- HEAT OF FORMATION OF THE CF2CL. RADICAL
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The difference in the energies of activation, combined with known thermochemical data gives a value for the heat of formation of the CF//2Cl. radical of 64. 3 kcal and a value for D(CH//2Cl-H) of 103. 8 kcal. Combination of this value with the measured appearance potential of (CF//2Cl) cation from CF//2Cl//2 gives a value for the ionization potential of the CF//2Cl. radical of 9. 1 ev. Bond- dissociation energies in several molecules containing the CF//2Cl. radicals have been determined from the appropriate appearance potentials of (CF//2Cl) cation.
- LEYLAND LM,MAJER JR,ROBB JC
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- Crossed molecular beam studies of the reactions of methyl radicals with iodoalkanes
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The I atom exchange reactions, CH3+RI->CH3I+R , were investigated at a collision energy of ca. 13 kcal/mol using the crossed molecular beams technique.The supersonic beam of methyl radicals was formed by pyrolyzing a mixture of ca. 1percent di-tert-butyl peroxide in helium in a quartz nozzle.A large fraction of the total energy available to the products from these reactions is channeled into relative translation suggesting that the dominant interaction among the products is repulsive.The CH3 I product from both reactions was observed to be entirely backward scattered with respect to the incident radical beam indicating that a roughly collinear C-I-C transition state geometry is favored.The present results are compared to those of earlier crossed beam studies of the CH3+IY->CH3I+Y (Y=Cl, Br, I) reactions; the differences observed among these reactions are explained with reference to the CH3I-Y and CH3I-R interaction potentials.
- Robinson, Gary N.,Nathanson, Gilbert M.,Continetti, Robert E.,Lee, Yuan T.
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- Competing pathways in the infrared multiphoton dissociation of hexafluoropropene
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The infrared multiphoton dissociation of hexafluoropropene was studied by photofragment translational spectroscopy. Two primary channels and one secondary channel were identified. The predominant primary channel produces CF3CF or C2F4 and CF2, with the heavier species undergoing further dissociation to two CF2 fragments. A number of dissociation mechanisms are proposed for the elimination of CF2, including direct cleavage of the carbon - carbon double bond. In the second primary channel, a simple bond rupture reaction produces CF3 and C2F3. As expected, the translational energy distribution for this channel peaks near zero, indicating no exit barrier is present. The activation energy for this simple bond rupture is estimated to be 100-105 kcal/mol. The branching ratio, [CF2]/[CF3], between the two primary pathways is 4.0 ± 1.0.
- Longfellow,Smoliar,Lee,Lee,Yeh,Lin
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- Reactivity of Negative Ions with Trifluoromethyl Halides
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The kinetics of the reactions of selected anions (A(-)) with the trifluoromethyl halides CF3X (X = F, Cl, Br, I) in the gas phase were measured at 300 K.Reaction rate constants and product branching fractions were determined using a selected ion flow tube (SIFT) instrument.The chosen anions were C5F5N(-), o-, m-, and p-CF3C6H4CN(-), C6F5Br(-), C6F5Cl(-), C6F5CF3(-), C6F5COCH3(-), Fe(-), FeCO(-), SF6(-), SO(-), SO2(-), NO(-), NO2(-), and NO3(-).The reactivity of these systems varies from unreactive to collisional, and a variety of reaction types was found.The results of our present and previous measurements on A(-) + CF3X reactions show that, in cases where nondissociative electron transfer (NDET) is energetically allowed, the total reactivity tends to be high, approaching collisional.This suggests that reactivity in these cases is initiated and controlled by electron transfer from the anion.In addition, association reactions tend to be preempted when NDET is energetically allowed.A few exceptions to these tendencies were found and are discussed.
- Morris, Robert A.,Viggiano, A. A.,Miller, Thomas M.,Seeley, John V.,Arnold, Susan T.,et al.
