17333-73-2Relevant academic research and scientific papers
Mass-Spectrometric Study on Ion-Molecule Reactions of CF3+ with Nitrogen-Containing Benzene Derivatives, Pyridine, Pyrrole, and Acetonitrile at Near-Thermal Energy
Tsuji, Masaharu,Aizawa, Masato,Ujita, Hiroki,Nishimura, Yukio
, p. 2385 - 2392 (1995)
The gas-phase ion-molecule reactions of CF3+ with nitrogen-containing benzene derivatives (C6H5Y : Y = NH2, NO2, and CN), pyridine, pyrrole, and acetonitrile have been studied at near-thermal energy using an ion-beam apparatus.The major product channels are charge transfer for aniline (71.7 +/- 0.5), O- abstraction for nitrobenzene (91.7 +/- 0.5percent), electrophilic addition leading to initial adducts ions for benzonitrile (97.5 +/- 0.8percent), acetonitrile (100percent), and pyridine (94.8 +/- 0.4percent), and electrophilic addition followed by HF elimination for pyrrole (80.0 +/- 1.4percent).The reaction mechanism is discussed based on product ion distributions and theoretical calculations of the energies of reaction pathways.
Hydrogen atom adducts to nitrobenzene: Formation of the phenylnitronic radical in the gas phase and energetics of wheland intermediates
Polasek, Miroslav,Turecek, Frantisek
, p. 9511 - 9524 (2000)
The phenylnitronic radical (1) was prepared in the gas phase by collisional electron transfer to stable C6H5NO2H+ cation (1+) and found to be stable on the microsecond time scale. The major unimolecular dissociation of 1 was loss of OH radical to form nitrosobenzene as determined by variable-time neutralization-reionization mass spectrometry. Ab initio calculations at the effective QCISD(T)/6-311+G(3df,2p) level and combined Moller-Plesset and density functional theory calculations identified loss of OH as the lowest-energy dissociation of 1 that proceeded at the thermochemical threshold with no reverse activation barrier. Dissociations of 1 by loss of syn- and anti-HONO and a hydrogen atom were more endothermic than loss of OH and had activation barriers above the thermochemical thresholds. The internal energy of 1 formed by electron transfer in the ground electronic state (X) was insufficient to cause the observed dissociations. The dissociations are postulated to take place from the metastable excited electronic B state formed by vertical electron transfer. Wheland intermediates for hydrogen atom additions to the ortho (2), meta (3), para (4), and ipso (5) positions in nitrobenzene were calculated to be 75, 98, 78, and 101 kJ mol-1 less stable than 1. Radicals 2-4 existed in substantially deep potential energy wells to allow their generation as transient intermediates. Radical 5 resided in a shallow potential energy minimum and was predicted to dissociate exothermically to benzene and NO2. Relative thermal rate constants for hydrogen atom additions to nitrobenzene were calculated and found to correlate with the regioselectivities for additions of other radicals.
Unimolecular Dissociation Rate Constants: Chlorobenzene Cations Revisited by Using a New Method
Stanley, R. J.,Cook, M.,Castleman, A. W.
, p. 3668 - 3674 (1990)
Unimolecular dissociation rates of metastable molecular ions formed at the laser focus of a time-of-flight mass spectrometer (TOFMS) have been determined by measuring the relative concentrations of parent metastable ions and the daugther fragment ions as a function of their retained kinetic energies upon dissociation.This is accomplished by the use of a simple one-stage ion mirror/energy analyzer.For a given reflection potential on the ion mirror, only those ions with a kinetic energy equal to or less than the reflection potential are detected.In this way, the relative concentrations of the parent and daughter ions as a function of their position of dissociation in the time-of-flight (TOF) lens can be measured, and consequently the dissociation lifetime can be derived.This technique has been applied to measuring the unimolecular dissociation rate of chlorobenzene ion (C6H5Cl+) in the three-photon energy range of 13.64-13.92 eV through resonance-enhanced two-photon state-selected ionization of chlorobenzene in a supersonic molecular jet.The method demonstrates a minimum dynamic range of 105 to 2*107 s-1 and is in good agreement with previous work.The data suggest that rotational temperature plays a role in the unimolecular dissociation lifetime of the metastable ions.
