Journal Articles (before-1995)
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Item Photolysis of 3-Methyl-3-chlorodiazirine(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (12), 1977) Frey, Henry M; Penny, David EThe photolysis of 3-methyl-3-chlorodiazirine has been investigated in the gas phase at pressures (with added bath gases) up to 6000 Torr (800 kPa). The principal products were vinyl chloride, nitrogen, acetylene, hydrogen chloride and 1,1-dichloroethane. The experimental results indicate that the vinyl chloride is formed with a very wide energy spread; at low pressures most of it decomposes to yield acetylene and HCl. Evidence is presented that the dichloroethane results from the reaction of methylchlorodiazomethane, formed by photoisomerization from the diazirine, with the HCl produced in the system. There is no evidence that trapping by HCl of methylchlorocarbene, formed as the primary decomposition product of the electronically excited methylchlorodiazirine, can be more than a minor reaction pathway.Item Energy Distribution and Mechanism in 3-Chloro-3-methyldiazirine Photolysis(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (04), 1978) Figuera, Juan M.; Perez, Juan M.; Tobar, AuroraGas-phase photolysis of pure 3-chloro-3-methyldiazirine over a wide range of pressure (133- 1.015 x 105 N m~2) was performed at 334 and 313 nm. The reaction produces “ hot ” vinyl chloride with enough energy to subsequently decompose. The fit ot calculated (RRKM) to experimental rates for this decomposition allows determination of energy distribution functions of the vinyl chloride compatible with the data. A close examination of these functions shows that at least two pathways of vinyl chloride formation are required to explain the experimental results.Item Photolysis of Cycloheptanon(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (07), 1974) Frey, Henry M.; Mautner, Gillian N.The photochemical decomposition of cyclohcptanonc lias been studied in the gas phase as a function of pressure, temperature and wavelength. The major products arc carbon monoxide, hcx-l-cnc, cyclohexane and hcpt-6-enal. Quantum yields of the hydrocarbons and aldehyde were determined at 313 nm and 100'C over a range of ketone pressures. The results indicate that the hydrocarbons have a common precursor and that they arc produced by a higher energy pathway than the aldehyde. A mechanism involving a triplet state intermediate is suggested.Item Photolysis of alkyloxy vanadium(V) chelates. A possible general route to alkyloxy radicals(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (05), 1977) Aliwi, Salah M.; Bamford, Clement H.We have studied the photochemical reactions (λ= 365 nm) of nineteen vanadium(V) chelates of structure VOQ2OR where Q is the 8-quinolyloxo ligand and R is an alkyl group. In all cases photolysis proceeds in a first-order fashion to yield the vanadium(IV) chelate VOQ2 identified by u.v.-visible and e.s.r. spectroscopy. The VV chelates photoinitiate free-radical polymerization and the quantum yields of photoinitiation with methyl methacrylate as monomer have been determined and compared with the quantum yields of chelate photodecomposition. Each molecule of chelate decomposing gives rise to one initiating radical. The dependence of the quantum yield of photodecomposition ϕd on the nature of R is discussed. The inductive effect of R, which influences the natures of the V[double bond, length as m-dash]O and V—OR bonds, also affects ϕd and a correlation between the stretching frequency of V[double bond, length as m-dash]O and ϕd has been found. The photolytic products in benzene solution have been examined by spin-trapping and g.l.c. techniques; results are consistent with the primary formation, isomerization and β-scission of alkyloxy radicals.Item Photolysis of azocyclohexane alone and in an oxygen atmosphere(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (10), 1974) Currie, James L.; Sidebottom, Howard W.; Tedder, John M.The photolysis of azocyclohexane involves excited molecules which can be deactivated by collision or decompose into cyclohexyl radicals and nitrogen. Arrhenius parameters for reaction (11) have been estimated, cyclo-C6H11·+(cyclo-C6H11)N2 [graphic omitted] cyclo-C6 H12+ cyclo-C6H11N2-cyclo-C6H10˙k11= 105.6±0.1 exp(–6600 ± 1000 cal mol–1/RT) dm3 mol–1 s–1 and a disproportionation/combination rate constant ratio of 0.99 ± 0.10 for cyclohexyl radicals has been determined. The photolysis of azocyclohexane in an oxygen atmosphere and in the presence of cyclohexane yields cyclohexyl hydroperoxide and cyclohexanone as principal products. The results