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- Photoinduced Sulfur-Nitrogen Bond Rotation and Thermal Nitrogen Inversion in Heterocumulene OSNSO
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An exotic ternary S, N, O heterocumulene OSNSO in syn-syn (A) and syn-anti (B) conformations has been generated in the gas phase through flash vacuum pyrolysis of CF3S(O)NSO at 700 K. Upon visible light irradiation (570 ± 20 or 532 nm), both A and B, isolated in cryogenic matrices (N2, Ne, Ar, and Kr, a higher-energy anti-anti conformer (C). The reverse conformational transformation occurs either through S=N bond rotation (C to A and B) under visible light irradiation (400 ± 20 nm) at 2.8 K or through thermal nitrogen inversion (C to A) in the temperature range of 20-30 K, for which an exceptionally low activation barrier of 1.18 ± 0.07 kcal mol-1 has been experimentally determined.
- Wu, Zhuang,Feng, Ruijuan,Xu, Jian,Lu, Yan,Lu, Bo,Yang, Tao,Frenking, Gernot,Trabelsi, Tarek,Francisco, Joseph S.,Zeng, Xiaoqing
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p. 1231 - 1234
(2018/02/09)
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- An experimental and modelling study of ignition delays in shock-heated ethane-oxygen-argon mixtures inhibited by 2H-heptafluoropropane
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Ignition delay times have been measured behind reflected shock waves in ethane-oxygenargon mixtures at temperatures between 1150 and 1500 K and pre-ignition pressures between 10 and 14 atm. Delay times have been measured both by pressure rise and OH absorption at 307 nm. Kinetic modelling of the ignition delays has been made using the GRIMech 3.0 mechanism which with addition of several reactions involving HO2 radicals and an increase in the barrier for reaction between C2H5 and O2 can satisfactorily model delays over the studied equivalence ratios of φ= 1.7 to 0.68. Addition of 2H-heptafluoropropane up to 13 mol % (of ethane) had little inhibition effect on stoichiometric ethane-oxygen-argon mixtures but inhibited ignition in a mixture of φ= 1.5. A kinetic mechanism is presented to model the inhibition process. by Oldenbourg Wissenschaftsverlag, Muenchen.
- Ikeda, Emi,Mackie, John C.
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p. 997 - 1009
(2007/10/03)
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- Kinetic study of the reactions of CF3O2 radicals with Cl and NO
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Kinetic studies of the reactions CF3O2 + Cl and CF3O2 + NO were performed at room temperature in the gas phase using the discharge flow mass spectrometric technique (DFMS). The reactions were investigated under pseudo- first-order conditions with Cl or NO in large excess with respect to the CF3O2 radicals. The rate constant for the reaction CF3O2 + NO was measured at 298 K and the value of (1.6 ± 0.3) x 10-11 cm3 molecule-1 s-1 is in very good agreement with all previous values. For the reaction CF3O2 + Cl, we obtain a rate constant at 298 K of (4.2 ± 0.8) x 10-11 cm3 molecule-1 s-1 in excellent agreement with the only published value. Product analysis shows that this reaction occurs via the major reaction pathway CF3O2 + Cl → CF3O + ClO at room temperature. In addition, an ab initio theoretical study was performed to gain insights on the different postulated reaction pathways. There is a significant disagreement between experimental and ab initio values recommended for the formation enthalpies of CF2O, CF3O and related molecules produced in this system. Consequently, we provide self-consistent values of enthalpies based on isodesmic reactions for the CF3O2 + Cl reaction system using the G2, G2(MP2) and CBS-Q methods. These values are also compared with BAC-MP4 heats of formation calculated in this work.
- Louis, Florent,Burgess Jr., Donald R.,Rayez, Marie-Therese,Sawerysyn, Jean-Pierre
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p. 5087 - 5096
(2007/10/03)
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- FTIR spectroscopic study of 1,1,1-trifluoro-2-chloroethyl and 1,1,1- trifluoro-2-chloroethylperoxyl radicals
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A combination of matrix isolation and FTIR spectroscopy was applied to investigate 1,1,1-trifluoro-2-chloroethyl (1) and 1,1,1-trifluoro-2- chloroethylperoxyl (2) radicals. Radical 2 was obtained by vacuum pyrolysis of 1,1,1-trifluoro-2-bromo-2-chloroethane (3). Corresponding peroxyl radicals was generated by co-condensation of pyrolysis products and molecular oxygen in an argon matrix. To assign the experimental bands DFT calculations (B3LYP/6-311G**) were carried out. The fundamental bands of O-O and C-O stretching vibrations of peroxyl radical CF3CHClOO (1102.1, 972.7, cm-1) were identified by their red shifts to 1044.7 and 954.1 cm-1 in the spectra of 18O substituted derivatives. UV photolysis of the radical 2 in the low- temperature matrix produced difluoroformaldehyde CF2O, radicals ClCO, CF3, as well as CO and HCl as the primary photoproducts.
