- Pyrolysis of Acrylonitrile at Elevated Temperatures. Studies with a Single-Pulse Shock Tube
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The thermal decomposition of acrylonitrile was studied behind reflected shocks in a single-pulse shock tube over the temperature range 1150-1430 K and overall densities of ca. 3 X 10-5 mol/cm3.Under these conditions the major reaction products are (1) hydrogen cyanide and acetylene and (2) hydrogen and cyanoacetylene: CH2=CHCN -> CH*CH + HCN (reaction 1) and CH2=CHCN -> CH*C-CN + H2 (reaction 7).In the presence of toluene, at a ratio of 0/0 ca. 10/1, a twofold decrease in the production rate of these products was observed, indicating a free-radical mechanism in parallel to the four-center eliminations.After the contribution of the free radical chain was subtracted, the following rate constants for the four-center eliminations were obtained: k1 = 1012.25 exp (-68 X 103/RT) s-1, and k2 = 1013.40 exp (-77 X 103/RT) s-1, where activation energies are expressed in units cal/mol.Ethylene was found in quantities roughly equal to those of cyanoacetylene.C2N2, CH3CN, CH4, C4H6 and C2H6 were found in the postshock mixtures but at much lower concentrations.Arrhenius parameters for the formation rate of the different reaction products are given and the general pyrolysis mechanism is discussed.
- Lifshitz, Assa,Bidani, Menashe,Suslensky, Aya,Tamburu, Carmen
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- Pyrolyses of aromatic azines: Pyrazine, pyrimidine, and pyridine
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The thermal decompositions of pyrazine, pyrimidine, and pyridine in shock waves have been investigated using the complementary techniques of laser-schlieren (LS) densitometry and time-of-flight (TOF) mass spectrometry (1600-2300 K, 150-350 Torr). A free radical chain reaction with initiation by ring C-H fission in the pyrolyses of all three azines is proposed. The measured C-H fission rates are compared and analyzed by RRKM theory. Barriers of 103 ± 2 kcal/mol for pyrazine, 98 ± 2 for pyrimidine, and 105 ± 2 for pyridine have been determined, supporting values lower than the barrier for C-H fission in benzene, 112 kcal/mol. The lower barriers for the azines are explained by the additional contributions of resonance structures of azyl radicals due to neighboring N-C interactions, which serve to further stabilize the azyl radicals. Detailed chain mechanisms are constructed to model the LS profiles and the TOF concentration profiles of the major products, hydrogen cyanide, acetylene, cyanoacetylene, and diacetylene. Of particular interest are the TOF observations and the mechanistic explanation of temperature dependent maxima seen in the formation of cyanoacetylene in the presence or absence of excess H2.
- Kiefer,Zhang,Kern,Yao,Jursic
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- The pyrolysis of 3-picoline: Ab initio quantum chemical and experimental (shock tube) kinetic studies
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The pyrolysis of 3-picoline dilute in argon was investigated using a single-pulse shock tube over the temperature range of 1400-1650 K and total pressures of 12-13 atm. The principal products observed were HCN, acetylene, benzene, cyanoacetylene, methane, and pyridine. Assuming that 3-picoline decomposes according to first-order kinetics, the rate constant for its overall disappearance was determined to be kdis = 1016.9(±0.8) exp[-99 (±6) kcal mol-1/RT] s-1. The principal initial decomposition routes were found to be via the formation of the 3-picolyl and m-pyridyl radicals whose subsequent ring-opening led to the observed products. A 68-step kinetic model was developed that successfully fits the experimental data. The dominant reactions, i.e., the formation of picolyl and pyridlyl radicals and their subsequent chain-opening reactions, were studied using ab initio quantum chemical techniques. The ab initio data were also incorporated into the kinetic model in the form of energies and A-factors for reactions for which no kinetic or thermochemical data were previously available. Optimization of the kinetic model yields a value of 64 ± (3) kcal mol-1 for the heat of formation of 3-picolyl, a value lower than that for 2-picolyl, suggesting that the decomposition of 3-picoline more closely resembles that of toluene, rather than its isomer 2-picoline.
- Jones, Jeffrey,Bacskay, George B.,Mackie, John C.
