Electron spin resonance studies of electron attachment to fluorocarbons and related compounds

Abstract

Radical anions of three perfluorocycloalkanes and several halogenofluoromethanes have been detected and identified by e.s.r. studies following Y irradiation at 77 K of solid solutions containing up to 5 mol % of the parent co:npound in neopentane or tetramethylsilane. The isotropic e.s.r. spectra of c-C3Fa, c-C4FC and c-C5F10 are photobleached by visible light and show the second-order structure characteristic of 6, 8 and 10 equivalent fluorines, respectively, the total 19F coupling being approximately the same value (1 170 & 20 G) in each case. Identical e.s.r. spectra were generated in photoionization experiments using tetramethyl-p-phenylenediamine, confirming the radical anion identifications. The equivalence of the fluorines indicates that the unpaired electron is delocalized over the entire molecular framework in an orbital of high symmetry. The e.s.r. spectra of the CF3X-radical anions (X = C1, Br, I) were anisotropic and showed clear evidence for axially symmetric hyperfine interactions with three equivalent fluorines and the unique halogen. On this basis, a matrix diagonalization program was used to calculate the line positions and the best-fit e.s.r. parameters obtained. Confirmation of the CF3X-identifications was achieved by parallel photoionization experiments and by studies showing that the decay of the CF3X-spectrum in neopentane above 100 K was accompanied by a growth in the spectrum of the CF3 radical. The spin density distributions calculated from the e.s.r. parameters of these congeneric radical anions suggest that the unpaired electron resides in an al (a*) antibonding orbital which is composed largely of thep orbitals from carbon and the unique halogen which lie along the C3" symmetry axis of the radical anion. Consistent with this proposal, the spin densities in the s andp oribtials of the unique halogen increase along the series C1, Br, I, which is the order expected for the effect of decreasing halogen electronegativity .* G (gauss) = lop4 T (tesla).

The chemical effects of ionizing radiations on fluorinated ethers

“…A wealth of valuable information also come from mass spectrometry studies; however, care should be taken in this case when extrapolating the results to condensed phases because of the ineffi- In this paper, the properties of the fluoroethers anion radicals are investigated by low-temperature UV-Vis matrix spectroscopy using photoelectrons emitted from N,N 0 -dimethyl paraphenylene diamine (TMPD) at 250-320 nm [40] and, because of solubility problems, the model compound HCF 2 OCF 2 CF 2 OCF 2 HÁ(HFC). The experiments were performed at 77 K using the neat HFC compound or HFC solutions in tetramethyl silane (Fig.…”

Electron attachment to CF3Cl and CH3Cl on the surface and in the bulk of solid Kr

“…28 In many of these studies, attachment of secondary electrons to molecules was postulated in order to explain the presence of anions. ESR studies on matrix isolated halocarbons following irradiation also revealed that certain products that exist as weakly bound negative ion complexes could arise from incomplete DEA, 32 suggesting that electron attachment to dissociative molecular states also leads to stabilization due to the constrictive cage effect of the crystalline lattice. The cage effect is similar to the resonance stabilization process; however, there is a subtle difference in the mechanisms between the resonance stabilization and the stabilization due to the cage.…”

A quantum mechanics-molecular mechanics study of dissociative electron transfer: The methylchloride radical anion in aqueous solution

“…in solution, these values being in good agreement with the degree of charge transfer observed for these complexes in argon matrix. 4,[10][11][12] Figure 4 shows the water hydrogens-chlorine atom radial distribution functions ͑RDF͒. In the case of the neutral molecule, the solutesolvent interaction is not enough to give a well-defined solvation shell around the chlorine atom.…”

“…9 The radical anions of organic halides can also be generated by ␥ irradiation in lowtemperature matrices of inert solvents and studied by means of EPR spectroscopy. [10][11][12] The most unstable halide radical anions are characterized as being of * type, i.e., the attached electron resides in a antibonding C-X orbital. Nitroaryl-containing radical anions, which are more persistent have the attached electron in a mixed * -* orbital.…”