Kinetic energy release in thermal ion-molecule reactions: The Nb2+ (benzene) single charge-transfer reaction
Gord, James R.,Freiser, Ben S.,Buckner, Steven W.
, p. 4282 - 4290 (1991)
We have adapted the techniques originally developed to measure ion kinetic energies in ion cyclotron resonance (ICR) spectrometry to study the single charge-transfer reaction of Nb2+ with benzene under thermal conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS).The partitioning of reaction exothermicity among the internal and translational modes available is consistent with a long-distance electron-transfer mechanism, in which the reactants approach on an ion-induced dipole attractive potential and cross to a repulsive potential at a critical separation of ca. 7.5 Angstroem when electron transfer occurs.The reaction exothermicity, 5.08 eV, is partitioned to translation of Nb+, 0.81 +/- 0.25 eV, translation of C6H6+, 1.22 +/- 0.25 eV, and internal excitation of C6H6+ to produce the la2u electronic state, which is ca. 3 eV above to ground state of the ion.We have also studied the kinetics of the reaction of Nb2+ with benzene and determined the rate constant, k = 1.4*10-9 cm3 molecule-1 s-1, and the efficiency, 0.60, of the process.These also support the proposed charge-transfer mechanism.In addition to the charge-transfer pathway, which accounts for 95percent of the reaction products, Nb2+ is observed to dehydrogenate benzene to form Nb2+ (benzyne).This process implies D(Nb2+ -benzyne) above 79 kcal/mol.
Infrared multiple-photon dissociation of the nitrobenzene radical cation. A paradigm for competitive reactions
Osterheld, Thomas H.,Baer, Tomas,Brauman, John I.
, p. 6284 - 6289 (1993)
The dissociation of nitrobenzene cation displays a variety of surprising and even apparently nonstatistical reaction behaviors. We have used infrared multiple-photon dissociation experiments to further study the reactions of this system. These experiments along with a previous photoelectron photoion coincidence study indicate that, for some products, the nitrobenzene cation dissociates to form an ion-neutral complex and then reassociates to give the phenyl nitrite cation. A reaction mechanism involving statistical dissociation is shown to account for the experimental data.
Unimolecular reaction dynamics from Kinetic Energy Release Distributions. III. A comparative study of the halogenobenzene cations
Urbain,Leyh,Remacle,Lorquet,Flammang,Lorquet
, p. 2911 - 2921 (1999)
The translational kinetic energy release distribution (KERD) in the halogen loss reaction of the chloro-, bromo-, and iodobenzene cations has been experimentally determined in the microsecond time scale and theoretically analyzed by the maximum entropy method. The KERD is constrained by the square root of the translational energy, i.e., by the momentum gap law. This can be understood in terms of quantum-mechanical resonances controlled by a matrix element involving a localized bound state and a rapidly oscillating continuum wave function, as in the case of a vibrational predissociation process. The energy partitioning between the reaction coordinate and the set of the remaining coordinates is nearly statistical, but not quite: less translational energy is channeled into the reaction coordinate than the statistical estimate. The measured entropy deficiency leads to values of the order of 80% for the fraction of phase space sampled by the pair of fragments with respect to the statistical value. In the case of the dissociation of the chlorobenzene ion, it is necessary to take into account a second process which corresponds to the formation of the chlorine atom in the excited electronic state 2P1/2 in addition to the ground state 2P3/2. The observations are compatible with the presence of a small barrier (of the order of 0.12 eV) along the reaction path connecting the D2A1 state of C6H5Cl+ to the Cl(2P1/2) + C6H5+(X1A1) asymptote.
A combined theoretical and experimental study of the dissociation of benzene cation
Klippenstein, Stephen J.,Faulk, James D.,Dunbar, Robert C.
