2143-53-5Relevant academic research and scientific papers
Substituent Effects by Deuterium and Alkyl Groups and 13C Hyperfine Coupling Constants of Cyclopentadienyl Radicals as Studied by Electron Spin Resonance
Kira, Mitsuo,Watanabe, Mieko,Sakurai, Hideki
, p. 5202 - 5207 (1980)
ESR spectra of the parent and six substituted cyclopentadienyl radicals (RC5H4; R = H, D, Me, Et, i-Pr, t-Bu, Me3SiCH2), generated from the corresponding RC5H4SnMe3 by an SH2 attack on Sn with the photochemically generated tert-butoxy radical, have been recorded over the temperature range -95 to +24 deg C.Judging from the proton coupling constants, the electron-releasing perturbation of alkyl groups is in the order (CH3)3SiCH2 > CH3 > C2H5 > (CH3)2CH > (CH3)3C.Preferred conformations of these alkyl groups are discussed from the temperature effects on the spectra.Notably, the methyl group rotates freely, while the (CH3)3SiCH2 group has a fixed conformation in which the (CH3)3Si group eclipses the p orbital on the C1 atom of the cyclopentadienyl.The resonance-integral perturbation effect is more important than the Coulomb-integral perturbation in the deuterium substitution.Finally the coupling constants of 13C for CnHn (n = 5-8) radical species are discussed.
Kinetics of the Cyclopentadiene Decay and the Recombination of Cyclopentadienyl Radicals with H-Atoms: Enthalpy of Formation of the Cyclopentadienyl Radical
Roy, K.,Braun-Unkhoff, M.,Frank, P.,Just, Th.
, p. 821 - 833 (2001)
The recombination of c-C5H5 with H-atoms has been studied behind reflected shock waves. The obtained rate coefficients are almost independent of temperature and were found to be krec = 2.6 x 1014 cm3 mol-1 s-1 for pressures around 2 bar in the temperature range between 1150 and 1500 K. Together with rate coefficients for the dissociation, obtained in an earlier work (Roy et al., Proc Combust Inst 1998, 27, 329-336) at pressures and temperatures close to those applied in the present work, we calculated equilibrium constants Kc(T) for C5H6 c-C5H5 + H. A "third law" analysis was performed. Data for the enthalpy of formation of cyclopentadienyl DHf,0 = 65.4 +/- 1 kcal mol-1 and DHf,298 = 62.5 +/- 1 kcal mol-1 were derived, respectively. The analysis was based upon new results on the entropy of cyclopentadienyl, recently calculated by Kiefer et al. (J phy chem, in press). Finally, our measured data were subjected to a fall-off analysis. The simulation turned out very satisfactorily.
Decomposition of Picolyl Radicals at High Temperature: A Mass Selective Threshold Photoelectron Spectroscopy Study
Reusch, Engelbert,Holzmeier, Fabian,Gerlach, Marius,Fischer, Ingo,Hemberger, Patrick
supporting information, p. 16652 - 16659 (2019/12/24)
The reaction products of the picolyl radicals at high temperature were characterized by mass-selective threshold photoelectron spectroscopy in the gas phase. Aminomethylpyridines were pyrolyzed to initially produce picolyl radicals (m/z=92). At higher temperatures further thermal reaction products are generated in the pyrolysis reactor. All compounds were identified by mass-selected threshold photoelectron spectroscopy and several hitherto unexplored reactive molecules were characterized. The mechanism for several dissociation pathways was outlined in computations. The spectrum of m/z=91, resulting from hydrogen loss of picolyl, shows four isomers, two ethynyl pyrroles with adiabatic ionization energies (IEad) of 7.99 eV (2-ethynyl-1H-pyrrole) and 8.12 eV (3-ethynyl-1H-pyrrole), and two cyclopentadiene carbonitriles with IE′s of 9.14 eV (cyclopenta-1,3-diene-1-carbonitrile) and 9.25 eV (cyclopenta-1,4-diene-1-carbonitrile). A second consecutive hydrogen loss forms the cyanocyclopentadienyl radical with IE′s of 9.07 eV (T0) and 9.21 eV (S1). This compound dissociates further to acetylene and the cyanopropynyl radical (IE=9.35 eV). Furthermore, the cyclopentadienyl radical, penta-1,3-diyne, cyclopentadiene and propargyl were identified in the spectra. Computations indicate that dissociation of picolyl proceeds initially via a resonance-stabilized seven-membered ring.
