Fluorine Coupling Constants Research Articles

ChemInform Abstract: SYNTHESIS AND FLUORINE‐19 NUCLEAR MAGNETIC RESONANCE SPECTRA OF TRIFLUOROMETHYLTHIO‐COMPLEXES OF PLATINUM, PALLADIUM, NICKEL, AND IRIDIUM

AbstractDie neuen Komplexe (I) bzw. (II) wurden durch oxidative Addition von Bis‐[tri‐ fluormethyl]‐disulfid an entsprechende Metall(O)‐Komplexe wie z.B. photochemische Reaktion von (SCF3)2 mit Tetrakis‐[triphenylphosphin]‐palladium oder metathetische Umsetzungen von Ag‐trifluormethylmercaptid mit Metallhalogenidkomplexen dargestellt.

The19F and31P magnetic resonance spectra of phosphorus trifluoride in nematic solution

The phosphorus and fluorine N.M.R. spectra of PF3 in a nematic solvent (EBBA) are discussed. The molecular geometry is found to agree with structures obtained from microwave and electron diffraction studies. The sign of the ordering parameter is assumed negative, the signs of the phosphorus fluorine coupling constant and of the chemical shift anisotropies follow from this assumption, and are found to be in agreement with theoretical predictions. The effect of temperature on the isotropic chemical shift of fluorine is discussed.

Synthesis and fluorine-19 nuclear magnetic resonance spectra of trifluoromethylthio-complexes of platinum, palladium, nickel, and iridium

Oxidative addition reactions of (SCF3)2 to low oxidation state metal complexes and metathetical reactions of AgSCF3 with metal halide complexes lead to the synthesis of the new complexes cis- and trans-[Pt(SCF3)2(PPh3)2], cis- and trans-[PtCl(SCF3)(PPh3)2], trans-[PtH(SCF3)(PPh3)2], trans-[PtH(SCF3)(PEt3)2], cis-[PtCl(SCF3)-(PEt3)2], cis- and trans-[Pd(SCF3)2(PPh3)2], trans-[PdCl(SCF3)(PPh3)2], trans-[PdCl(SCF3)(PEt3)2], trans-[Ni(SCF3)2(PPh3)2] and trans-[Ir(SCF3)(CO)(PPh3)2]. 19F N.m.r. spectra of these complexes are described and used to assign the stereochemistry. The trans-influence of the SCF3 ligand is discussed and the platinum–fluorine coupling constants in a series of SCF3 complexes are used to establish a trans-influence series: H > PEt3∼ PPh3 > SCF3 > Cl.

Fluorine nuclear coupling constants in fluorobenzenes: the influence of the orbital term on J meta FF

Calculations by the perturbed self-consistent molecular orbital INDO method on hexafluorobenzene, pentafluoroaniline, and pentafluoronitrobenzene give almost constant values for the ortho and para fluorine–fluorine coupling constants, in agreement with experiment, and show that the large variation in some of the meta coupling constants is due to the orbital term.

Intramolecular screening effects on nuclear magnetic resonance chemical shifts. Part V. The fluorine-19 magnetic resonance spectra of some bridgehead substituted fluorobicyclo[2,2,1]heptenes

The 19F resonance spectra of some bridgehead-substituted fluorobicyclo[2,2,1]heptanes are reported and analysed to give approximate values for chemical shifts and geminal fluorine coupling constants. The 19F shifts for 1H-undecafluoro- and 1H, 4H-decafluorobicyclo[2,2,1]heptane are calculated by use of an intramolecular electric field approach and found to be consistent with those observed. The apparently anomalous trends in observed shifts with the electronegativity of the substituents in a series of fluorobicyclo[2,2,1]heptanes are also discussed in terms of electric fields.

NMR Spectra of Some CF3-Substituted Triphenylphosphines. Evidence for “Through-Space” P–F Spin–Spin Coupling

In the ortho-substituted compounds (o-CF3Φ)3P, (o-CF3Φ)2PΦ, and (o-CF3Φ)PΦ2, JPF is 55.00 ± 0.17 Hz, 52.82 ± 0.12 Hz, and 53.41 ± 0.20 Hz, respectively. In contrast, we could not observe any phosphorus–fluorine coupling in the compounds (m-CF3Φ)3P and (p-CF3Φ)3P. These results, together with the very short phosphorus–fluorine distance in the ortho-substituted compounds, strongly suggest that the P–F coupling results from a “through-space” mechanism in the ortho-substituted compounds. This hypothesis is supported by the strong positive temperature dependence found for JPF, which is similar to that found for JFF in compounds in which the “through-space” mechanism is believed to make a major contribution to the fluorine–fluorine coupling constant.