, p. 243 - 256 (1993)
Variational Rice-Ramsperger-Kassel-Marcus (RRKM) theory calculations of the energy and angular momentum dependence of the rate constant for the dissociation of C6H6+ into C6H5+ and an H atom are reported.In these variational calculations both the definition of the reaction coordinate and its value are independently optimized.A model potential-energy surface which interpolates between a Morse potential at short range and an ion-induced dipole potential at long range is employed in these variational calculations.The fully optimized variational results indicate that the transition state for this dissociation occurs at separation distances of about 3-4 Angstroem and that the available phase space in the transition state is typically a factor of 5 lower than the predicted by phase space theory.Experimental measurements were made of the time-resolved product ion intensity resulting from the laser-induced dissociation of a thermal (ca. 375 K) distribution of benzene cations.An ion cyclotron resonance trap was used over a range of photolysis wavelengths from 266 to 285 nm.The observed time dependences in the product ion signals are a result of both dissociative and radiative relaxation processes with a deconvolution procedure yielding estimated dissociation rate constants. Satisfactory agreement between the theoretical and experimental results, including the previous experimental results of Neusser and co-workers is obtained for an assumed dissociation energy of 3.88 eV to the lowest triplet state of C6H5+.
Time-Dependent Mass Spectra and Breakdown Graphs. 6. Slow Unimolecular Dissociation of Bromobenzene ions at Near Threshold Energies
Malinovich, Y.,Arakawa, R.,Haase, G.,Lifshitz, C.
, p. 2253 - 2260 (1985)
Time-resolved photoionization mass spectrometry (TPIMS) in the millisecond range has been employed to study the reaction C6H5Br(1+) radical -> C6H5(1+) + Br radical in bromobenzene.Experimental photoionization efficiency curves were fitted with a QET model calculation by assuming a critical energy Eo = 2.76 eV and an activation entropy ΔS(excit.) = 8.07 eu.The activation entropy coresponds to the totally loose (orbiting) transititon state.Ultraslow unimolecular dissociations having microcanonical rate coefficients k(E) /= 10 /sec, at near threshold energies, can be sampled by TPIMS, in spite of competing IR-raditive decay of the parent ion.
C6H5Br+? → C6H5+ + Br? occurs via orbiting transition state
Lim, Sang-Hyun,Choe, Joong Chul,Kim, Myung Soo
, p. 7375 - 7381 (1998)
Photodissociation of the bromobenzene molecular ion has been investigated on a nanosecond time scale by photodissociation mass-analyzed ion kinetic energy spectrometry. The rate constant and kinetic energy release distribution have been determined. The present experimental data together with the previous milli- to microsecond data have been compared with theoretical calculations. The rate-energy data available over 6 orders of magnitude in time scale could be fit with a nontotally loose transition state model (RRKM) reported by Rosenstock and co-workers. However, the model has been found to predict rate constant values larger than theoretically acceptable at high internal energy. The completely loose transition state model, namely the reaction occurring via orbiting transition state, seems to be a better description of the reaction.
Mass-Spectrometric Study on Ion-Molecule Reactions of CF3+ with PhX at Near-Thermal Energy
Tsuji, Masaharu,Aizawa, Masato,Nishimura, Yukio
, p. 3497 - 3506 (1995)
The gas-phase ion-molecule reactions of CF3+ with benzene, toluene, ethylbenzene, styrene, and ethynylbenzene have been studied at near-thermal energy using an ion-beam apparatus.The major product channels are electrophilic addition followed by HF elimination for benzene (93.4+/-2.2percent), toluene (84.3+/-2.4percent) and ethynylbenzene (76.9+/-0.9percent).The dominant product channels for ethylbenzene are electrophilic addition followed by C2H4 and C2H4+HF eliminations (78.9+/-4.7percent), while those for styrene are electrophilic addition followed by one or two HF eliminations and C2H2F2 elimination (91.7+/-0.4percent).Only ethynylbenzene gives an initial adduct ion with a small branching ratio of 6.2+/-0.4percent.As minor product channels, hydride transfer occurs for benzene (6.6+/-2.2percent) and toluene (7.8+/-1.5percent), and charge transfer takes place for toluene (7.9+/-2.0percent), styrene (8.3+/-1.4percent), and ethynylbenzene (6.2+/-0.4percent).The reaction mechanisms are discussed on the basis of product ion distributions and semi-empirical calculations of potential energies of reaction pathways.
