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Title Reaction (title + reaction)
Selected AbstractsKinetic isotope effects for the H2 + C2H , C2H2 + H reaction based on the ab initio calculations and a global potential energy surfaceINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2010Liping Ju In the present paper, kinetic isotope effects of the title reaction are studied with canonical variational transition state theory on the modified Wang Bowman (MWB) potential energy surface (PES) (Chem Phys Lett 2005, 409, 249) and the ab initio calculations at the quadratic configuration interaction (QCISD (T, full))/aug-cc-pVTZ//QCISD (full)/cc-pVTZ level. The calculated rate constants for the isotopic variants of this title reaction on the MWB PES have good agreement with those of the present ab initio calculations over the temperature range of 20,5000 K for the forward reactions and 800,5000 K for the reverse reactions, respectively. In particular, the forward rate constants for the title reaction and its isotopically substituted reactions have negative temperature dependences at about 40 K. Rate expressions are presented for all the studied reactions. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 289,298, 2010 [source] Evaluation of data for atmospheric models: Master Equation/RRKM calculations on the combination reaction ClO + NO2 , ClONO2, a recurring issueINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2009David M. Golden Experimental data for the title reaction have been modeled using Master Equation/RRKM methods based on the Multiwell suite of programs. The starting point for the exercise was the empirical fitting provided by the NASA and IUPAC data evaluation panels, which represent the data in the experimental pressure ranges rather well. Despite the availability of quite reliable parameters for these calculations (molecular vibrational frequencies and a value of the bond dissociation energy of ClONO2, DH298(ClONO2) = 26.5 kcal mol,1, corresponding to ,H00 = 25.35 kcal mol,1 at 0 K) and use of RRKM/Master Equation methods, fitting calculations to the reported data was anything but straightforward. Using these molecular parameters resulted in a discrepancy between the calculations and the database of rate constants of a factor of ca 4 at, or close to, the low-pressure limit. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 573,581, 2009 [source] CH3 + Cl = CH3Cl: RRKM/master equation modelingINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2009David M. GoldenArticle first published online: 30 DEC 200 Data for the title reaction have been fitted using an RRKM/master equation approach. Energy transfer was modeled using an exponential decay with downward step sizes, ,Ed, as a fitting parameter. The low temperature (200 < T (K) < 300) combination of CH3 with Cl atoms in He can be accommodated with ,Ed (cm,1) = 400. Higher temperature (1600 < T (K) < 2100) decomposition in Ar required ,Ed(T) (cm,1) = 694(T/300)0.46. Previous analysis of the analogous system CH4 = CH3 + H required ,Ed(T) (cm,1) = 100(T/300) for He and ,Ed(T) (cm,1) = 150(T/300) for Ar. Understanding of the magnitudes and temperature dependence of ,Ed remains the greatest detriment to quantitative calculation, extrapolation, and prediction of unimolecular rate constants. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 245,254, 2009 [source] Dynamics and kinetics of the S + HO2 reaction: A theoretical studyINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 9 2008M. Y. Ballester We report a quasi-classical trajectory study of the S + HO2 reaction using a previously reported global potential energy surface for the ground electronic state of HSO2. Zero-point energy leakage is approximately accounted for by using the vibrational energy quantum mechanical threshold method. Calculations are carried out both for specific ro-vibrational states of the reactants and thermalized ones, with rate constants being reported as a function of temperature. The results suggest that the title reaction is capture type, with OH and SO showing as the most favorable products. The internal energy distribution of such products and the reaction mechanism are also investigated. