High-resolution 19F Research Articles

High resolution fluorine-coupled 13C nuclear magnetic resonance spectra of substituted pentafluorobenzenes. Theoretical and empirical correlations of J CF

The high resolution 19F and 19F-coupled 13C n.m.r. spectra of several substituted pentafluorobenzenes, C6F5X (X = H, F, NH2, NO2, Cl, Br, CHCH2, OCH3, CH3, I, CN, OH, and CHO), have been completely analysed, and all the signs and magnitudes of the 13C–19F coupling constants determined. INDO MO calculations of nJFF and nJCF have been performed, and comparisons are made with the experimental values. The calculations include the Fermi contact, orbital, and spin–dipolar contributions to the coupling and are shown to reproduce the substituent effects upon nJFF. The calculations of nJCF values are less successful. 1JC(4)F(4) correlates well with σp whereas the correlation of the other 1JCF values is less successful. No improvement in the correlations occur with a dual parameter equation. All the couplings, nJCF, that show a sufficient variation with the substituent change are successfully correlated with a three parameter equation involving F, R, and Q. In particular 2JC(1)F(2) and 3JC(2)F(6), in close proximity to the substituent, are successfully correlated by this equation.

Molecular structure of vinylidene fluoride-hexafluoracetone copolymers

High resolution 19F NMR spectra and IR absorption spectra of vinylidene fluoride (VF) and hexafluoracetone (HFA) copolymers containing up to 31 mole % HFA were obtained. It was shown that polymerization takes place by opening the carbonyl double bond. A small part of HFA is added to polymer chain ends with retention of the carbonyl group. HFA units are mainly combined with an oxygen atom to the CF 2 group of VF and with a C(CF 3) 2 group to the CH 2 group. It was found that HFA units are absent from copolymer molecules. VF units and alternating segments of copolymer units are mainly formed by the “head-tail” type. The existence was indicated of a conformation transition in VF units and a transition related to rotation of HFA units. Conditions of these transitions were examined. A relation was derived to determine copolymer composition. It was shown that the distribution of monomer nits in copolymer molecules conforms to the statistics of first order Markoff chains. Copolymerization constants were determined.

A19F NMR Study on the Interaction of the Hexafluoroanions of Group IV Elements with Cations in Solutions

Abstract In view of previous studies of tetrafluoroborate solutions1, it appeared interesting to continue further investigations on the interactions of fluorocomplexes with different cations, in general, and of the MF6 2- fluoro complexes, in particular. In this communication, the high resolution 19F NMR data are given for the aqueous and water-acetone solutions of silicon, germanium, tin and titanium hexafluorocomplexes, containing paramagnetic (Co2+, Ni2+, Cu2+, Cr3+) and diamagnetic (Be2+, Mg2+, Zn2+, NH4 +) cations.

High Resolution Nuclear Magnetic Resonance Spectra of Bifluoride Ion and its Homologues

The high resolution 1H and 19F nuclear magnetic resonance (n.m.r.) spectra of the four bihalide ions have been observed in aprotic solvents. The 1H shielding is, in every case, 14 p.p.m. less than that in the related molecule. The spin–spin coupling in FHF− is 120.5 ± 0.3 Hz.

NMR Studies of Inorganic Fluorides. I. High-Resolution 19F Spectra of Si2F6 and (SiF3)2O

Fluorine NMR spectra of hexafluorodisilane and hexafluorodisiloxane have been recorded and analyzed. The 19F–19F and 29Si–19F spin coupling constants were obtained from the satellite spectra arising from the 29Si-substituted molecules present in natural abundance. The ``near'' and ``far'' 29Si–19F coupling constants in Si2F6 were found to be of opposite sign.

The nuclear magnetic resonance spectra of aromatic fluorocarbons. Part I. Amino- and nitro-substituted perfluorobenzenes

The high-resolution 19F n.m.r. spectra of several amino- and nitro-substituted perfluorobenzenes have been analysed. Substituent shielding effects are found to be closely additive and independent of the degree of substitution with both groups. Mean shielding parameters, which closely resemble those obtained for substitution in monofluorobenzene, are derived.