12
- 全文大小：234 K
文摘
Using low-temperature NMR (1H, 19F) technique in the slow exchange regime, the solutions containing tetrabutylammonium (TBA) acetate and HF have been studied in an aprotic freon mixture, CDF3/CDF2Cl, exhibiting a dielectric permittivity, which increases strongly by lowering the temperature. Two different hydrogen bonded anionic clusters, a 1:1 cluster of the type AcOδ−
HF−1+δ+ ([AcOHF]−) and a 2:1 cluster of the type AcOHF−HOAc ([(AcOH)2F]−) have been detected in equilibrium with each other, both forming ion pairs with the TBA countercation. [AcOHF]− exhibits an extremely strong hydrogen bond, with a proton shared between partially negatively charged oxygen and fluorine atoms. The NMR chemical shifts and scalar spin–spin coupling constants, 1J(FH), have been measured in the temperature range between 110 and 160 K, where separate NMR signals are observed for both species. In addition, H/D isotope effects on the 19F NMR chemical shielding have been measured for both clusters.
HF−1+δ+ ([AcOHF]−) and a 2:1 cluster of the type AcOHF−HOAc ([(AcOH)2F]−) have been detected in equilibrium with each other, both forming ion pairs with the TBA countercation. [AcOHF]− exhibits an extremely strong hydrogen bond, with a proton shared between partially negatively charged oxygen and fluorine atoms. The NMR chemical shifts and scalar spin–spin coupling constants, 1J(FH), have been measured in the temperature range between 110 and 160 K, where separate NMR signals are observed for both species. In addition, H/D isotope effects on the 19F NMR chemical shielding have been measured for both clusters.