Conformational analysis of fluorinated copolymers of tetrafluoroethylene

Conformational analysis of fluorinated copolymers of tetrafluoroethylene (TFE) is performed by taking into account only intramolecular effects (isolated-chain model). In particular, variations of the chain conformation, which are induced by incorporating different side groups, such as –Cl, –CF₃, –OCF₃, –OCF₂CF₃, and –OCF(CF₃)₂, are investigated and discussed with respect to qualitative correlations between conformation, crystal structure, and supramolecular morphology.     

Vibrational satellite of Na(3d ← 3s) dipole-forbidden transition in Na/CF4 mixture

Excitation spectra of Na fluorescence in mixtures with CF₄ display a new band shifted by the energy of one-vibrational quantum of the IR active ν₃-mode of CF₄ (1281 cm⁻¹) from Na 3d states. This band is attributed to a Na(3s)CF₄(ν₃ = 0) → Na(3d)CF₄(ν₃ = 1) transition and its intensity is explained by coupling with Na(4p)CF₄(v₃ = 0) resonance state which lies  180 cm⁻¹ below in energy. An analogous satellite of the Na 6p state combined with the same vibration and lying close to the Na 7p state is reported and discussed.     

Radiation chemistry of CF2 Cl2 in the gas and liquid phases: Effect of doses rate

The dose rate dependence of CF₂ Cl₂ decomposition was studied in both, gas and liquid phase, for the range of 2.95·10^{1 7}–1.9·10^{1 9} eV·g^–1·h^–1. The major products were found to be CF₃Cl, CFCl₃, CF₂Cl–CF₂Cl and CF₂Cl–CFCl₂. The decomposition of CF₂Cl₂ was found to decrease with decreasing dose rate for the liquid phase, while an opposite trend was found for gas phase radiolysis. A new mechanism which explains these contrasting findings was suggested. The contribution of radical and of ionic (or molecular) processes to the yields of the various products was estimated.     

Electron structure and reactivity of organofluorine compounds. 3. Mndo and ami calculations of the ground state of perfluoroalkyl chlorides,bromides, and iodides

The semiempirical quantum chemical MNDO and AMI methods were used to determine the equilibrium geometries and electron properties of molecules of perfluoroalkyl halides (R_FX): CF₃X, CF₃CF₂X, (CF₃)₂CFX, (CF₃)₃CX for X=Cl, Br, and I. It was determined that the effective charge on the Cl atom in R_FCl is negative, positive on the I atom in R_FI, and depends on R_F for the Br atom in R_FBr. The CF₃ group can act as either an electron acceptor or donor in various perfluoroalkyl halides. The strongest C–I bond in the perfluoroalkyl halides occurs with a tertiary RF group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1059–1063, May, 1990.     

Intramolecular multiple scattering in electron diffraction from fluoro-methyl halides

Relative elastic differential cross sections for scattering of 1 keV electrons from CF₃H, CF₄, CF₃Cl, CH₃F and CH₃Cl molecules were measured for momentum transfer from 3 Å^?1 to 29 Å^?1. The oscillatory residuals remaining after substraction of the atomic scattering and the molecular interference contributions calculated in the independent atom model are ascribed to the influence of intramolecular multiple scattering. The data reflect the dominant contributions of the CF₃-group and show larger oscillations than obtained from triple scattering calculations according to the method of Liu and Bonham using the second Born approximation.     

Über die oxidative Fluorierung von (CF3)(R) (R = CF3, Cl) und die Kristallstruktur von (CF3)(Cl)F+ AsF6−

Oxidative Fluorination of (CF₃)(R) (R = CF₃, Cl) and the Crystal Structure of (CF₃)(Cl) F⁺ AsF₆^? Oxidative fluorination of (CF₃)(R) (R = CF₃, Cl) with XeF⁺MF₆^? (M = As, Sb) in anhydrous HF results in formation of monofluorsulfonium hexafluorometalates. The salts are characterized by vibrational, NMR, and mass spectra. (CF₃)(Cl)F⁺ AsF₆^? crystallizes in the monoclinic space group P2₁/c with a = 9.955(10) Å, b = 11.050(5) Å, c = 12.733(15) Å, β = 97.77(5)°, and Z = 4.     

