497-20-1Relevant academic research and scientific papers
Matrix-Controlled Photochemistry of Benzene and Pyridine
Johnstone, Duncan E.,Sodeau, John R.
, p. 165 - 169 (1991)
Dewar benzene has been shown to be a primary product from the photolysis of benzene in low temperature argon matrices at 253.7 nm.This is the first observation of Dewar benzene production at this wavelength and a mechanism is proposed that involves benzene S1-S2 state mixing induced by the matrix environment.Analogous experiments on the photolysis of pyridine show that the only primary products are isomeric species derived at least in part from a triplet state of pyridine, probably T1.This is the first observation of photochemistry from the T1 state and may be the process responsible for the small values of τp and ψp in pyridine.Analysis of the IR spectral bands points to the main product being Dewar pyridine although other isomers cannot be ruled out.In contrast to the gas phase, no decomposition of pyridine was found in matrices poducing compounds such as acrylonitrile, ethyne, and hydrogen cyanide.
Formation of fulvene in the reaction of C2H with 1,3-butadiene
Lockyear, Jessica F.,Fournier, Martin,Sims, Ian R.,Guillemin, Jean-Claude,Taatjes, Craig A.,Osborn, David L.,Leone, Stephen R.
, p. 232 - 245 (2015/04/14)
Abstract Products formed in the reaction of C2H radicals with 1,3-butadiene at 4 Torr and 298 K are probed using photoionization time-of-flight mass spectrometry. The reaction takes place in a slow-flow reactor, and products are ionized by tunable vacuum-ultraviolet light from the Advanced Light Source. The principal reaction channel involves addition of the radical to one of the unsaturated sites of 1,3-butadiene, followed by H-loss to give isomers of C6H6. The photoionization spectrum of the C6H6 product indicates that fulvene is formed with a branching fraction of (57 ± 30)%. At least one more isomer is formed, which is likely to be one or more of 3,4-dimethylenecyclobut-1-ene, 3-methylene-1-penten-4-yne or 3-methyl-1,2-pentadien-4-yne. An experimental photoionization spectrum of 3,4-dimethylenecyclobut-1-ene and simulated photoionization spectra of 3-methylene-1-penten-4-yne and 3-methyl-1,2-pentadien-4-yne are used to fit the measured data and obtain maximum branching fractions of 74%, 24% and 31%, respectively, for these isomers. An upper limit of 45% is placed on the branching fraction for the sum of benzene and 1,3-hexadien-5-yne. The reactive potential energy surface is also investigated computationally. Minima and first-order saddle-points on several possible reaction pathways to fulvene + H and 3,4-dimethylenecyclobut-1-ene + H products are calculated.
Shock Tube Study of Thermal Rearrangement of 1,5-Hexadiyne over Wide Temperature and Pressure Regime
Tranter, Robert S.,Tang, Weiyong,Anderson, Ken B.,Brezinsky, Kenneth
, p. 3406 - 3415 (2007/10/03)
The pyrolysis of 1,5-hexadiyne has been studied in a high-pressure single pulse shock tube to investigate the mechanisms involved in the production of benzene from propargyl radicals. Analysis of the reaction products by gas chromatography and matrix isolation Fourier transform infrared spectroscopy has positively identified six linear C6H6 species and two cyclic C6H6 species. Of these species cis-1,3-hexadien-5- yne and trans-1,3-hexadiene-5-yne have been unambiguously identified for the first time and provide vital information concerning a low-temperature route to benzene that does not involve the formation of fulvene; however, the data also provide support for two high-temperature paths from propargyl radicals to benzene via fulvene. Thus experimental evidence has been gained that supports two different routes to benzene formation. The mechanisms and rate coefficients that have been obtained in this work are discussed.
Kinetics and products of the self-reaction of propargyl radicals
Shafir, Eugene V.,Slagle, Irene R.,Knyazev, Vadim D.
