Trifluoroethylene radical

Table 6. Regioselectivities of addition of some fluoroalkyl radicals to trifluoroethylene [94]...

According to this literature survey, most investigations have been performed photochemically and in most cases, the monoadduct is composed of two isomers, the ratio of which depends upon the electrophilicity of the telogen radical. In the case of fluoroalkyl iodides, such an olefin exhibits the same reactivity towards these telogens, whatever their structure. In addition, trifluoroethylene seems less reactive than vinylidene fluoride but more reactive than hexafluoro-propene. 

The fluorine atoms in trifluoroethylene enhance the rate of attack by the nucleophilic methyl radicals, but retard attack by the electrophilic trifluoromethyl radicals. Methyl radicals add preferentially to the most substituted end of trifluoroethylene, in direct contradiction of the resonance stabilization hypothesis. In fact we can see that the reaction of methyl radicals... 

Table 12 there is a marked increase in the orientation ratio as the attacking radical becomes more bulky. With vinylidene fluoride the orientation ratio for perfluoro-t-butyl radicals is too large to measure. Even with perfluoro-isopropyl the orientation ratio (kjk is 103. In the other tables the orientation ratios for addition to vinyl fluoride and trifluoroethylene vary only slightly, but in Table 12 there is a marked increase as the radical becomes more branched. Perhaps the most striking feature of the table is that the increase in orientation ratio is almost entirely due to a reduction in the rate of addition to the most substituted end of the olefin. The relative rates of attack at the unsubstituted ends of vinyl fluoride and vinylidene fluoride vary only slightly across the table. In other words, the high orientation ratio is almost entirely due to the difficulty of addition at the substituted end of the olefin, a conclusion supported by the great variation in the relative rate of addition to tetrafluoroethylene (i.e. where both ends are fully substituted). 

The orientation ratios (vinyl fluoride and trifluoroethylene... 

The simple model predicts that the highly electronegative CF3- radical should add preferentially to CH2 in vinyl fluoride and CHF in trifluoroethylene. For the weakly electropositive methyl radical, either weak thermodynamic control or even contrathermodynamic control is predicted. The ab initio minimal basis set calculations fall in line with these qualitative predictions, except that for the attack of CH3 on trifluoroethylene no preferential site of attack is found. The activation energy differences calculated by Salem are compared with the experimental results in Table 21. Although the absolute values of the activation energies are too large, the differences reproduce qualitatively the experimental trend. 

Free radicals with single electrons on the carbons of the trifluoroethylene combine with the double bond of butadiene in both possible ways carbon of the difluoromethylene joins either the terminal carbon of the butadiene or the internal end of the double bond of the butadiene. The biradicals thus formed cyclize to R, 2,3,3-trifhioro-l-vinylcyclobutane, and S, 2,2,3-trifluoro-l-vinylcyclobutane, both as 1 1 mixtures of cis- and trans-isomers. 

Fluorine and hydrogen appear comparable as radical-stabilizing groups, for both 1,1-difluoroethylene and trifluoroethylene react with butadiene to give mixtures of [2 + 2] regioisomers, as well as some [2 + 4] products. " Captodative substituted alkenes, not surprisingly, are well suited to [2 + 2] cycloadditions. ... 

The majority of vinyl polymers are regioregular with a head-to-tail sequence of monomer units (0, i.e. they are isoregic (2). Some of the most notable exceptions are the polymers obtained by free-radical addition reactions of the fluoroethylenes vinyl fluoride (VF), vinylidene fluoride (VF2), and trifluoroethylene (F3E), which incorporate significant amounts of head-to-head and tail-to-tail structural defects caused by reverse monomer addition (3). 

Chlorotrifluoroethylene n. C1FC=CF2. A colorless gas. The monomer for poly-chlorotrifluoroethylene. It is obtained by either dehalogenation or dehydrohaloge-nation of saturated chlorofluorocarbons or chlorohydrocarbons, e.g., by reacting 1,1,2-trichlorotrifluoroethane with zinc. The monomer for the preparation of po-lychloro-trifluoroethylene by free radical polymerization in aqueous systems. 

The most comprehensive table of relative results is Table VI in which the orientation ratios for the addition of an extensive range of fluoroalkyl radicals to vinyl fluoride, 1, 1-difluoro-ethylene and trifluoroethylene are listed. Although all radicals add preferentially to the CH2- end of vinyl fluoride and 1, 1-di-fluoroethylene, the orientation of addition to trifluoroethylene depends on the radical. The "electrophilic" radicals adding preferentially to the CHF- site and the nucleophilic radicals adding preferentially to the CF2- site. In the radical series... 

Orientation Ratios ( p) for the Addition of Alkyl Radicals to Vinyl Fluoride, 1, 1-Difluoroethylene and Trifluoroethylene at 1500... 

Re-investigation of the thermally-initiated addition reactions between trifluoroiodomethane and vinyl fluoride and propene has shown that at 200 °C both olefins yield a mixture of 1 1 adducts, but in each case the major isomer is derived from trifluoromethyl radical attack on the CH, group. Bi-directional addition was also observed in thermal reactions between trifluoroiodomethane and trifluoroethylene and hexafluoropropene, the product isomer ratios following closely those found in u.v.-initiated reactions."... 

Free-radical Reactions.— Publications have appeared dealing with the results of kinetic studies on the following gas-phase reactions photoaddition of hydrogen bromide to tetrafluoroethylene, trifluoroethylene, cis- and trans-1,2-difiuoroethylene, and vinyl fluoride the thermal reaction of tetra-fiuoroethylene with hydrogen iodide to yield mainly 1,1,2,2-tetrafluoroethane and iodine photoaddition of perfluoro-n-propyl iodide to trifluoroethylene, vinylidene fluoride, and vinyl fluoride photochlorination of perfluoro-... 

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