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- Photodissociation of acrylonitrile at 193 nm: A photofragment translational spectroscopy study using synchrotron radiation for product photoionization
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We have investigated the photodissociation of acrylonitrile (H2CCHCN) at 193 nm using the technique of photofragment translational spectroscopy. The experiments were performed at the Chemical Dynamics Beamline at the Advanced Light Source and used tunable vacuum ultraviolet synchrotron radiation for product photoionization. We have identified four primary dissociation channels including atomic and molecular hydrogen elimination. HCN elimination, and CN elimination. There is significant evidence that all of the dissociation channels occur on the ground electronic surface following internal conversion from the initially optically prepared state. The product translational energy distributions reflect near statistical simple bond rupture for the radical dissociation channels, while substantial recombination barriers mediate the translational energy release for the two molecular elimination channels. Photoionization onsets have provided additional insight into the chemical identities of the products and their internal energy content.
- Blank, David A.,Suits, Arthur G.,Lee, Yuan T.,North, Simon W.,Hall, Gregory E.
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- Shock Tube Pyrolysis of Pyridine
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The kinetics of pyridine dilute in argon have been studied in a single-pulse shock tube, using cappilary column GC together with GC/MS and FTIR spectroscopy for product determination, over the temperature range of 1300-1800 K and total pressures of 7-11 atm.At the lower end of the studied temperatures, cyanoacetylene was found to be the principal nitrogen-containing product.At elevated temperature hydrogen cyanide predominated.Other major products were acetylene and hydrogen.Thermochemical estimates of the isomeric cyclic pyridyls produced in the pyrolysis indicate that the ortho isomer is unique in being able to undergo facile cleavage to an open-chain cyano radical from which cyanoacetylene is produced.Several sources of HCN were identified in the system.The m- and p-pyridyls may eliminate HCN in a molecular process.An important source of HCN at high temperatures is the addition of H-atoms to cyano compounds, especially cyanoacetylene, but also acetonitrile and acrylonitrile which are produced in the pyrolysis.The pyrolysis is a chain process initiated principally by C-H bond fission to form o-pyridyl.A 58-step reaction model is presented and shown to substantially fit the observed profiles of the major product species.From this model we derive a value for the rate constant of the principal initiation reaction, C5H5N --> o-C5H4N + H (1), of k1=1015.9+/-0.4exp(-98 +/- 3 kcal mol-1/RT)s-1 between 1300 and 1800 K and at a total pressure of about 10 atm.
- Mackie, John C.,Colket III, Meredith B.,Nelson, Peter F.
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- Kinetics of Thermal Decomposition of the Diazines: Shock-tube Pyrolysis of Pyrimidine
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The kinetics of pyrolysis of pyrimidine diluted in argon have been studied behind reflected shock waves over the temperature range 1200-1850 K, at uniform gas residence times of 850-1000 μs and pressures of 13-15 atm.The major products of pyrimidine pyrolysis were found to be acetylene, HCN, acrylonitrile, cyanoacetylene and H2.Using both end-product analysis and real-time UV spectrometry the kinetics of pyrimidine disappearance were found to be first order with respect to reactant concentration over the concentration range of 0.07-0.3 molpercent.The two techniques yielded a first-order rate constant (kdis) for the disappearance of pyrimidine given by the expression 1012.3(+/-0.4)exp-1/RT>s-1.A detailed reaction model incorporating a free-radical mechanism for the decomposition of pyrimidine has been developed, and shown to predict the reactant and product concentrations between 1250 and 1600 K.Important radicals in the mechanism were found to be o- and p-pyrimidyl, with H atoms and CN radicals being radical chain carriers.Sensitivity and flux analysis of the kinetic model has shown the most important initiation pathway to be the loss of an H atom from pyrimidine to yield o-pyrimidyl.Optimisation of the Arrhenius parameters for this initiation reaction yields an activation energy cosistent with a heat of formation of the o-pyrimidyl radical of 376(+/-10) kJ mol-1.
- Doughty, Alan,Mackie, John C.
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- Total Synthesis of Aetokthonotoxin, the Cyanobacterial Neurotoxin Causing Vacuolar Myelinopathy
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Aetokthonotoxin has recently been identified as the cyanobacterial neurotoxin causing Vacuolar Myelinopathy, a fatal neurologic disease, spreading through a trophic cascade and affecting birds of prey such as the bald eagle in the USA. Here, we describe the total synthesis of this specialized metabolite. The complex, highly brominated 1,2’-biindole could be synthesized via a Somei-type Michael reaction as key step. The optimised sequence yielded the natural product in five steps with an overall yield of 29 %.
