F NMR Spectroscopy

Chemical Shifts of CF2R j, CHFR2, and CFR3 Groups (6 in ppm)  

5-diphenylpyrazole were reported 1996MR46 . In the solid state, these compounds form various hydrogen-bonded complexes. The principal values of the chemical-shift tensors (CSTs) of amine and imine nitrogen atoms are derived by line-shape analysis of the NMR spectra of the static powders obtained under the conditions of 

The synthesis of a series of l//-pyrazolo[3,4-3]quinoxalines (flavazoles) 55 by acylation, alkylation, halogenation, and aminomethylation of the parent compound was reported and their structures were investigated by H, and N NMR spectroscopy 2005T2373 . Restricted rotation about the partial C-N double bond of the A -acyl derivatives was studied by dynamic NMR spectroscopy and the barriers to rotation were determined. N NMR data of a series of 3-alkyl [aryl]-substituted 5-trichloromethyl-l,2-dimethyl-l//-pyrazolium chlorides 56 (where the 3-substituents are H, Me, Et, -Pr, -Bu, -Pent, -Hex, (CH2)sC02Et, CH2Br, Ph, and 4-Br-C6H4) were reported 2002MRC182 . The N substituent chemical shift (SCS) parameters were determined and these data were compared with the SCS values and data obtained by molecular orbital (MO) calculations. 

Two desmotropes, 3-phenyl-17/-pyrazole 57 and 5-phenyl-1/7-pyrazole 58, were isolated and the conditions for their interconversion were established 2002HCA2763 . The X-ray structure of 58 was determined and both tautomers 59 and 60 were characterized by NMR in the solid state ( C and N CP/MAS). In the case of 3-phenyl-l//-indazoIe 59 and 5-phenyl-2/7-indazole 60, two concomitant polymorphs of 59 were analyzed by X-ray crystallography, and their NMR spectral properties were determined. 

The molecular and crystal structures of the hydrochloride and hydrobromide salts of 3(5)-methyl-5(3)-phenyl-pyrazole of 61 and 62 and the hydrobromide salt of 63 were determined by X-ray analysis and C CPMAS NMR methods 1997JMT(415)81 . A structural study of pyrazole-l-carboxamides 64 was made by X-ray crystallography and C CPMAS NMR spectroscopy 1999JMT(478)81 . 

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Several problems m basic methodologies have persisted over the 25 years since F-NMR spectroscopy was first apphed to a biochemical question Most hmiting IS that of NMR sensitivity High substrate concentrabons, relative to the naturally occumng biological levels, are required for NMR detection Although most NMR studies use millimolar and somebmes submilhmolar concenbatrons, many bio molecules exist at micromolar or lower levels... 

Infrared spectra and F-NMR spectroscopy showed the presence of IF5 and covalently bonded fluorine. Grafoil turns white upon intercalation with IF, this is reminiscent of graphite fluoride, CFi.ij (1,6). The IF, intercalate also evolves IF5 upon heating, but at much higher temperatures than C/IF5 this has been attributed to the lowered mobility of IF5 in the fluorinated matrix, which may no longer be planar. At 450°C, considerable amounts of fluorocarbons are evolved. 

EPR investigations are necessarily carried out in frozen solution at low temperature. Room temperature binding of thiols to FeMoco has been monitored by F NMR spectroscopy using /J-CF3C6H4S as the reporter ligand. These experiments revealed that the binding of thio-late is characterized by a dynamic equilibrium between the FeMoco and thiolate (159) and that cyanide and methyl isocyanide can bind to isolated FeMoco complexed with thiol (160). 

This polymerization proceeds quickly at ambient temperatures to give an oligomeric material (7) with M of 4000 to 6000 (Table 4.1). Compound 6 was also homopolymerized under similar conditions to afford an oligomer (8) with My, 5000.1 These new oligomers were characterized by H- and F-NMR spectroscopy as well as elemental analysis. 

Morphology based on chemical environment can be probed using F NMR spectroscopy because the chemical shifts of F atoms in the side chains are considerably separated from those in the backbone. Conformational dynamics as affected by domain-selective solvent incorporation are reflected in the widths of static F peaks. These conformational motions, in turn, can influence the migration of solvent penetrants. 

With counteranions of lower nucleophilicity the " Sn NMR chemical resonance of solutions of tributyl tin salts is further shifted to lower field. Lambert and Kuhlmann reported for the tiibutylstarmyl borate Bu3SnB(C6F5)3H 8" Sn = 360 in benzene and Kira and co-workers found for the related BusSnTFPB 8 Sn = 356 in CD2Cl2. In the latter case, F NMR spectroscopy indicates no cation-anion interaction. Finally, for Bu3SnTPFPB in toluene at —60 °C 5" Sn = 434.2 was reported by Piers et The solvent dependence of the Sn NMR chemical shift suggests... 

