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1.
Jimmy W. Viers John C. Schug Michael D. Stovall Jeffrey I. Seeman 《Journal of computational chemistry》1984,5(6):598-605
MNDO molecular orbital calculations have been employed to investigate limited reaction pathways and potential energy surfaces for a series of SN2 reactions. Model calculations for X? + CH3X (X = H, F, OH, OCH3, and CN) indicate that the MNDO method gives qualitative agreement with ab initio studies except for the hydride–CH4 exchange. Studies involving alkylation of pyridine (Menschutkin reaction) were also carried out. For the reaction of pyridine with CH3Cl, which involves charge separation, our MNDO studies (which do not include solvation effects) do not produce a characteristic SN2 pathway. For the reaction of pyridine with trimethyloxonium cation [(CH3)3O+] as the alkylating agent, a well defined SN2 reaction pathway was obtained; this reaction involves charge transfer. A potential energy surface for the pyridine–trimethyloxonium cation reaction shows the presence of a saddle point transition state that resembles starting materials, in agreement with the Hammond postulate for this exothermic reaction. 相似文献
2.
E. W. Meijer 《Journal of polymer science. Part A, Polymer chemistry》1986,24(9):2199-2208
Using a model reaction we have studied the crosslinking chemistry of hydroxy-functional polymers and hexamethoxymethylmelamine. The transetherification of optically active monofunctional alcohols and hexamethoxymethylmelamine was monitored with polarimetry and 1H-NMR. The reaction rate constants for both the forward (k1) and the backward (k?1) reaction of the sulphonic-acid-catalyzed alcoholysis were determined. Primary and secondary alcohols showed the same reaction rate and activation energy (Ea = 96 kJ/mol) for the forward reaction. However, the backward reaction in the equilibrium is considerably slower for primary alcohols than for secondary alcohols, with activation energies of Ea = 96 and 79 kJ/mol, respectively. When amine salts of sulphonic acids are used as catalysts, the Ea is increased from 97 to 116 kJ/mol in the case of primary alcohols. In concentrated aprotic solutions the reaction order in acid is 2.5. The same order in acid is found for the alcoholysis of acetaldehyde diethyl acetal. All the results strongly support the statement that the crosslinking reaction proceeds by an Sn-1 mechanism. The results of this model study are compared with results obtained in network-forming reactions. The important role of the evaporation of the condensation product methanol is discussed. 相似文献
3.
LCAC‐SW (linear combination of arrangement channel‐scattering wavefunction) method was used to calculate collinear state‐to‐state reaction probabilities for the reaction F + H2(v = 0) → HF(v′) + H on the 6SEC potential energy surface. The results show that reaction probabilities P02 and P03 [i. e., v′ = 2,3 for reaction F + H2 (v = 0) + HF(v′) + H] are primary, the population of product vibrational states is inverse and the reaction probabilities are oscillatory with collision energies, i.e., there is energy resonance in this reaction, which agrees with a new experiment. 相似文献
4.
The urethane reaction of 1,2‐propanediol with phenyl isocyanate was investigated with ferric acetylacetonate (Fe(acac)3) as a catalyst. In situ Fourier transform infrared spectroscopy was used to monitor the reaction, and catalytic kinetics of Fe(acac)3 was studied. The reaction rates of both hydroxyl groups were described with a second‐order equation, from which the influence of the Fe(acac)3 concentration and reaction temperature was discussed. It was very surprising that the relationship between 1/C and t became constant when reaction temperature increased, which indicated that there was no reactive distinction between the two hydroxyl groups. Although the phenomenon differed with the variation of temperature, it was unaffected by the Fe(acac)3 concentration. It was attributed to the transformation of the reaction mechanism with the increase in temperature. Furthermore, activation energy (Ea), enthalpy (ΔH*), and entropy (ΔS*) for the catalyzed reaction were determined from Arrhenius and Eyring equations, which testified to the transformation of the reaction mechanism. 相似文献
5.
The rate law ? d[O3]/ dt = k1[A][O3] + k3[A][O3]2/ (k4 + k5[O2]) has been found to obtain for the reaction of ozone with allene and with 1,2-butadiene. We now find that this rate law also applies to the reaction of ozone with ethylene and presumably with all lower alkenes. This generalizes the inhibiting effect of oxygen and accounts for the simplifed rate law found in the presence of excess oxygen. Oxygen itself is a product of the ozone–ethylene reaction, and we find that as [O3]0 increases, the (O2 formed)/(O3 used) ratio approaches 1.5. Values of k1, k3/k5 for ethylene are compared with those for allene, 1,3-butadiene, and propene. A generalized mechanism is postulated for the reaction of ozone with alkenes involving a chain sequence that produces oxygen and which accounts for the observed rate law. A specific mechanism is postulated for the reaction of O3 with ethylene, and the thermochemistry of the chain sequence is examined in detail. 相似文献
6.
