Fluorine atoms, abstraction reaction

The experimental investigations by Fagerstrom et al have shown that at a total pressure of 1000 mbar of SF6, the reaction is still in the fall-off regime. The fluorine atoms abstraction reactions, produced by radiolysis of the gas mixture containing SF6 in great excess, can initiate the H-abstraction reactions... 

The reactions of fluorine atoms with hydrocarbons are similar to those of active nitrogen in that they provide an essentially universal response. Fluorine atoms abstract H atoms from hydrocarbons at near-collisional reaction rates. Reactions with fluorine are highly exothermic, forming strong H—F (=570 kJ mol-1) and C—F (=485 kJ mol-1) bonds while breaking much weaker C—H (=414 kJ mor1) and C—C (=368 kJ mol-1) bonds. The hydrogen abstraction reaction... 

The low energy collisions of Si+ with perfluorohexane have been studied in the search for analogies with the ion-surface reactions at fluorinated alkane monolayer surfaces. A fluorine atom abstraction product was observed, SiF+, in analogy to the corresponding ion/surface reaction, though its abundance was relatively low with respect to fluorocarbon fragment ions39. 

Several different methods have been used successfully to generate a detectable concentration of short-lived free radicals inside the resonant cavity. The simplest method is a microwave discharge in the flowing gas, located upstream of the resonant cavity discharges in water vapour, for example, yield readily detectable concentrations of OH radicals. Shorter lived species have been produced by atom abstraction reactions inside the cavity, for example, by mixing fluorine atoms, produced by a microwave discharge in CF4, with a suitable secondary gas. Reaction of F atoms with OCS, for example, produces detectable concentrations of the SF radical [4],... 

The NH2 and OH radicals were produced by pulse radiolysis of the gas mixture SF6/NH3/H20, with SF6 always in great excess. The fluorine atoms formed initiate the hydrogen atom abstraction reactions... 

The reactions of F( P) atoms have been studied kinetically in a discharge-flow apparatus at 297 K. The major reaction channel for the F-hICl reaction forms IF + Cl, although a minor process yields CIF + I. Fluorine atoms react with CO and Xe slowly to yield COF2 and XeFj, respectively, but no reaction was detected with either He or Kr. Fluorine atoms abstracted hydrogen from HOF, generating OF radicals. The mechanisms of the reactions of F and OF radicals with NOF have been investigated by Schumacher et al. Quantum yields were shown to be... 

DFT calculations for the activation of fluoromethane and fluorobenzene at Ce and Ho have been performed revealing a harpoon-type mechanism for the metal-mediated fluoride abstraction.The reactions of the lanthanoid cations La Ce, Pr, and Yb with fluoromethane have also been investigated by DFT calculations. After coordination of Ln, electron transfer from Ln to fluoromethane takes place, followed by formation of LnF and a methyl radical. Mass spectrometric investigations which show gas-phase collisions of Nb with hexafluoro- and tetrafluorobenzene have been reported. The reaetions involve the transfer of four fluorine atoms to Nb. A systematic study on the reactivity of transition metal eations toward hexafluorobenzene in the gas phase has been performed by inductively coupled plasma (ICP) tandem mass spectrometry.Multiple fluorine atom abstraction dominates the chemistry observed for early transition metals, while association of hexafluorobenzene to the metal cation has been found for late transition metals. 

CFjCl, CFjCl CFaCl, and CFs CFaCT and CFCl, >-i have been made, and Arrhenius parameters for the rate-determining step F + RQ - R + CIF determined the heat of this reaction was estimated for each substrate, and the values were used to calculate a large number of C—Cl, C—F, and C—C bond strengths [e.g. Z)°(CC1 F—Cl) = 300 8 kJ mol ]. Kinetic isotope effects for H-atom abstraction reactions of fluorine atom with chloroform, methane, and hydrogen have been measured the results are those expected from the differences in zero-point energies for the relevant vibrations, so H-atom transfer by quantum mechanical tunnelling is apparently unimportant. ... 

The gaseous products of the "Co y-radiolysis (in Pyrex ampoules) of liquid trifluoroacetic acid at 23 C and of the polycrystalline acid at - 196°C have been identified (CgF, CHFg, COg, CO, Ha, and CgF, CHF3, COg, respectively) and their C-values determined. Failure to detect the formation of carbon tetrafluoride, tetrafluoroethylene, or silicon tetrafluoride was taken as circumstantial evidence for the non-occurrence of reactions involving fluorine-atom abstraction by trifluoromethyl radical or the generation of... 

The fluorination reaction is best described as a radical-chain process involving fluorine atoms (19) and hydrogen abstraction as the initiation step. If the molecule contains unsaturation, addition of fluorine also takes place (17). Gomplete fluorination of complex molecules can be conducted using this method (see Fluorine compounds, organic-direct fluorination). 

There are no abstractable hydrogen atoms on CF30, so that reaction with 02 is negligible (k < 4 X 10-17 cm3 molecule-1 s-1 at 373 K Turnipseed et al., 1994 Niki et al., 1994). In addition, the C-F bond is too strong for decomposition to give a fluorine atom and CFzO to take place. However, CF3Q reacts with NO,... 

No thermal reactions were observed at temperatures up to 350 °C. and there was no evidence for the abstraction of fluorine atoms. 

All aspects of the structure, reactivity and chemistry of fluorine-containing, carbon-based free radicals in solution are presented. The influence of fluorine substituents on the structure, the stability and the electronegativity of free radicals is discussed. The methods of generation of fluorinated radicals are summarized. A critical analysis of the reactivities of perfluoro-n-alkyl, branched chain perfluoroalkyl and partially-fluorinated free radicals towards alkene addition, H-atom abstraction, and towards intramolecular rearrangement reactions is presented. Lastly, a summary of the synthetically-useful chemistry of fluorinated radicals is presented. 

Due to the multiple desorption products, the etching of the surface with halogen appears to be quite complex. A multi-step reaction mechanism has been suggested to account for the SiCl2 desorption species. In the case of fluorine atom adsorption, F atom abstraction and dissociative chemisorption mechanisms have been suggested. In order to account for the complex surface reactions, more studies are needed. 

Of the two chain-propagating steps, then, step (2) is more difficult than step (3) (see Fig. 2.8). Once formed, methyl radicals react easily with any of the halogens it is how fast methyl radicals are formed that limits the rate of overall reaction. Fluorination is fast because fluorine atoms rapidly abstract hydrogen atoms from methane E cx. is only 1 kcal. lodination does not take place because iodine atoms. And it virtually impossible to abstract hydrogen from methane tLCt is more than 33 kcal. 

The free radicals CH3 and OH can be produced by different methods. A wide group of radicals is formed in the hydrogen abstraction reactions of hydrogen-containing molecules with fluorine atoms. Fluorine atoms can be produced by pulse radiolysis of the three-component mixtures SF6/CH4/H2O in the reactions... 

Valuable information on the kinetics and mechanism of CF3 + N02 comes from the experimental and theoretical study by Pagsberg et al,226 The experiments, performed using time-resolved infrared diode laser spectroscopy, were supported by ab initio calculations to provide insight into the potential energy surface of the reaction system. The reaction was initiated by pulse radiolysis of Ar/SF6/CF3I mixtures. The abstraction reaction of the iodine atom from CF3I by fluorine atoms leads to the formation of CF3 radicals. The reactions... 

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