2396-02-3Relevant academic research and scientific papers
Magnetic Field Effects on the Photodissociation Reaction of Triarylphosphine in Nonviscous Homogeneous Solutions
Sakaguchi, Yoshio,Hayashi, Hisaharu
, p. 3421 - 3429 (2007/10/03)
The magnetic field effects (MFEs) on the photodecomposition reactions of triphenylphosphine and its halogen and methyl derivatives are investigated in fluid solutions. The yield of diarylphosphinyl radicals decreased with increasing magnetic field from 0.1 to 5 T but was stationary below 0.1 T and above 5 T. The MFE becomes larger by the substitution of halogen atoms and the 3- or 4-methyl group. In cyclohexane, the yields of the escaped diarylphosphinyl radicals at 1 T are reduced to 0.69, 0.55, 0.59, and 0.56 of those at 0 T for triphenylphosphine and its tris(4-chloro), tris(3-methyl), and tris(4-methyl) derivatives, respectively. This magnetic field dependence was ascribed to originate from the deactivation process of the excited triplet state, which is a variant of the d-type triplet mechanism originally proposed by Steiner. The interaction between the closely lying nπ* and ππ* states makes their solvent dependence complicated.
Chromium(ii)-mediated reactions of iodonium tetrafluoroborates with aldehydes: Umpolung of reactivity of diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates
Chen, Da-Wei,Ochiai, Masahito
, p. 6804 - 6814 (2007/10/03)
The method described herein allows us, for the first time, to perform umpolung of reactivity of diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates. The method involves generation of organochromium(III) species via reaction of iodonium salts with anhydrous chromium dichloride, followed by their nucleophilic addition to aldehydes to yield alcohols. In contrast to the reaction of aryl and alkenyl halides with chromium dichloride, these iodonium salts are so active that organochromium(III) could be generated without using a nickel catalyst. Substituent effects of unsymmetrically substituted diaryliodonium salts on the product profiles are in good agreement with the reported mode of decomposition of the intermediate unsymmetrical diaryliodanyl radicals. Alkenyl(mesityl)iodonium tetrafluoroborates undergo exclusive alkenylation of aldehydes with no signs of the formation of an arylation product.
Excess Energy and Structural Dependence of the Rate of Energy Redistribution during the Photodissociation of Iodotoluenes
Freitas, John E.,Hwang, Hyun Jin,El-Sayed, M. A.
, p. 3322 - 3329 (2007/10/02)
The ortho (2-), meta (3-), and para (4-) iodotoluenes (C7H7I) are photodissociated at 266 and 304 nm and studied with state-selective one-dimensional photofragment translational spectroscopy.Angular, velocity, and translational energy distributions are obtained for the ground state I(2P3/2) and spin-orbit excited state I*(2P1/2) iodine atoms produced upon photodissociation.As has been observed in iodobenzene, the ground-state I channel observed in each isomer of iodotoluene exhibits both a prompt alkyl iodide-like dissociation channel following a parallel excitation to the alkyl iodide 3Q0(n,?*) repulsive state and curve crossing to the 1Q1(n,?*) state, and a slower, indirect dissociation channel following a competitive excitation to aromatic charge-transfer (?,?*) predissociative excited states at both 266 and 304 nm.The I* channel observed at both 266 and 304 nm for each isomer results from a prompt dissociation resulting from parallel absorption to an alkyl iodide type 3Q0(n,?*) state.The rapid I and I* dissociative channels observed for each isomer are found to exhibit strong dependence on the excess excitation.This is discussed in terms of a strong coupling between the dissociation coordinate and the more dense vibrational states of the toluene ring.Dissociation times and rates of internal energy redistribution (IER) from the slow dissociative channel (β) are estimated for each isomer.For 2-iodotoluene, the rate of IER for the slow I channel increases from 20 kcal/mol*ps at 304 nm to 30 kcal/mol*ps at 266 nm, while the rates of IER for 3- and 4-iodotoluene (16 kcal/mol*ps and 15 kcal/mol*ps, respectively) remain unchanged as the photon energy is increased.The difference in the observed excess energy dependence of the rates of IER in these isomers is discussed in terms of the complex coupling schemes between the optical doorway states and the n,?* repulsive states that produce the iodine atoms, monitored in the experiment.
