Migration Of Fluorine Atoms Research Articles

Rearrangements of the Radical Cations of 3-Aryl-5-fluoroisoxazoles: Further Evidence for Existence of Benzocyclopropenyl Cation.

The fragmentation reaction of the radical cations of 3-aryl-5-fluoroisoxazoles formed via EI-MS is described. A new rearrangement accompanied by fluorine atom migration is discovered. A mechanistic rationale for the rearrangement supporting the existence of a fluorinated benzocyclopropenyl cation was proposed based on the experimental data and quantum chemical calculations.

Probing the Reaction Mechanisms of 3,5-Difluoro-2,4,6-Trinitroanisole (DFTNAN) through a Comparative Study with Trinitroanisole (TNAN).

To probe the thermal decomposition mechanisms of a novel fluorinated low-melting-point explosive 3,5-difluoro-2,4,6-trinitroanisole (DFTNAN), a comparative study with trinitroanisole (TNAN) was performed under different heating conditions. The thermal decomposition processes and initial reactions were monitored by DSC-TG-FTIR-MS and T-jump-PyGC-MS coupling analyses, respectively. The results show that fluorine decreased the thermal stability of the molecular structure, and the trigger bond was transferred from the ortho-nitro group of the ether to the para-nitro group. The possible reaction pathway of DFTNAN after the initial bond breakage is the rupture of the dissociative nitro group with massive heat release, which induces the ring opening of benzene. Major side reactions include the generation of polycyclic compounds and fluorine atom migration. Fluorine affects the thermal stability and changes the reaction pathway, and fluorinated products appear in the form of fluorocarbons due to the high stability of the C-F bond.

1,2-Fluorine Radical Rearrangements: Isomerization Events in Perfluorinated Radicals.

Devising effective degradation technologies for perfluoroalkyl substances (PFASs) is an active area of research, where the molecular mechanisms involving both oxidative and reductive pathways are still elusive. One commonly neglected pathway in PFAS degradation is fluorine atom migration in perfluoroalkyl radicals, which was largely assumed to be implausible because of the high C-F bond strength. Using density functional theory calculations, it was demonstrated that 1,2-F atom migrations are thermodynamically favored when the fluorine atom migrated from a less branched carbon center to a more branched carbon center. Activation barriers for these rearrangements were within 19-29 kcal/mol, which are possible to easily overcome at elevated temperatures or in photochemically activated species in the gas or aqueous phase. It was also found that the activation barriers for the 1,2-F atom migration are lowered as much as by 10 kcal/mol when common oxidative degradation products such as HF assisted the rearrangements or if the resulting radical center was stabilized by vicinal π-bonds. Natural bond orbital analyses showed that fluorine moves as a radical in a noncharge-separated state. These findings add an important reaction to the existing knowledge of mechanisms for PFAS degradation and highlights the fact that 1,2-F atom shifts may be a small channel for isomerization of these compounds, but upon availability of mineralization products, this isomerization process could become more prominent.

Absence of a stable atomic structure in fluorinated graphene.

Based on the results of first-principles calculations we demonstrate that significant distortion of graphene sheets caused by adsorption of fluorine atoms leads to the formation of metastable patterns for which the next step of fluorination is considerably less energetically favorable. Existence of these stable patterns oriented along the armchair direction makes possible the synthesis of various CFx structures. The combination of strong distortion of the nonfluorinated graphene sheet with the doping caused by the polar nature of C-F bonds reduces the energy cost of migration and the energy of migration barriers, making possible the migration of fluorine atoms on the graphene surface as well as transformation of the shapes of fluorinated areas. The decreasing energy cost of migration with increasing fluorine content also leads to increasing numbers of single fluorine adatoms, which could be the source of magnetic moments.

Structure and solvent-resistant property of fluorinated polyurethane elastomer

A series of main-chain fluorinated casting polyurethane elastomer (CFPU) based on fluoropoly(oxyalkylene)diol (FPOA) were prepared via bulk polymerization and prepolymer process. Polybutylene adipate glycol (PBA) was combined with FPOA as a soft-segment. It was found that the significant difference of solubility parameters of PBA soft-segment and FPOA soft-segment, and two detectable peaks corresponding to the Tg of these two segments from DMA analysis indicated that the two blocks were immiscible and formed the phase separation structure. By SEM analysis, three types of micro-structure of CFPU can be observed. With increasing FPOA/PBA mass ratio, the size of the spherical dispersion phase formed by PBA soft-segment block embedded in FPOA soft-segment block declined, and the more uniform dispersion and the more clear interface indicated the increasing phase separation. With increasing FPOA/PBA mass ratio, the equilibrium swelling ratio and the swelling rate constant k in cyclohexanone and xylene decreased, while for the sample after etching in cyclohexanone, the matrix folds almost disappeared, and the “worm like” structure became unobvious, resulting in an enhanced solvent resistance of CFPU by a shield protective effect of FPOA soft segment on the hydrocarbon chain segment. Moreover, the migration of fluorine atoms to the surface of the sample of CFPU resulted in a decrease of surface polarity and the surface tension. With increasing FPOA/PBA mass ratio, the tensile strength and elongation at break, hardness and storage modulus all decreased.

