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1.
V. L. Lobachev 《Theoretical and Experimental Chemistry》1999,35(1):40-44
The substrate selectivity in the hydroxylation of methylbenzenes in the H2O2−H2SO4 (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate
selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that
the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex.
L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg
ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February,
1999. 相似文献
2.
《Chemical physics letters》1986,123(5):405-408
Ab initio molecular orbital calculations on the transition states and barrier heights for the addition of atomic hydrogen to silaethylene are carried out. The activation energy for the addition to the silicon site is lower than that to the carbon site, while the exothermicity is smaller. 相似文献
3.
《Radiation Physics and Chemistry》2009,78(3):191-194
In a recent paper (Radiation Physics and Chemistry, 2005, vol. 74, pp. 210) it was suggested that the anomalous increase of molecular hydrogen radiolysis yields observed in high-temperature water is explained by a high activation energy for the reaction H+H2O→H2+OH. In this comment we present thermodynamic arguments to demonstrate that this reaction cannot be as fast as suggested. A best estimate for the rate constant is 2.2×103 M−1 s−1 at 300 °C. Central to this argument is an estimate of the OH radical hydration free energy vs. temperature, ΔGhyd(OH)=0.0278t−18.4 kJ/mole (t in °C, equidensity standard states), which is based on analogy with the hydration free energy of water and of hydrogen peroxide. 相似文献
4.
Theoretical studies on reactions of the stabilized H2COO with HO2 and the HO2···H2O complex 总被引:1,自引:0,他引:1
Long B Tan XF Long ZW Wang YB Ren DS Zhang WJ 《The journal of physical chemistry. A》2011,115(24):6559-6567
The reactions of H(2)COO with HO(2) and the HO(2)···H(2)O complex are studied by employing the high-level quantum chemical calculations with B3LYP and CCSD(T) theoretical methods, the conventional transition-state theory (CTST), and the Rice-Ramsperger-Kassel-Marcus (RRKM) with Eckart tunneling correction. The calculated results show that the proton transfer plus the addition reaction channel (TS1A) is preferable for the reaction of H(2)COO with HO(2) because the barriers are -10.8 and 1.6 kcal/mol relative to the free reactants and the prereactive complex, respectively, at the CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(d,p) level of theory. Furthermore, the rate constant via TS1A (2.23 × 10(-10) cm(3) molecule(-1) s(-1)) combined with the concentrations of the species in the atmosphere demonstrates that the HO(2) radical would be the dominant sink of H(2)COO in some areas, where the concentration of water is less than 10(17) molecules cm(-3). In addition, although the single water molecule would lower the activated barrier of TS1A from 1.0 to 0.1 kcal/mol with respect to the respective complexes, the rate constant is lower than that of the reaction of HO(2) with H(2)COO. 相似文献
5.
The rate coefficients for the capture process CH + H(2)→ CH(3) and the reactions CH + H(2)→ CH(2) + H (abstraction), CH + H(2) (exchange) have been calculated in the 200-800 K temperature range, using the quasiclassical trajectory (QCT) method and the most recent global potential energy surface. The reactions, which are of interest in combustion and in astrochemistry, proceed via the formation of long-lived CH(3) collision complexes, and the three H atoms become equivalent. QCT rate coefficients for capture are in quite good agreement with experiments. However, an important zero point energy (ZPE) leakage problem occurs in the QCT calculations for the abstraction, exchange and inelastic exit channels. To account for this issue, a pragmatic but accurate approach has been applied, leading to a good agreement with experimental abstraction rate coefficients. Exchange rate coefficients have also been calculated using this approach. Finally, calculations employing QCT capture/phase space theory (PST) models have been carried out, leading to similar values for the abstraction rate coefficients as the QCT and previous quantum mechanical capture/PST methods. This suggests that QCT capture/PST models are a good alternative to the QCT method for this and similar systems. 相似文献
6.
In reply to “Comment on the possible role of reaction H+H2O→H2+OH in the radiolysis of water at high temperatures” (Bartels, 2009 Comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) we present an alternative thermodynamic estimation of the reaction rate constant k. Based on the non-symmetric standard state convention we have calculated that the Gibbs energy of reaction ΔrG=57.26 kJ mol?1 and the reaction rate constant k=7.23×10?5 M?1 s?1 at ambient temperature. Re-analysis of the thermodynamic estimation (Bartels, 2009 Comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) showed that the upper limit for the rate constant at 573 K is k=1.75×104 M?1 s?1 compared to the value predicted by the diffusion-kinetic modelling (3.18±1.25)×104 M?1 s?1 (Swiatla-Wojcik, D., Buxton, G.V., 2005. On the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 74(3–4), 210–219). The presented thermodynamic evaluation of k(573) is based on the assumption that k can be calculated from ΔrG and the rate constant of the reverse reaction which, as discussed, are both uncertain at high temperatures. 相似文献
7.