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 533,540, 2008 [source] Direct ab initio dynamics calculations of the rate constants for the reaction of CHF2CF2OCH3 with ClINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2007Lei Yang A dual-level direct dynamics method is employed to reveal the dynamical properties of the reaction of CHF2CF2OCH3 (HFE-254pc) with Cl atoms. The optimized geometries and frequencies of the stationary points and the minimum energy path (MEP) are calculated at the B3LYP/6-311G(d,p) level by using GAUSSIAN 98 program package, and energetic information is further refined by the G3(MP2) method. Two H-abstraction channels have been identified. For the reactant CHF2CF2OCH3 and the two products, CHF2CF2OCH2 and CF2CF2OCH3, the standard enthalpies of formation are evaluated with the values of ,256.71 ± 0.88, ,207.79 ± 0.12, and ,233.43 ± 0.88 kcal/mol, respectively, via group-balanced isodesmic reactions. The rate constants of the two reaction channels are evaluated by means of canonical variational transition-state theory (CVT) including the small-curvature tunneling (SCT) correction over a wide range of temperature from 200 to 2000 K. The calculated rate constants agree well with the experimental data, and the Arrhenius expressions for the title reaction are fitted and can be expressed as k1 = 9.22 × 10,19 T2.06 exp(219/T), k2 = 4.45 × 10,14T0.90 exp(,2220/T), and k = 4.71 × 10,22 T3.20) exp(543/T) cm3 molecule,1 s,1. Our results indicate that H-abstraction from CH3 group is the main reaction pathway in the lower temperature range, while H-abstraction from CHF2 group becomes more competitive in the higher temperature range. © 2007 Wiley Periodicals, Inc. 39: 221,230, 2007 [source] The First General, Highly Enantioselective Lewis Base Organo- catalyzed Hydrosilylation of Benzoxazinones and QuinoxalinonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Zhou-Yang Xue Abstract The first general, highly enantioselective hydrosilylation of benzoxazinones and quinoxalinones has been developed. The chiral Lewis base organocatalysts that are readily accessible from (1S,2R)-ephedrine and (1R,2S)-ephedrine promoted the title reaction to afford various chiral dihydrobenzoxazinones and dihydroquinoxalinones with good yields as well as good enantioselectivities. [source] Theoretical study on the mechanism of the 1CHCl + NO2 reactionsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2004Jia-Xu Zhang Abstract The radical-molecule reaction mechanism of 1CHCl with NO2 has been explored theoretically at the B3LYP/6-311G(d, p) and CCSD(T)/6-311G(d, p) (single-point) levels of theory. Thirteen minimum isomers and 29 transition states are located. The initial association between 1CHCl and NO2 proceeds most likely through the carbon-to-middle-nitrogen attack leading to an energy-rich adduct a (HClCNO2), which is found to be a barrierless process. Staring from a, the most feasible channel is to undergo a concerted O-shift and CN bond rupture leading to product P2 (NO + HClCO). The minor product pathways are the direct O-extrusion of a to P3 (O + HClCNO- cis) as well as the 1,3-H-shift of a to isomer b (ClCNOOH) followed by a concerted OH-shift leading to d (HOClCNO), which will dissociate to product P8 (NO + ClCOH) via CN cleavage. Because the transition states and isomers involved in the most feasible channel all lie below the reactants, the title reaction is expected to be rapid, as is consistent with the measured rate constant at 296 K. The comparison with the analogous reactions 3CH2 + NO2 are discussed. The present study may be useful for further experimental investigation of the title reaction. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1184,1190, 2004 [source] CH3CH2SCH3,+,OH radicals: temperature-dependent rate coefficient and product identification under atmospheric pressure of air,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Gabriela Oksdath-Mansilla Abstract Relative rate coefficients have been determined for the gas-phase reaction of hydroxyl (OH) radicals with ethyl methyl sulfide (EMS) using isobutene as a reference compound. The experiments were performed in a 1080,L quartz glass photoreactor in the temperature range of 286,313,K at a total pressure of 760,±,10,Torr synthetic air using in situ FTIR absorption spectroscopy to monitor the concentration-time behaviors of reactants and products. OH radicals were produced by the 254,nm photolysis of hydrogen peroxide (H2O2). The kinetic data obtained were used to derive the following Arrhenius expression valid in the temperature range of 286,313,K (in units of cm3,molecule,1,s,1): The rate coefficient displays a negative temperature dependence and low pre-exponential factor which supports the existence of an addition mechanism for the reaction involving reversible OH-adduct formation. The results are compared with previous data of other sulfides from the literature and are rationalized in terms of structure,reactivity relationships. Additionally, product identification of the title reaction was performed for the first time by the FTIR technique under atmospheric conditions. Sulfur dioxide, formaldehyde, and formic acid were observed as degradation products in agreement with the two possible reaction channels (addition/abstraction). Copyright © 2010 John Wiley & Sons, Ltd. [source] Correlation of relative rates of chromyl chloride oxidation and chromic acid oxidation of acyclic alkenes versus alkene IPs and HOMOsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2004Donna J. Nelson Abstract Plots of logarithms of relative reaction rates of