Ultrafast electron diffraction of transient cyclopentadienyl radical: A dynamic pseudorotary structure
Ihee, Hyotcherl,Feenstra, Jonathan S.,Cao, Jianming,Zewail, Ahmed H.
, p. 325 - 334 (2008/10/08)
Ultrafast electron diffraction (UED) is applied here in the study of the reaction of cylcopentadienyl cobalt dicarbonyl (CpCo(CO)2) which proceeds to give product structures. These structures were probed by picosecond electron pulses. The major product of the fragmentation was found to be the cyclopentadienyl radical. The dynamic nature of the radical was best represented by a pentagonal molecular structure having D5h symmetry with elevated mean amplitudes of vibration. Comparisons between theory and experiment are presented. The structure is that of the transition state between the compressed (dienylic) and the elongated (allylic) conformations but with longer bond distances, reflecting the dynamics of the pseudorotary surface.
Detailed kinetics of cyclopentadiene decomposition studied in a shock tube
Burcat, Alexander,Dvinyaninov, Michael
, p. 505 - 514 (2007/10/03)
Mixtures of cyclopentadiene diluted with argon were used to investigate its decomposition pattern in a single pulse shock tube. The temperatures ranged from 1080 to 1550 K and pressures behind the shock were between 1.7-9.6 atm. The cyclopentadiene concentrations ranged from 0.5 to 2%. Gas-chromatographic analysis was used to determine the product distribution The main products in order of abundance were acetylene, ethylene, methane, allene, propyne, butadiene, propylene, and benzene. The decomposition of cyclopentadiene was simulated with a kinetic scheme containing 44 species and 144 elementary reactions. This was later reduced to only 36 reactions The ring opening process of the cyclopentadienyl radical was found to be the crucial step in the mechanism. 1997 lohn Wiley and Sons, Inc.
Rate Constants for Termination and TEMPO Trapping of Some Resonance Stabilized Hydroaromatic Radicals in the Liquid Phase
Arends, I.W.C.E.,Mulder, P.,Clark, K.B.,Wayner, D.D.M.
, p. 8182 - 8189 (2007/10/02)
The rate constants for the termination reaction (2k1) of some resonance stabilized carbon centered radicals (SR.) derived from hydroaromatics (Sr. + SR. -> P) have been determined at 294 +/- 2 K by laser flash photolysis with UV-vis detection.The radicals were generated by hydrogen atom abstraction by t-BuO-radicals from the corresponding hydrocarbon (SRH + t-BuO. -> SR. + t-BuOH. k4).The extinction coefficients (e) of the SR., essential to calculate 2k1, were obtained using a relative kinetic technique.The change in 2k1 for the radicals derived from 1,4-cyclohexadiene, fluorine, 9,10-dihydroanthracene, diphenylmethane, tetralin, indan, indene, and phenol appeared to be modest; a range of 2k1 = 2-10 x 1E9 M-1 s-1 in mixtures of benzene and di-tert-butyl peroxide was observed.Most of the rate constants are near the diffusion controlled limit.In contrast, quenching the radicals with a persistent radical, 2,2,5,5-tetramethylpiperidin-1-oxyl (TEMPO), resulted in a larger variation of -1 s-1.The strength of the N-O bond formed in the latter process may have an important contribution to the observed rate constant.