Matrix Isolation of the Elusive Fluorocarbonylsulfenyl Fluoride Molecule FC(O)SF

The syn and anti conformers of the hitherto unknown fluorocarbonylsulphenyl fluoride FC(O)SF were formed through the photochemical reactions between OCS and F(2), isolated in solid Ar. The reactions were followed by Fourier transform infrared (FTIR) spectroscopy, and the unknown products were proposed by comparison of the observed IR absorptions with their computed IR spectra. The reactions occur through a 1:1 molecular complex between OCS and F(2), forming the anti-FC(O)SF first, which subsequently transforms into the syn form, through a randomization process. At longer times of irradiation, FC(O)SF decomposes by extrusion of a CO molecule with the concomitant formation of SF(2) and the formation of a difluorophosgene molecule, O═CF(2). The migration of fluorine atoms in the matrixes is proposed to explain the formation of SF(4) and SF(6).

Surface immobilisation of fluorinated polystyrene-acrylate latex nanoparticles with core-shell structure by crosslinking

Fluorinated polystyrene-acrylate (PSA) latex nanoparticles with core–shell structure were synthesised by two-stage seeded emulsion polymerisation method in the presence of reactive emulsifier DNS-86. Diallyl phthalate (DAP) and Vinyltriethoxysilicone (VTES) were used as crosslinking agent to immobilise the fluorinated copolymer on the surface of the latex film. Fourier transform infrared spectroscopy (FTIR) spectra show that fluorine and siloxane monomers were effectively involved in the emulsion copolymerisation. Transmission electron microscope (TEM) observation shows that the prepared emulsion particles had a core–shell structure with fluorinated copolymer in the shell. X-ray photoelectron spectroscopy (XPS) analysis reveals that fluorine atom has the tendency of migrating to the film–air interface and the incorporation of VTES helps the migration of fluorine atom towards the film–air interface. Water contact angle (WCA) test proved that DAP and VTES as crosslinking agent can immobilise the fluorinated copolymer on the surface of the latex films. © 2011 Canadian Society for Chemical Engineering

Intra–Intermolecular Criss‐cross Cycloaddition of Nonsymmetrical Allenylazines with Fluorinated Enones as an Initial Step in the Synthesis of4H‐Pyrrolo[1,2‐b]pyrazoles

AbstractNonsymmetrical allenylazines undergo, in boiling xylene, intramolecular cycloaddition by forming an unstable 1,3‐dipole that reacts with an added dipolarophile. In this paper we report the first intra–intermolecular criss‐cross cycloaddition with a fluorinated enone. Although the expected products with three fused heterocycles were not isolated, new bicyclic products were found and characterized. These compounds are formed by a spontaneous transformation involving fluorine atom migration and hydrogen fluoride elimination. A mechanism of the reaction is discussed to explain the formation of these new heterocycles. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Elimination of difluorocarbene from the molecular ions of α,α,α‐Trifluorocresols with a fluorine atom migration in an ion trap mass spectrometer

The elimination of difluorocarbene (CF2) from the molecular ions of m-α,α,α-trifluorocresol (MW 162, 1) and p-α, α, α-trifluorocresol (MW 162, 2) upon electron impact have been investigated using a quadrupole ion trap mass spectrometer. This reaction involves a fluorine (F) atom migration from the trifluoromethyl group to the benzene ring. In the case of 1, an F atom migrates via a four-membered ring transition state to give rise to the molecular ion of p-fluorophenol (MW 112, 5) and a small amount of o-fluorophenol (MW 112, 3). On the other hand, in the case of 2, an F atom migrates to the ipso position of the benzene ring via a three-membered ring transition state to give rise to 5+. These conclusions were confirmed by the comparison of the energy-resolved mass spectra (collision-induced dissociation (CID) spectra versus collision energy) of the m/z 112 ions from 1+ and 2+ with those of reference compounds, o-, m- and p-fluorophenol (3–5). Copyright © 1999 John Wiley & Sons, Ltd.

