- Synthesis and reactions of the first cyclopentadienyl isonitriles
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6-Azidofulvenes without a further substituent in the exocyclic position were transformed into new 1-isocyano- and 2-isocyanocyclopenta-1,3-dienes by photolysis in methanol. These novel functionalized cyclopentadienes are useful building blocks, e.g. as dienes in Diels-Alder reactions.
- Banert, Klaus,K?hler, Frank,Meier, Barbara
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- Decomposition of Picolyl Radicals at High Temperature: A Mass Selective Threshold Photoelectron Spectroscopy Study
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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.
- Reusch, Engelbert,Holzmeier, Fabian,Gerlach, Marius,Fischer, Ingo,Hemberger, Patrick
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supporting information
p. 16652 - 16659
(2019/12/24)
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- Contrasting Photolytic and Thermal Decomposition of Phenyl Azidoformate: The Curtius Rearrangement Versus Intramolecular C-H Amination
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The decomposition of phenyl azidoformate, PhOC(O)N3, was studied by combining matrix isolation spectroscopy and quantum chemical calculations. Upon UV laser photolysis (193 and 266 nm), the azide isolated in cryogenic noble gas matrices (Ne and Ar, 2.8 K) decomposes into N2 and a novel oxycarbonylnitrene PhOC(O)N, which was identified by matrix-isolation IR spectroscopy (with 15N labeling) and EPR spectroscopy (|D/hc| = 1.620 cm-1 and |E/hc| = 0.024 cm-1). Subsequent visible-light irradiation (532 nm) causes rearrangement of the nitrene into phenoxy isocyanate PhONCO with complex secondary fragmentation (PhO· + ·NCO) and radical recombination species in matrices. The observation of PhONCO provides solid evidence for the Curtius rearrangement of phenyl azidoformate. In sharp contrast, flash vacuum pyrolysis (FVP) of PhOC(O)N3 at 550 K yields N2 and exclusively the intramolecular C-H amination product 3H-benzooxazol-2-one. FVP at higher temperature (700 K) leads to further dissociation into CO2, HNCO, and ring-contraction products. To account for the very different photolytic and thermal decomposition products, the underlying mechanisms for the Curtius rearrangement (concerted and stepwise) of PhOC(O)N3 and the intramolecular C-H amination of the nitrene in both singlet and triplet states are discussed with the aid of quantum chemical calculations using the B3LYP, CBS-QB3, and CASPT2 methods.
- Wan, Huabin,Xu, Jian,Liu, Qian,Li, Hongmin,Lu, Yan,Abe, Manabu,Zeng, Xiaoqing
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p. 8604 - 8613
(2017/11/24)
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- Gas-phase thermolysis of benzotriazole derivatives. Part 3: Kinetic and mechanistic evidence for biradical intermediates in pyrolysis of aroylbenzotriazoles and related compounds
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Gas-phase pyrolysis (static and FVP) of 1-aroylbenzotriazoles gave the corresponding substituted benzoxazole, benzimidazole, benzamide, N-phenylbenzamide, phenanthridin-6(5H)-one derivatives and 1- cyanocyclopentadiene. The present kinetic and mechanistic findings also provide further evidence of the involvement of biradical or carbene reactive intermediates in the reaction pathway of gas-phase pyrolysis of benzotriazoles.
- Al-Awadi, Nouria A.,George, Bobby J.,Dib, Hicham H.,Ibrahim, Maher R.,Ibrahim, Yehia A.,El-Dusouqui, Osman M. E.
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p. 8257 - 8263
(2007/10/03)
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- The photochemical transformation and tautomeric composition of matrix isolated benzotriazole
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Photolysis of benzotriazole isolated in argon and nitrogen matrices at 12-14 K has been studied by means of UV-visible and IR absorption spectroscopy. Short wavelength irradiation resulted in N-NH bond scission to give diazoimine 3 and minor products: cyanocyclopentadiene 6 and ketenimine 5. The compound 3 was easily bleachable. With 420 nm light, the major pathway was cycloreversion to benzotriazole, but at shorter wavelengths photolysis of 3 led first to the ketenimine product and ultimately to cyanocyclopentadiene. The photoproducts were identified by means of their characteristic IR absorptions. Identification of 3 was additionally supported by comparison of experimental and computed IR transitions, which also indicated that 3 was generated predominantly as its E isomer. Detailed analysis of the benzotriazole IR spectra recorded prior to and after photolysis pointed towards the co-existence of both tautomeric forms, 1H-benzotriazole (1) and 2H-benzotriazole (2), frozen from the gas phase during matrix deposition. An estimate of 1.6:1 was obtained for the gas-phase [1H]:[2H] ratio at ca. 315 K, in fair agreement with another recent estimate. The benzotriazole tautomers exhibited different photoreactivity, but attempts to utilize this in identifying the IR bands of the individual tautomers were hampered by band overlap, and only a few unequivocal assignments could be made.
