Fluorine, NMR studies

Cornelissen, G., P. C. M. van Noort, G. Nachtegaal, and A. P. M. Kentgens, A solid-state fluorine-NMR study on hexafluorobenzene sorbed by sediments, polymers, and active carbon , Environ. Sci. Technol., 34, 645-649 (2000). 

Nuclear magnetic resonance spectroscopy has emerged as the most powerful tool for elucidating the molecular structures of cyclophos-phazene derivatives in solution. Proton NMR spectroscopy has been widely used because of its easy accessibility. The recent development of sophisticated instrumental facilities and the application of broadband proton decoupling have greatly improved the quality and usefulness of the 31P spectra (252) of cyclophosphazenes, and it is likely that this technique will become increasingly popular in the future. Fluorine NMR studies are useful for deducing the structures of fluorocyclophosphazenes, and the potential of this technique has been demonstrated in recent years (209, 210, 213, 307, 308, 343). 

Fluorine NMR studies in the solid state, excluding polymers... 

X. FLUORINE NMR STUDIES OF POLYMERS The table is ordered according to the monomers forming the polymer, with the lowest molecular weight monomer appearing first. 

Fluorine NMR studies using liquid crystal solutions... 

R 576 I.J. Rowland, Biomedical Fluorine NMR Studies in Humans , Dansk Kemi, 2004,85,22... 

MAS has been applied to a highly viscous cubic phase of a lyotropic LC formed by 1-monooleolyl-rac-glycerol and water in order to obtain liquid-like and 13C spectra.330 Deuterium, sodium, and fluorine NMR spectroscopy have been applied to study the phase behaviour of several dilute lamellar systems formed by low concentrations of an ra-hexadecylpyridinium salt, a sodium salt (e.g., NaBr, NaCl, or sodium trifluoroacetate), 1-hexanol, and D20.331 The 2H, 19F, and 23Na splittings were used to monitor the phase equilibria. The last two studies are motivated by the search of new lyotropic LC for the alignment of biomolecules. 

In still other NMR studies of mixtures, Douglass and McBrierty have considered the homogeneity of polyvinylidene fluoride - poly methylmethacrylate blends.(38) Here the energy exchange between proton and fluorine magnetic spins is efficient only if the nuclei are adjacent. The results indicate, when taken around 40°C, that either the fluorine nuclei in a 40 polyvinylidene fluoride/60 poly methylmethacrylate blend are... 

Recently, 500 MHz i fluorine NMR was used to study adsorption of Nafion ionomer on PEFC catalysts and the supporting carbons in aqueous solution. It was observed that Nafion adsorbs strongly on carbon as well as on Pt and PtRu. The adsorption was classified into primary and secondary adsorption. At low concentration of Nafion ionomer, the adsorption was found to follow a Langmuir isotherm (primary adsorption). Although there was uncertainty in the types of adsorption isotherms at high concentration of Nafion ionomer, the secondary adsorption isotherms were fitted to a Langmuir isotherm as well. 

Diirr UHN (2005) Solid-state F-NMR studies on fluorine-labeled model compounds and biomolecules. PhD thesis. Institute of Organic Chemistry. Universitat Karlsruhe (TH), Karlsruhe, p 163... 

A. Joseph, C. Davenport, L. Kwock, C.T. Burt, R.E. London, Fluorine-19 NMR studies of tumor-bearing rats treated with difluoromethylomithine, Magn. Reson. Med. 4 (1987) 137-143. 

A. Ohno, M. Shimizu, S. Yamada, Fluorinated vitamin D analogs to probe the conformation of vitamin D in its receptor complex F-NMR studies and biological activity, Chem. Pharm. Bull. 50 (2002) 475-483. 

Amphotericin B (AmB) is a polyenic macrolide used in fungal infections and leishmaniasis, despite severe side effects (Figure 4.60). Fluorination of the macrolide skeleton has been performed using Selectfluor for F NMR studies on the mechanism of ion-channel formation in membranes by amphotericin B. ... 

Examples of kinetic analysis of NMR spectra in the transition between slow and fast exchange (on the NMR time scale) are somewhat limited. Treatment of fluorine exchange in sulfur tetrafluoride is selected here because this exchange process exemplifies the type of kinetic process ideally suited to NMR study. The fluorine atoms of the two nonequivalent environments in this molecule of C2v symmetry give rise to two triplets under conditions of very slow exchange at temperatures below —85° (at 40 Mc/sec). 

However, 19F NMR studies indicate that a small amount of the BF3 NH2C2H5 may slowly convert to BF4 and to another species which we do not detect in the 19F spectrum. There is an apparent loss of fluorine as illustrated in Table 2. The small percentage of BF3(OH) species present in the unannealed sample disappears after a 1-h annealing at 85 °C, presumably as a result of either reaction with species at the glass sample tube surface or formation of... 

F NMR studies, illustrated in Table 4, indicate that the TGDDM epoxide enhances BF4 salt formation in DMSO solution. For example, after exposure to 115 °C for 1 h, all the BF3 NH2C2HS species have disappeared in the presence of TGDDM. However, in DMSO solution in the absence of TGDDM, 50% of the total fluorine species are still in the form of BF3 NH2C2H5 after 1 h exposure at 115 °C (Table 3). 

By careful control of the conditions of the reaction one can obtain preferentially oxidation of sulfur to its four coordinate oxidation state and by using a second set of conditions one can obtain the oxidation to the six-coordinate sulfur species. The dynamic NMR study of SF3CF2SF3 is currently in progress in collaboration with A. H. Cowley (60). This differentiation of oxidation states is extremely promising, and work in progress shows that this is not at all an isolated situation. Mercaptans and other organosulfur compounds definitely exhibit this capacity in fluorine reactions. 

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