Dynamic reduction of a CH4/air chemical mechanism appropriate for investigating vortex–flame interactions

This paper describes two methods, piecewise reusable implementation of solution mapping (PRISM) and dynamic steady‐state approximation (DYSSA), in which chemistry is reduced dynamically to reduce the computational burden in combustion simulations. Each method utilizes the large range in species timescales to reduce the dimensionality to the number of species with slow timescales. The methods are applied within a framework that uses hypercubes to partition multidimensional chemical composition space, where each chemical species concentration, plus temperature, is represented by an axis in space. The dimensionality of the problem is reduced uniquely in each hypercube, but the dimensionality of chemical composition space is not reduced. The dimensionality reduction is dynamic and is different for different hypercubes, thereby escaping the restrictions of global methods in which reductions must be valid for all chemical mixtures. PRISM constructs polynomial equations in each hypercube, replacing the chemical kinetic ordinary differential equation (ODE) system with a set of quadratic polynomials with terms related to the number of species with slow timescales. Earlier versions of PRISM were applied to smaller chemical mechanisms and used all chemical species concentrations as terms. DYSSA is a dynamic treatment of the steady‐state approximation and uses the fast–slow timescale separation to determine the set of steady‐state species in each hypercube. A reduced number of chemical kinetic ODEs are integrated rather than the original full set. PRISM and DYSSA are evaluated for simulations of a pair of counterrotating vortices interacting with a premixed CH₄/air laminar flame. DYSSA is sufficiently accurate for use in combustion simulations, and when relative errors are less than 1.0%, speedups on the order of 3 are observed. PRISM does not perform as well as DYSSA with respect to accuracy and efficiency. Although the polynomial evaluation that replaces the ODE solver is sufficiently fast, polynomials are not reused sufficiently to enable their construction cost to be recovered. © 2007 Wiley Periodicals, Inc. 39: 204–220, 2007     

Ring-Opening Reaction of a Dihydrozirconafuran (= 2,5-Dihydro-1,2-oxazirconole): An equilibrium studied by NMR methods,and its chemical consequences

The dihydrozirconafuran 3 (2,2-di(cyclopenta-2,4-dien-l-yl)-2,5-dihydro-5,5-dimethyl-3,4-bis(trimethylsilyl)-1,2-oxazirconole) is a valuable synthetic equivalent to the 14-electron fragment Cp₂Zr

1 Throughout this paper, C_p=η⁵?C₅H₅

. The reactions of this metallacycle suppose an equilibrium with an ‘opened’ form [ZrCp₂(RC?CR)(acetone)], the latter paving the way to numerous ligand replacements. In a solution containing the dihydrozirconafuran and acetone, these reactions are reversible and degenerate, and can be studied by NMR methods: by two-dimensional spectroscopy and by observation of the isotope-induced chemical shifts that occur upon incorporation of (D₆)acetone into the metallacycle. The findings give an indirect proof of the described equilibrium.     

Coordinating Abilities Towards Sodium of Oxygenated Solvents

Tetracoordination of the sodium cation is indicated by the ²³Na-NMR. chemical shifts for NaClO₄ in binary mixtures of ether and alcohol solvents. Solvent exchange occurs by a sequential process, and involves one or several intermediates. In competition with tetrahydrofurfuryl alcohol, whereas glyme corresponds to monocyclic intermediates, diglyme and triglyme

1 For abbreviations see Table 1.

favor formation of bicyclic intermediates. The relevant conformational factors are analysed, and also serve to explain the better coordinating abilities of diglyme and triglyme, as compared to glyme. The mechanism for solvent exchange is discussed.     

Carbon-13 nuclear magnetic resonance spectroscopy IX—monosubstituted ethylenes

Carbon-13 chemical shifts of sixteen monosubstituted ethylenes were obtained. In order to explain the chemical shifts, σ and π electron densities of these compounds are calculated by the σ-included ω-HMO method.

1 See Ref. 8.

A linear relationship exists between carbon-13 chemical shifts and the calculated electron densities, and also between substituent constants and electron densities. A slope of unity is obtained between the chemical shifts of α carbons of monosubstituted ethylenes and those of carbons adjacent to the substituents in monosubstituted benzenes. On the other hand, a plot of chemical shifts of C_ortho of benzene derivatives against that of the β carbon in ethylene derivatives gives a slope of 3. These slopes can be explained by the calculated electron densities. A slope of 4/3 is obtained between the direct coupling constant ¹J(C? H) of the α carbon in monosubstituted ethylenes and that in the corresponding substituted methanes.     

Isolierung,Struktur und Synthese des Metaboliten von Azapropazon-dihydrat

The renal excretion of AZAPROPAZONE-DIHYDRATE (X)

1 Handelsname: PROLIXAN®. Hersteller: Siegfried AG, Zofingen.

by humans was investigated. Following oral administration a new substance was detected in the urine besides X by TLC. Both compounds were separated by preparative layer chromatography and shown to be unchanged X and its hydroxylated metabolite VIII. The structure of VIII was established by chemical and spectroscopic methods (IR., NMR.) and confirmed by synthesis (Scheme 1).     