- Kiszka, Mariusz,Dunkin, Ian R.,Gebicki, Jerzy,Wang, Hong,Wirz, Jakob
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p. 2420 - 2426
(2007/10/03)
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- Kinetics of Pyrolysis of a Coal Model Compound, 2-Picoline, the Nitrogen Heteroaromatic Analogue of Toluene. 2. The 2-Picolyl Radical and Kinetic Modeling
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The pyrolysis of 2-picoline, investigated experimentally in our previous paper, has been successfully modeled using a 70-reaction free-radical mechanism.The mechanism includes decomposition pathways for o-pyridyl and 2-picolyl, both of which are formed through the principal initiation reactions of 2-picoline.The proposed mechanism for 2-picolyl decomposition involves the direct ring opening of the 2-picolyl radical.Further reactions of the open chain isomer of 2-picolyl resulted in the formation of the major products HCN and acetylene and the minor products 1-cyanocyclopentadiene and cyclopentadiene.Kinetic modeling confirmed the feasability of this mechanism by predicting the observed profiles of these species.Optimizing of the heat of formation of 2-picolyl through kinetic modeling resulted in a value of 68 (+/-5) kcal mol-1.This value suggests a lower level of resonance stabilization for 2-picolyl compared to benzyl.This interference is supported by the "normal" value of the rate constant for 2-picolyl + H recombination found by modeling to be in the range 1x10-13-6x10-13 cm3 mol-1 s-1.The reactant and product profiles predicted by the kinetic model were found to be very sensitive to the rate of the initiation reaction yielding methyl and o-pyridyl radicals, allowing the heat of formation of the o-pyridyl radical to be determined.The optimized rate constant for this initiation reaction was found to be 1016.1(+/-0.2) exp (-91.5 (+/-2) kcal mol-1/RT) s-1, corresponding to a heat of formation for the o-pyridyl radical of 84.1 (+/-2) kcal mol-1.
- Doughty, Alan,Mackie, John C.
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p. 10339 - 10348
(2007/10/02)
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- Flash-vacuum Pyrolysis of 1-Acylbenzotriazole: Direct Observation of Cyclopenta-2,4-dienylidenemethaneimines by Tandem Mass Spectrometry and Low-temperature Infrared Spectrometry
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A real-time analysis of the flash-vacuum pyrolysis products of 1-acetylbenzotriazole (1) and 1-benzoylbenzotriazole (2) was performed by tandem mass spectrometry.In the temperature range 500-600 deg C, these compounds lose nitrogen, yielding N-acetyl- and N-benzoylcyclopenta-2,4-dienylidenemethaneimines (10 and 17, respectively).At higher pyrolysis temperatures, 1 gives 2-methylbenzoxazole, cyanocyclopentadiene, methylcyanocyclopentadiene(s), benzonitrile and ketene, which were identified by collision-activated mass spectrometry.Low-temperature infrared experiments confirmed the pyrolytic transformation 1(2) -> 10(17) at mediated temperatures.
- Maquestiau, Andre,Beugnies, Didier,Flammang, Robert,Freiermuth, Beat,Wentrup, Curt
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p. 197 - 203
(2007/10/02)
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- Identification of the Pyrolysis Products of Some Aromatic Amines using Microwave Spectroscopy
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The pyrolysis products of some aromatic amines have been identified using microwave spectroscopy.Aniline is found to produce 1-cyanocyclopenta-1,3-diene, N-methylaniline a mixture of 1-cyanocyclopenta-1,3-diene and benzonitrile, N,N-dimethylaniline produces benzonitrile, and N,N-dimethylpyridine-2-amine produces pyridine.In the pyrolysis of N-methylaniline the proportion of 1-cyanocyclopenta-1,3-diene to benzonitrile is estimated to be 4:1 from the integrated relative intensities of the low-resolution microwave band spectra of the two substances.
- Cervellati, Rinaldo,Corbelli, Giorgio,Esposti, Alessandra Degli,Lister, David G.,Todesco, Paolo E.
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p. 585 - 590
(2007/10/02)
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- Photolysis of Benztriazole in Alcoholic Glass at 77 K
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The photolysis of benztriazole (1) in alcoholic glass at 254 nm has been studied by UV absorption, emission, IR, and mass spectroscopies.Bond scission of the N-NH bond of 1 originates from the S1(?,?*) state to give the azo compound 2, having an absorption band at 423 nm and an IR absorption band at 2070 cm-1.This yellow azo intermediate is decomposed thermally or photochemically.Iminocyclohexadienylidene (3) with resonance structures of a carbene (3a) and a biradical (3b) may be produced as a colorless second intermediate.On the basis of reaction product analysis from the rigid-phase photolysis of 1 at 77 K compared to those in liquid solution and gas-phase photolyses, the reaction paths of 3 to yield aniline, o-anisidine, o-ethoxyaniline, and 1-cyanocyclopentadiene are discussed in terms of the spin states of 3.
- Shizuka, Haruo,Hiratsuka, Hiroshi,Jinguji, Mamoru,Hiraoka, Hiroyuki
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p. 1793 - 1797
(2007/10/02)
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