, p. 8893 - 8903 (2007/10/03)
The kinetics and product branching of the self-reaction of propargyl radicals, C3H3 + C3H3 → products (1), have been studied as functions of temperature. Rate constants of reaction 1 were obtained in direct real-time experiments by laser photolysis/photoionization mass spectrometry over the temperature interval 500-1000 K and at a bath gas density of (3-6) × 1016 molecules cm-3. Propargyl radicals were produced by the 248 nm laser photolysis of oxalyl chloride ((CCIO)2) followed by a fast conversion of the produced chlorine atoms into propargyl radicals and HCl via the reaction with propyne. No active species other than C3H3 were present in the system during the kinetics of C3H3 decay. The values of the rate constant of reaction 1 were determined from the [C3H3] temporal profiles. The rate constants of reaction 1 decrease from (3.30 ± 0.35) × 10-11 cm3 molecule-1 s-1 at 500 K to (2.74 ± 0.43) × 10-11 cm3 molecule-1 s-1 at 700 K and to (1.20 ± 0.14) × 10-11 cm3 molecule-1 s-1 at 1000 K. The value obtained at 1000 K is likely to be influenced by falloff effects and secondary reactions initiated by the H + C6H5 products of reaction 1. The rate constants of reaction 1 determined in the current study at elevated temperatures correlate well with the room temperature value of ～4 × 10-11 cm3 molecule-1 s-1 obtained in several earlier studies. Combination of the results of the current work with those of earlier room temperature investigations results in the following temperature dependence of the high-pressure-limit rate constant of reaction 1: k1∞ = 4.49 × 10-9T-0.75 exp(-128 K/T) cm3 molecule-1 s-1 (295-700 K). Product channels of reaction 1 were studied using final product analysis by gas chromatography/mass spectrometry in the 500-1100 K temperature interval. Several C6H6 isomers were detected as products of the self-reaction of propargyl radicals: 1,5-hexadiyne, fulvene, benzene, and two unknown species identified in the text as unknown 1 and unknown 2. The distribution of products depends on the temperature. At lower temperatures, 1,5-hexadiyne, unknown 1, and benzene were observed. The fraction of benzene increases with temperature; it becomes the major product at 900 K and above. Fulvene and unknown 2 were observed in minor amounts in the 900-1100 K range. The product analysis provides evidence for the appearance of the reaction channel 1b (C6H5 + H) at high temperatures: formation of C8H6 and C9H8 was observed and attributed to the fast reaction of the phenyl radical with the excess of propyne present in the reactor.
Carbon-oxygen bond strength in diphenyl ether and phenyl vinyl ether: An experimental and computational study
Van Scheppingen, Wibo,Dorrestijn, Edwin,Arenas, Isabel,Mulder, Peter,Korth, Hans-Gert
, p. 5404 - 5411 (2007/10/03)
The thermal decomposition of gaseous diphenyl ether (DPE) and phenyl vinyl ether (PVE) has been studied, at atmospheric pressure in hydrogen and in a very low-pressure reactor, over a temperature range of 1050-1200 K. The high-pressure rate constant for homolytic bond cleavage C6H5O-C6H5 → C6H5O? + C6H5? (1) obeys k1 (s-1) = 1015.50 exp(-75.7/RT). Two pathways can be distinguished for C6H5OC2H3: C6H5? + C2H3O? (2) and C6H5O? + C2H3? (3). The overall rate constant follows k2+3 (s-1) = 1015.50 exp(-73.3/RT). The rate ratio, v2/v3, amounts to 1.8 and appears to be temperature independent These findings result in bond dissociation energies (BDE) at 298 K for C6H5O-C6H5, C6H5-OC2H3, and C6H5O-C2H3 of 78.8 ,75.9, and 76.0 kcal mol-1, respectively. The enthalpies for reactions 1-3 have been also determined at 298 and 1130 K by ab-initio calculations using the density functional theory formalism on the B3LYP/6-31G(d) and B3LYP/ 6-311++G(d,p) level. Comparison between experiments and theoretical calculations reveals distinct variances (ca 3-4 kcal mol-1) for the BDE(C-O) in aryl ethers and the BDE(O-H) in phenol and vinyl alcohol but a close agreement for the BDE(C-H) in the related hydrocarbons: toluene, benzene, and ethene.
Thermal Rearrangements, XXIII. - The Thermogram of a C6H6 Chemistry in the Temperature Range from 450 to 730 deg C
Zimmermann, Gerhard,Nuechter, Matthias,Remmler, Matthias,Findeisen, Matthias,Hopf, Henning,et al.