N.M.R. studies of fluorinated phenoxy radicals: Spin densities from N.M.R. linewidths

We have investigated the N.M.R. and E.S.R. spectra of a series of phenoxy radicals with partially fluorinated substituents. Proton and fluorine coupling constants were determined from the shifts of N.M.R. lines. The spin density in the fluorine 2p orbitals were estimated from the widths of the N.M.R. lines. The fluorine spin densities were used along with those determined for the adjacent carbon atoms to calculate spin polarization parameters.

Solvent effects on the boron–fluorine coupling constant and on fluorine exchange in the tetrafluoroborate anion

The 11B—19F spin–spin coupling constant in AgBF4 is shown to have an opposite sign in water from that found in a number of organic solvents. Application of the hypothesis of Bell and Danyluk indicates that it has a positive sign in water. Evidence is presented for association, probably in the form of solvent-separated ion pairs, in aqueous LiBF4 and NaBF4 solutions, and for the formation of more tightly bound ion pairs in solvents of lower dielectric constant. In contrast, there apparently is no solute association in AgBF4 solutions in water, DMSO, DMF, or acetonitrile. The pronounced changes observed in the 11B—19F coupling constant support the postulate that its small size is a result of near cancellation of large opposing terms.The collapse of the 10B—11B isotope shift at high temperatures in the 19F spectra of solutions of AgBF4 in acetonitrile and in acetone provides evidence for exchange of fluorine among boron atoms; a mechanism is proposed for this process.

The calculation of fluorine hyperfine interactions in π-electron radicals

Q factors have been calculated for fluorine hyperfine interaction in π-electron radicals using an independent-electron model for the σ orbitals. It is shown that the off-diagonal elements give an important contribution to fluorine coupling constants. Combining these Q factors with calculated π-electron spin densities of fluoro-nitrobenzenes gives good agreement with experimental coupling constants.

Spectroscopic studies of inorganic fluoro-complexes. Part II. 19F nuclear magnetic resonance studies of tin(IV) fluoro-complexes

Approximately 100 anions of the general type SnF6–nXn2– have been characterised in solution by 19F n.m.r. spectroscopy, where X is one of a wide range of unidentate ligands or half a bidentate ligand. Complexes containing two different groups X, and mononegative anions containing a neutral ligand, have also been studied. cis/trans ratios have been obtained for many of the geometrical isomers. 19F chemical shifts and tin–fluorine and fluorine–fluorine coupling constants are reported. The 19F chemical shifts δ(relative to the SnF62– ion) of a fluorine atom in these complexes are given, to a good approximation, by δ=pC+qT, where C and T are constants characteristic of the ligand X, and p and q are the number of substituents cis and trans to the fluorine atom respectively. It is suggested that the effect of ligands in cis-positions is largely due to intramolecular van der Waals interactions. Approximate equilibrium constants have been obtained for the displacement of fluoride ion from SnF62– by chloride, bromide, and hydroxide ions, and by water.

Signs of fluorine–fluorine coupling constants in cyclobutenes

Signs of fluorine–fluorine coupling constants in cyclobutenes

Medium dependence of the proton chemical shift and H—H, H—F, F—F coupling constants in 1,1-difluoroethylene

The solvent dependence of the proton chemical shift, the geminal proton–proton, the cis and trans proton–fluorine, and the geminal fluorine–fluorine coupling constants in 1,1-difluoroethylene is reported for 25 solvents. The shift and the couplings involving protons depend primarily on the dielectric constant of the medium, but the Onsager reaction field model is inadequate to describe the changes observed. The fluorine–fluorine coupling depends also on dispersion interactions with the solvent molecules. A comparison with the solvent behavior of the spectral parameters of vinyl fluoride, 1-chloro-1-fluoroethylene, and trifluoroethylene indicates the importance, in varying degrees, of reaction field effects, hydrogen bonding, dispersion interactions, the orientation of the solute dipole moments, and the polarizability of specific bonds in the solute molecule in determining their solvent-induced changes.

Solvents effects on the proton chemical shift and H—H, H—F coupling constants in 1-chloro-1-fluoroethylene. Reaction field and dispersion interactions

The proton chemical shift and the geminal proton–proton and cis proton–fluorine coupling constants in 1-chloro-1-fluoroethylene depend primarily on the dielectric constant of the medium, although this dependence is not given by the Onsager reaction field model. A roughly linear relationship is found with the square root of the dielectric constant. The proton coupling constant decreases algebraically while the cis proton–fluorine coupling constant increases as the dielectric constant of the medium increases. The trans proton–fluorine coupling depends on dispersion interactions with the solvent molecules and increases as these interactions increase. The geminal coupling constant varies between − 3.8 and − 4.8 c.p.s., the cis coupling between 7.6 and 12.3 c.p.s., and the trans coupling between 36.9 and 38.6 c.p.s.