chromyl chloride oxidation and of chromic acid oxidation of alkenes (log,krel values) versus alkene ionization potentials (IPs) and versus their highest occupied molecular orbital energy levels (HOMOs) demonstrate excellent correlations. Each plot has a similar appearance and shows a single line with a positive slope. The results indicate that the rate-determining step of each title reaction involves an electrophilic attack on the alkene ,-bond without significant steric effects; this supports a proposed 2,+,3 cycloaddition mechanism and disfavors a proposed stepwise 2,+,2 cycloaddition mechanism. Comparison is made with other d0 transition metal complexes that oxidize alkenes. Copyright © 2004 John Wiley & Sons, Ltd. [source] Substituent effect on the [2,+,3] cycloaddition of (E)-,-Nitrostyrene with (Z)- C,N -Diarylnitrones,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 2 2002Andrzej Baranski Abstract The kinetics of the title reaction were studied in toluene at 80,°C by means of HPLC. The overall rate constant (ktotal) of the reaction of (E)-,-nitrostyrene (1) with (Z)- C -phenyl- N -arylnitrones (2a,g) was found to increase with increasing Hammett ,-constant, whereas in the case of (Z)- C -aryl- N -phenylnitrones (2g,p) and the same nitrostyrene the rate decreased. The substituent effect in these reactions is inconsistent with FMO treatments of cycloaddition rates. For both reaction series good linear relationships were obtained between log ktotal and the net charge on the carbon atom in the >CN(O), moiety of the nitrones calculated by the AM1 method. Copyright © 2001 John Wiley & Sons, Ltd. [source] Addition of Me3SiCN to trifluoromethyl derivates of N -(pyridylmethylidene) anilines catalyzed by Lewis acidsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2001Irina Iovel Abstract A series of novel Shiff bases (1a,h) was synthesized by condensation of pyridinecarboxaldehydes (1,4) with 3- and 4-trifluoromethylanilines (5, 6) in the presence of molecular sieves (4 Å). It was found that AlCl3 and AlBr3 catalyzed the addition of Me3SiCN to the CN bond of the imines obtained, whereas the other Lewis acids studied (YCl3, LaCl3, ZnI2) were not active. The reactivity of the imines in the title reaction, on the whole, correlated with their basicity. Besides the addition giving the expected ,-amino nitriles (2a,b,d,f,h), an unusual reaction leading to unsaturated nitriles (3a,h) was observed. The structures of saturated and unsaturated products 2d and 3c were determined by X-ray diffraction. Copyright © 2001 John Wiley & Sons, Ltd. [source] On the importance of the reaction between OH and RO2 radicalsATMOSPHERIC SCIENCE LETTERS, Issue 2 2009A. T. Archibald Abstract A new model, BAMBO (Bristol's Atmospheric Marine Boundary layer mOdel), was developed in order to investigate the reaction between peroxy radicals (RO2) and the hydroxyl radical (OH) under typical marine boundary layer (MBL) conditions. The results of this work have shown that the inclusion of the title reaction has negligible effects on inorganic species and ozone but can have significant effects on predicted atmospheric mixing ratios of oxygenated volatile organic compounds (OVOCs), which are generally poorly represented in atmospheric models. This work highlights that the title reaction may be important to modelling trace gas composition in the MBL. However, thorough experimental and theoretical studies are needed to clarify many of the assumptions made. Copyright © 2009 Royal Meteorological Society [source] ChemInform Abstract: Photoinduced Electron Transfer-Initiated Selective Cyclization Reactions of (Z)-N-Benzoyl-,-dehydro(1-naphthyl)alaninamides into 4,5-Dihydrooxazole Derivatives.CHEMINFORM, Issue 36 2010Yuhki Sato Abstract The substituent and solvent effects on the title reaction are studied. [source] ChemInform Abstract: New Indenyl Phosphinooxazoline Complexes of Iron and Their Catalytic Activity in the Mukaiyama Aldol Reaction.CHEMINFORM, Issue 35 2010Matthew Lenze Abstract It is demonstrated that a new iron-indenyl PHOX complex is efficient for the title reaction of the 1-siloxy 1-methoxyethene with aromatic aldehydes. [source] ChemInform Abstract: Organocatalytic Asymmetric Diels,Alder Reaction of Furan under High Pressure.CHEMINFORM, Issue 34 2010Akiko Mimoto Abstract The combined use of high pressure and organocatalysis promotes the title reaction. [source] ChemInform Abstract: Efficient Aerobic Ruthenium-Catalyzed Oxidation of Secondary Alcohols by the Use of a Hybrid Electron Transfer Catalyst.CHEMINFORM, Issue 33 2010Eric V. Johnston Abstract An efficient biomimetic catalyst system for the title reaction is developed. [source] ChemInform Abstract: Catalytic Enantioselective 1,3-Dipolar Cycloaddition of C,N-Cyclic Azomethine Imines with ,,,-Unsaturated Aldehydes.CHEMINFORM, Issue 33 2010Takuya Hashimoto Abstract A titanium/(S)-BINOL complex catalyzes the title