共查询到20条相似文献,搜索用时 15 毫秒
1.
ZHANG Xinzhuang ZHEN Zhen & LIU Xinhou Technical Institute of Physics Chemistry of Chinese Academy of Sciences Beijing China 《中国科学B辑(英文版)》2005,48(4)
HNCO is a convenient photolytic source of NCO and NH radicals for laboratory kinetics studies of elementary reaction[1] and plays an important role in the combustion and atmosphere chemistry. It can re- move deleterious compounds rapidly from exhausted ga… 相似文献
2.
Ab initio UMP2 and UQCISD(T) calculations, with 6-311G** basis sets, were performed for the titled reactions. The results show that
the reactions have two product channels: NH2+ HNCO?NH3+NCO (1) and NH2+HNCO?N2H3+CO (2), where reaction (1) is a hydrogen abstraction reaction via an H-bonded complex (HBC), lowering the energy by 32.48
kJ/mol relative to reactants. The calculated QCISD(T)//MP2(full) energy barrier is 29.04 kJ/mol, which is in excellent accordance
with the experimental value of 29.09 kJ/mol. In the range of reaction temperature 2300–2700 K, transition theory rate constant
for reaction (1) is 1.68×1011–3.29×1011 mL·mol-1·s-1, which is close to the experimental one of 5.0×1011mL·mol-1·s-1or less. However, reaction (2) is a stepwise reaction proceeding via two orientation modes,cis andtrans, and the energy barriers for the rate-control step at our best calculations are 92.79 kJ/mol (forcis-mode) and 147.43 kJ/mol (fortrans-mode), respectively, which is much higher than reaction (1). So reaction (1) is the main channel for the titled reaction. 相似文献
3.
A method applying ab initio direct dynamics has been utilized in studying the hydrogen abstraction reaction HCN + OH → CN + H2O. The geometries of the reactants, products, and the transition state have been optimized at the QCISD/6-311G(d, p) level.
Single-point energies were further evaluated at the QCISD(T)/6-311+G(2df, 2p)//QCISD/6-311G(d, p) level. The barrier heights
for the forward and reverse reactions were predicted to be 15.95 and 7.51 kcal mol−1 at the QCISD(T)/6-311 + G(2df, 2p)//QCISD/6-311G(d, p) level, respectively. The reaction rate constants were calculated in
the temperature range from 298 to 4,000 K using the canonical variational transition-state theory with a small-curvature tunneling
correction. The results of the calculation show that the theoretical rate constants are in good agreement with experimental
data over the measured temperature range of 400–2,600 K.
Received: 18 August 2002 / Accepted: 30 August 2002 / Published online: 20 November 2002
Acknowledgements. Our thanks are due to D.G. Truhlar for providing the POLYRATE 8.2 program. This work was supported by the National Science
Foundation of China. We also thank D.C. Fang and Y. M. Xie for their valuable help, and P.R. Yan for reading our paper.
Correspondence to: Q. S. Li e-mail: qsli@mh.bit.edu.cn 相似文献
4.
Theoretical studies on the reactions of hydroxyl radicals with trimethylsilane and tetramethylsilane
Hui Zhang Gui-Ling Zhang Ying Wang Xiao-Yang Yu Bo Liu Jing-Yao Liu Ze-Sheng Li 《Theoretical chemistry accounts》2008,119(4):319-327
The multiple-channel reactions OH + SiH(CH3)3 → products (R1) and the single-channel reaction OH + Si(CH3)4 → Si(CH3)3CH2 + H2O (R2) have been studied by means of the direct dynamics method at the BMC-CCSD//MP2/6-311+G(2d,2p) level. The optimized geometries,
frequencies and minimum energy path are all obtained at the MP2/6-311+G(2d,2p) levels, and energy information is further refined
by the BMC-CCSD (single-point) level. The rate constants for every reaction channels are calculated by canonical variational
transition states theory (CVT) with small-curvature tunneling (SCT) contributions over the temperature range 200–2,000 K.