Stevens CJ Dallanegra R Chaplin AB Weller AS Macgregor SA Ward B McKay D Alcaraz G Sabo-Etienne S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(10):3011-3020
The IrIII fragment {Ir(PCy3)2(H)2}+ has been used to probe the role of the metal centre in the catalytic dehydrocoupling of H3B?NMe2H ( A ) to ultimately give dimeric aminoborane [H2BNMe2]2 ( D ). Addition of A to [Ir(PCy3)2(H)2(H2)2][BArF4] ( 1 ; ArF=(C6H3(CF3)2), gives the amine‐borane complex [Ir(PCy3)2(H)2(H3B?NMe2H)][BArF4] ( 2 a ), which slowly dehydrogenates to afford the aminoborane complex [Ir(PCy3)2(H)2(H2B? NMe2)][BArF4] ( 3 ). DFT calculations have been used to probe the mechanism of dehydrogenation and show a pathway featuring sequential BH activation/H2 loss/NH activation. Addition of D to 1 results in retrodimerisation of D to afford 3 . DFT calculations indicate that this involves metal trapping of the monomer–dimer equilibrium, 2 H2BNMe2 ? [H2BNMe2]2. Ruthenium and rhodium analogues also promote this reaction. Addition of MeCN to 3 affords [Ir(PCy3)2(H)2(NCMe)2][BArF4] ( 6 ) liberating H2B? NMe2 ( B ), which then dimerises to give D . This is shown to be a second‐order process. It also allows on‐ and off‐metal coupling processes to be probed. Addition of MeCN to 3 followed by A gives D with no amine‐borane intermediates observed. Addition of A to 3 results in the formation of significant amounts of oligomeric H3B?NMe2BH2?NMe2H ( C ), which ultimately was converted to D . These results indicate that the metal is involved in both the dehydrogenation of A , to give B , and the oligomerisation reaction to afford C . A mechanism is suggested for this latter process. The reactivity of oligomer C with the Ir complexes is also reported. Addition of excess C to 1 promotes its transformation into D , with 3 observed as the final organometallic product, suggesting a B? N bond cleavage mechanism. Complex 6 does not react with C , but in combination with B oligomer C is consumed to eventually give D , suggesting an additional role for free aminoborane in the formation of D from C . 相似文献
8.
《Chemical physics》1986,107(1):25-31
The results of a comparative theoretical study of the dipole moment derivatives and infrared absorption intensities within the double harmonic approximation are presented for the isoelectronic, isostructural C2v molecules: H2F+, H2O and NH−2. The calculations, performed at the ab initio SCF and CI levels of theory, utilize basis sets of triple zeta+two polarization functions quality. For the ions H2F+ and NH−2, in the absence of adequate experimental data the equilibrium geometries and force constants were also calculated. The trends observed in the dipole moment derivatives for the three systems are indicative of the amount of electronic charge associated with the hydrogen atoms and are very similar to the trends noted for a set of C3v hydrides. 相似文献
9.
《Fluid Phase Equilibria》1988,39(1):101-110
Bubble-point pressures of the H2COCO2 system were measured at temperatures from 253.15 to 303.15 K and pressures up to 9 MPa. Multiple bubble-points were observed within certain limits of hydrogen compositions. The data have been compared with the calculated results by the Redlich-Kwong and the Peng-Robinson equations of state. 相似文献
10.
Sergey S. Skiba Eduard G. Larionov Andrey Yu. Manakov Sergey I. Kozhemjachenko 《Journal of inclusion phenomena and macrocyclic chemistry》2010,67(3-4):353-359
Decomposition curves of gas hydrates formed in the ethane–hydrogen–water system were studied in the pressure interval 2–250 MPa. Gas hydrates synthesized at low (up to 5 MPa) pressures were also studied with use of X-ray powder diffraction and Raman spectroscopy. It was shown that ethane–hydrogen mixtures with hydrogen contents 0–30 mol.% form cubic structure I gas hydrates. Higher hydrogen concentration most probably results in appearance of another hydrate phase. We speculate that the gas mixtures with the hydrogen content above 60 mol.% form cubic structure II double hydrate of hydrogen and ethane at temperatures below ≈280 K and pressures above 25 MPa. 相似文献
11.
The solubility of components in the system Mg(ClO3)2-2NH2C2H4OH · H3C6H5O7-H2O was studied from the complete freezing temperature ?59.4°C to 20.0°C. A polythermal solubility diagram was constructed, in which the crystallization fields were determined for ice, Mg(ClO3)2 · 16H2O, Mg(ClO3)2 · 12H2O, Mg(ClO3)2 · 6H2O, 2NH2C2H4OH · H3C6H5O7 · H2O, 2NH2C2H4OH · H3C6H5O7, and two new compounds, [(HOC(CH2COOH)2COO)2Mg · 2H2O] and [HOC(CH2COO)2MgCOOH · 2H2O], which were identified by chemical and physicochemical analysis methods. 相似文献
12.