- Baskir,Korolev,Nefedov
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p. 519 - 522
(2007/10/03)
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- Products of the ultraviolet photodissociation of trifluoroacetic acid and acrylic acid
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The photodissociation of trifluoroacetic and acrylic acids by the ultraviolet light from a flashlamp has been investigated by measuring the relative yields of some of the major products by time-resolved infrared absorption using tunable, narrow band diode lasers. Yields of CO2 were measured both in the absence and presence of added O2. The former experiments measure the CO2 produced directly by decarboxylation of the acid, channel (2) below, the latter the sum of the yields from channels (1) and (2) since HOCO is rapidly converted to CO2. The yields of CO from the decarbonylation channel (3) have also been measured. For trifluoroacetic acid, the relative yields are found to be [HOCO]: [CO2]: [CO] = (0.28 ± 0.07): (0.61 ± 0.09): (0.11 ± 0.06) and, for acrylic acid, [HOCO]: [CO2]: [CO] = (0.32 ± 0.08): (0.37 ± 0.08) :(0.31 ± 0.09). The results are discussed in relation to the other, limited, measurements on the photodissociation of these acids and whether these three processes are likely to occur independently of one another.
- Osborne, Michael C.,Li, Qiang,Smith, Ian W. M.
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p. 1447 - 1454
(2007/10/03)
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- Infrared multiphoton dissociation of two perfluorobutenes
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Photofragment translational spectroscopy was used to examine the infrared multiphoton dissociation of octafluoro-1-butene and octafluoro-2-butene. The predominant unimolecular reaction in octafluoro-1-butene at moderate laser fluences is cleavage of a carbon-carbon single bond to give the products CF3 and C3F5. The two other reactions that take place are CF2 elimination and the formation of equal weight fragments with the chemical composition C2F4; both reactions take place via a diradical intermediate. Dissociation of octafluoro-1-butene to the resonance stabilized perfluoroallyl radical is suggested to account for the favoring of simple bond rupture. These three reaction pathways were also observed in octafluoro-2-butene dissociation, however, the branching fraction is different than from octafluoro-1-butene. In octafluoro-2-butene all three channels occur with roughly equal probability. The reactions involving CF2 loss and C2F4 formation in octafluoro-2-butene are thought to proceed through the same diradical intermediate as in octafluoro-1-butene, necessitating a 1,2-fluorine migration.
- Longfellow, Cheryl A.,Berrie, Cindy L.,Suits, Arthur G.,Lee, Yuan T.
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p. 7202 - 7208
(2007/10/03)
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- Kinetics of the IO radical. 1. Reaction of IO with ClO
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The rate coefficient for the IO + ClO → products (5) reaction was measured by coupling discharge flow and pulsed laser-induced fluorescence techniques. Rate coefficients were measured from 200 to 362 K by monitoring the temporal profile of IO in an excess of ClO. The rate coefficient is described by the expression: k5(T) = (5.1 ± 1.7) × 10-12 exp[(280 ± 80)/T] cm3 molecules-1 s-1 where the quoted uncertainties include estimated systematic errors. Atomic iodine was identified as a major product of reaction 5. A branching ratio of Φ = 0.14 ± 0.04 at 298 K was obtained for the sum of channels which do not produce I atoms.
- Turnipseed, Andrew A.,Gilles, Mary K.,Burkholder, James B.,Ravishankara
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p. 5517 - 5525
(2007/10/03)
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- Ionization Energies, Appearance Energies, and Thermochemistry of CF2O and FCO
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With the discharge flow-photoionization mass spectrometer (DF-PIMS) coupled to the U-11 beamline at the National Synchrotron Light Source, we have measured the ionization energies of C2F4, CF2, and CF2O and appearance energy of FCO+ from CF2O.The PIMS results corroborate those determined by other techniques.With high-level ab initio calculations that utilize a large basis set and isogyric corrections, we have determined an ionization energy of 9.3 +/- 0.1 eV for FCO.At 298 K, the heats of formation of FCO (-152 +/- 12 kJ/mol) and FCO+ (745.3 +/- 9.6 kJ/mol) fH0298(CF2O) = -607.9 +/- 7.1 kJ/mol> were determined and agree to within the uncertainties of other measurements but with much higher precision.We have evaluated the bond strengths D0298(F-CFO) and D0298(F-CO) to be 535 +/- 12 and 121 +/- 12 kJ/mol, respectively.