- Ricardo, Manuel G.,Schwark, Markus,Llanes, Dayma,Niedermeyer, Timo H. J.,Westermann, Bernhard
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- Photochemistry of Acetylene, Hudrogen Cyanide, and Mixtures
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Photoluses of HCN, C2H2, and mixtures were accomplished including various ratios of HCN/C2H2 and time periods.The photolysis of HCN yielded (CN)2, CH4, NH3, CH3NH2, (NH)2, and a brown polymer.The products from C2H2 were diacetylene (C4H2), C2H4, C6H6, vinylacetylene, phenylacetylene, and a polymer.Products from a relatively low HCN/C2H2 ratio (5:1) where 90percent of the light is absorbed by C2H2 were similar to those of C2H2 except for the additional formation of acrylonitrile (C2H3CN).At relatively higher ratios of HCN/C2H2 where 37-56percent of the light is absorbed by HCN, cyanoacetylene (C2HCN) was formed in addition to the foregoing products and the C4H2 substantially reduced.The proposed principal path for formation of C4H2 is attack of C2H. on C2H2, while for C2H3CN the principal path is attack of C2H3. on HCN.The proposed principal path for production of C2HCN is via CN. attack on C2H2.Several products from HCN are proposed to be the result of progressive H atom addition.Other products from C2H2 and HCN are the result of radical-radical recombination.We believe these results could have relevance to Jovian atmosphere chemistry and formation of several molecules found in interstellar space.
- Becker, Ralph S.,Hong, J. H.
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- The microwave spectrum of cyanophosphaacetylene, H2P{single bond}C{triple bond, long}C{single bond}C{triple bond, long}N
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The a type transitions of the microwave rotational spectra of cyanophosphaacetylene, H2P{single bond}C{triple bond, long}C{single bond}C{triple bond, long}N, have been investigated in the frequency region between 5 and 26.5 GHz by Fourier transformation microwave (FTMW) spectroscopy. Rotational, centrifugal distortion and 14N nuclear quadrupole coupling constants have been determined. Density functional theory level ab initio calculations were performed to predict the molecular constants, and the predicted values are in good agreement with our experimentally determined results. The 13C and 15N isotopomer transitions were also observed. The derived r0 structure is quite comparable to the calculated H2P{single bond}C{triple bond, long}C{single bond}C{triple bond, long}N equilibrium geometry.
- Kang, Lu,Minei, Andrea J.,Novick, Stewart E.
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- Kinetics of Pyrolysis of a Coal Model Compound, 2-Picoline, the Nitrogen Heteroaromatic Analogue of Toluene. 1. Product Distributions
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The pyrolysis of 2-picoline in dilute mixtures with argon has been investigated using the single-pulse shock tube and was found to decompose over the temperature range 1300-1550 K, at an average residence time of 800 μs and uniform pressure of 14-16 atm.The major products observed were acetylene, methane, hydrogen, HCN, and cyanoacetylene.Over the studied range of mixture compositions (0.06-0.20 molpercent of 2-picoline) the overall rate of disappearance of 2-picoline obeyed first-order kinetics.Arrhenius parameters for disappearance of picoline were found to be Adis=1017.4+/-1.1 s-1 and Ea,dis=98+/-7 kcal mol-1.From the distribution of observed products it is concluded that the principal initiation reactions were analogous to those known to occur in toluene, the hydrocarbon analogue of 2-picoline, and were found to be C-C bond fission to yield o-pyridyl and methyl radicals and C-H fission to yield H atoms and 2-picolyl, the N-containing analogue of benzyl.Major products were observed from decomposition of both the o-pyridyl and the 2-picolyl radicals.Cyanoacetylene arises principally from the secondary reactions of o-pyridyl.A product with m/z 91 was observed at the lowest temperatures at which 2-picoline decomposition could be detected.It has been identified as 1-cyanocyclopentadiene and arises from loss of H from the 2-picolyl radical.Other products arising from secondary decomposition of 2-picolyl at higher temperatures include HCN and cyclopentadienyl radicals.
- Terentis, Andrew,Doughty, Alan,Mackie, John C.