The mass spectra of some α-aminooxy acids

The mass spectrometric behaviour of six simple α-aminooxy acids is described. Comparison is made with the electron-impact-induced fragmentation of the parent α-amino acids. The differences are in accordance with the observed

1 See Ref. 1.

chemical character of the α-aminooxy acids.     

Chemie von α-Aminonitrilen. 12. Mitteilung. Sondierungen über thermische Umwandlungen von α-Aminonitrilen

Chemistry of α-Amino Nitriles

1 11. Mitteilung: [1].

. Exploratory Experiments on Thermal Reactions of α-Amino Nitriles The paper extends a previously published report [4] 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.     

Zum chemischen Transport im System Mn?O unter Berücksichtigng des Sauerstoffkoexistenzdruckes (I)

Chemical Transport in the System Mn? O in Consideration of the Oxygen Coexistence Pressure (I) The chemical transport of the coexistent phases Mn₂O₃? Mn₃O₄ and Mn₃O₄? MnO with Cl₂, Br₂, I₂, HCl, HBr, and HI was analysed thermodynamically and experimentally. The mentioned transport agents are able to transport the following phases:

1 Index (o) bedeutet obere, (u) untere Phasengrenze (index (o) – upper phase boundary, (u) – lower phase boundary).

.     

Characteristic ratio of the mean-square end-to-end distance of poly(vinylidene fluoride) with microstructural defects

The segment length distribution of isoregic head-to-head and tail-to-tail sequences in poly-(vinylidene fluoride) (PVF₂)

1 System. name: poly(1,1-difluoroethylene).

chains is calculated from ¹⁹F NMR literature data. It is found that the average length of inverse segments is very close to one unit; therefore almost all head-to-head defects are immediately repaired by an adjacent tail-to-tail addition. The role of microstructure on the characteristic ratio of the end-to-end distance is then investigated. Results obtained by two different methods indicate that, in agreement with previous Monte Carlo calculations, defects play a minor role for the conformational characteristics of PVF₂. However, a slight contraction of about 4% is expected for very defective chains.     

Spectres RMN et analyse conformationnelle de germa-4 dioxannes-1,3

Methods for the calculation of the torsional angle of the C? C linkage

1 Voir Réf. 1.

are applied to some 4-germa-1,3-dioxanes. It is thereby shown that 4,4-diethyl-2trichloromethyl-4-germa-1,3-dioxane in CCl ₄ and C ₆ D ₆ adopts the chair conformation, with the equatorial C? Cl ₃ group distorted by the presence of the germanium: the torsional angle of the Ge-CH ₂ -CH ₂ -O-fragment is 45°. The most stable 6-alkyl derivatives ( cis isomers) have the same conformation; the less stable trans - tert -butyl isomer prefers a skew-boat form compatible with a torsional angle of about 60°.     

Zum chemischen Transport im System Mn?O unter Berücksichtigung des Sauerstoffkoexistenzdruckes. II

Chemical Transport in the System Mn? O in Consideration of the Oxygen Coexistence Pressure. II The chemical transport of the coexistent phases Mn₂O₃? Mn₃O₄ and Mn₃O₄? MnO with TeCl₄ and SeCl₄ was analysed thermodynamically and experimentally. This two transport agents are able to transport the following phases:

1 Index (o) bedeutet obere, (u) untere Phasengrenze (index (o) – upper phase boundary, (u) – lower phase boundary)

     

Yield of 16OS18O from the 18OH initiated oxidation of CS2 in 16O2

The yield of ¹⁶OS¹⁸O from the ¹⁸OH initiated oxidation of CS₂ in ¹⁶O₂ was measured by using a discharge flow reactor coupled to a chemical ionization mass spectrometer. ¹⁶OS¹⁸O is the dominant SO₂ isotopomer produced with a yield of 0.90 ± 0.20 relative to ¹⁸OH loss. The errors are estimates for the uncertainty at the 95% confidence level. The implications of these results to the understanding of the CS₂ oxidation mechanism are discussed. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Erratum: Synthesis of functional phosphines with ortho‐substituted aryl groups: 2‐RC6H4PH2 and 2‐RC6H4P(SiMe3)2 (R = i‐Pr‐ or t‐Bu)

The synthesis and characterization of 2‐i‐PrC₆H₄PCl₂ ( 3 ), 2‐t‐BuC₆H₄PCl₂ ( 4 ), 2‐i‐PrC₆H₄PH₂ ( 5 ), 2‐t‐BuC₆H₄PH₂ ( 6 ), 2‐i‐PrC₆H₄P(SiMe₃)₂ ( 7 ), and 2‐t‐BuC₆H₄P(SiMe₃)₂ ( 8 ) are described. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:355–360, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20619 *

1 This is a revised version of the article originally published in Volume 21, Number 4 (Heteroatom Chem 21:265‐270, 2010; DOI 10.1002/hc.20606). Due to an unfortunate publisher's error, the earlier version was posted online and approved for press before the journal's production team had received the authors' proof corrections. The publisher regrets the oversight.

