Fluoride-carbon bond, stability

It was found that treatment of a mixture of 120 and 121 with tris(diethylamino-sulfonium) trimethyldifluorosilicate [TASF(Et)] resulted in smooth addition-elimination to the naphthoquinone to form the y-alkylation product 125 (85 %). TASF(Et) is a convenient source of soluble, anhydrous fluoride ion [47]. It is believed that exposure of 121 to TASF(Et) results in fluoride transfer to generate a hypervalent silicate anion, as depicted in structure 124. The transfer of fluoride between TASF(Et) and 121 may be driven by stabilization of the anionic species 124 by delocalization of the carbon-silicon bond into the LUMO of the unsaturated ketone. 1,4-Addition-elimination of this species to the naphthoquinone 120 would then form the observed product. 

Equilibrium distributions of aqueous and solid-phase uranium at various pH and CO2 conditions were calculated by the computer code MD TEQA2 [7]. The version 3.11 of MD TEQA2 contains 63 kinds of complexation reactions of U with ligands and the stability constants of each reaction. The U species, considered in these complexation reactions are U02 and U. The ligands such as hydroxide, chloride, carbonate, fluoride, sul te, phosphate, and silicate are included. In this study, 20 kinds of complexation reactions of U were added to the code to increase the reliability of the model calculations. The stability constants in the code were also updated. New complexation reactions and stability constants were referred to by the studies of Grenthe and Bond [8,9]. In this model calculation, complexation reactions of U02 with hydroxide and carbonate ions were considered. The species of and ligands such as chloride, sul te and phosphate were not included considering our experimental conditions. 

Host commercially available fluoroelastomers consist of copolymers of vlnylidmie fluoride (VF2 ) with hexafluoropropylene (HFP), and, optionally, tetrafluoroethylene (TFE)(1,2) these highly fluorinated polymers of 62-70 wt % fluorine have remarkable resistance to flame, chemicals, solvents and oxidative attack. This stability has been attributed to the strength of the carbon-fluorine bond compared to that of the carbon-hydrogen bond, to steric hindrance due to the presence of fluorine, and to strong van der Haals forces between hydrogen and fluorine atoms present in the macromolecules. 

The last two trends are particularly relevant to the elimination reactions of the 2-hexyl halides. As indicated by the data in Table 10.7, leaving group ability in methanol solution follows the trend I > Br > Cl > F. In comparison with the other 2-hexyl halides, therefore, the transition structure for 2-hexyl fluoride should have relatively more carbanion character. Therefore, the stabilities of the developing carbon-carbon double bonds are less important in determining values of AG for 2-hexyl fluoride than is the case for the other 2-hexyl halides. ° ... 

The reaction of tetramethylsilane with fluorine led to the isolation of several, partially fluorine-substituted tetramethylsilanes (see Tables VII-IX), and preservation of over 80% of the silicon-carbon bonds in the initial, tetramethylsilane reactant. The stability of many of the partially fluorinated germanes and silanes (some are stable to over 100°C) is very surprising, for the possibility of elimination of hydrogen fluoride is obvious. Indeed, before the first reported synthesis (12) of... 

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