The theoretical total rate constants are in good agreement with the available experimental data, and the three-parameter expression
k
1 = 2.53×10−21
T
3.14 exp(1, 352.86/T), k
2 = 6.00 × 10−19
T
2.54 exp(−106.11/T) (in unit of cm3 molecule−1 s−1) over the temperature range 200–2,000 K are given. Our calculations indicate that at the low temperature range, for reaction
R1, H-abstraction is favored for the SiH group, while the abstraction from the CH3 group is a minor channel.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
Ab initio UMP2 and UQCISD(T) calculations, with 6-311G** basis sets, were performed for the titled reactions. The results show that the reactions have two product channels: NH2+ HNCO→NH3+NCO (1) and NH2+HNCO-N2H3+CO (2), where reaction (1) is a hydrogen abstraction reaction via an H-bonded complex (HBC), lowering the energy by 32.48 kJ/mol relative to reactants. The calculated QCISD(T)//MP2(full) energy barrier is 29.04 kJ/mol, which is in excellent accordance with the experimental value of 29.09 kJ/mol. In the range of reaction temperature 2300-2700 K, transition theory rate constant for reaction (1) is 1.68 × 1011- 3.29 × 1011 mL · mol-1· s-1, which is close to the experimental one of 5.0 ×1011 mL× mol-1· s-1 or less. However, reaction (2) is a stepwise reaction proceeding via two orientation modes, cis and trans, and the energy barriers for the rate-control step at our best calculations are 92.79 kJ/mol (for cis-mode) and 147.43 kJ/mol (for trans-mode), respectively, which is much higher than 相似文献
6.
The relative thermodynamic stabilities of 2,5-dihydrofuran (1) and 2,3-dihydrofuran (2), and of 3,4-dihydro-6H-pyran (3) and 3,4-dihydro-2H-pyran (4), were determined at several temperatures by base-catalyzed equilibration in DMSO solution. For 1 → 2, = –15.4±0.1 kJ mol−1, =–12.6±0.5 kJ mol−1, and =9.5±1.3 J K−1 mol−1 at 298.15 K. The second-law reaction enthalpy agrees with literature data based on calorimetric enthalpies of hydrogenation of the isomeric forms in hexane. For 3 → 4, =–19.3±0.2 kJ mol−1, = –18.9±1.1 kJ mol−1 and =1.1±3.0 J K−1 mol−1 at 298.15 K: the experimental reaction enthalpy is in marked disagreement with literature data based on estimation. On the other hand, both of the experimental reaction enthalpies of the present study are in good agreement with DFT calculations using the B3LYP functional and 6-311+G(2d,p) basis set. 相似文献
7.
The mechanism of addition reaction between carbene and epoxyethane has been investigated employing the MP2 and B3LYP/6-311+G*
levels of theory. Geometry optimization, vibrational analysis, and energy property for the involved stationary points on the
potential energy surface have been calculated. Based on the calculated results at the MP2/6-311+G* level of theory, it can
be predicted that there are two reaction mechanisms (1) and (2). In the first reaction carbene attacks the atom O of epoxyethane
to form an intermediate 1a (IM1a), which is a barrier-free exothermic reaction. Then, IM1a can isomerize to IM1b via a transition
state 1a (TS1a), where the potential barrier is 48.6 kJ/mol. Subsequently, IM1b isomerizes to a product epoxypropane (Pro1)
via TS1b with a potential barrier of 14.2 kJ/mol. In the second carbene attacks the atom C of epoxyethane firstly to form
IM2 via TS2a. Then IM2 isomerizes to a product allyl alcohol (Pro2) via TS2b with a potential barrier of 101.6 kJ/mol. Correspondingly,
the reaction energies for the reactions (1) and (2) are −448.4 and −501.6 kJ/mol, respectively. Additionally, the orbital interactions are also discussed for the leading intermediate.
The results based on the B3LYP/6-311+G* level of theory are paralleled to those on the MP2/6-311+G* level of theory. Furthermore,
the halogen and methyl substituent effects of H2C: on the two reaction mechanisms have been investigated. The calculated results indicate that the introductions of halogen
or methyl make the addition reaction difficult to proceed. 相似文献
8.