reaction of azomethine imines (I) to give a variety of pharmaceutically attractive chiral pyrazolo-fused tetrahydroisoquinolines. [source] Mechanism of Reppe's Nickel-Catalyzed Ethyne Tetramerization to Cyclooctatetraene: A DFT StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2004Bernd F. Straub Dr. Abstract In this B3,LYP model study, homoleptic nickel(0) ethyne complexes have been predicted as the catalyst resting state for the title reaction. Ethyne ligand coupling of Ni(C2H2)3 yields monoethyne nickelacyclopentadiene in the rate-determining step. Ethyne coordination is followed by insertion of an ethyne ligand into the NiC , bond. A highly strained monoethyne trans -nickelacycloheptatriene is formed. This trans intermediate is unable to reductively eliminate benzene without prior isomerization to a cis -structure. Instead, it rapidly collapses to a nickelacyclononatetraene. Ethyne coordination induces reductive elimination to the cyclooctatetraene complex Ni(,2 -C2H2)(,2 -C8H8), followed by facile ligand exchange. Other ethyne coupling pathways have been computed to be less favored. The cyclooctatetraene ligand binds significantly weaker to nickel(0) than ethyne, both for mononuclear, and for dinuclear species. For this reason, CC bond formation steps at Ni2(,-cot) fragments have been predicted to feature prohibitively high overall reaction barriers. In dieser B3,LYP-Studie werden homoleptische Nickel(0)-Ethinkomplexe als Katalysatorruhezustand von Reppes Cyclooctatetraensynthese vorhergesagt. Kupplung zweier Ethinliganden in Ni(C2H2)3 ergibt Monoethin-Nickelacyclopentadien im geschwindigkeitsbestimmenden Schritt. Der Koordination von Ethin folgt die Insertion eines Ethinliganden in die NiC ,-Bindung. Ein hoch gespanntes Monoethin- trans -Nickelacycloheptatrien wird gebildet. Dieses trans -Intermediat ist nicht in der Lage, Benzol reduktiv zu eliminieren, ohne vorher in eine cis -Struktur zu isomerisieren. Stattdessen kollabiert es schnell zu Nickelacyclononatetraen. Koordination von Ethin induziert eine barrierefreie reduktive Eliminierung zum Cyclooctatetraen Komplex Ni(,2 -C2H2)(,2 -C8H8), gefolgt von einem einfach verlaufenden Ligandenaustausch. Andere Ethinkupplungspfade wurden als weniger begünstigt berechnet. Der COT-Ligand bindet sowohl für mononukleare als auch für dinukleare Spezies deutlich schwächer an Nickel(0) als Ethin. Aus diesem Grund werden für CC-Bindungsbildungsschritte am Ni2(,-cot)-Fragment prohibitiv hohe freie Aktivierungsenthalpien vorhergesagt. [source] Kinetics of the gas-phase reactions of chlorine atoms with CH2F2, CH3CCl3, and CF3CFH2 over the temperature range 253,553 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2009E. J. K. Nilsson Relative rate techniques were used to study the title reactions in 930,1200 mbar of N2 diluent. The reaction rate coefficients measured in the present work are summarized by the expressions k(Cl + CH2F2) = 1.19 × 10,17T2 exp(,1023/T) cm3 molecule,1 s,1 (253,553 K), k(Cl + CH3CCl3) = 2.41 × 10,12 exp(,1630/T) cm3 molecule,1 s,1 (253,313 K), and k(Cl + CF3CFH2) = 1.27 × 10,12 exp(,2019/T) cm3 molecule,1 s,1 (253,313 K). Results are discussed with respect to the literature data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 401,406, 2009 [source] Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2002D. Rajarathnam The ammonolysis of several substituted phenyl thiolacetates is kinetically studied in aqueous medium, 18°C, ionic strength 0.1 M (KCl). By following the leaving groups spectrophotometrically (,max = 260,410 nm), under excess free ammonia, pseudo-first-order rate coefficients (kobs) are obtained. The plots of (kobs , kH) against free ammonia concentration are linear at constant pH. The macroscopic nucleophilic substitution rate coefficients (kN) are obtained as the slopes of these plots and found to be pH-independent for all the thiolesters. The Brönsted-type plot (log kN against pKa of leaving groups) and the Hammett plot (log kN against , values of substituents) obtained for the title reactions of thiolesters are linear with slope values of ,lg = ,0.34 and , = 0.74 respectively. From the magnitude of these values, experimental data, the kinetic law, and the analysis of products, it is deduced that the ammonolysis of thiolesters proceeds through a simple bimolecular nucleophilic substitution pathway with a zwitterionic tetrahedral addition intermediate (T±), whereby its formation is rate-determining (k1 step). Comparison of this reaction of thiolesters with a similar reaction of analogue oxyesters shows a mechanistic difference. Further, for thiolesters there is a rate enhancement with larger kN values. The change in mechanism and enhanced reactivity observed by substitution of the oxygen atom by sulphur atom on the phenyl moiety are discussed in detail. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 18,26, 2002 [source] | ||||||||||||||||||||||