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- 3,5-Pyridyne-A Heterocyclic meta-Benzyne Derivative
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3,5-Pyridyne (3) has been generated by flash vacuum pyrolysis of 3,5-diiodopyridine (20) and 3,5-dinitropyridine (21) and characterized by IR spectroscopy in cryogenic argon matrices. The aryne can clearly be distinguished from other side products by its photolability at 254 nm, inducing a rapid ring-opening presumably to (Z)-1-aza-hex-3-ene-1,5-diyne. As byproducts of the pyrolysis, HCN and butadiyne were identified, together with traces of acetylene, cyanoacetylene, (E)-1-aza-hex-3-ene-1,5-diyne, and the 3-iodo-5-pyridyl radical (from 20). Several pathways for rearrangements and fragmentations of 3 and of the parent meta-benzyne (1) have been explored computationally by density functional theory and ab initio quantum chemical methods. The lowest energy decomposition pathway of biradicals 1 and 3 is a ring-opening process accompanied by hydrogen migration, leading to (Z)-hex-3-ene-1,5-diyne [(Z)-10] and (Z)-3-aza-hex-3-ene-1,5-diyne [(Z)-24], respectively. Both reactions require activation energies of 45-50 kcal mol -1. Mechanisms leading from (Z)-24 or directly from 3 to the experimentally observed byproducts are discussed. Upon replacement of the C(5)H moiety by N in meta-benzyne, high-level calculations predict a modest shortening of the interradical distance by 5-7 pm and a reduction of the singlet-triplet energy splitting by 3 kcal mol-1, in good agreement with isodesmic equations, according to which the singlet ground state of 3 is destabilized relative to 1 by 3-4 kcal mol-1. In contrast to 3,5-borabenzyne (2), which is found to be doubly aromatic, nucleus-independent chemical shifts of 3 are almost identical to that of pyridine, indicating the absence of paramagnetic ring current effects that may be associated with in-plane antiaromaticity . As compared with 1, the overall perturbation caused by the nitrogen atom in 3 is weak, and four electron, three center interaction is of minor importance in this molecule.
- Winkler, Michael,Cakir, Bayram,Sander, Wolfram
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- Microwave spectra and molecular structures of (Z)-pent-2-en-4-ynenitrile and maleonitrile
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Accurate equilibrium structures have been determined for (Z)-pent-2-en-4-ynenitrile (8) and maleonitrile (9) by combining microwave spectroscopy data and ab initio quantum chemistry calculations. The microwave spectra of 10 isotopomers of 8 and 5 isotopomers of 9 were obtained using a pulsed nozzle Fourier transform microwave spectrometer. The ground-state rotational constants were adjusted for vibration-rotation interaction effects calculated from force fields obtained from ab initio calculations. The resultant equilibrium rotational constants were used to determine structures that are in very good agreement with those obtained from high-level ab initio calculations (CCSD(T)/cc-pVTZ). The geometric parameters in 8 and 9 are very similar; they also do not differ significantly from the all-carbon analogue, (Z)-hex-3-ene-1,5-diyne (7), the parent molecule for the Bergman cyclization. A small deviation from linearity about the alkyne and cyano linkages is observed for 7-9 and several related species where accurate equilibrium parameters are available. The data on 7-9 should be of interest to radioastronomy and may provide insights on the formation and interstellar chemistry of unsaturated species such as the cyanopolyynes.
- Halter,Fimmen,McMahon,Peebles,Kuczkowski,Stanton
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- Synthesis and characterization of 2,4-pentadiynenitrile - A key compound in space science
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(Chemical Equation Presented) Spaced out: Cyanobutadiyne (3) was synthesized in pure form from 1,3-butadiynyltributylstannane (1) and p-toluene-sulfonyl cyanide (2). Diyne 3 might be formed in the atmosphere of Titan or in the interstellar medium by photolysis of mixtures of acetylene and cyanoacetylene or dicyanoacetylene or of butadiyne and dicyanoacetylene. Only 1,6-addition is observed with nucleophiles.
- Trolez, Yann,Guillemin, Jean-Claude
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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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- Crossed beam reaction of cyano radicals with hydrocarbon molecules. IV. Chemical dynamics of cyanoacetylene (HCCCN;X 1Σ+) formation from reaction of CN(X 2Σ+) with acetylene, C2H2(X 1Σg+)
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The chemical reaction dynamics to form cyanoacetylene, HCCCN (X 1Σ+), via the radical-neutral reaction of cyano radicals, CN(X 2Σ+; ν = 0), with acetylene, C2H2(X 1Σg+), are unraveled in crossed molecular beam experiments at two collision energies of 21.1 and 27.0 kJ mol-1. Laboratory angular distributions and time-of-flight spectra of the HCCCN product are recorded at m/e = 51 and 50. Experiments were supplemented by electronic structure calculations on the doublet C3H2N potential energy surface and RRKM investigations. Forward-convolution fitting of the crossed beam data combined with our theoretical investigations shows that the reaction has no entrance barrier and is initiated by an attack of the CN radical to the ? electron density of the acetylene molecule to form a doublet cis/trans HCCHCN collision complex on the 2A' surface via indirect reactive scattering dynamics. Here 85 percent of the collision complexes undergo C-H bond rupture through a tight transition state located 22 kJ mol-1 above the cyanoacetylene, HCCCN (X 1Σ+) and H(2S1/2) products (microchannel 1). To a minor amount (15 percent) trans HCCHCN shows a 1.2-H shift via a 177 kJ mol-1 barrier to form a doublet H2CCCN radical, which is 46 kJ mol-1 more stable than the initial reaction intermediate (microchannel 2). The H2CCCN complex decomposes via a rather loose exit transition state situated only 7 kJ mol-1 above the reaction products HCCCN (X 1Σ+) and H(2S1/2). In both cases the geometry of the exit transition states is reflected in the observed center-of-mass angular distributions showing a mild forward/sideways peaking. The explicit identification of the cyanoacetylene as the only reaction product represents a solid background for the title reaction to be included in reaction networks modeling the chemistry in dark, molecular clouds, outflow of dying carbon stars, hot molecular cores, as well as the atmosphere of hydrocarbon rich planets and satellites such as the Saturnian moon Titan.