Photodissociation laser isotope effects

Marked differences in the laser action (1.315 μm) observed following the flash photolysis of CD₃I and CH₃I are reported (substantially greater outputs are observed with CD₃I). These differences result from the significantly smaller cross section for quenching of I(5 ²P ) by CD₃I, relative to that for CH₃I. Absolute values for the quenching cross sections have been determined using time resolved atomic absorption spectrophotometry. These data were employed in a computer simulated model which satisfactorily reproduced the light output from CH₃I, CD₃I and CF₃I photochemical laser systems. It is concluded that isotopic substitution can markedly influence the cross section for quenching of an excited state and thus influence partitioning between the various available channels.     

The Raman OH stretching bands of liquid water

In this work, from the discussion on water structure and clusters, it can be deduced that the OH stretching vibration is closely related to local hydrogen-bonded network for a water molecule, and different OH vibrations can be assigned to OH groups engaged in various hydrogen bonding. At ambient condition, the main local hydrogen bonding for a molecule can be classified as DDAA (double donor–double acceptor), DDA (double donor–single acceptor), DAA (single donor–double acceptor) and DA (single donor–single acceptor) and free OH vibrations. As for water at 290 K and 0.1 MPa pressure, the OH stretching region of the Raman spectrum can be deconvoluted into five sub-bands, which are located at 3014, 3226, 3432, 3572, and 3636 cm⁻¹, and can be assigned to ν_DAA-OH, ν_DDAA-OH, ν_DA-OH, ν_DDA-OH, and free OH₂ symmetric stretching vibrations, respectively.     

Polar addition of perfluoro-tert-hexyl iodide to alkenes and alkynes

The effective charges on the atoms in molecules of perfluoroalkyl halides of general formula (CF₃)_nCF_3–nX (X=Cl, Br, I) have been calculated by the AM1 semiempirical method. In polar solvents perfluoro-tert-hexyl iodide is reduced under the action of alkenes and aromatic hydrocarbons to form 2-hydroperfluoro-2-methyl-pentane and perfluoro-2-methyl-2-pentene. In ethyl acetate the regio- and stereo-specific addition of perfluoro-tert-hexyl iodide to alkenes, butadiene, and alkynes takes place, which is associated with the realization of a polar ion-radical mechanism for the reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2057–2061, September, 1989.     

A hexanuclear gold carbonyl cluster

The hexanuclear gold carbonyl cluster [PPh₄]₂[Au₆(CF₃)₆Br₂(CO)₂] (4) has been obtained by spontaneous self-assembly of the following independent units: CF₃AuCO (1) and [PPh₄][Br(AuCF₃)₂] (3). The cyclo-Au₆ aggregate 4, in which the components are held together by unassisted, fairly strong aurophilic interactions (Au···Au ∼310 pm), exhibits a cyclohexane-like arrangement with chair conformation. These aurophilic interactions also result in significant ν(CO) lowering: from 2194 cm^–1 in the separate component 1 to 2171 cm^–1 in the mixed aggregate 4. Procedures to prepare the single-bridged dinuclear component 3 as well as the mononuclear derivative [PPh₄][CF₃AuBr] (2) are also reported.     

Gas-phase reactions of CF3 and CF2 with atomic and molecular fluorine: Their significance in plasma etching

Reaction rate coefficients have been measured at 295 K for both CF₃ and CF₂ with atomic and molecular fluorine. The reaction between CF₃ and F was studied over a gas number density range of (2.4–23)×10¹⁶ cm^–3 with helium as the bath gas. The measured rate coefficient increased from (1.1–1.7)×10^–11 cm³ s^–1 as the gas number density increased over this range. In contrast to this relatively small change in rate coefficient with gas number density, the rate coefficient for CF₂+F increased from (0.4–2.3)×10^–12 cm³ s^–1 as the helium gas number density increased from (3.4–28.4)×10¹⁶ cm^–3. Even for the highest bath gas number density employed, the rate coefficient was still more than an order of magnitude lower than earlier measurements of this coefficient performed at comparable gas number densities.Both these association reactions are examined from the standpoint of the Gorin model for association of radicals and use is made of unimolecular dissociation theory to examine the expected dependence on gas number density. The calculations reveal that CF₃+F can be explained satisfactorily in these terms but CF₂+F is not well described by the simple Gorin model for association.CF₃ was found to react with molecular fluorine with a rate coefficient of (7±2)×10^–14 cm³ s^–1 whereas only an upper limit of 2×10^–15 cm³ s^–1 could be placed on the rate coefficient for the reaction between CF₂ and F₂. The values obtained for this set of reactions mean that the reaction between CF₃ and F will play an important role in plasmas containing CF₄. The high rate coefficient will mean that, under certain conditions, this particular reaction will control the amount of CF₄ consumed. On the other hand, the much lower rate coefficient for reactions between CF₂ and F means that CF₂ will attain much higher concentrations than CF₃ in plasmas where these combination reactions are dominant.     

