2396-01-2Relevant articles and documents
Halogen Atom Abstraction Dynamics of Fluorine Atoms Reacting with Allyl Bromide and Iodobenzene Molecules
Wang, J. J.,Zhu, Z. Z.,Smith, D. J.,Grice, R.
, p. 10787 - 10793 (1994)
Reactive scattering of F atoms with C3H5Br and C6H5I molecules leading to Br and I atom abstraction has been studied at an initial translational energy E ca. 40 kJ mol-1 using a supersonic beam of F atoms seeded in He fuffer gas.The center-of-mass angular distributions of BrF and IF scattering show peaking in the forward and backward directions, which is consistent with reaction via persistent C3H5-Br-F and C6H5-I-F complexes with lifetimes greater than two rotational periods.The sharply peacked angular distribution observed for F + C3H5Br is consistent with a microcanonical description, whereby reactive scattering arises from a product transition state which approximates to a strongly prolate symmetric top.The mildly peaked angular distribution observed for F + C6H5I is consistent with a phase space description whereby unconstrained rotation is established between the nascent molecules in the product transition state.The product translational energy distributions are both consistent with randomization of energy over internal modes of the collision complex.The lifetime of the C3H5BrF collision complex greatly exceeds that of the FCH2-.CH-CH2Br free radical intermediate in the Br atom displacement pathway, showing that these radicals are not coupled via a four-membered-ring transition state.Similarly, the rate of coupling to the .CH2-CHF-CH2Br radical must be slower than the rate of dissociation of the C3H5BrF radical, and the rate of migration of the F atom to the ? system of the very long-lived C6H5IF radical must also be slower than its rate of dissociation.
Migita et al.
, p. 51,53 (1973)
Velocity-map ion-imaging of the NO fragment from the UV-photodissociation of nitrosobenzene
Obernhuber, Thorsten J.,Kensy, Uwe,Dick, Bernhard
, p. 2799 - 2806 (2003)
The velocity and angular distribution of NO fragments produaed by UV photodissociation of nitrosobenzene have been determined by velocity-map ion-imaging. Excitation of the S2-state by irradiation into the peak of the first UV absorption band at 290.5 nm leads to a completely isotropic velocity distribution with Gaussian shape. The average kinetic energy in both fragments correlates with the rotational energy of the NO fragment and increases from 6% of the excess energy for j = 6.5 to 11% for j = 29.5. A similar isotropic distribution albeit with larger average velocity is observed when the ionization laser at 226 nm is also used for photodissociation, corresponding to excitation into a higher electronic state Sn (n ≥ 3) of nitrosobenzene. It is concluded that photodissociation occurs on a timescale much slower than rotation of the parent molecule, and after redistribution of the excess energy into the vibrational degrees of freedom.
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Hardie,Thomson
, p. 1286,1289 (1958)
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Kinetics of phenyl radical reactions with propane, n-butane, n-hexane, and n-octane: Reactivity of C6H5 toward the secondary C-H bond of alkanes
Park,Wang, Liming,Lin
, p. 49 - 56 (2004)
The kinetics of C6H5 reactions with n-CnH2n+2 (n = 3, 4, 6, 8) have been studied by the pulsed laser photolysis/mass spectrometric method using C6H5COCH3 as the phenyl precursor at temperatures between 494 and 1051 K. The rate constants were determined by kinetic modeling of the absolute yields of C6H6 at each temperature. Another major product C6H5CH3 formed by the recombination of C6H5 and CH3 could also be quantitatively modeled using the known rate constant for the reaction. A weighted least-squares analysis of the four sets of data gave k (C3H8) = (1.96 ± 0.15) × 1011 exp[-(1938 ± 56)/T], and k (n-C4H10) = (2.65 ± 0.23) × 1011 exp[-(1950 ± 55)/T], k (n-C6H14) = (4.56 ± 0.21) × 1011 exp[-(1735 ± 55)/T], and k (n-C8H18) = (4.31 ± 0.39) × 1011 exp[-(1415 ± 65)/T] cm3 mol-1 s-1 for the temperature range studied. For the butane and hexane reactions, we have also applied the CRDS technique to extend our temperature range down to 297 K; the results obtained by the decay of C6H5 with CRDS agree fully with those determined by absolute product yield measurements with PLP/MS. Weighted least-squares analyses of these two sets of data gave rise to k (n-C4H10) = (2.70 ± 0.15) × 1011 exp[-(1880 ± 127)/T] and k (n-C6H14) = (4.81 ± 0.30) × 1011 exp[-(1780 ± 133)/T] cm3 mol-1 s-1 for the temperature range 297-1046 K. From the absolute rate constants for the two larger molecular reactions (C6H5 + n-C6H14 and n-C8H18), we derived the rate constant for H-abstraction from a secondary C-H bond, ks-CH = (4.19 ± 0.24) × 1010 exp[-(1770 ± 48)/T] cm3 mol-1 s-1.