The products were identified by F NMR spectroscopy. The chemical shifts 8 (using CFCI3 as an external standard) and spin-spin coupling constants J of liquid fluorides are listed in Table I. Compound CF3SF... 

Although the exact geometry of CIFgO has not yet been established, its approximate structure is known from vibrational and F NMR spectroscopy. Its UV spectrum has also been reported 228). 

Under all applied conditions only C 0F4g is formed, probably as three different optical isomers [24—26] (Figure 9.1). Gakh and co-workers determined the correct structure on the basis of F NMR spectroscopy [24]. The structure was confirmed by resolution of the X-ray crystal structure [25, 26]. This shows that, probably, all three optical isomers - namely the two enantiomeric forms with Dj-symmetry and the mesoform with Sg-symmetry- can be foimd in the crystal (Figure 9.1, structures 11 and 12). 

X-ray and Electron Diffraction NMR Spectroscopy "C, N, and F NMR Spectroscopy UV Spectroscopy IR Spectroscopy ESR Spectroscopy... 

Unfortunately, the utility of this method for many of the more interesting enzymes is restricted by the complexity of the protein. If more than one type of cluster is present, the multiple component analysis on the extruded mixture may lead to ambiguous conclusions. In addition non-metallochromophores may interfere. Holm and co-workers (Wong et ai, 1979) circumvented some of these problems for Fe S proteins by their choice of spectral analysis and exogenous thiolate ligand. Namely, they used F NMR spectroscopy to analyze the products of thiolate extrusion with /)-trifluoromethylbenzenethiol. Contact shifts for the fluorine resonances are considerably different for 2Fe and 4Fe clusters. Important restrictions on the use of the F NMR detection are the quantity of protein needed, the synthesis of the ligand, and access to the spectrometer. 

R.P. Mason, F.M.H. Jeffrey, C.R. Malloy, E.E. Babcock, P.P. Antich, A noninvasive assessment of myocardial oxygen tension F NMR spectroscopy of sequestered perfluorocarbon emulsion, Magn. Reson. Med. 27 (1992) 310-317. 

Further, a 1,2-oxathiane 2,2-dioxide derivative was obtained as a by-product (15-25%) in the enantioselective synthesis of Oasomycin A <2007AG545> all efforts to suppress this side reaction were not successful, and the reaction products of the hexafluorobutadiene sulfotrioxidation (among the main products a 4,5-dihydro-l,2-oxathiin 2,2-dioxide derivative) were identified by F NMR spectroscopy <2007RJA424>. 

Determination of Enantiomeric Purity of Chiral Aldehydes Using F-NMR Spectroscopy of Their Diastereomeric Imidazolidines... 

Fluorobiphenyls are formed by irradiation of o-, m- and / -RC6H4I (R = OH, OCH3, CH3, H, F, Cl, COOCH3, N02) in fluorobenzene and by irradiation of o-, m- andp-FC6H4I in C6H5R (R = OH, OCH3, CH3, F, Cl, COOCH3, NO,)480. Relative yields were determined and F-NMR spectroscopy was used for the identification of the substituted fluorobiphenyls. The results are discussed in terms of electronic and steric substituent effects. 

Tetramethyldiarsane and trimethylarsane form unstable, probably dipolar, 1 1 complexes as suggested by F NMR spectroscopy. In the former a four-membered ring is formed with the two arsenic atoms acting as donor and acceptor sites (72). Tris(dimethylamino)stibane reacts with HFA with insertion into all three Sb—N bonds (83). 

NMR spectra of HFA adducts with compounds containing active hydrogen atoms like alcohols 93a, amines 95, and thiols 126 have been reported (173). HFA also forms unstable ketal esters with a series of carboxylic acids. The equilibrium has been investigated by means of F NMR spectroscopy (206). 

Like HFA, indanetrione reacts with tetrakis(triphenylphosphane)platinum to form a platinaoxirane, which readily adds one molecule of HFA to yield 183. Further action of HFA affords a rather unstable seven-membeied ring compound (184), which thermally loses either indanetrione or HFA to reform a platinadioxolane. Whether isomer a or b is formed cannot be deduced from F NMR spectroscopy 145). 

Furthermore, the six fluorine atoms of HFA provide the chemist with a versatile tool for the investigation of dynamic processes by means of F NMR spectroscopy. 

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

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