- Huang, L. C. L.,Asvany, O.,Chang, A. H. H.,Balucani, N.,Lin, S. H.,Lee, Y. T.,Kaiser, R. I.,Osamura, Y.
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- Ab Initio Quantum Chemical and Experimental (Shock Tube) Studies of the Pyrolysis Kinetics of Acetonitrile
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The pyrolysis kinetics of acetonitrile dilute in argon has been studied in the temperature range 1400-2100 K at an average pressure of 12 atm in single-pulse shock tube experiments. The principal products are HCN, C2H2, CH4, and H2, while the minor products include HCCCN, H2CCHCN, C2H4, and C4H2. The overall kinetics is successfully simulated by an 87 step kinetic model that accurately accounts for the temperature profiles of the major products and also provides an acceptable fit for the minor products. The thermochemistry and rate parameters of a number of key reactions have been obtained by ab initio quantum chemical calculations carried out at CASSCF, CASPT2, and Gaussian-2 levels of theory. Several distinct reaction pathways were studied, whereby the geometries, vibrational frequencies, and energies of approximately 70 molecular species representing reactants, products, intermediates, and transition states were computed. The pyrolysis of acetonitrile is initiated by CH bond fission, forming a cyanomethyl radical. This reaction is the most sensitive one in the kinetic model. On the basis of sensitivity analyses of the model as well as ab initio calculations, the heat of formation of cyanomethyl has been revised as ΔfH2980(CH2CN) = 263 ± 9 kJ mol-1. The limiting highpressure value of the corresponding rate constant, as obtained by ab initio variational transition state calculations, is k1 ∞ = 1.2 × 10116 exp(- 413 kJ mol-1/RT) s-1, which is in good agreement with our extrapolated experimental measurement. A number of the observed products, including HCCCN and H2CCHCN, largely arise from the decomposition of succinonitrile, a key intermediate, that forms by the recombination of two cyanomethyl radicals.
- Sendt, Karina,Ikeda, Emi,Bacskay, George B.,Mackie, John C.
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- The 193-nm excimer laser photofragmentation of alkane and alkene nitriles in argon matrices
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Excimer laser irradiation at 193 nm has been coupled with the matrix isolation technique for the study of fragmentation and rearrangement processes for acrylonitrile, crotononitrile, and 2-methyl-2-butenenitrile. For each of these systems, multiple fragmentation pathways were implicated, and the products for each system were characterized by infrared spectroscopy. For example, laser irradiation of acrylonitrile led to the formation of acetylene, hydrogen cyanide, and 2-propynenitrile. Irradiation was carried out both during the deposition process and after the matrix was rigidly frozen in place; differences were attributed to cage restrictions on recombination processes. Several simple alkyl nitriles were also subjected to laser irradiation, but for these systems no photoproducts were detected.
- Machara, Nicholas P.,Ault, Bruce S.
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- Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism
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A minimal cell can be thought of as comprising informational, compartment-forming and metabolic subsystems. To imagine the abiotic assembly of such an overall system, however, places great demands on hypothetical prebiotic chemistry. The perceived differences and incompatibilities between these subsystems have led to the widely held assumption that one or other subsystem must have preceded the others. Here we experimentally investigate the validity of this assumption by examining the assembly of various biomolecular building blocks from prebiotically plausible intermediates and one-carbon feedstock molecules. We show that precursors of ribonucleotides, amino acids and lipids can all be derived by the reductive homologation of hydrogen cyanide and some of its derivatives, and thus that all the cellular subsystems could have arisen simultaneously through common chemistry. The key reaction steps are driven by ultraviolet light, use hydrogen sulfide as the reductant and can be accelerated by Cu(I)-Cu(II) photoredox cycling.
- Patel, Bhavesh H.,Percivalle, Claudia,Ritson, Dougal J.,Duffy, Colm D.,Sutherland, John D.