Gennady V. Oshovsky Maria Zablocka Carine Duhayon Jean‐Pierre Majoral Anne‐Marie Caminade 《无机化学与普通化学杂志》2017,643(14):903-908
A versatile reactivity from the cage compound P(NMeNMe)3P is presented. The Staudinger reaction with Me3SiN3 is carried out. The crystal structure of the compound issued from the reaction on both sides (Me3SiN=P(NMeNMe)3P=NSiMe3) is reported. When the reaction occurs on only one side, the remaining free phosphorus atom is complexed with RuCl2(p‐cymene). P(NMeNMe)3P reacts with PCl3, leading to the heterocyclic compound ClP(NMeNMe)2PCl. This heterocycle also displays a versatile reactivity. Substitution reaction with HNiPr2 leads to iPr2NP(NMeNMe)2PNiPr2. Very complex 1H and 13C NMR spectra suggest that the cis isomer is the largely major isomer of this compound. The cis structure is confirmed by X‐ray diffraction. Besides the reaction on the P–Cl functions, the reaction on the lone pair of ClP(NMeNMe)2PCl is carried out, leading to the complex (p‐cymene)Cl2RuPCl(NMeNMe)2ClPRuCl2(p‐cymene). Characterization of this compound by X‐ray diffraction displays a cis isomer for this compound also. 相似文献
7.
We report on the synthesis of the II-IV-N2 semiconductors ZnSiN2, MnSiN2, and the Zn1–xMnxSiN2 solid solutions by a one-step solid-state metathesis reaction. The successful syntheses were carried out by reacting the corresponding metal halides with stoichiometric amounts of silicon nitride and lithium azide in sealed tantalum ampoules. After washing out the reaction byproduct LiCl, powder X-ray diffraction patterns were indexed with orthorhombic space group Pna21. Single phase products were obtained without applying external pressure and at a moderate reaction temperature of 700 °C. The resulting ZnSiN2 was found to consist of nano-sized grains and needle-shaped nano-crystals. With increasing manganese content in the Zn1–xMnxSiN2 solid solution, we found the reaction product to be increasingly crystalline. Both the cell parameters and the bandgap values across the different compositions of the solid solutions change linearly. The sample Zn0.95Mn0.05SiN2 synthesized by means of solid-state metathesis reaction is an intense red emitter with a broad emission maximum at λmax ≈ 619 nm when excited with ultraviolet light after annealing the sample at a pressure of 6 GPa and a temperature of 1200 °C. 相似文献
8.
Michael D. Ravenscroft Peter Skrabal Bettina Weiss Heinrich Zollinger 《Helvetica chimica acta》1988,71(3):515-520
The N2-molecule-aryl-cation pair formed as the first intermediate in dediazoniations of arenediazonium ions can be trapped with CO in H2O with formation of the corresponding arenecarboxylic acids. This reaction is considered as a model for the reverse of dediazoniation, since CO is isoelectronic with N2. The evaluation of the yields of arenecarboxylic acids formed from substituted benzenediazonium ions using Taft's dual substituent parameter treatment demonstrates that the field reaction constant pF and the resonance reaction constant pR are positive and negative, respectively, as expected for a reaction which corresponds electronically to the addition of N2 to aryl cations. 相似文献
9.
The sphingolipids 1a , b and 2a , b which play important roles in epidermal barrier function, were synthesized by N-acylation of C18-sphingosine 3 and 1-O-glucosylated C18-sphingosine 6 , respectively, with ω-acyloxy-substituted fatty acids 4 and 5 (Scheme 1). These fatty acids were obtained from ω-hydroxy-substituted fatty acids 8 and 9 by esterification with linoleic acid ( 7 ). The C34-fatty acid 8 was prepared as follows: C25-Compound 18 was obtained by means of a Wittig reaction of C13-aldehyde 13 with C12-phosphonium salt 15 or of C12-aldehyde 24 with C13-phosphonium salt 21 , respectively, and subseqent hydrogenation and O-deprotection (Scheme 2). Alternatively, 8 was prepared via 30 by copper-catalyzed coupling of C13-alkyl halide 19 with the Grignard reagent derived from C12-alkyl bromide 14 (Scheme 2). Oxidation of 18 to aldehyde 39 and Wittig reaction with C9-phosphonium salt 41 furnished the desired ω-hydroxy-substituted fatty acid 8 , after O-deprotection (Scheme 3). Similarly, Wittig reaction of C11-phosphonium salt 22 with C12-aldehyde 24 furnished C23-aldehyde 40 , after hydrogenation, O-deprotection, and oxidation; Wittig reaction with compound 41 and subsequent deprotection afforded the desired C32-fatty and 9 (Scheme 3). an alternative strategy furnished compound 8 by a coupling reaction of alkyne 53 with ω-bromo-substitued fatty acid 52 , obtained from compounds 24 and 47 by Wittig reaction, hydrogenation, and introduction of bromide (Scheme 4). Hydrogenation (Lindlar's catalyst) of the resulting C34-alkyne 54 and deprotection furnished 8 . 相似文献
10.