Vibrational relaxation and dissociation in the perfluoromethyl halides,CF3Cl,CF3Br,andCF3I

The processes of vibrational relaxation and unimolecular dissociation of the perfluoromethyl halides CF₃Cl, CF₃Br, and CF₃I have been studied in the shock tube with the laser-schlieren technique. Vibrational relaxation was resolved in pure CF₃Cl and CF₃Br (400–484 K and 400–500 K, respectively), and in the mixtures; 2% CF₃Cl/Kr (500–1000 K), 10% CF₃Cl/Kr (440–670 K), 4% CF₃Br/Kr (450–850 K), and 2% CF₃I/Kr (620–860 K). Relaxation in the pure gases is extremely rapid, but shows a well-resolved, accurately exponential decay which provides very precise relaxation times in close agreement with ultrasonic results. Relaxation times as short as 0.1 μs-atm can be resolved, showing the method has a resolution within a factor 2–3 of the best ultrasonic methods. Relaxation dilute in rare gas shows a complex double exponential behavior consistent with a two-stage series process. Rates of CF₃(SINGLEBOND)X fission in these mixtures were measured over 1800–3000 K, P<0.55 atm, for CF₃Cl; 1600–2500 K, P<0.55 atm, in CF₃Br; and 1260–2100 K, P<0.34 atm, in CF₃I. Rates for dissociation were derived from a full profile modeling using a secondary mechanism of six CF₃ reactions. RRKM analysis showed all dissociations to lie near the low pressure limit. Using literature barriers, these rates are best fit with (ΔE)_all=−270 cm⁻¹ for CF₃Cl, 〈ΔE〉_down=0.3 T for CF₃Br, and 〈ΔE〉_down=800 cm⁻¹ for CF₃F. All these transfers are on the large side, similar to those found in other halogenated methanes. © 1997 John Wiley & Sons, Inc.     

Preparation of 2-chloro-3-pentafluorosulfur tetrafluoropropylene, and its use in telomerization reactions

The synthesis of a new SF monomer, 2-chloro-3-pentafluorosulfur tetrafluoropropylene, SF₅CF₂C(Cl)=CF₂. is reported.We wish to report the synthesis of a new SF monomer, 2-chloro-3-pentafluorosulfur tetrafluoropropylene, SF₅CF₂C(Cl)=CF₂. The synthesis involves the following sequence of reactions:

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The preparation of (I), 1,2-dibromo-1,1,3,3-tetrafluoropropane, was carried out according to the method of Tarrant et al [1]. The preparation of (II), tetrafluoroallene (TFA), was essentially that of Muehlner [2] with slight modification. We were able to obtain consistent yields of about 70% using a larger excess of KOH with an efficient ice condenser. The reactor was heated slowly and held at about 90°C with a nitrogen sweep to remove TFA as it was formed. The preparation of (III), 2-chloro-3-pentafluorosulfur tetrafluoropropylene was carried out in a metal bomb at 90–100°C for 1 to 16 hours with a yield of 20 percent.     

Electron structure and reactivity of organofluorine compounds. 4. AMI calculations of anion radicals of primary,secondary, and tertiary perfluoroalkyl chlorides,bromides, and iodides

Calculations were carried out using the semiempirical quantum chemical AMI method for anion radicals (AR) of the perfluoroalkyl halides (R_FX): CF₃X, CF₃CF₂X, (CF₃)₂-CFX, and (CF₃)₃CX for X=Cl, Br, and I. All the AR's studied are thermally stable. The electron affinity of the perfluoroalkyl halides, and consequently, the thermal stability of their AR's increases in the series from F-methyl to F-tertbutyl halides and from the chlorides to bromides and iodides. During formation of an AR the spin density is preferentially localized on the * orbital of the C–X bond which leads to an increase in the distance between these atoms. Dissociation of the AR of tert-perfluorobutyl iodide to a perfluorocarbanion and an I atom is thermodynamically more favorable than dissociation with formation of a perfluoroalkyl radical and I^–.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1064–1068, May, 1990.     