Pathways and kinetic energy disposal in the photodissociation of nitrobenzene
Galloway, Douglas B.,Bartz, Jeffrey A.,Huey, L. Gregory,Crim, F. Fleming
, p. 2107 - 2114 (2007/10/02)
Vacuum-ultraviolet photoionization molecular-beam mass spectrometry is a means of identifying primary photodissociation products and determining their recoil energies.At several photolysis wavelengths between 220 and 320 nm, we have observed three primary photodissociation pathways for nitrobenzene.Two of the pathways are C6H5NO2 C6H5 + NO2 and C6H5NO2 C6H5NO + O.The third pathway produces NO by one or both of the processes C6H5NO2 C6H5O + NO and C6H5NO2 C5H5 + CO + NO.The relative yield of the pathways producing NO2 and NO varies strongly with the photolysis wavelength.The production of NO2 exceeds that of NO by about 50percent for the 280 nm photolysis, but increases to almost a sixfold excess in 222 nm dissociation.The second pathways has a threshold energy that is about 0.50 eV greater that the thermodynamic limit for the formation of nitrosobenzene (C6H5NO) and an oxygen atom from nitrobenzene, probably reflecting the energy required to produce triplet nitrosobenzene and, perhaps, a barrier to dissociation on the triplet surface.The distribution in arrival times for a fragment provides an estimate of the recoil energy at each photolysis wavelength in these experiments.The channel producing nitric oxide (NO) radicals releases a relatively large amount of kinetic energy.Assuming the channel producing nitric oxide (NO) also produces phenoxy (C6H5O), we calculate a linear increase in kinetic energy from 0.29 eV at 320 nm to 1.1 eV at 220 nm.By contrast, the other two channels release only a small amount of kinetic energy (ca. 0.1 eV) at all wavelengths.An impulsive model does not describe the observed kinetic energy release for these low energy channels, suggesting that the energy release is more nearly statistical.The recoil energy predicted by an impulsive model for the channel producing nitric oxide and phenoxy radicals is closer to the observed kinetic energy release.
Unimolecular dissociation of cyclopentadiene and indene
Yi, Whikun,Chattopadhyay, Arun,Bersohn, Richard
, p. 5994 - 5998 (2007/10/02)
The dissociation of hydrogen atoms from the methylene group of cyclopentadiene (CP) and indene (ID) excited with a 193 nm photon has been studied by hydrogen atom laser induced fluorescence.The rate of dissociation of IND was 7.4*106 s-1 but that of CP was too fast to measure.The ratio of H atoms to D atoms generated from 5-deuteriocyclopentadiene (5-dCP) was 3.910.46.Rice-Ramsberger-Kassel-Marcus theory was used to calculate the rates of dissociation of CP and 5-dCP.The quantum yield for dissociating H atoms from CP was 0.850.07.The ejected H atoms have a Maxwell velocity distribution with temperatures which are equal to the vibrational temperatures, 3690 and 2479 K for CP and IND, respectively.The most important result of the work is this confirmation of an earlier finding on a different set of molecules that the translational temperature of the fragments after the dissociation is equal to the vibrational temperature before the dissociation.This is explained by the assumption that the motion of the fast, light hydrogen atom is partly decoupled from that of the heavier, slower atoms.
Thermal Decomposition of Methyl Phenyl Ether in Shock Waves: The Kinetics of Phenoxy Radical Reactions
Lin, Chin-Yu,Lin, M. C.
, p. 425 - 431 (2007/10/02)
The unimolecular decomposition of methyl phenyl ether (anisole) was studied in incident shock waves covering the temperature range from 1000 to 1580 K and the pressure range from 0.4 to 0.9 atm.The CO formed in the reaction, monitored by resonance absorption using a stabilized CW CO laser, could be satisfactorily accounted for by a four-reaction mechanism: C6H5OCH3->C6H5O+CH3 (1), C6H5O->CO+C5H5 (2), CH3+C6H5O->o- and p-CH3C6H4OH (3), and CH3+CH3->C2H6 (4).Kinetic modelling of observed CO production profiles based on the above mechanism with 70 sets of data led to k1(1.2+/-0.3)*1016exp(-33100/T) s-1, k2=1011.40+/-20exp(-22100+/-450/T) s-1, and k3=(5.5+/-2.0)*1011 cm3*mol-1*s-1.The relatively low A factor and activation energy measured for the phenoxy radical decomposition reaction support the mechanism A involving a tight intermediate.
AN ESR STUDY OF THE PHOTOLYSIS OF DICYCLOPENTADIENYLTITANIUM DICHLORIDE
Brindley, Peter B.,Davies, Alwyn G.,Hawari, Jalal A.-A.
, p. 247 - 256 (2007/10/02)
ESR spectroscopy has been used to monitor the radicals which are formed when dicyclopentadienyltitanium dichloride is photolysed in solution alone or in the presence of various reagents (oxygen, ethers, pyridine, phosphines, 2-methyl-2-nitropropane, nitro