show that these are formed through a radical/radical reaction and no chain process is involved. Evidence is presented to show that the minor products, cyclohexene and water, are formed via a cyclohexyl-trioxyl radical cyclo-C6H11O3˙.Item Quenching and Isomerization in the Photolysis of trans-But-2-ene and cis-Pent-2-ene at 185 nm and 203 nm(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (2), 1972) Borrell, Peter; Cervenka, AAdditional results on the effect of additives on the product yields in the vapour-phase photolysis of trans-but-2-ene and cis-pent-2-ene are reported. They confirm, extend and reconcile our previous results with those of Chesick. The main photoreaction could be quenched by all additives at both wavelengths; at 203 nm, and with some additives at 185 nm, quenching was accompanied by photoisomerization. The effects can be correlated with the two states, Rydberg and V(π→π*), which are excited at the two wavelengths. Collisional deactivation of the V state results in photoisomerization while when the R state is deactivated no isomerization occurs. Apparently there is no ready collisional interconversion of the R and V states.Item Photochemistry of Anhydrides: Part 2.—Photolysis of Perfluoropropionic Anhydride : A New Source of C2F5 Radicals(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Chamberlain, G. A.; Whittle, E.The photolysis of the vapour of (C2F5CO)2O in the temperature range 20–213°C is described quantitatively by the overall reaction (C2F5CO)2O +hν→ CO + CO2+ n-C4F10, with the effective primary process being (C2F5CO)2O +hν→ CO + CO2+ 2C2F5. The anhydride was photolyzed in the presence of both CH4 and cyclohexane and the following reactions occur: C2F5+ CH4→ C2F5H + CH3(7), C2F5+ c-C6H12→ C2F5H + c-C6H11(8), C2F5+ C2F5→ C4F10. (4) For these reactions, log(k7/k½c)/(cm[fraction three-over-two] mol–½ s–½)=(5.01 ± 0.28)–(11490 ± 560)/θ, log(k8/k½c)/(cm[fraction three-over-two] mol–½ s–½)=(5.68 ± 0.25)–(6440 ± 380)/θ, where θ= 2.303 RT/cal mol–1 and kc is the rate constant for reaction (4). It is concluded that Arrhenius parameters for abstraction of H from a given RH by CF3, C2F5 and n-C3F7 radicals are almost identical. When (C2F5CO)2O is photolyzed with cyclohexene both H-abstraction (kH) and addition to the double bond (kadd) occur with log(kH/kadd)=(0.67 ± 0.07)–(2530 ± 120)/θ.Item Photochemistry of Anhydrides: Part 1.—Photolysis of Perfluoroacetic Anhydride Vapour: A New Source of CF3 Radicals(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Chamberlain, G. A.; Whittle, E.The photolysis of perfluoroacetic anhydride was studied in the temperature range 19–177°C using wavelengths in the range 254–265 nm. The photolysis is exceptionally simple and is quantitatively described by the reactions (CF3CO)2O +hν→ 2CF3+ CO + CO2, CF3+ CF3 [graphic omitted] C2F6, The anhydride was tested as a source of CF3 radicals by photolyzing it in the presence of CH4 and of cyclohexane. For the reactions CF3+ CH4→ CF3H + CH3(7), CF3+ c-C6H12→ CF3H + c-C6H11, (12), we obtain log(k7/k1c)/(cm3/2 mol–1/2 s–1/2)=(5.93 ± 0.32)–(12500 ± 700)/θ, (logk12/k1/2c)/(cm3/2 mol–1/2 s–1/2)=(5.18 ± 0.15)–(5560 ± 220)/θ, where θ= 2.303 RT/cal mol–1. These results agree with previous ones obtained using conventional sources of CF3 radicals. We conclude that perfluoroacetic anhydride is a convenient new source of CF3 radicals.Item Photolysis of Dibromodifluoromethane at 265 nm(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (8), 1972) Walton, J CThe gas phase photolysis of CF2Br2 at 265 nm has been studied over a range of pressures and temperatures. The products are formed by combination reactions of the bromodifluoromethyl radicals and bromine atoms. Quantum yield measurements on the dimer CF2BrCF2Br suggest that the combination of bromodifluoromethyl radicals with bromine atoms is third order at the pressures studied. The quantum yield decreases with increasing pressure of CF2Br2, or CO2, added as diluent, which indicates that the primary process involves formation of an excited CF2Br2 molecule.Item Energy Partition in the Photolysis of HI and of H2S(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (12), 1972) Oldershaw, G. A.; Porter, D. A.; Smith, A.Yields of nitrogen from reaction (1) were used to determine the initial kinetic energy of hydrogen atoms produced by photolysis of HI and H2S in the presence of N2O. H* + N2O->N2 + OH. (1) The results show that the proportion of excited (52P±) iodine atoms formed by photolysis of HI at 279 nm is 0.11 ±0.14, and that 90±10 % of the residual energy following photolysis of H2S at 248 nm appears in translation of H and SH.