, p. 1747 - 1754 (2007/10/02)
The thermal isomerization of 1,5-hexadiyne (1) and its 2>-labeled derivative (1a) was studied in the temperature range 450 - 730 deg C and in the presence of different carrier gases (N2, H2, D2, N2/toluene).By detailed analysis (GC, GCMS, NMR) all volatile reaction products were identified and determined quantitatively by using hexafluorobenzene as an internal standard.The experimental data show clearly that the reaction products are formed by two different routes: (i) electrocyclization leading to dimethylene cyclobutene (3) at temperatures up to about 600 deg C and (ii) radical reaction leading to benzene (4) and pentafulvene (5) at temperatures above 550 deg C.Cyclopentadienylmethyl radicals are supposed to be the essential radical intermediates. - Key Words: Isomerization, thermal / Radicals / D-Labeling / 1,5-Hexadiyne / Pentafulvene / Rearrangement, homoallyl
The Energy Well of Diradicals, V. - 1,3,5-Cyclohexatriene-1,4-diyl and 2,4-Cyclohexadiene-1,4-diyl
Roth, Wolfgang R.,Hopf, Henning,Horn, Carina
, p. 1765 - 1780 (2007/10/02)
The energy profile of the Bergman rearrangement of (Z)-3-hexene-1,5-diyne (4) has been established from the NO and oxygen dependance of the trapping rate of the intermediate diradical 1 which leads to a heat of formation for 1,4-didehydrobenzene (1) of ΔH0f = 138.0 +/- 1.0 kcal * mol-1.By the same technique the heat of formation of 1,2,4-cyclohexatriene (2), generated by thermolysis of (Z)-1,3-hexadien-5-yne (10), gives ΔH0f = 105.1 +/- 1.0 kcal * mol-1 which indicates a high diradical character for 2. - Key Words: Diradicals / NO and O2 trapping / Heat of formation / Energy well / Rearrangements / Bergman cyclisation
Propargyl Stabilisation Energy
Roth, Wolfgang R.,Hopf, Henning,Horn, Carina
, p. 1781 - 1796 (2007/10/02)
For the alkynyl-substituted olefines 1 - 14 activation parameters for the geometrical isomerisation have been determined in the gasphase by the single-pulse shoke-tube technique.By comparison of these barriers with the corresponding one of the isolated double bonds, each corrected by the steric energy contribution of the ground and transition state, a value of 7.8 +/- 1.3 kcal * mol-1 for the propargyl stabilisation energy (PrSE) has been derived. - Key Words: Resonance energy / Stabilisation energy / Propargyl resonance / Force field calculation / Intrinsic rotational barrier / Single pulse shock tube / Gasphase kinetics / Heats of hydrogenation
FORMATION OF PENTAFULVENE IN FLASH VACUUM THERMOLYSIS OF 5- MELDRUM'S ACID OVER BITUMINOUS CARBON: EVIDENCE FOR CYCLOPENTADIENYLIDENE CARBENE.
Wiersum, Ulfert E.,Jenneskens, Leonardus W.
, p. 129 - 130 (2007/10/02)
The formation of pentafulvene (12) and benzene (11) upon flash vacuum thermolysis of 5- Meldrum's acid (9) over a hydrogen donating bituminous carbon matrix, provides the first experimental evidence for the occurrence of cyclopentadienylidene carbene (2) as a discrete species on the C6H4 energy surface.
On the Gas-Phase Pyrolysis of 2-Ethinyl-1,3-butadiene and Its Thermal Cycloisomerization
Remmler, Matthias,Zimmermann, Gerhard,Ondruschka, Bernd,Bader, Hubert,Hopf, Hennig
, p. 1375 - 1380 (2007/10/02)
The gas-phase pyrolysis of 2-ethinyl-1,3-butadiene (2) has been investigated in the 500-to-700 deg C temperature range.Besides several fragmentation products ( C4 hydrocarbons) benzene and fulvene (5) are the main products.Under the same conditions 2-(ethinyl)-1,3-butadiene (2a) furnishes the monodeuteriofulvenes 5a - c.The cycloisomerization of 2/2a presumably begins with an acetylene-vinylidenecarbene rearrangement, which may be followed by a deuterium scrambling mechanism involving either benzvalene (9) or vinylcyclobutadiene (10) intermediates.When 1-ethinyl-1-cyclohexene (6) is employed as a precursor for 2, styrene is produced in significant amounts besides the products observed from 2.Pyrolysis of 1-(ethinyl)cyclohexene (6a) provides -styrene whose isotopic label is scrambled over both the vinyl substituent and the aromatic nucleus.