The kinetics of H2S destruction in the radiolysis of CH4–H2S and CH4–H2S–O2 mixtures has been studied. It has been shown that G(–H2S) depends on amounts of hydrogen sulfide and the presence of oxygen in the starting mixture and is within the range of 5–13 mol/100 eV. G(H2) decreases with the increases of O2 content and amounts to the constant value of 2. 相似文献
13.
Golden DM Peng J Goumri A Yuan J Marshall P 《The journal of physical chemistry. A》2012,116(24):5847-5855
RRKM theory has been employed to analyze the kinetics of the title reaction, in particular, the once-controversial negative activation energy. Stationary points along the reaction coordinate were characterized with coupled cluster theory combined with basis set extrapolation to the complete basis set limit. A shallow minimum, bound by 9.7 kJ?mol(-1) relative to C(2)H(5) + HBr, was located, with a very small energy barrier to dissociation to Br + C(2)H(6). The transition state is tight compared to the adduct. The influence of vibrational anharmonicity on the kinetics and thermochemistry of the title reaction were explored quantitatively. With adjustment of the adduct binding energy by ~4 kJ?mol(-1), the computed rate constants may be brought into agreement with most experimental data in the literature, including new room-temperature results described here. There are indications that at temperatures above those studied experimentally, the activation energy may switch from negative to positive. 相似文献
14.
Thermal rate constants and kinetic isotope effects for the title reaction are calculated by using the quantum instanton approximation within the full dimensional Cartesian coordinates. The obtained results are in good agreement with experimental measurements at high temperatures. The detailed investigation reveals that the anharmonicity of the hindered internal rotation motion does not influence the rate too much compared to its harmonic oscillator approximation. However, the motion of the nonreactive methyl group in C(2)H(6) significantly enhances the rates compared to its rigid case, which makes conventional reduced-dimensionality calculations a challenge. In addition, the temperature dependence of kinetic isotope effects is also revealed. 相似文献
15.
The surface region of sulfate aerosols (supercooled aqueous concentrated sulfuric acid solutions) is the likely site of a number of important heterogeneous reactions in various locations in the atmosphere, but the surface region ionic composition is not known. As a first step in exploring this issue, the first acid ionization reaction for sulfuric acid, H2SO4 + H2O HSO4– + H3O+, is studied via electronic structure calculations at the Hartree–Fock level on an H2SO4 molecule embedded in the surface region of a cluster containing 33 water molecules. An initial H2SO4 configuration is selected which could produce H3O+ readily available for heterogeneous reactions, but which involves reduced solvation and is consistent with no dangling OH bonds for H2SO4. It is found that at 0 K and with zero-point energy included, the proton transfer is endothermic by 3.4 kcal/mol. This result is discussed in the context of reactions on sulfate aerosol surfaces and, further, more complex calculations.Contribution to the Jacopo Tomasi Honorary Issue 相似文献
16.
《Chemical physics letters》1985,114(4):343-347
We have predicted the absorption spectrum of the transition state configurations for the collinear reaction H + H2 → H3 → H2 + H by solving the time-dependent Schrödinger equation for the nuclear motion. The spectral features have been interpreted in terms of the build up of the probability density function in the inner repulsive wall of the potential-energy surface. 相似文献
17.
Some attempts to employ the singlet oxygen generated from molybdate-catalyzed decomposition of hydrogen peroxide are presented. Reduction of ascaridole with diimide is also described, along with the preliminary results of the cleavage study using Fe-cysteinate as a simple model for Fe-S type redox species. There were strong indications that S-alkylation occurred as observed in similar cleavage of the potent antimalarial qinghaosu. 相似文献
18.
19.
Reactions of alkenols with H2O2??LiBr??Ce(NO3)3·6H2O or H2O2??LiBr??Ce(NH4)2(NO3)6 system led to bromination of the double bond to yield vicinal dibromoalkanols. The reaction proceeded highly selectively, no oxidation of the hydroxyl group virtually occurred. 相似文献
20.
《Chemical physics letters》1987,138(1):43-48
The experimentally observed effect of the Cs1 fine-structure level on the title reaction is reproduced by a rough (collinear, one dimensional) dynamical treatment using accurate long-distance entrance channel potentials, as obtained from an effective Hamiltonian method, and hemiquantal dynamics in the collision energy range 0.03 to 0.13 eV. The system is shown to behave adiabatically at large distances, to undergo a transition from adiabatic to diabatic behaviour with respect to spin-orbit coupling in the 11–8.5 au Cs-H distance range, and to transfer adiabatically the whole 2Σ+ weight of the electronic wavefunction into theionic channel in the harpooning region. 相似文献