Matrix IR studies on hydrogen-bonded complexes of hydrogen chloride and hydrogen bromide with ketene

Infrared spectra of matrices codeposited Ar/HX (X=Cl, Br) with Ar/H₂CCO mixtures have been examined. Isotopic substitutions (HX, DX, H₂CCO, D₂CCO) showed that ketene formed the 1:1 hydrogen-bonded complex with HX. The HX stretching modes were observed at 2684 cm⁻¹ in the H₂CCO–HCl complex and at 2384 cm⁻¹ in the H₂CCO–HBr complex. The ν₁ modes of the ketene submolecules were shifted to low frequency and the ν₉ modes to high frequency. It was proposed for the structure of the complex that the acid proton is bonded to the C=C pi electron system.     

1,1,1,3,3,-pentafluorobutane (HFC-365mfc): atmospheric degradation and contribution to radiative forcing

The rate constant for the reaction of the hydroxyl radical with 1,1,1,3,3-pentafluorobutane (HFC-365mfc) has been determined over the temperature range 278–323K using a relative rate technique. The results provide a value of k(OH+CF₃CH₂CF₂CH₃)=2.0×10⁻¹²exp(−1750±400/T) cm³ molecule⁻¹ s⁻¹ based on k(OH+CH₃CCl₃)=1.8×10⁻¹² exp (−1550±150/T) cm³ molecule⁻¹ s⁻¹ for the rate constant of the reference reaction. Assuming the major atmospheric removal process is via reaction with OH in the troposphere, the rate constant data from this work gives an estimate of 10.8 years for the tropospheric lifetime of HFC-365mfc. The overall atmospheric lifetime obtained by taking into account a minor contribution from degradation in the stratosphere, is estimated to be 10.2 years. The rate constant for the reaction of Cl atoms with 1,1,1,3,3-pentafluorobutane was also determined at 298±2 K using the relative rate method, k(Cl+CF₃CH₂CF₂CH₃)=(1.1±0.3)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹. The chlorine initiated photooxidation of CF₃CH₂CF₂CH₃ was investigated from 273–330 K and as a function of O₂ pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. Under all conditions the major carbon-containing products were CF₂O and CO₂, with smaller amounts of CF₃O₃CF₃. In order to ascertain the relative importance of hydrogen abstraction from the (SINGLE BOND)CH₂(SINGLE BOND) and (SINGLE BOND)CH₃ groups in CF₃CH₂CF₂CH₃, rate constants for the reaction of OH radicals and Cl atoms with the structurally similar compounds CF₃CH₂CCl₂F and CF₃CH₂CF₃ were also determined at 298 K k(OH+CF₃CH₂CCl₂F)=(8±3)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(OH+CF₃CH₂CF₃)=(3.5±1.5)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(Cl+CF₃CH₂CCl₂F)=(3.5±1.5)×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹]; k(Cl+CF₃CH₂CF₃)<1×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹. The results indicate that the most probable site for H-atom abstraction from CF₃CH₂CF₂CH₃ is the methyl group and that the formation of carbonyl compounds containing more than a single carbon atom will be negligible under atmospheric conditions, carbonyl difluoride and carbon dioxide being the main degradation products. Finally, accurate infrared absorption cross-sections have been measured for CF₃CH₂CF₂CH₃, and jointly used with the calculated overall atmospheric lifetime of 10.2 years, in the NCAR chemical-radiative model, to determine the radiative forcing of climate by this CFC alternative. The steady-state Halocarbon Global Warming Potential, relative to CFC-11, is 0.17. The Global Warming Potentials relative to CO₂ are found to be 2210, 790, and 250, for integration time-horizons of 20, 100, and 500 years, respectively. © 1997 John Wiley & Sons, Inc.     