The mechanism and kinetics of the production of hydroxymethyl hydroperoxide (HMHP) in ethene/ ozone/water gas-phase system were investigated at room temperature (298±2 K) and atmospheric pressure (1×105 Pa). The reactants were monitored in situ by long path FTIR spectroscopy. Peroxides were measured by an HPLC post-column fluorescence technique after sampling with a cold trap. The rate constants (k3) of reaction CH2O2 H2O→HMHP (R3) determined by fitting model calculations to ex-perimental data range from (1.6―6.0)×10?17 cm3·molecule?1·s?1. Moreover, a theoretical study of reac-tion (R3) was performed using density functional theory at QCISD(T)/6-311 (2d,2p)//B3LYP/6-311 G(2d, 2p) level of theory. Based on the calculation of the reaction potential energy surface and intrinsic reac-tion coordinates, the classic transitional state theory (TST) derived k3 (kTST), canonical variational tran-sition state theory (CVT) derived k3 (kCVT), and the corrected kCVT with small-curvature tunneling (kCVT/SCT) were calculated using Polyrate Version 8.02 program to be 2.47×10-17, 2.47×10-17 and 5.22×10-17 cm3·molecule-1·s-1, respectively, generally in agreement with those fitted by the model. 相似文献
9.
Xiaojun Tan Weihua Wang Ping Li Xiuli Yang Gengxiu Zheng Yuxiang Ma Zhuangdong Yuan 《Theoretical chemistry accounts》2007,118(2):357-362
The formations of the phosphinidene derivative HPNaF and its insertion reactions with R–H (R=F, OH, NH2, CH3) have been systematically investigated employing the density functional theory (DFT), such as the B3LYP and MPW1PW91 methods.
A comparison with the results of MP2 calculations shows that MPW1PW91 underestimates the barrier heights for the four reactions
considered. Similarly, the same is also true for the B3LYP method depending on the selected reactions, but by much less than
MPW1PW91, where the barrier heights of the four reactions are 25.2, 85.7, 119.0, and 142.4 kJ/mol at the B3LYP/6-311+G* level
of theory, respectively. All the mechanisms of the four reactions are identical to each other, i.e., an intermediate has been
located during the insertion reaction. Then, the intermediate could dissociate to substituted phosphinidane(H2RP) and NaF with a barrier corresponding to their respective dissociation energies. Correspondingly, the reaction energies
for the four reactions are −92.2, −68.1, −57.2, and −44.3 kJ/mol at the B3LYP/6-311+G* level of theory, respectively, where
both the B3LYP and MPW1PW91 methods underestimate the reaction energies compared with the MP2 results. The linear correlations
between the calculated barrier heights and the reaction energies have also been observed. As a result, the relative reactivity
among the four insertion reactions should be as follows: H–F > H–OH > H–NH2 > H–CH3. 相似文献
10.
A. N. Egorova M. V. Vener I. S. Zhukov G. D. Kozak V. G. Tsirelson 《Russian Chemical Bulletin》2008,57(6):1179-1186
Conformational analysis of cumene hydroperoxide PhCMe2OOH (1) has been carried out using the density functional methods B3LYP/6-31G(d,p) and B3LYP/6-311+G(3df,2p). Ignoring rotation
of methyl groups, molecule 1 has seven conformers differing in orientation of the — CMe2OOH fragment relative to the benzene ring and in mutual position of atoms in this fragment. The molecular structures, relative
energies, and statistical distribution of the conformers were determined, and intramolecular rotational barriers were estimated.
The enthalpies of formation of all conformers of molecule 1 were calculated using two approximations with inclusion of zero-point vibrational energy and temperature correction. Calculations
using the isodesmic reaction (IDR) scheme made it possible to reduce the systematic error of the determination of the enthalpy
of reactions. The total enthalpy of formation of compound 1 calculated with inclusion of statistical distribution of rotamers equals −19.7±3.6 kcal mol−1. The combination of the B3LYP/6-31G(d,p) approximation and the IDR scheme gives fairly accurate results (relative error is
±0.4 kcal mol−1) as compared to those obtained with the extended basis set 6-311+G(3df,2p).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1157–1164, June, 2008. 相似文献
11.