Spectroscopic studies of inorganic fluoro-complexes. Part I. The 19F nuclear magnetic resonance and vibrational spectra of hexafluorometallates of Groups IVA and IVB

The infrared, Raman, and 19F n.m.r. spectra of the hexafluoro-anions of the Group IVA and IVB elements have been measured. We conclude that the predominant species present in aqueous solutions of the ammonium salts are the octahedral AF62– ions (except where A = Pb, when no definite conclusions could be drawn). In solution, the HfF72– ion dissociates into HfF62– and F–. Fluorine exchange is much more rapid when A is Zr, Hf, or Pb than when A is Si, Ge, Sn, or Ti. The tin–fluorine coupling constants in the SnF62– ion are appreciably solvent-dependent.

Pentafluorophenyl derivatives of transition metals. Part VI. Nuclear magnetic resonance spectra of some nickel, palladium, and platinum complexes

The fluorine and the proton n.m.r. spectra of several pentafluorophenyl complexes of nickel, palladium, and platinum have been studied. A relatively large shift to low field was observed for the ortho-fluorine nuclei of the pentafluorophenyl groups. In the trans-isomers of [(C2H5)3P]2Pt(C5F6)X an attempt was made to relate chemical-shift differences between para- and meta-fluorine atoms to the presumed π-bonding characteristics of the ligand X. The observed platinum–fluorine coupling constants are large, and are a function of the nature of X, increasing in the sequence CH3 < CN < NO2 < I ∼ NCS < Br < Cl < ONO2, i.e., in the reverse order to the trans-directing ability of these ligands. By measuring proton n.m.r. spectra and using the virtual coupling concept, the stereochemistry of several of the complexes, previously established by other methods, has been confirmed. Several coupling constants of interest are reported. The synthesis of some new pentafluorophenyl-metal complexes is described.

Nuclear Magnetic Resonance Spectroscopy. Conformational Properties of Cyclobutanes. Variation of Vicinal Hydrogen—Fluorine Coupling Constants with Temperature1

The observation of substantial temperature variations of the vicinal hydrogen-fluorine coupling constants in a series of cyclobutanes is consistent with the existence of an equilibrium between conformations. The temperature dependencies are discussed in terms of the models developed previously. The magnitude of these couplings as a function of the dihedral angle appears to follow a relationship similar to that described by Karplus for proton-proton couplings.

Effect of Solvents on 19F Spin—Spin Coupling Constants

The effects of solvents on the coupling constants of the compounds CF2=CFBr, CF3CFCl2, and CF2BrCFBrClhave been studied. The coupling constants are found to vary with the solvents. This implies that intermolecular interactions affect coupling constants to a degree that is not negligible. The variations in the coupling constants are to some extent correlated with the size, electronic character, and dipolar nature of the solvent molecules. The temperature dependence of fluorine coupling constants that has been reported previously may be due to this temperature-dependent molecular interaction as well as the population of excited vibrational states.

THE 19F N.M.R. SPECTRUM OF IF7

It is shown that the line shape calculated for the n.m.r. spectrum of a magnetic nucleus attached to a nucleus of spin 5/2 undergoing quadrupole relaxation agrees well with the observed spectrum of iodine heptafluoride. The iodine–fluorine coupling constant was found to be[Formula: see text] The apparent magnetic equivalence of the fluorine atoms in IF7 is discussed.

Phosphorus-31 nuclear magnetic resonance studies of phosphorus—fluorine compounds

P 31 NMR chemical shifts and phosphorus—fluorine coupling constants are reported for a wide variety of phosphorus fluorides, in which the coordination number of phosphorus can have the values three, four, five, and six. The chemical shifts extend over a wide range (∼350 ppm) but are relatively constant for any particular class of compounds, and become more positive as the coordination number of phosphorus increases. The P 31 NMR spectra of the fluorophosphoranes, R n PF 5− n , confirm the previous conclusions regarding their stereochemistry.

N.M.R. STUDIES: PART VI. THE COMPLETE ANALYSIS OF THE PROTON SPECTRA OF TWO ISOMERIC METHYL FLUOROBROMOPROPANOATES WITH THE AID OF HETERONUCLEAR SPIN DECOUPLING

The 60 Mc/s proton spectra of methyl 2-bromo-3-fluoropropanoate and the 3-bromo-2-fluoro isomer have been analyzed completely with the aid of heteronuclear spin decoupling to illustrate an extension of the double resonance technique to ABCX spin systems. These results provide confirmatory evidence of the magnitude and relative signs of geminal and vicinal proton–proton and proton–fluorine coupling constants.