     

Three chlorinated bipyridine compounds: Quantum calculations and their relationship to the molecular structure and physicochemical properties of the molecules considered

The Cl³⁵ nuclear quadrupole resonances were measured for three chlorinated bipyridine compounds. The number of resonances obtained is explained in terms of the position of one ring of the compound with respect to the other. Quantum chemical calculations

1 Details of the computer programs used are available from the author on request.

confirm the explanation given.     

Nachbargruppeneffekte in der Gas-Phase: Intramolekulare Deacetalisierung von Hydroxyacetalen unter den Bedingungen der chemischen Ionisation

Neighboring-Group Participation in the Gas Phase: Intramolecular Deacetalization of Hydroxyacetals under the Conditions of Chemical Ionization

1 Herrn Prof. Dr. Christoph Tamm zum 70. Geburtstag gewidmet

Under the conditions of chemical ionization (NH₃, isobutane, ND₃), hydroxyacetals do not show the expected [M + H⁺] signal, but the peak corresponding to the loss of the alcohol component of the acetal. This reaction is dependent on the presence of the OH group in the vicinity of the acetal and on the ring size of the heterocycle being formed. M^+· is detected to a small extent as a consequence of charge exchange during chemical ionization.     

2–Butoxyethanol and benzyl alcohol reactions with the nitrate radical: Rate coefficients and gas‐phase products

The bimolecular rate coefficients k and k were measured using the relative rate technique at (297 ± 3) K and 1 atmosphere total pressure. Values of (2.7 ± 0.7) and (4.0 ± 1.0) × 10^?15 cm³ molecule^?1 s^?1 were observed for k and k, respectively. In addition, the products of 2‐butoxyethanol + NO₃^? and benzyl alcohol + NO₃^? gas‐phase reactions were investigated. Derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine and N, O‐bis (trimethylsilyl)trifluoroacetamide and gas chromatography mass spectrometry (GC/MS) were used to identify the reaction products. For 2‐butoxyethanol + NO₃^? reaction: hydroxyacetaldehyde, 3‐hydroxypropanal, 4‐hydroxybutanal, butoxyacetaldehyde, and 4‐(2‐oxoethoxy)butan‐2‐yl nitrate were the derivatized products observed. For the benzyl alcohol + NO₃^? reaction: benzaldehyde ((C₆H₅)C(?O)H) was the only derivatized product observed. Negative chemical ionization was used to identify the following nitrate products: [(2‐butoxyethoxy)(oxido)amino]oxidanide and benzyl nitrate, for 2‐butoxyethanol + NO₃^? and benzyl alcohol + NO₃^?, respectively. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with a plausible 2‐butoxyethanol or benzyl alcohol + NO₃^? reaction mechanisms based on previously published volatile organic compound + NO₃^? gas‐phase mechanisms. © 2012 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

© 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 778–788, 2012     

The reaction Ne+H 2 + (v=0, 1, 2, 3, 4)→NeH++H: 3D potential energy surface and quasiclassical trajectory calculations

A three-dimensional potential energy surface for the endoergic reaction Ne+H ₂ ⁺ →NeH⁺+H in the² A′ ground state of the system NeH ₂ ⁺ has been calculated by quantum chemical ab initio methods (CEPA approximation). The calculated points on this surface were fitted to an analytic ansatz in terms of an extended LEPS functional form augmented by a correction function. The latter was expanded in polynomials in inverse powers of the internuclear distances. This analytic form was used for quasiclassical trajectory calculations of reactive cross sections. In agreement with experimental investigations a strong vibrational enhancement is observed, i.e. the reaction is markedly favored if the necessary reaction energy is supplied as vibrational energy of H ₂ ⁺ rather than as relative translational energy. Other properties of the reaction dynamics such as the backward to forward scattering ratio, the lifetime of the collision complex NeH ₂ ⁺ , and final rotational and vibrational state distributions are also discussed on the basis of the quasiclassical trajectory calculations.     

Thermodynamic properties of poly(2,6-dimethyl-1,4-phenylene ether)

The thermodynamic properties of crystalline and amorphous poly(2,6-dimethyl-1,4-phenylene ether) (PPO

1 Registered trademark of General Electric Company.

polymer, General Electric Co.) have been studied calorimetrically between 80 and 570°K. The calculated configurational entropy of this polymer, of similar magnitude to other glass-forming liquids, is consistent with the combination of an unusually high ratio of T_g/T_m, and a low melting entropy.