- Buckley, T. J.,Johnson, R. D.,Huie, R. E.,Zhang, Z.,Kuo, S.C.,Klemm, R. B.
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p. 4879 - 4885
(2007/10/02)
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- Time-Resolved REMPI Detection of Methyl Radicals Generated in Laser-Induced Unimolecular Reactions
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The specific rate constants for the photofragmentation of four substituted benzene molecules (ethylbenzene, tert-butylbenzene, toluene, benotrifluoride) following pulsed laser excitation at λ=193 nm were measured in a molecular beam experiment by monitoring the change of the intensity of the nascent products as a function of time delay between excitation and detection laser pulses.In the case of toluene (C6H5CH3), ethylbenzene (C6H5CH2CH3), and tert-butylbenzene (C6H5C(CH3)3) a (3+1)REMPI process a Λ=450.8 nm was used to ionize the CH3 products, which were detected in a time-of-flight mass spectrometer.Following dissociation of benzotrifluoride (C6H5CF3) the trifluormethyl radical CF3 was detected at λ=455 nm.The measured specific rate constants can be modeled satisfactorily by using the SACM (statistic adiabatic channel model) statistical theory.
- Froechtenicht, Ralf,Hartmann, Matthias
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p. 16290 - 16295
(2007/10/02)
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- Kinetics of the Reaction of CF3O with NO
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The reaction between CF3O and NO has been studied by laser flash photolysis/transient diode laser absorption over the range 213 K a small extent (Φ=0.15).A significant fraction of the CF3O (ca. 30percent) is born with sufficient internal excitation to dissociate into F2CO and F atoms.The presence of NO leads to additional F2CO formation.The analysis of this formation rate, as well as the NO loss rate, yields a temperature dependent rate constant of (4.4 +/- 1.5) x 10-11e(+100+/-88)/T cm3 s-1 for the CF3O + NO reaction.The measured rate constants agree well with previous results based on observations of CF3O disappearance.They confirm expectations that the reaction yields exclusively the products FNO and F2CO and that it serves as an efficient stratospheric sink for the CF3O radical.The reaction between CF3O and HCl has also been examined, and an upper limit of 2 x 10-13 cm3 s-1 has been determined for its rate constant at 295 K.The small rate constant for this reaction relative to the rapid removal of CF3O by NO severely limits the possibility that hydrofluorocarbons contribute to stratospheric ozone depletion by their CF3O degradation product liberating chlorine atoms from HCl.
- Dibble, Theodore S.,Maricq, M. Matti,Szente, Joseph J.,Francisco, Joseph S.
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p. 17394 - 17402
(2007/10/02)
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- Reaction of Trifluoromethyl Iodide on Ni(100)
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We have studied the surface chemistry of trifluoromethyl iodide adsorbed on Ni(100) under ultrahigh-vacuum conditions.Temperature-programmed desorption and reflection absorption infrared spectroscopy were used to determine gas-phase products and species formed at the surface.Several reaction products were found from trifluoromethyl iodide dissociation on Ni(100).Iodine atoms and nickel fluoride, NiF2, desorb at high temperatures near 1000 and 800 K, respectively.At high coverages, carbon-containing species desorb from the surface as well.CF3I and CF3 desorb at 168/136 K (mono/multilayer) and 316 K, respectively.In the presence of background hydrogen, HF and CH2F2, are also detected in temperature-programmed desorption at 178 and 235 K, respectively.The infrared spectra of multilayer, monolayer, and submonolayer coverages of CF3I on the surface and adsorbed CFx groups have been measured.The temperature-programmed desorption and infrared data show that both carbon-iodine and carbon-fluorine bonds are readily activated on nickel at low temperatures.It is estimated that approximately 90percent of adsorbed CF3I decomposes on Ni(100).