Lixin Zhou 《Theoretical chemistry accounts》2000,105(1):86-92
Results of ab initio self-consistent-field (SCF) and density functional theory (DFT) calculations of the gas-phase structure,
acidity (free energy of deprotonation, ΔGo), and aromaticity of 1,2-diseleno-3,4-dithiosquaric acid (3,4-dithiohydroxy-3-cyclobutene-1,2-diselenone, H2C4Se2S2) are reported. The global minimum found on the potential energy surface of 1,2-diseleno-3,4-dithiosquaric acid presents a
planar conformation. The ZZ isomer was found to have the lowest energy among the three planar conformers and the ZZ and ZE
isomers are very close in energy. The optimized geometric parameters exhibit a bond length equalization relative to reference
compounds, cyclobutanediselenone, and cyclobutenedithiol. The computed aromatic stabilization energy (ASE) by homodesmotic
reaction (Eq 1) is −20.1 kcal/mol (MP2(fu)/6-311+G** //RHF/6-311+G**) and −14.9 kcal/mol (B3LYP//6-311+G**//B3LYP/6-311+G**).
The aromaticity of 1,2-diseleno-3,4-dithiosquaric acid is indicated by the calculated diamagnetic susceptibility exaltation
(Λ) −17.91 (CSGT(IGAIM)-RHF/6-311+G**//RHF/6-311+G**) and −31.01 (CSGT(IGAIM)-B3LYP/6-311+G**//B3LYP/6-311+G**). Thus, 1,2-diseleno-3,4-dithiosquaric
acid fulfils the geometric, energetic and magnetic criteria of aromaticity. The calculated theoretical gas-phase acidity is
ΔGo
1(298K)=302.7 kcal/mol and ΔGo
2(298K)=388.4 kcal/mol. Hence, 1,2-diseleno-3,4-dithiosquaric acid is a stronger acid than squaric acid(3,4-dihydroxy-3-cyclobutene-1,2-dione,
H2C4O4).
Received: 11 April 2000 / Accepted: 7 July 2000 / Published online: 27 September 2000 相似文献
12.
The relative enthalpies, ΔHo (0) and ΔHo (298.15), of stationary points (four minimum and three transition structures) on the •O3H potential energy surface were calculated with the aid of the G3MP2B3 as well as the CCSD(T)–CBS (W1U) procedures from which
we earlier found mean absolute deviations (MAD) of 3.9 kJ mol−1 and 2.3 kJ mol−1, respectively, between experimental and calculated standard enthalpies of the formation of a set of 32 free radicals. For
CCSD(T)-CBS (W1U) the well depth from O3 + H• to trans-•O3H, ΔHowell(298.15) = −339.1 kJ mol−1, as well as the reaction enthalpy of the overall reaction O3 + H•→O2 + •OH, ΔrHo(298.15) = −333.7 kJ mol−1, and the barrier of bond dissociation of trans-•O3H → O2 + •OH, ΔHo(298.15) = 22.3 kJ mol−1, affirm the stable short-lived intermediate •O3H. In addition, for radicals cis-•O3H and trans-•O3H, the thermodynamic functions heat capacity Cop(T), entropy So (T), and thermal energy content Ho(T) − Ho(0) are tabulated in the range of 100 − 3000 K. The much debated calculated standard enthalpy of the formation of the trans-•O3H resulted to be ΔfHo(298.15) = 31.1 kJ mol −1 and 32.9 kJ mol −1, at the G3MP2B3 and CCSD(T)-CBS (W1U) levels of theory, respectively. In addition, MR-ACPF-CBS calculations were applied
to consider possible multiconfiguration effects and yield ΔfHo(298.15) = 21.2 kJ mol −1. The discrepancy between calculated values and the experimental value of −4.2 ± 21 kJ mol−1 is still unresolved.