Homogenous Gas-Phase Formation and Destruction of Anthranil from o-Nitrotoluene Decomposition
He, Y. Z.,Cui, J. P.,Mallard, W. G.,Tsang, W.
, p. 3754 - 3759 (2007/10/02)
Dilute quantities of o-nitrotoluene and anthranil have been pyrolyzed in comparative rate single pulse shock tube experiments.Rather than C-NO2 bond cleavage and NO2 isomerization found as major channels in p-nitrotoluene decomposition, we demonstrate that the important pathway for pyrolysis involves the formation of anthranil with the following overall rate expression: k(o-nitrotoluene -> anthranil) = 1.2 x 1013 exp(-26020/T)/s.The anthranil that is formed is very unstable under our conditions; the rate expression for disappearence has been found to be the following: k(anthranil)d = 3.7 x 1015 exp(-25800/T)/s.Arguments are presented that suggest that the first rate expression is representative of a retroene reaction and the second expression is for the breaking of the N-O bond in anthranil.These conclusions emphasize the difference in results from shock tube and laser pyrolysis experiments.Their implications on the initiation reactions in the decomposition of nitroaromatic explosives are discussed.
Reductive Fragmentation of 9,9-Diarylfluorenes. Concurrent Radical Anion and Dianion Cleavage. Electron Apportionment in Radical Ion Fragmentations
Walsh, Thomas D.
, p. 1511 - 1518 (2007/10/02)
Both Radical anions and dianions of 9,9-diarylfluorenes cleave an aryl ring after reduction by alkali metals or naphtalenide radical anions in ether solvents.The relative amount of cleavage through each intermediate depends on the alkali metal cation, the solvent, and the presence or absence of 18-crown-6-ether.The tendency for dianion cleavage parallels that for disproportionation of radical anions to dianions and neutral hydrocarbons.Radical anion fragmentation is proposed to proceed via heterolytic cleavage in which electron flow is in the direction which offsets the charge distribution in the radical ion.In the present case, this initially affords 9-arylfluorenyl radical and aryl anion, which subsequently indergo electron exchange to form the more stable 9-arylfluorenyl anion and aryl radical.
ESR Spectra of Gamma Irradiated Chloramine-T and Chloramine-B
Mahadevappa, D. S.,Suryanarayana, D.
, p. 673 - 674 (2007/10/02)
ESR spectra of gamma irradiated chloramine-T (CAT) and chloramine-B (CAB) from the ambient to liquid nitrogen temperature (77-298 K) are reported.Spectrum of CAT shows the presence of an aromatic radical and a second radical involving the side chain sulphur.Line intensities point towards a hindered methyl rotation.The benzene analogue shows a triplet spectrum which is unaffected by changes in temperature.
Free-Radical Reductions of Arenediazonium Ions in Aqueous Solution. V. Pulse-Radiolytic Determination of Rate Constants for Some para-Substituted Benzenediazonium Ions
Packer, John E.,Moenig, Joerg,Dobson, Brian C.
, p. 1433 - 1441 (2007/10/02)
Some rate constants for the reduction of para-substituted benzenediazonium ions by the radicals eaq-, .CH2OH, (CH3)2.COH and some semiquinone radical anions have been measured.The substituent group has no effect on the rates with eaq-, but as the reduction potential of the reducing radical becomes more positive, the substituent effect increases, electron-withdrawing groups enhancing the rates.No free halide is formed on reduction of p-BrC6H4N2+ or p-IC6H4N2+ by eaq- or .CH2OH.
Free-Radical Reductions of Arenediazonium Ions in Aqueous Solution. IV. Kinetics of Reactions of para-Substituted Diazonium Ions with Benzyl Alcohol, Isopropyl Alcohol And Methanol
Packer, John E.,Heigway, Christopher J.,Miller, Helen M.,Dobson, Brian C.
, p. 965 - 977 (2007/10/02)
Electron-withdrawing substituents are shown to increase the chain length of free-radical hydrodediazoniation reactions, but the actual reaction step causing the substituent effect depends on the relative rates of propagation and termination reactions.With benzyl alcohol as reducing agent the rate of the slow propagation step is increased, while with isopropyl alcohol the rate of the termination step is decreased.Rate constants for some reactions of radicals with diazonium ions are reported, and the nature of some of these reactions and their implication foran understanding of the homolysis of aromatic diazo compounds are discussed.