11.
Vanadia transport, which is a minor reaction flux in the solid state reaction between V2O5 and MoO3, was studied using chemical and neutron activation analyses and electron spectroscopy for chemical analysis. It was found
that negligible quantities of vanadia were transferred in a molybdena briquette during the reaction. Vanadia was presumably
localized in thin external layers of molybdena grains. The reaction potential difference U
r across a Pt|MoO3|V2O5|Pt cell was studied. It was shown that in this cell U
r was produced at the molybdena briquette and was due to vanadia transport. The U
r value changed with time in two stages. The reaction potential difference U
r was constant (or diminished slightly) at the first stage and dropped abruptly at the second stage. The duration of the first
stage depended on the initial thickness of the MoO3 briquette: the thicker the briquette, the longer the U
r value was nearly constant. Causes and probable mechanisms of U
r generation are discussed in different terms: chemical reaction, variation of a
O
2 at the boundary between the reaction product and initialoxides, or surface spreading of the minor (V2O5 or V9Mo6O40) diffusant. The last mechanism, which received the least study in the general case, was shown to be the most probable one
for the reaction at hand.
Electronic Publication 相似文献
12.
Reaction of γ-dicarboxylic acids amides and imides with trifluoromethanesulfonamide and formaldehyde
M. Yu. Moskalik V. I. Meshcheryakov B. A. Shainyan 《Russian Journal of Organic Chemistry》2009,45(11):1644-1650
Three-component condensation of trifluoromethanesulfonamide with paraformaldehyde and succinamide depending on the reaction
conditions led alongside bis(trifluoromethanesulfonamido)methane to the formation of a substitution product, bis[(trifluoromethylsulfonyl)aminomethyl]succinamide,
or to a cyclization product, N-[trifluoromethylsulfonyl)aminomethyl]succinimide. The attempt to obtain the latter by the reaction of the trifluoromethanesulfonamide
sodium salt CF3SO2NHNa with N-chloromethylsuccinimide unexpectedly resulted in N,N-bis(succinimidomethyl)-trifluoromethanesulfonamide. Analogously the reaction of CF3SO2NHNa with N-chloromethyl-phthalimide gave N,N-bis(phthalimidomethyl)trifluoromethanesulfonamide. The reaction of CF3SO2NHNa with succinimide and phthalimide in water and alcohol solution resulted in the ring opening and further transformation
of the formed monosubstituted N-(trifluoromethylsulfonyl)amides of succinic and phthalic acids. 相似文献
13.
Thermochemical Properties and Decomposition Kinetics of Ammonium Magnesium Phosphate Monohydrate 总被引:1,自引:0,他引:1
Ammonium magnesium phosphate monohydrate NH4MgPO4·H2O was prepared via solid state reaction at room temperature and characterized by XRD, FT-IR and SEM. Thermochemical study was performed by an isoperibol solution calorimeter, non-isothermal measurement was used in a multivariate non-linear regression analysis to determine the kinetic reaction parameters. The results show that the molar enthalpy of reaction above is (28.795 ± 0.182) kJ/mol (298.15 K), and the standard molar enthalpy of formation of the title complex is (-2185.43 ± 13.80) kJ/mol (298.15 K). Kinetics analysis shows that the second decomposition of NH4MgPO4·H2O acts as a double-step reaction: an nth-order reaction (Fn) with n=4.28, E1=147.35 kJ/mol, A1=3.63×10^13 s^-1 is followed by a second-order reaction (F2) with E2=212.71 kJ/mol, A2= 1.82 × 10^18 s^-1. 相似文献
14.
Kinetics and Mechanism of Catalytic Reduction of U(VI) with Hydrazine on Platinum Catalysts in Nitric Acid Media
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Xiao-teng Zhang Shuai Hao Fei-fei Tang Bin Li Xian-ming Zhou Li-sheng Liu Liang-shu Xia 《化学物理学报(中文版)》2022,35(5):813-822
The kinetics of U(IV) produced by hydrazine reduction of U(VI) with platinum as a catalyst in nitric acid media was studied to reveal the reaction mechanism and optimize the reaction process. Electron spin resonance (ESR) was used to determine the influence of nitric acid oxidation. The effects of nitric acid, hydrazine, U(VI) concentration, catalyst dosage and temperature on the reaction rate were also studied. In addition, the simulation of the reaction process was performed using density functional theory. The results show that the influence of oxidation on the main reaction is limited when the concentration of nitric acid is below 0.5 mol/L. The reaction kinetics equation below the concentration of 0.5 mol/L is found as: -dc(UO22+)/dt)=kc0.5323(UO22+)c0.2074(N2H5+)c-0.2009(H+). When the temperature is 50 ℃, and the solid/liquid ratio r is 0.0667 g/mL, the reaction kinetics constant is k=0.00199 (mol/L)0.4712/min. Between 20 ℃ and 80 ℃, the reaction rate gradually increases with the increase of temperature, and changes from chemically controlled to diffusion-controlled. The simulations of density functional theory give further insight into the influence of various factors on the reaction process, with which the reaction mechanisms are determined according to the reaction kinetics and the simulation results. 相似文献
15.