- Myli, K. B.,Grassian, V. H.
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p. 1498 - 1504
(2007/10/02)
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- Rate constants and equilibrium constants for X + CF3I ? CF3 + IX, where X = Br, C1
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Equilibrium constants for X + CF3I ?k(-1)k(1) CF3 + XI, where X = Cl or Br, have been calculated from molecular constants of CF3I, IBr, and IC1 using statistical thermodynamics. The rate constant of the direct reaction for X ≡ Br has been measured by the temperature-jump method. Rate constants of the reverse reactions have been calculated.
- Dymov,Skorobogatov,Khripun
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p. 714 - 719
(2008/10/08)
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- Gas-phase reactions of oxide and superoxide anions with CF4, CF3Cl, CF3Br, CF3I, and C2F4 at 298 and 500 K
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Rate constants and product branching fractions have been measured for the gas-phase reactions of oxide (O-) and superoxide (O2-) anions with the halocarbons CF4, CF3Cl, CF3Br, CF3I, and C2F4 using a variable temperature-selected ion flow tube (VT-SIFT) instrument operated at 298 and 500 K.The reactions of O- with CF3X (X = Cl, Br, I) are fast and produce F-, XF-, and XO- for all X.For CF3Cl and CF3Br, X- is also formed.For CF3I, CF3- and IOF- are minor products.O- reacts rapidly with C2F4 producing F- as the major ionic product, along with contributions from reactive detachment and minor formation of FCO-, CF3-, and C2F3O-.The reaction of O2- with CF3Cl is slow, and both clustering and X- formation were observed.For CF3Br and CF3I, the reactions with O2- are fast, and nondissociative charge transfer was observed in addition to X- formation.O2- reacts rapidly with C2F4 by reactive detachment, in addition to producing F- as the major ionic product with smaller amounts of F2-, FCO-, FCO2-, CF3O-, and C2F4O-.O- and O2- were both found to be unreactive with CF4 at 298 and 500 K.The efficiencies of the reactions of both O- and O2- with CF3X are greater for the heavier halides at both 298 and 500 K.The rate constants for the reactions of O2- with CF3X appear to correlate both with the rates of thermal electron attachment to CF3X and with the electron affinities of CF3X, indicating that the O2- + CF3X reaction mechanism may involve initial electron transfer followed by dissociation.Thus the negative electron affinity of CF3Cl may explain the very slow rate for reaction with O2- despite the available exothermic pathways.
- Morris, Robert A.
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p. 2372 - 2381
(2007/10/02)
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- Reactions of Ar+ with halocarbons and of I+ with CF3I
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The gas phase reactions of Ar+ with the halocarbons CF3Cl, CF3Br, CF3I, CF4, C2F6, and C2F4 have been studied using a variable temperature-selected ion flow tube (VT-SIFT) instrument operated at 298 and 500 K.Rate constants and product branching percentages were measured at both temperatures.Ar+ reacts at the collisional rate with all of the above neutrals at both 298 and 500 K.The reactions with CF3X yield CF3+ and CF2X+ for all X (the reaction with CF4 produces only CF3+).For X = I, there is an additional channel leading to the ionic product I+.The reaction of Ar+ with C2F6 produces both CF3+ and C2F5+.The reaction of Ar+ with C2F4 forms a rich product spectrum consisting of the ions CF+, CF2+, CF3+, C2F3+, and C2F4+.The reaction product distributions are compared with results from ionization experiments such as photoion-photoelectron coincidence (PIPECO) and electron impact mass spectrometry, and in some cases excellent agreement is found.The reaction of I+ with CF3I, which is a secondary reaction in the Ar+/CF3I system, was investigated at 298 K in separate experiments.This reaction is rapid and forms four product ions: CF3+, CF2I+, CF3I+, and I2+.The results are compared with previously published information.
- Morris, Robert A.,Doren, Jane M. Van,Viggiano, A. A.,Paulson, John F.
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p. 173 - 179
(2007/10/02)
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- Spherical granules having core and their production
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The spherical granules having a core coated with spraying powder containing a drug and low substituted hydroxypropylcellulose, because of their excellent hardness, can be coated further evenly, (e.g. sustained release coating, gastric coating, enteric coating), and at the time the granules are excellent in disintegration.