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p. 301 - 307
(2015/04/14)
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- UV laser photodeposition of nanomagnetic soot from gaseous benzene and acetonitrile-benzene mixture
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Megawatt KrF laser gas-phase photolysis of benzene and acetonitrile-benzene mixture was studied by using mass spectroscopy-gas-chromatography and Fourier transform infrared spectroscopy for analyses of volatile products, and by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, electron microscopy and magnetization measurements for analyses of solid products deposited from the gas-phase. The results are consistent with carbonization of benzene and decomposition of non-absorbing acetonitrile in carbonizing benzene through collisions with excited benzene and/or its fragments. The solid products from benzene and acetonitrile-benzene mixture have large surface area and are characterized as nanomagnetic amorphous carbonaceous soot containing unsaturated C centers prone to oxidation. The nanosoot from acetonitrile-benzene mixture incorporates CN groups, confirms reactions of benzene fragments with CN radical and has a potential for modification by reactions at the CN bonds.
- Pola, Josef,Ouchi, Akihiko,Mary?ko,Vorlí?ek,?ubrt, Jan,Bakardjieva,Bastl, Zdeněk
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experimental part
p. 188 - 194
(2012/02/02)
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- Photochemistry of matrix-isolated 5-cyano-2H-pyran-2-one (δ-cyano-α-pyrone) and cyanocyclobuta-1,3-diene
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Matrix-isolation photochemistry ( > 299 nm; Ar, 10 K) of 5-cyano-2H-pyran-2-one (5, -cyano - pyrone) shows complete conversion to a mixture of several ring-opened ketene isomers (6) and a ring-closed Dewar lactone (7), as detected by infrared spectroscopy. Subsequent irradiation ( > 200 nm) causes decarboxylation of the Dewar lactone (7) to produce cyanocyclobuta-1,3-diene (8). Continued irradiation ( > 200 nm) results in the photodecomposition of cyanocyclobuta-1,3-diene (8) to cyanoacetylene and acetylene. 4-Cyanopyridine (10) was explored as an alternative photochemical precursor to cyanocyclobuta-1,3-diene (8). It was found, however, that 10 does not exhibit observable photochemistry under our irradiation conditions.
- Menke, Jessica L.,McMahon, Robert J.
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body text
p. 186 - 194
(2011/04/23)
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- AMIDE COMPOUND
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There is provided a FAAH inhibitor and a prophylactic or therapeutic agent for cerebrovascular disorders or sleep disorders comprising it. The prophylactic or therapeutic agent comprises a compound of the formula (I0): wherein Z is oxygen or sulfur; R1 is aryl which may be substituted, or a heterocyclic group which may be substituted; R1a is a hydrogen atom, a hydrocarbon group which may be substituted, hydroxyl, etc.; R2 is piperidin-1,4-diyl which may be substituted, or piperazin-1,4-diyl which may be substituted; R3 is a group formed by eliminating two hydrogen atoms from a 5-membered aromatic heterocyclic group having 1 to 3 heteroatoms selected from nitrogen, oxygen and sulfur, which may be further substituted, -CO-, etc.; and R4 is a hydrocarbon group which may be substituted, or a heterocyclic group which may be substituted; or a salt thereof.
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Page/Page column 88
(2008/06/13)
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- Radical pathways in the thermal decomposition of pyridine and diazines: A laser pyrolysis and semi-empirical study
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The mechanisms of thermal decomposition of pyridine and the three isomeric diazines have been investigated by IR laser pyrolysis in conjunction with stable end-product analysis by FTIR, NMR and GC-MS, and radical detection by EPR spectroscopy. Calculations at semi-empirical and ab initio levels have provided confirmation of potential reaction pathways. For pyridine, reaction is initiated by formation of pyridyl radicals, as indicated by extensive isotope exchange with added deuterium. Experiments with bromopyridines show that open chain radicals arising from ring opening of 2-pyridyl and 3-pyridyl radicals each lead to stable gaseous products, while 4-pyridyl radicals produce solid deposits, and may be the principal agents in soot formation. The evidence suggests that 1,2-diazine decomposes via a molecular route leading to stoichiometric production of HCN and C2H2, while 1,3- and 1,4-diazine follow a pattern of H loss and ring radical opening analogous to that of pyridine.
- Hore, Nathan R.,Russell, Douglas K.
