Showing papers by "Ffrancon Williams published in 2006"

Structures of tetrafluorocyclopropene, hexafluorocyclobutene, octafluorocyclopentene and related perfluoroalkene radical anions revealed by electron spin resonance spectroscopic and computational studies.

Abstract: Isotropic and anisotropic ESR spectra were observed for the radical anions of hexafluorocyclobutene (c-C4F6-), octafluorocyclopentene (c-C5F8-) and perfluoro-2-butene (CF3CF=CFCF3-) in ?-irradiated ...

EPR studies of amine radical cations. Part 2. Thermal and photo-induced rearrangements of propargylamine and allylamine radical cations in low-temperature freon matrices.

Abstract: Matrix EPR studies and quantum chemical calculations have been used to characterize the consecutive H-atom shifts undergone by the nitrogen-centered parent radical cations of propargylamine (1b•+) and allylamine (5•+) on thermal or photoinduced activation. The radical cation rearrangements of these unsaturated parent amines occur initially by a 1,2 H-atom shift from C1 to C2 with π-bond formation at the positively charged nitrogen; this is followed by a consecutive reaction involving a second H-atom shift from C2 to C3. Thus, exposure to red light (λ > 650 nm) converts 1b•+ to the vinyl-type distonic radical cation 2•+ which in turn is transformed on further photolysis with blue-green light (λ ≈ 400−600 nm) to the allene-type heteroallylic radical cation 3•+. Calculations show that the energy ordering is 1b•+ > 2•+ > 3•+, so that the consecutive H-atom shifts are driven by the formation of more stable isomers. Similarly, the parent radical cation of allylamine 5•+ undergoes a spontaneous 1,2-hydrogen atom...