Infrarot-Spektren und Normalkoordinatenanalyse von Salzen mit den AnionenX 3CSO 3 − (X=H,D, F,Cl)

Zusammenfassung Die IR-Spektren verschiedener Salze mit den Anionen CH₃SO₃ ^–, CD₃SO₃ ^–, CF₃SO₃ ^– und CCl₃SO₃ ^– sowie ein Raman-Skektrum des Ag[CF₃SO₃] werden mitgeteilt. Für die gen. Anionen sowie CH₃PO₃ ^2– und CD₃PO₃ ^2– wird mit einem für alle Ionen ähnlichen allgemeinen Valenzkraftfeld eine Normalkoordinatenanalyse durchgeführt. An den A₁-Schwingungen von CF₃SO₃ ^– und CCl₃SO₃ ^– sind mehrere Koordinaten beteiligt; eine charakterisische CS-Valenzschwingung tritt in diesen Ionen nicht auf.

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Infrared spectra and normal coordinate analysis of compounds with the anionsX ₃CSO₃ ^– (X=H, D, F, Cl)

The infrared spectra of several salts with the anions CH₃SO₃ ^– CD₃SO₃ ^–, CF₃SO₃ ^–, and CCl₃SO₃ ^– and Raman data for Ag[CF₃SO₃] are reported. A normal coordinate analysis using a GVFF is performed for these anions as well as for CH₃PO₃ ^2– and CD₃PO₃ ^2–. The A₁ modes of CF₃SO₃ ^– and CCl₃SO₃ ^– are mixed; consequently no characteristic CS stretching vibration occurs.

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Mit 3 Abbildungen     

Atmospheric chemistry of CF3CFCH2: Products and mechanisms of Cl atom and OH radical initiated oxidation

The products of Cl atom and OH radical initiated oxidation of CF₃CFCH₂ were studied in 700 Torr of N₂/O₂ diluent at 296 ± 1 K. The reactions of Cl atoms and OH radicals with CF₃CFCH₂ proceed via electrophilic addition to the double bond. The reaction with chlorine atoms proceeds 56 ± 5% via addition to the central carbon. The chlorine atom initiated oxidation of CF₃CFCH₂ gives CF₃C(O)F in a molar yield which is indistinguishable from 100% and independent of [O₂], and HC(O)Cl in a molar yield which increased from 30% to 59% as [O₂] was increased from 3 to 700 Torr. The OH radical initiated oxidation of CF₃CFCH₂ gives CF₃C(O)F as major product in a yield of 91 ± 6%. The results are discussed with respect to the atmospheric chemistry and environmental impact of CF₃CFCH₂.     

Towards the understanding of the spectroscopic behaviour of the C–H oscillator in C–HO hydrogen bonds: the effect of solvent polarity

The effect of solvent polarity versus specific C–HO contacts on the vibrational νC–H mode is studied using CHCl₃ as a model system. Ab initio SCI–PCM calculations show that the overall shift of the νC–H band, sometimes ascribed to the C–HO hydrogen bonding, can in fact be explained by the electrostatic interaction with a dielectric environment. The presence of a new νC–H band – assigned to the C–HO bonded forms – remains as the most reliable evidence of C–HO hydrogen bonding.     

Structures, electron affinities, and vibrational frequencies of the mono-, di-substituted SF6 radicals

Optimized molecular structures, electron affinities, and IR-active vibrational frequencies have been predicted using five different hybrid Hartree–Fock/density functional theory (DFT) methods for a series of mono-, di-substituted SF₆ compounds. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated [J.C. Rienstra-Kiracofe, G.S. Tschumper, H.F. Schaefer, S. Nandi, G.B. Ellison, Chem. Rev. 102 (2002) 231]. The equilibrium configurations of the anions and are found to be a zigzag geometry with ²A electronic state. Three different types of the neutral-anion energy separation reported in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The most reliable adiabatic electron affinities of the mono-, di-substituted SF₆ compounds obtained at the KMLYP function are 1.48 eV (SF₆), 3.20 eV (SF₅Cl), 3.49 eV (SF₅Br), 1.59 eV (SF₅CF₃), 3.21 eV (CF₃SF₄Cl), 3.59 eV (CF₃SF₄Br), 1.36 eV (CF₃SF₄CH₃), 2.32 eV (CF₃SF₄CF₃), respectively.