Elimination of difluorocarbene from the molecular ions of alpha, alpha,alpha-trifluorocresols with a fluorine atom migration in an ion trap mass spectrometer.

The elimination of difluorocarbene (CF(2)) from the molecular ions of m-alpha,alpha,alpha-trifluorocresol (MW 162, 1) and p-alpha, alpha, alpha-trifluorocresol (MW 162, 2) upon electron impact have been investigated using a quadrupole ion trap mass spectrometer. This reaction involves a fluorine (F) atom migration from the trifluoromethyl group to the benzene ring. In the case of 1, an F atom migrates via a four-membered ring transition state to give rise to the molecular ion of p-fluorophenol (MW 112, 5) and a small amount of o-fluorophenol (MW 112, 3). On the other hand, in the case of 2, an F atom migrates to the ipso position of the benzene ring via a three-membered ring transition state to give rise to 5(+). These conclusions were confirmed by the comparison of the energy-resolved mass spectra (collision-induced dissociation (CID) spectra versus collision energy) of the m/z 112 ions from 1(+) and 2(+) with those of reference compounds, o-, m- and p-fluorophenol (3-5).

Fluorine migration in dimerization of tetrafluorodisilacyclobutene mediated by Group VI transition metal carbonyls

The photochemical dimerization of 1,1,2,2-tetrafluoro-1,2-disilacyclobutene mediated by Group VI transition metal carbonyls generates (fluorosilyl)(trifluorosilyl)alkenes ( 5) by fluorine atom migration. The electronic properties (hardness) of the central metal influence the selection of the reaction pathway: F migration to give the dimer 5 or further oxidative addition to give the tetrasilyl transition metal compound 7 or 9.

Loss of CO from the molecular ions of o‐, m‐ and p‐anisoyl fluorides, CH3OC6H4COF, with fluorine atom migration

AbstractLoss of CO from the molecular ions ([CH3OC6H4COF]+˙) of o‐, m‐ and p‐anisoyl fluorides has been investigated by mass‐analysed ion kinetic energy (MIKE) spectrometry. This reaction involves fluorine atom migration from the carbonyl group to the benzene ring.In the cases of o‐ and p‐anisoyl fluorides, the fluorine atom migrates via a three‐membered transition state to form the molecular ions ([CH3OC6H4F]+˙) of o‐ and p‐fluoroanisoles, respectively. On the other hand, in the case of m‐anisoyl fluoride, the fluorine atom migrates from the carbonyl group to the benzene ring via a three‐ or four‐membered transition state.

ChemInform Abstract: A Study of Ion‐Molecule Reactions in the Gas Phase. Part 3. The Reactions of Methyl and Fluoromethyl Cations with Alkenes and Fluoroalkenes in the Gas Phase.

AbstractThe reactions of CH3+, CH2F+, CHF2+, and CF3+ with ethene, fluoro‐, 1,1‐difluoro‐, trifluoro‐, and tetrafluoro‐ethene and with propene, but‐1‐ene, but‐2‐ene, and 2‐methylpropene have been studied in the gas phase.

A study of ion–molecule reactions in the gas phase. Part 3. The reactions of methyl and fluoromethyl cations with alkenes and fluoroalkenes in the gas phase

The reactions of CH3+, CH2F+, CHF2+, and CF3+ with ethene, fluoro-, 1,1-difluoro-, trifluoro-, and tetrafluoro-ethene and with propene, but-1-ene, but-2-ene, and 2-methylpropene have been studied in the gas phase. As well as simple charge exchange, addition reactions were observed in which the initial adduct broke down to yield neutral fragments and ions of either general formula (CnX2n+1)+ or (CnX2n–1)+, where X = H and/or F. The fragmentation of the initial transient adduct ion was often associated with hydrogen atom and/or fluorine atom migration.

Photolysis of perfluoro-alicyclic ketones

Photolysis in the gas phase of perfluorocyclo-pentanone, -hexanone, -heptanone, and -octanone at 3130 A is reported. Migration of fluorine atoms is not observed, and in the case of the pentanone and hexanone, the only products observed were carbon monoxide and a cyclic fluorocarbon. From perfluorocycloheptanone, perfluorocyclohexane, carbon monoxide, perfluorocyclopentane, and tetrafluoroethylene were the photolysis products. Photolysis of the perfluorocyclo-octanone gave rise to perfluorocycloheptane, carbon monoxide, perfluorocyclohexane, perfluorocyclopentane, and tetrafluoroethylene. A mechanism involving diradical intermediates is proposed.