Note added in proof: Yu-Ran Luo and J. Alistair Kerr, based on the discussion in reference 12, recently presented an experimental
value of ΔfHo(298.15) = 29.7 ± 8.4 kJ mol−1 in the 85th edition of the CRC Handbook of Chemistry and Physics (in progress). 相似文献
13.
AnYong Li 《中国科学B辑(英文版)》2008,51(7):623-631
Ab initio quantum chemistry methods were applied to study the bifurcated bent hydrogen bonds Y··· H2CZ (Z = O, S, Se) and Y···H2CZ2 (Z = F, Cl, Br) (Y = Cl−, Br−) at the MP2/6-311++G(d,p) and MP2/6-311++G(2df,2p) levels. The results show that in each complex there are two equivalent
blue-shifted H-bonds Y···H-C, and that the interaction energies and blue shifts are large, the energy of each Y···H-C H-bond
is 15–27 kJ/mol, and Δr(CH) = −0.1 − −0.5 pm and Δv(CH) = 30 − 80 cm−1. The natural bond orbital analysis shows that these blue-shifted H-bonds are caused by three factors: large rehybridization;
small direct intermolecular hyperconjugation and larger indirect intermolecular hyperconjugation; large decrease of intramolecular
hyperconjugation. The topological analysis of electron density shows that in each complex there are three intermolecular critical
points: there is one bond critical point between the acceptor atom Y and each hydrogen, and there is a ring critical point
inside the tetragon YHCH, so these interactions are exactly H-bonding. 相似文献
14.
Nucleophilic vinylic substitutions of 4H-pyran-4-one and 2-methyl-4H-pyran-4-one with ammonia were calculated by the B3LYP method using the 6-31G(d,p) basis set. Bulk solvent effects of aqueous
solution were estimated by the polarized continuum and Poisson–Boltzmann self-consistent reaction field models using the 6-311+G(d,p)
basis set. In the gas phase different mechanisms were found for the two reaction systems calculated. The reaction of 4H-pyran-4-one proceeds through enol, whereas a feasible path for the less reactive 2-methyl-4H-pyran-4-one is the mechanism through a keto intermediate. Addition of ammonia in concert with proton transfer is the rate-determining
step ofthe reaction. The mechanism proceeding either by a bimolecular nucleophilic substitution (SN2) or by one involving a tetrahedral zwitterionic intermediate is shown to be unlikely in the gas phase or nonpolar solution.
The effects of bulk solvent not only consist in a reduction of the various activation barriers by about 25–40 kJ mol−1 but also in a change in the reaction mechanism.
Received 26 May 2002 / Accepted 26 July 2002 /
Published online: 14 February 2003 相似文献
15.
Y. Liu X. M. Pan Z. S. Li X. J. Jia S. Li R. S. Wang C. C. Sun 《Theoretical chemistry accounts》2007,118(5-6):869-879
In gas phase, the hydrations of pentafulvenone to generate three types of cyclopentadienyl carboxylic acids are studied theoretically
at the MP2/6-311+G**//B3LYP/6-311+G** level. A water molecule attacking the C=O double bond of pentafulvenone can yield cyclopentadienyl
carboxylic acids via the formation of fulvenediols, and attacking the C=C double bond of pentafulvenone can directly yield
cyclopentadienyl carboxylic acid. The barriers of rate-determining transition states are 42.2 and 30.4 kcal mol−1, respectively. The barriers of rate-determining transition states for two water molecules system are 20.2 and 19.6 kcal
mol−1, respectively. The products can isomerize to each other. In aqueous solvent, the hydrations of pentafulvenone are investigated
using PCM-UAHF model at the MP2 (PCM)/6-311+G**// B3LYP (PCM)/6-311+G** and MP2 (PCM)/6-311+G**// B3LYP/6-311+G** levels.
The barriers of all rate-determining transition states are decreased. The added water molecule acts as catalyst in both gas
phase and aqueous solvent.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
16.