Elementary Photoprocesses in Benzene Clusters
Schriver, K. E.,Camarena, A. M.,Hahn, M. Y.,Paguia, A. J.,Whetten, R. L.
, p. 1786 - 1789 (1987)
The article reports the use of the resonant two-photon ionization technique to selectively excite a molecular ion within a cluster and observe the dynamical outcome.We have excited clusters containing up to 14 benzene molecules to energies of 10.00 or 12.84 eV and measured the probability that an initially formed C6H6+ attacks a neighboring benzene unit of the cluster according to the vapor-phase reaction C6H6+ + C6H6 -> C7H7+ + C5H5, ΔH = 0.63 eV.The C5H5 radical is expelled from the cluster.At either energy excitation proceeds through an X112 vibrational level of benzene (X = 6 or 8) but in the latter case the benzene cation is also produced electronically excited.Accordingly, at low-energy excitation the above pathway is entirely absent, while the 12.84-eV excitation leads to reaction with a probability increasing with cluster size, as predicted by solvation models.This result makes it appear quite likely that >12-eV excitation of condensed benzene will lead to transient tropylium ion centers for conduction electrons, accompained by variable trapping of C5H5.
Experimental and theoretical studies of the unimolecular decomposition of nitrosobenzene: High-pressure rate constants and the C-N bond strength
Park,Dyakov,Mebel,Lin
, p. 6043 - 6047 (1997)
The unimolecular decomposition of nitrosobenzene has been studied at 553-648 K with and without added NO under atmospheric pressure. Kinetic modeling of the measured C6H5NO decay rates by including the rapid reverse reaction and minor secondary processes yielded the high-pressure first-order rate constant for the decomposition C6H5NO → C6H5 + NO (1), k∞1 = (1.42 ± 0.13) × 1017 exp [-(55 060 ± 1080)/RT] s-1, where the activation energy is given in units of cal/mol. With the thermodynamics third-law method, employing the values of k∞1 and those of the reverse rate constant measured in our earlier study by the cavity ring-down technique between 298 and 500 K, we obtained the C-N bond dissociation energy, D○0 (C6H5-NO) = 54.2 kcal/mol at 0 K, with an estimated error of ±0.5 kcal/mol. This new, larger bond dissociation energy is fully consistent with the quantum mechanically predicted value of 53.8-55.4 kcal/mol using a modified Gaussian-2 method. Our high-pressure rate constant was shown to be consistent with those reported recently by Horn et al. (ref 13) for both forward and reverse reactions after proper correction for the pressure falloff effect.
Low-Temperature Photolysis of Benzoyl Peroxide
Kuzina,Bol’shakov,Kulikov,Mikhailov
, p. 189 - 195 (2020/03/31)
Abstract: The photolysis of dry benzoyl peroxide (BP) at 77 K in the 480–236 nm range of wavelengths and an ethanol solution is studied via EPR. It is determined that the main photochemical process in irradiating BP at λ = 480–365 nm is the direct photodi
Investigating the mechanisms of aromatic amine-induced protein free radical formation by quantitative structure-activity relationships: Implications for drug-induced agranulocytosis
Siraki, Arno G.,Jiang, Jinjie,Mason, Ronald P.
experimental part, p. 880 - 887 (2011/03/17)
Aromatic amine drugs have been associated with agranulocytosis (neutrophil depletion) for which the mechanism is unknown. We have previously shown that the metabolism of two aromatic amine drugs by human myeloperoxidase (MPO) results in phenyl radical metabolite formation and also in protein free radical formation on MPO. Because the concentration of drug required to produce a maximum signal for MPO protein free radical (MPO?) detection was different for each drug, this prompted us to consider that other aromatic amines may also show varying degrees of ability to induce MPO? formation. Immunoassay experiments using the immuno-spin-trapping technique were performed, which evaluated the potency of different aromatic amines containing the aniline substructure to generate the MPO?. Each reaction contained equal amounts of H2O2, 5,5-dimethyl-1-pyrroline- N-oxide, MPO, and variable concentrations of aniline derivatives. Several physicochemical parameters for aniline derivatives were used to derive quantitative structure-activity relationship equations, which showed that the Hammett constant (-) best correlated with the MPO? formation for all aniline derivatives. More statistically robust equations were derived if the anilines were separated into mono- and disubstituted groups. However, some aniline derivatives did not induce MPO? formation. Using electron spin resonance spectroscopy, we evaluated the ability of all aniline derivatives tested to produce phenyl radical metabolites, as previously shown by spin trapping for the aromatic amine drugs. Interestingly, we found that only those aniline derivatives that produced a phenyl radical also formed MPO ?. We propose that the phenyl radical is the reactive free radical metabolite responsible for generating the MPO?+.
