Hexafluoride radicals

This also proves an earlier conclusion on hyperconjugation in an 0CH20 fragment of the 1,3-dioxolane cation radical this conclusion was based on mass spectrometry (To-dres, Kukovitskii et al. 1981). As calculated, the carbon-hydrogen bonds corresponding to 0CH20 in the radical cation are weaker than those in the neutral molecule. For this reason, this site exhibits a maximal probability that deprotonation will result in the formation of the 2-yl radical (Belevskii et al. 1998). In experiments, photoirradiation of 1,3-dioxolane solutions in sulfur hexafluoride at 77 K really leads to formation of the cation radical of 1,3-dioxolane and the l,3-dioxolan-2-yl radical as a result of deprotonation. Consecutive ring... 

Uranium trioxide is slightly basic, but with the exception of uranium hexafluoride, the salts formed by interaction with acids still contain two-thirds of its oxygen in the form of the uranyl radical, compounds of the type UOjR g being produced. On the other hand, however, the oxide acts towards strong bases as an acid anhydride, similar to chromic anhydride, and produces stable uranates. In contact with water it readily forms uranic acid, U02(0H)2. ... 

Syathesis of Perfluoro Aromatic Radical Cation Salts. Hexafluoro-benzeae Hexafluoroiridate(V). Hexafluorobenzene (2.6 mmol) was dissolved in tungsten hexafluoride (2 mL) in a fused silica reactor to give a yellow-green solution. Iridium hexafluoride (2 mmol) was condensed into the reactor at 77 K. At about 273 K, the reaction mixture melted, and a bright orange solid rose to the surface of the WFg. The solvent and excess CgF were removed under vacuum at 298 K. The dry orange solid decomposed rapidly, producing volatile carbon fluorides. Some of the iridium was reduced to the metal. 

The electron affinity of [XeF] (g) is therefore equal to —/(Xe) = —281 kcal. mole, plus the difference in bond-energy of [XeF]+(g) and XeF(g). If the latter is comparable to the average bond-energy in XeF2 (30 kcal. mole ) and the former is taken to be 60 kcal. mole, F(XeF ) = —251 kcal. mole. But the bond-energy in XeF radical cou d be lower, in which case F(XeF+) would be less exothermic, and could be brought as low as —236 kcal. mole". A value of (XeF (g) = 244 8 kcal. mole ) is realistic. This value is consistent with the instability of the salt [XeF]+[OsFj] towards decomposition to the noble-metal hexafluoride and xenon as in equation (1) and also with the stability of the iridium and platinum compounds towards such decomposition. 

In addition to iodonium, sulfonium and selenonium compounds, onium salts of bromine, chlorine, arsenic, and phosphoras are also stable and can act as sources of cation radicals as well as Bronsted acids, when irradiated with light. Performance of diaryl chloronium and diaryl bromonium salts was studied by Nickers and Abu. Also, aryl ammonium and aryl phosphonium, and an alkyl aryl sulfonium salt were investigated. It appears that the general behavior of these materials is similar to diphenyl iodonium and triphenyl sulfonium salts. These are formations of singlet and triplet states followed by cleavages of the carbon-onium atom bonds and in-cage and out of cage-escape reactivity. The anions of choice appear to be boron tetrafluoride, phosphorus hexafluoride, arsenic hexafluoride, and antimony hexafluoride. 

A recent approach in polymerization studies in our laboratory is the use of binary fluid mixtures of carbon dioxide with a traditional solvent to increase the precipitation thresholds and thus achieve higher molecular weights [26]. In this context AIBN initiated free-radical polymerization of styrene has been reported in mixtures of carbon dioxide with pentane, toluene and sulfur hexafluoride [26]. 

Figure 7. Weight average molecular weight of polystyrene ( x 10 ) from free-radical polymerization of styrene in carbon dioxide + sulfur hexafluoride mixtures. Left. Influence of SF6 content at 56 MPa and 51 °C, 5 hr polymerization time. Right Influence of pressure in the solvent mixture containing 30 % by mass SFe at 51 °C. Pressure dependence of the density (in g/cm ) of the solvent mixture is shown on the right coordinate. [1 MPa = 10 bar],...

It is apparent that substitution of fluorine for hydrogen initially causes a reduction in reactivity towards the electrophilic oxy n atom, but tetra-fluoroethylene is anomalous. A further study has indicated that substitution by trifluoromethyl has a strong deactivating effect compared with methyl, which has an activating effect. A study of the reactions of nearly thermal i F atoms, produced by F(n,2n) F and moderated by collisions with an excess of sulphur hexafluoride, with fluoro-oleflns (modes of addition were identified by scavenging the radicals produced with hydrogen iodide) has indicated that F atoms react preferentially with less-fluorinated olefins, and at the less-fluorinated end of a particular olefin. ... 

Full details are now available of the oxidative cleavage of ethers by uranium hexafluoride. An interesting new mild method of oxidative removal of p-methoxybenzyl ethers (used as alcohol protecting groups) employs as an electron-transfer reagent the stable cation radical (69), used either stoicheiometrically or in catalytic quantities, and regenerated electrochemically during the reaction (Scheme 48). 

Hexafluoroacetone has been used as a photochemical source of trifluoro-methyl radicals in kinetic studies dealing with attack of the latter on ethylene," di-isopropyl ketone, methylchlorosilanes, the methylsilanes MejSi, MejSiF, MeaSiFj, and MeSiFj, methyl acetate and deuteriated methyl acetates, dimethyl and di-isopropyl ether, tetramethyltin (less precise data were obtained with McsB, Me Si, and Me Ge), methyl formate, and hydrogen sulphide, deuterium sulphide, hydrogen chloride, and deuterium chloride. The photolysis of hexafluoroacetone alone has received further detailed attention and trifluoromethyl radicals thus generated have been shown not to attack sulphur hexafluoride even at temperatures up to 36S °C. ... 

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