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).

EPR spectra for the radical cations of a series of fluorinated benzenes, generated by irradiation with γrays in halocarbon solid matrices, have been observed at low temperatures. The spectra consist of a hyperfine structure with axially symmetric anisotropy mainly due to fluorine nuclei. The observed spectra have been analysed by simulation. Ab initio calculations have been conducted for the cation radicals to obtain their optimized geometries. The results reveal that an unambiguous deformation in geometry is brought about by cationization in each case. INDO calculations have been performed for the optimized geometries of these radical cations to calculate the hyperfine couplings. The calculated couplings strongly support the observed ones. The symmetry of the SOMO for the radical cations resembles that of the HOMO of their neutral mother molecules. The deformed geometries of these radical cations suggests that in the process of releasing an electron from an HOMO, those chemical bonds with bonding nature in the HOMO become elongated and those bonds with antibonding nature become shortened. It is concluded that the structure and symmetry of the SOMO of these radical cations are affected not only by the number of substitutions by fluorine but also by the position of substitution.

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Exposure of dilute solutions of stannanes in freon (CFCI,) at 77 K to 6oCo y-rays gave the parent radical cations. SnH, gave two well defined centres, both exhibiting very large hyperfine coupling to l17Sn and 119Sn. One, with CgV symmetry, showing strong coupling to a unique proton, is thought to have the unpaired electron confined to one Q Sn-H orbital with a large 5s contribution from tin. The other (C2" symmetry), with strong coupling to two equivalent protons, and formed initially in almost equal