19F NMR spectroscopy

Mooney, E F An Introduction to 19F NMR Spectroscopy, Heyden Sons, London, 1970... 

Howell and Moss [289] confirmed, by 19F NMR spectroscopy, that NbOF52 complex is present in hydrofluoric acid solutions of up to 30%. Increase in HF concentration leads to the formation of NbF6 complex ions. 

The cyclometalated dichlorocarbonyliridium(III) complex [IrCl2(CO) PPh2CH2C(tBu)=N-N=CH-(C6F4) ], (231), has been characterized by 31P, 13C, 19F NMR spectroscopy, and a singlecrystal diffraction study.403... 

The zinc teflate Zn(OTeF5)2 has been synthesized and characterized by IR and 19F NMR spectroscopy. The interaction with a number of weakly coordinating solvents was studied and the single-crystal X-ray structures determined for nitrobenzene derivatives [Zn(OTeF5)2 (PhN02)2]2 and Zn(0TeF5)2(PhN02)3.428... 

Over the past decade or so, NMR spectroscopy has emerged as a screening tool to facilitate the drug discovery process, and nowhere has this been more the case than with 19F NMR spectroscopy (more about this in Chapter 2). 

Another possibility to find out more about the structure of these dendrimers was chosen by incorporating fluorine atoms. The use of 19F-NMR spectroscopy offered an additional tool to study the conformation of the dendrimer, especially with the fluorines attached close to the stereogenic centers [91 ]. Following our previously developed methods [92], fluorine-containing 1st- and 2nd-genera-tion chiral dendrimers such as 76 were synthesized (Fig. 24). 

Yeste et al.7 have developed chiral derivatization protocols for determination of enantiopurity of chiral diols by the H and 19F NMR spectroscopy. Three-component method has required the treatment of diol with 2-formylphenylboronic acid and a-methyl-4-fluorobenzylamine [4],... 

Hannant et al. also reported the synthesis (Scheme 44) of cationic zinc complexes bearing bulky diazabutadiene ligands.1 7 19F NMR spectroscopy showed that the borate anions of these compounds are non-coordinating in... 

P and 19F NMR spectroscopy), and attempts to record a CP/MAS solid-state NMR spectrum (19F, 31P, 23Na) failed because of the large line-broadening by the 23Na ions (I = 3/2) and strong spin-spin coupling. 

Product (92) containing the CF3 group in the a position is the only compound, in which the contribution of the cis isomer of SENA is rather high, and both isomers can be observed by 19F NMR spectroscopy. However, the trans isomer of this compound is also thermodynamically more favorable. 

This polymerization16 proceeds quickly at ambient temperatures to give an oligomeric material (7) with Mw of 4000 to 6000 (Table 4.1). Compound 6 was also homopolymerized under similar conditions to afford an oligomer (8) with Mw 5000.+ These new oligomers were characterized by H- and 19F-NMR spectroscopy as well as elemental analysis. 

Evidence for the existence of most of the possible substitution products has been obtained by 19F-NMR spectroscopy (3). 

Finch, J.R., E.I.Dadey, S.L.Smith, L.I.Harrison, and G.A.Digenis. 1995. Dynamic monitoring of total-body absorption by 19F-NMR spectroscopy one hour ventilation of HFA-134a in male and female rats. Magn. Reson. Med. 33 409—413. 

The products of reactions 4-9 have been characterized in SO2CIF solution by l3C and 19F NMR spectroscopy (Table 2). All solid products and their SO2CIF solutions were stable indefinitely at temperatures approaching-20 °C. 

In 1H- and 19F-NMR spectroscopy studies of the metabolites of fluclox-acillin (5.52) in rat urine, the presence of both (5R)- and (5.S )-flucloxacillin penicilloic acids was demonstrated [154], During the first collection period, the concentration of the (R)-epimer largely exceeded that of the f.S )-epimer. The (R)/(S) ratio then decreased progressively until an excess of f.S )-epimer was reached. These findings are in agreement with the hypothesis that the f.S )-cpimer is formed by epimerization in urine (see above) [152],... 

M. Tandon, P. Kumar, G. Wiebe, L. I. Wiebe, Detection of New Metabolites of Triflu-ridine (F3TdR) Using 19F NMR Spectroscopy , Biochem. Pharmacol. 1992, 44, 2223 -2228. 

Pig liver esterase (PLE, E.C. 3.1.1.1) is one of the most successful enzymes for the enantiotopos-differentiating hydrolysis of dicarboxylic diesters and diacetates of diols as exemplified by the two examples, dimethyl cv. y-4-cydohexene-l,2-dicaiboxylate (I)100 - " 2 and (l/ ,2.S,3S)-l,3-di-acetoxy-2-nitrocyclohexane (3)113. The monoester 2 is obtained with the same results when prepared on a 100 mol scale114. The ee values of the monoester 2 may be determined conveniently by H-NMR spectroscopy in the presence of (+)- or ( )-ephedrine and that of the monoacetate 4, after conversion to the corresponding Mosher ester, by 19F-NMR spectroscopy. 

Further evidence against the ECbECN carbocation mechanism is claimed by Sartori and co-workers [186] from their work on the fluorination of N,N-dime-thyltrifluoromethanesulphonamides at different temperatures (-15°C and + 5°C). According to the carbocation mechanism, it is stated, introduction of fluorine atoms into the sulphonamide should take place stepwise, first in one methyl group and then into the other however, detailed examination of the reaction mixture by 19F NMR spectroscopy showed no trace of compounds containing the moieties... 

To a solution of tile alkenc (1 mmol) in anhyd C112C12 (4mL) was added. V-(phenylselanyl)phthalimide (1.5 cquiv) and Et3N 3HF (6 equiv) and the mixture was stirred at 25 C (for reaction time sec Tabic 14). The mixture was then poured onto Et20/ aq NaHCOj, the organic products were extracted into the ethereal layer, dried, and the solvents and Et3N evaporated. The residue was analyzed by 19F NMR spectroscopy and purified by chromatography. Selected results arc given in Table 14, for further examples, see ref 216. 

To a solution of ZnF2 (0.03 mol) in pyridine (30 mL) was added the aroyl chloride or the arenesulfonyl chloride (0.03 mol) with stirring at 25 °C. Stirring was continued until the reaction was complete (checked by 19F NMR spectroscopy) then treated by either Method A or B as follows. 

A well-stirred soln of V-Teoc-(aTfm)Xaa-OMe (2 mmol), Fmoc-Xaa-F (3 mmol) and tetra-ethylammonium fluoride (cat. amount) in MeCN (3mL) was heated at 50 °C under an inert gas atmosphere until complete conversion was reached (usually 1-2 weeks, as monitored by 19F NMR spectroscopy). The solvent was removed and the product purified by flash chromatography Fmoc-Gly-(aTfm)Leu-OMe, yield 77% Fmoc-Ala-(aTfm)Leu-OMe, yield 77% Fmoc-Ala-(aTfm)Phe-OMe, yield 55%. 

Over the past 40 years fluorine nuclear magnetic resonance (19F-NMR) spectroscopy has become the most prominent instrumental method for structure elucidation of organofluorine compounds. Consequently the amount of spectral data published has grown almost exponentially Unfortunately NMR data for fluonnated compounds are not as well, or as easily, organized as proton data To facilitate retrieval of fluorine NMR information and comparison of data, acquisition parameters should be clearly defined Guidelines for publication of NMR data have been established by the International Union for Pure and Applied Chemistry (IUPAC) [7] The following niles for acquisition and reporting of NMR data should be strictly observed... 

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