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- Outer-sphere and inner-sphere processes in organic chemistry. Reaction of trifluoromethyl bromide with electrochemically generated aromatic anion radicals and sulfur dioxide anion radicals
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The reduction of CF3Br by electrochemically generated aromatic anion radicals gives rise to purely catalytic currents. An activation-driving force relationship characterizing outer-sphere electron donors can thus be established. Electrochemically generated sulfur dioxide anion radicals do not give rise to catalytic currents upon reaction with CF3Br but rather produce trifluoromethyl sulfinate according to an overall two electron per molecule stoichiometry. The rate constant of the rate-determining step of the reaction is at least 4 orders of magnitude larger than that of an aromatic anion radical of the same standard potential, unambiguously showing that SO2(·-) does not react as an outer-sphere electron donor. Among the various possible inner-sphere processes, bromine atom abstraction appears as the most likely.
- Andrieux,Gelis,Saveant
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p. 786 - 791
(2007/10/02)
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- Outer-sphere dissociative electron transfer to organic molecules: A source of radicals or carbanions? Direct and indirect electrochemistry of perfluoroalkyl bromides and iodides
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As an example of the general problem posed in the title, the reduction of CF3Br, CF3I, C6F13I, and C8F17I by outer-sphere heterogeneous (glassy-carbon electrodes) and homogeneous (aromatic anion radicals) reagents is investigated, in aprotic solvents containing tetralkylammonium salts, by cyclic voltammetry and preparative-scale electrolysis. A RF. chemistry is thus triggered in all cases with the exception of CF3Br where a mixed RF./RF- chemistry is obtained by direct electrochemical reduction or by electron transfer from aromatic anion radicals having a close reduction potential. Quantitative analysis of the reduction kinetics of RFX (X = Br, I) and of RF. led to the following conclusions. RFX most likely undergoes a concerted electron-transfer-bond-breaking reduction involving a substantial overpotential (ca. 1.5 V for C-Br and 1.0 V for C-I), mainly governed by the C-X bond dissociation energy. RF. radicals are strongly stabilized by interaction with the solvent but are nevertheless easier to reduce than alkyl radicals on thermodynamical grounds, exhibiting however a high intrinsic barrier of the same order as for alkyl radicals. Unlike alkyl radicals, but similar to aryl radicals, RF. radicals are good H-atom scavengers and do not couple with aromatic anion radicals.
- Andrieux, Claude P.,Gélis, Laurence,Medebielle, Maurice,Pinson, Jean,Savéant, Jean-Michel
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p. 3509 - 3520
(2007/10/02)
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- Negative ion production in collisions between K(nd) Rydberg atoms and CF3Br and CF2Br2
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Negative ion production via electron transfer in collisions between K(nd) Rydberg atoms and CF3Br and CF2Br2 has been investigated over a wide range of of n (10n70).For both species, the major negative ion observed is Br-, although with C
- Kalamarides, A.,Marawar, R. W.,Ling, Xi,Walter, C. W.,Lindsay, B. G.,et al.
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p. 1672 - 1676
(2007/10/02)
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- Generation, Thermodynamics, and Chemistry of the Diphenylcarbene Anion Radical (Ph2C.-)
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Dissociative electron attachment with Ph2C=N produced Ph2C.- (m/z 166).The reactions of Ph2C.- with potential proton donors of known gas-phase acidity were used to bracket PA(Ph2C.-) = 380 +/- 2 kcal mol-1 from which ΔHf0(Ph2C.-) = 81.8 +/- 2 kcal mol-1 was calculated.The reactions of Ph2C.- with CH3OH and C2H5OH proceeded with major and minor amounts, respectively, of a H2.+-transfer channel, forming Ph2CH2, RCHO, and an electron.The kinetic nucleophilicity of Ph2C.- in SN2 displacement reactions with CH3X and C2H5X molecules was shown to be medium, which requires a significant intrinsic barrier in these reaction.The reactions of Ph2C.- with various aldehydes, ketones, and esters were fast and established two principal product-forming channels: (1) H+ transfer if the neutral reactant contains activated C-H bonds and (2) carbonyl addition followed by radical β-fragmentation of one of the groups originally attached to the carbonyl carbon.The order for the ease of radical β-fragmentation in the tetrahedral intermediates was RO > alkyl >> H, and CO2CH3 > CH3.Since the reactions of Ph2C.- with the simple esters HCO2CH3 and CH3CO2CH3 were fast, it should now be possible to examine the reactions of carbonyl-containing organic molecules, which are expected to react slower than these esters and obtain their relative reactivities.