Gataullin R. R. Afon"kin I. S. Fatykhov A. A. Spirikhin L. V. Abdrakhmanov I. B. 《Russian Chemical Bulletin》2001,50(12):2466-2467
The reaction of 6-(cyclopent-1-enyl)-N-ethoxycarbonyl-2-methylaniline with Br2 or its reaction with NH3 followed by the reaction with Br2 afforded 2"-bromo-8-methylspiro(4H-3,1-benzooxazine-4,1"-cyclopentan)-2(1H)-one and 2-amino-2"-bromo-8-methylspiro(4H-3,1-benzooxazine-4,1"-cyclopentane), respectively. 相似文献
16.
Yu-Yong Wu Li-Sheng Wang Zhong-Wei Wang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2667-2677
The Friedel-Crafts reaction of phosphorus trichloride and benzene in [Et 4 N]Br-XAlCl 3 ([Et 4 N]Br = tetraethylammonium bromide) ionic liquids (ILs) was investigated for the clean synthesis of dichlorophenylphosphine (DCPP). A simple product isolation procedure was achieved, and the effects of IL's composition, reaction time, and quantity on this reaction were studied. The [Et 4 N]Br-XAlCl 3 ILs gave this reaction a green character. From the isolation experiments, it was found that (a) because of the formation of the complex of DCPP and AlCl 3 , the catalytic activity of the [Et 3 NH]Cl-XAlCl 3 ([Et 3 NH]Cl = triethylhydrogenamonium chloride) was reduced; (b) with the addition of quaternary ammonium to the IL's residue, additional DCPP could be recovered. 相似文献
17.
18.
L. -K. Wu K. -Y. Chen S. -Y. Cheng B. -S. Lee C. -M. Shu 《Journal of Thermal Analysis and Calorimetry》2008,93(1):115-120
Hydrogen peroxide (H2O2) is popularly employed as a reaction reagent in cleaning processes for the chemical industry and semiconductor plants. By
using differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2), this study focused on the thermal decomposition
reaction of H2O2 mixed with sulfuric acid (H2SO4) with low (0.1, 0.5 and 1.0 N), and high concentrations of 96 mass%, respectively. Thermokinetic data, such as exothermic
onset temperature (T
0), heat of decomposition (ΔH
d), pressure rise rate (dP/dt), and self-heating rate (dT/dt), were obtained and assessed by the DSC and VSP2 experiments. From the thermal decomposition reaction on various concentrations
of H2SO4, the experimental data of T
0, ΔH, dP/dt, and dT/dt were obtained. Comparisons of the reactivity for H2O2 and H2O2 mixed with H2SO4 (lower and higher concentrations) were evaluated to corroborate the decomposition reaction in these systems. 相似文献
19.
It is shown that the 2-(hydroxymethyl)-1-methylazulenes 6 are being oxidized by activated MnO2 in CH2Cl2 at room temperature to the corresponding azulene-1,2-dicarbaldehydes 7 (Scheme 2). Extension of the MnO2 oxidation reaction to 1-methyl- and/or 3-methyl-substituted azulenes led to the formation of the corresponding azulene-1-carbaldehydes in excellent yields (Scheme 3). The reaction of unsymmetrically substituted 1,3-dimethyl-azulenes (cf. 15 in Scheme 4) with MnO2 shows only little chemoselectivity. However, the observed ratio of the formed constitutionally isometric azulene-1-carbaldehydes is in agreement with the size of the orbital coefficients in the HOMO of the azulenes. The reaction of guaiazulene ( 18 ) with MnO2 in dioxane/H2O at room temperature gave mainly the expected carbaldehyde 19 . However, it was accompanied by the azulene-diones 20 and 21 (Scheme 5). The precursor of the demethylated compound 20 is the carbaldehyde 19 . Similarly, the MnO2 reaction of 7-isopropyl-4-methyalazulene ( 22 ) as well as of 4,6,8-trimethylazulene ( 24 ) led to the formation of a mixture of the corresponding azulene-1,5-diones and azulene-1,7-diones 20 / 23 and 25 / 26 , respectively, in decent yields (Schemes 6 and 7). No MnO2 reaction was observed with 5,7-dimethylazulene. 相似文献