O. A. Gapurenko T. N. Gribanova R. M. Minyaev V. I. Minkin 《Russian Chemical Bulletin》2007,56(5):856-862
The energy characteristics and geometric parameters of the dodecahedrane endohedral complexes X@C20H20 (X = C4−, N3−, O2−, F−, Ne) were studied by the density functional theory B3LYP method with the 6-311G(d,p), 6-311+G(d,p), and 6-311G(df,p)) basis
sets. In all structures the central atoms X are characterized by a coordination number of 20. The energy of formation of the
complexes decreases in the order X = C4−, N3−, O2−, F−, Ne. The coordination number of the central atom remains unchanged upon adding Li+ counterions to anionic systems.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 824–830, May, 2007. 相似文献
17.
Al2F2分子结构与稳定性的ab initio计算研究 总被引:1,自引:0,他引:1
用abinitio方法在UMP2/6-311G(d)水平下计算了Al2F2分子可能的异构体构型和AlF二聚化成Al2F2分子的反应能。UMP2/6-311G(d)和UQCISD(T)/6-311+G(3df)//UMP2/6-311G(d)水平下的能量值均说明具有D2h对称性、1^Ag电子态的异构是Al2F2分子的最稳定构型,其Al-F键长为0.19074nm,键角Al-F-Al和F-Al-F分别为104.62°和75.38°,以及两个强振动,441.27cm^-1和401.93cm^-1,均与实验结果相符合。电子结构分析表明,具有D2h对称性的异构体的活性中心在2个Al原子上,在形成衍生物时是主要的反应加成位置。在UMP2/6-311G(d)和UQCISD(T)6-311+G(3df)//UMP2/6-311G(d)水平下得到了AlF二聚化能量分别为-75.01kJ/mol和-66.07kJ/mol,与文献估计算基本一致,说明AlF二聚化反应能量上是有利的。 相似文献
18.
The water effect on peroxy radical measurement by chemical amplification was determined experimentally for HO2 and HO2 OH, respectively at room temperature (298±2) K and atmospheric pressure (1×105 Pa). No significant difference in water effect was observed with the type of radicals. A theoretical study of the reaction of HO2·H2O adduct with NO was performed using density functional theory at CCSD(T)/6-311 G(2d, 2p)//B3LYP/6-311 G(2d, 2p) level of theory. It was found that the primary reaction channel for the reaction is HO2·H2O NO→HNO3 H2O (R4a). On the basis of the theoretical study, the rate constant for (R4a) was calculated using Polyrate Version 8.02 program. The fitted Arrenhnius equation for (R4a) is k = 5.49×107 T 1.03exp(?14798/T) between 200 and 2000 K. A chemical model incorporated with (R4a) was used to simulate the water effect. The water effect curve obtained by the model is in accordance with that of the experiment, suggesting that the water effect is probably caused mainly by (R4a). 相似文献
19.
Structures and stability of isomers of [Si,N,N,P] system 总被引:1,自引:0,他引:1
KAN Wei YU Haitao LI Mingxia FU Honggang & SUN Jiazhong . College of Chemistry Chemical Engineering Heilongjiang University Harbin China . State Key Laboratory of Theoretical Computational Chemistry Institute of Theoretical Chemistry Jilin University Changchun China 《中国科学B辑(英文版)》2004,47(2):98-105
Recently, silicon- and nitrogen-containing small molecules, such as SiN, SiC, SiC2, and NP, which have been identified in interstellar medium[1—3] and well characterized for the formation, structures, spec-tra, and reactivity using theoretical and experimental methods[4—8], have attracted more attentions because of their potential importance in chemical kinetics, in-terstellar chemistry, astrophysics, and material science. The systems with three, four, and five atoms, for ex-ample, Si2N, … 相似文献
20.
The dissociation pressure for the process PtCl2(s) → Pt(s) + Cl2(g) was measured by the static method with diaphragm zero-pressure gauges. The approximating equation for the temperature
dependence on the dissociation pressure for the above reaction was found. The enthalpy (137.7±0.3 kJ mol−1) and entropy (163.6±0.4 J mol−1 K−1) of PtCl2(s) dissociation and enthalpies of formation and absolute entropies of platinum di- and trichlorides at 298.15 K were calculated.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1345–1348, June, 2005. 相似文献