- McDonald, Richard N.,Gung, Wei Yi
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p. 7328 - 7334
(2007/10/02)
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- CH3(.) vs. CF3(.): Relative Rates of Formation from β-Scission
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The relative rates of formation of CH3(.) and CF3(.) from β-scission reactions of trifluoro-t-butoxy radical (1) have been measured to be about 10:1 by thermolysing both trifluoro-t-butyl hypochlorite (4) and bis(trifluoro-t-butyl) peroxydicarbonate (14) in CCl4 at 160 and 140 deg C.
- Jiang, Xi-Kui,Li, Xing-Ya,Wang, Ke-Yang
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p. 745 - 746
(2007/10/02)
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- Gas-Phase Nucleophilic Reactivities of Phenylnitrene (PhN-*) and Sulfur Anion Radicals (S-/.) at sp3 and Carbonyl Carbon
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The reactions of PhN-/. with a series of carbonyl-containing molecules (aldehydes, ketones, and esters) were shown to proceed via an addition/fragmentation mechanism, PhN-* + R2C=O -> -)R2> -> PhN=C(O-)R + *R, producing various acyl anilide anion products.In several cases, the tetrahedral intermediate anion radicals were observed as minor ions.The intrinsic reactivity of the carbonyl-containing molecules was aldehydes > ketones > esters, where similar R groups were involved.The overall exothermicities of these reactions did not appear to play the major role in determining the relative rates (krelC=O) for these reactions.From the reaction of PhN-* with cyclobutanone, a new type of anion radical, PhN=C(O-)CH2* (m/z 133) (+ C2H4) was produced; the loss of C2H4 was considered due to the ring strain in the ketone.With cyclopentanone, cyclohexanone, and cycloheptanone, the anion radicals PhN=C(O-)(CH2)n* (n = 4-6) were the exclusive product ions.PhN-* was shown to be a poor nucleophile in SN2 displacement reactions with CH3X molecules (X = Cl, Br, O2CCF3).S-* was shown to exhibit modest SN2 nucleophilicity with CH3Cl and CH3Br.The reactions of S-* with CF3CO2R proceed via both SN2 displacement and carbonyl addition/fragmentation mechanisms: with R = CH3, the anion products were 65percent CF3CO2- and 35percent CF3COS-; from R = C2H5, the product ions were 4percent CF3CO2- and 96percent CF3COS-.These data yield the ratio kCH3/kC2H5 = 16 for SN2 displacement by S-* at these alkyl groups.The reactions of PhN-* with CO2, COS, CS2, and O2 are also reported.The reaction of PhN-* with CS2 to produce S-* as a major channel was used as the source of this atomic anion radical.In several reactions occuring at nearly the collison limit, selectivity was observed for (a) which of two reaction centers were attacked to give products and (b) which of two mechanisms would be dominant in the overall reaction.
- McDonald, Richard N.,Chowdhury, A. Kesem
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p. 198 - 207
(2007/10/02)
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- IR MATRIX ISOLATION SPECTRA OF SOME PERFLUORO ORGANIC FREE RADICALS PART III. n-C3F7 and iso-C3F7
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The perfluoro radicals n-C3F7 and iso-C3F7 have been prepared by pyrolyzing the corresponding iodides in a platinum effusion tube at temperatures between 450-550 deg C and isolated in argon matrices.By eliminating absorption bands attributed to known fluorine compounds and applying relative absorption band intensity correlations, several absorption bands have been assigned, some 30 to n-C3F7 and 29 to iso-C3F7, in the spectral range 2000-200 cm-1.A tentative vibrational assignment is presented for both species on the assumption of Cs symmetry.Some thermodynamic implications of the findings are also dicussed.
- Butler, R.,Snelson, A.
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