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p. 269 - 275
(2007/10/03)
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- Thermal decomposition of quinoline and isoquinoline. The role of 1-indene imine radical
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The thermal reactions of quinoline and isoquinoline were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1275-1700 K and densities of ~3 ×10-5 mol/ cm3. The decomposition products found in the postshock mixtures of quinoline and isoquinoline and their production rates were identical for both isomers. They were C2H2, C6H5CN, HC≡CCN, C6H6, HCN, C6H5-C≡CH and C4H2. Trace quantities of C6H4, C5H5N and C5H4N-C≡CH were also found. The total disappearance rates of quinoline and isoquinoline are the same, and in terms of a first-order rate constant they are given by ktotal = 1013.0exp(-75.5 × 103/RT) s-1 where R is expressed in units of cal/(K mol). The same product distribution in the two isomers can be accounted for if the production of 1-indene imine radical as an intermediate is assumed. A kinetic scheme containing the reactions of both quinoline and isoquinoline with 72 species and 148 elementary reactions accounts for the observed product distribution. The reaction scheme is given, and the results of computer simulation and sensitivity analysis are shown.
- Laskin, Alexander,Lifshitz, Assa
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p. 928 - 946
(2007/10/03)
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- Isomerization and decomposition of indole. Experimental results and kinetic modeling
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The thermal reactions of indole were studied in a pressurized driver single-pulse shock tube. Three isomerization products are obtained such as benzyl cyanide, o- and m-tolunitriles as a result of the pyrrole ring opening. The mechanism of indole-tolunitrile isomerization involves a series of unimolecular steps which are preceded by the very fast indole-indolenine tautomerism. The thermal decomposition of indole is initiated by H-atom ejection from the reactant. First-order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested and results of computer simulation and sensitivity analysis are shown. Differences and similarities in the reactions of pyrrole and indole are discussed.
- Laskin,Lifshitz
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p. 7787 - 7801
(2007/10/03)
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- A study on the scope of the photochemical ring contraction of substituted 2-amino-3-cyano-4H-pyrans to cyclobutenes: Crystal structure of 3-carbamoyl-3-cyano-1-ethoxycarbonyl-4-isopropyl-2-phenylcyclobutene
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A study on the influence of substitution on the photochemical reactivity of a series of differently substituted 2-amino-4H-pyrans 10a-h has been carried out. All of the compounds undergo ring contraction to the corresponding cyclobutenes 11a-h on direct irradiation. Variable amounts of the enamides 12 and the alkynes 13 were also obtained, as secondary photoproducts. The results obtained show that the cyclization takes place in reasonable yields with alkyl, phenyl and hydrogen substitution at C-4 and at C-6. Cyano, ethoxycarbonyl and benzoyl substitution at C-5 also promotes the reaction. A high degree of stereochemical control was observed in most cases. The molecular geometry of cyclobutene 11a1 has been established by X-ray diffraction analysis. This study also shows that the crystal packing is formed by a system of chains linked by strong hydrogen bonds.
- Armesto, Diego,Albert, Armando,Cano, Felix H.,Martin, Nazario,Ramos, Ana,Rodriguez, Miriam,Segura, Jose L.,Seoane, Carlos
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p. 3401 - 3405
(2007/10/03)
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- Chemistry of α-Amino Nitriles. Exploratory Experiments on Thermal Reactions of α-Amino Nitriles
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The paper extends a previously published report on chemical properties of α-amino nitriles and of members of the C3H4N2 ensemble (Scheme 1) as observed in experiments carried out under non-aqueous conditions.The reactions investigated and the observations made are summarized in some detail in the English footnotes (*) referring to Schemes 1-17 and Fig. 1.
- Xiang, Yi-Bin,Drenkard, Susanne,Baumann, Karl,Hickey, Deirdre,Eschenmoser, Albert
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p. 2209 - 2250
(2007/10/02)
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- EXPERIMENTAL STUDY OF THE SYNTHESIS OF DICYANOACETYLENE BY DEHYDRATION OF ACETYLENEDICARBOXAMIDE WITH PHOSPHORIC ANHYDRIDE IN THE MODE OF A SELF-PROPAGATING STATIONARY HEAT WAVE
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The feasibility of ensuring a wave mode of heat propagation in the mixture of acetylenedicarboxamide (ADCA) and phosphoric anhydride has been experimentally shown.The limiting concentrations of ADCA, restricting the occurrence range of the wave process, have been found.The yields of dicyanoacetylene and by-products obtained in the wave process have been determined as functions of the concentration of ADCA and initial temperature of the reaction mixture.
- Alekseev, Yu. I.,Pashkevich, D. S.
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p. 1794 - 1797
(2007/10/02)
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- Selected-ion flow tube studies of reactions of the radical cation (HC3N)+. in the interstellar chemical synthesis of cyanoacetylene
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The radical cation (HC3N)+. was produced in a Selcted-Ion Flow Tube (SIFT) apparatus from cyanoacetylene by electron impact and reacted at room temperature in helium buffer gas with a selection of molecules including H2, CO, HCN, CH4, H2O, O2, HC3N, C2H2, OCS, C2H4, and C4H2.The observed reactions exhibited a wide range of reactivity and a variety of pathways including charge transfer, hydrogen atom transfer, proton transfer, and association.Association reactions were observed with CO, O2, HCH and HC3N.With the latter two molecules association was observed to proceed close to the collision limit, which is suggestive of covalent bond formation perhaps involving azine-like N-N bonds.For HC3N an equally rapid association has been observed by Buckley et al. with ICR (Ion Cyclotron Resonance) measurements at low pressures and this is suggestive of radiative association.The hydrogen atom transfer reaction of ionized cyanoacetylene with H2 is slow while similar reactions with CH4 and H2O are fast.The reaction with CO fails to transfer a proton.These results have implications for synthetic schemes for cyanoacetylene as proposed in recent models of the chemistry of interstellar gas clouds.Proton transfer was also observed to be curiously unfavourable with all other molecules having a proton affinity higher than (C3N)..Also, hydrogen-atom transfer was inefficient with the polar molecules HCN and HC3N.These results suggest that informations at close separations may lead to preferential alignment of the reacting ion and molecule which is not suited for proton transfer or hydrogen atom transfer.
- Fox, A.,Raksit, A. B.,Dheandhanoo, S.,Bohme, D. K.
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p. 399 - 403
(2007/10/02)
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- Rates of Base-Catalyzed Hydrogen Exchange of Terminal Acetylenes in Aqueous Solution. Absence of Resonance Interaction
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Rates of detritiation of 13 monosubstituted acetylenes labeled at the acetylenic hydrogen position were measured in aqueous amine buffer solution at 25 deg C, and hydroxide ion catalytic coefficients were evaluated.These rate constants, plus a few additional values from the literature, give a good correlation against inductive or field substituent constants: log(kHO-/M-1s-1) = 1.46+/-0.12 + (8.00+/-0.50)?I.This correlation is not improved by addition of resonance substituted constants, and the coefficients of the resonance term in two different dual parameter (resonance plus field) treatments of the data are in fact zero.
- Kresge, A. J.,Powell, M. F.
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p. 819 - 822
(2007/10/02)
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- Heterocyclic β-Enamino Esters, 44: 2,3,3a,7a-Tetrahydrobenzofurans, -benzothiophene, and 2,3,3a,7a-Tetrahydroindole by Cycloaddition with Cyanoacetylene
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With two molecules cyanoacetylene the (4,5-dihydro-2-furyl- (1a-c), -2-pyrrolinyl- (1d), and -2-thienylimino (1e))triphenylphosphoranes and the furan β-enaminonitrile 1f afford the 2,3,3a,7a-tetrahydrobenzofurans 2a-c,f, the 2,3,3a,7a-tetrahydroindole 2d, and the benzothiophene 2e, respectively.The structure of 2b is established by X-ray diffraction.
- Wamhoff, Heinrich,Fassbender, Franz-Josef,Hermes, Dieter,Knoch, Falk,Appel, Rolf
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p. 2723 - 2730
(2007/10/02)
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- The Detection of the New Molecule Prop-2-ynylideneamine, H-CC-CH=NH, by Microwave Spectroscopy
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The new molecule prop-2-ynylideneamine, H-CC-CH=NH, has been produced by flowing propargylamine over N-chlorosuccinimide, and then over potassium t-butoxide; the molecule was detected by microwave spectroscopy and its rotational parameters determined as a necessary preliminary to a radioastronomical search.
- Kroto, Harold W.,McNaughton, Don,Osman, Osman I.
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p. 993 - 994
(2007/10/02)
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- Pyrazolo(1,5-c)quinazoline derivatives and related compounds
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Compounds are provided having the structure STR1 wherein R1 is hydrogen, alkyl of 1-3 carbons, phenyl optionally substituted by R4 ; R2 is cyano; STR2 (wherein Z is a single bond or STR3 X is O or S); STR4 (wherein R9 is hydrogen or alkyl, Q is CH or N); STR5 wherein R6 is amino, alkylamino, dialkylamino, haloalkyl or STR6 and R4 and R5 are the same or different and represent hydrogen, lower alkyl, lower alkoxy, alkanoyloxy, benzyloxy, substituted benzyloxy, hydroxy, halogen (Cl, Br and F), nitro and trifluoromethyl; and R7, R8, m and n are defined hereinafter.
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