Theoretical study of the reaction of Cu with OCS

The reactivity of Cu⁺ with OCS on both singlet and triplet potential energy surfaces (PES) has been investigated at the UB3LYP/6-311+G(d) level. The object of this investigation was the elucidation of the reaction mechanism. The calculated results indicated that both the C–S and C–O bond activations proceed via an insertion–elimination mechanism. Intersystem crossing between the singlet and triplet surfaces may occur along both the C–S and C–O bond activation branches. The ground states of CuS⁺ and CuO⁺ were found to be triplets, whereas CuCO⁺ and CuCS⁺ have singlet ground states. The C–S bond activation is energetically much more favorable than the C–O bond activation. All theoretical results are in line with early experiments.     

Theoretical study on the mechanism of OH + HCNO reaction

A detailed mechanistic study of the OH + HCNO reaction, in which the products P _i with i=1, 2, . . . ,7 are involved, is carried out by means of CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE computatio-nal method to determine a set of reasonable pathways. It is shown that P ₆ (CO + H₂NO) and P ₃ (HNO +HCO) are the major product channels with a minor contribution from P ₅ (NO + H₂CO), whereas the other channels for P ₁ (H₂O + NCO), P ₂ (NH₂ + CO₂), P ₄ (HCN + HO₂) and P ₇(CO + H₂ + NO) are less favorable. All these theoretical results are in harmony with experimental facts.     

Theoretical study of the reaction of Sc with SCO in gas phase

In order to elucidate the mechanism of reaction M⁺ + SCO, both triplet and singlet potential energy surfaces (PESs) for the reaction of Sc⁺ + SCO have been theoretically investigated using the DFT (B3LYP/6-311+G*) level of theory. The geometries for reactants, intermediates, transition states and products were completely optimized. All the transition states were verified by the vibrational analysis and the intrinsic reaction coordinate calculations. The involving potential energy curve-crossing dramatically affects reaction mechanism, reaction rate has been discussed, and the crossing points (CPs) have been localized by the approach suggested by Yoshizawa et al. The present results show that the reaction mechanism are insertion–elimination mechanism both along the C–S and C–O bond activation branches, but the C–S bond activation is much more favorable in energy than the C–O bond activation. All theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction.     

NCO自由基与O和N反应的理论研究

采用密度泛函和量子化学从头算方法, 对NCO自由基和O, N原子反应的势能面进行了理论研究, 讨论了主要的反应通道. 这两种自由基反应的机理比较类似, 初始都有两种进攻方式. NCO与O的主反应通道是O原子从N端无势垒加合, 经过一低垒过渡态, 得到稳定产物P1(CO+NO), 而对NCO与N反应得到了一完整反应通道和无垒加合产物.     

Theoretical study on reaction mechanism of the vinyl radical with nitrogen atom

The complex triplet potential energy surface of the C₂H₃N system is investigated at the UB3LYP and CCSD(T) (single-point) levels in order to explore the possible reaction mechanism of C₂H₃ radical with N(⁴S). Eleven minimum isomers and 18 transition states are located. Possible energetically allowed reaction pathways leading to various low-lying dissociation products are obtained. Starting from the energy-rich reactant C₂H₃+N(⁴S), the first step is the attack of the N atom on the C atom having one H atom attached in C₂H₃ radical and form the intermediate C₂H₃N(1). The associated intermediate 1 can lead to product P₁ CH₂CN+H and P₂ ³CH₂+³HCN by the cleavage of C–H bond and C–C bond, respectively. The most favorable pathway for the C₂H₃+N(⁴S) reaction is the channel leading to P₁, which is preferred to that of P₂ due to the comparative lower energy barrier. The formation of P₃ ³C₂H₂+³NH through hydrogen-abstraction mechanism is also feasible, especially at high temperature. The other pathways are less competitive comparatively.     

O+HCNO反应势能面的理论研究

采用CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE方法对反应O＋HCNO进行了研究. 通过反应势能面揭示了该反应的机理, 通过H或O迁移等多步反应路径得到3种产物, 其中, P1(HCO+NO)为主要产物, P2(HNO+CO)和P3(NCO+OH)为次要产物. 为进一步实验研究提供了参考.     

乙醇醛光解离机理的理论研究

采用多参考态方法, 在CASPT2//CASSCF/6-311+G(2df, 2p) 水平上计算了乙醇醛(HOCH2CHO)分子在三个最低电子态(S0、S1和T1)上驻点的电子结构和解离势能面。结合势能面交叉点,探讨了HOCH2CHO与波长有关的光解离机理,分析了可能的光解离产物。结果表明, 在实验光解波长240 – 400 nm的激发下,HOCH2CHO分子主要发生S1态上的解离反应或通过S0和S1态之间的振动相互作用驰豫到基态,随之发生基态解离反应。C-C键断裂生成基态光解产物HOCH2 (2A′)+ HCO (2A′)是最主要的反应途径;而在一定波长下,生成CH3OH + CO的基态协同反应、脱醛基氢及脱羟基通道都是能量上可行的反应途径。本文的计算结果和实验观察一致。     

H+HCNO反应势能面的理论研究

在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE水平下, 对反应H＋HCNO进行了研究. 建立了反应势能面, 揭示了该反应的反应机理, 通过H迁移、N—O键或C—N键断裂等多步反应, 得到4种产物, 其中最主要产物为P1(HCN+OH).     

NO+HCCCO反应势能面的理论研究

在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE水平下, 对反应NO＋HCCCO进行了研究. 建立了反应势能面, 揭示了该反应的反应机理, 通过O迁移、C—C键或N—O键断裂等多步反应, 得到4种产物, 其中, 最主要产物为P1(HCCO+NCO).     

BH+2与C2H2反应势能面的量子化学研究

用B3LYP/6-311G(d,p) 密度泛函方法和高级电子相关的CCSD(T)/6-311G(2df,p)偶合簇法研究BH+2与C2H2反应势能面. 结果表明 该势能面上存在(a) H2B+*C2H2, (b) HBCHCH2+, (c) H2BCCH+2和(d) H2*BHCCH+四种异构体, 其中(b)能量最低且在动力学上最稳定, (a), (c)和(d)在动力学上均不稳定; BH+2通过对C2H2的分步亲电加成以及随后的氢迁移和H2消除等反应形成离解产物HBCCH++H2, 该反应不需要活化能且大量放热. 计算结果有助于深入了解BH+2等缺电子硼氢正离子的反应行为.     

Theoretical study of the reaction of Cr+ with SCO in gas phase

To elucidate the mechanism of reaction M⁺ + SCO, the reaction of Cr⁺ + SCO has been investigated using density functional theory (DFT) with the popular hybrid functional, B3LYP, in conjunction with 6‐311+G* basis set on both the sextet and quartet potential energy surfaces (PESs). To obtain an accurate evaluation of the activation barrier and reaction energy, the coupled cluster single‐point calculations using the B3LYP structures is performed. The crossing points (CPs) of the different PESs have been localized with the approach suggested by Yoshizawa and colleagues. The involving potential energy curve‐crossing dramatically affects reaction mechanism. The present results show that the reaction mechanism is insertion‐elimination mechanism both along the C? S and C? O bond activation branches, but the C? S bond activation is much more favorable than the C? O bond activation in energy. All theoretical results not only support the existing conclusions inferred from early experiment study, but also complement the pathway and mechanism for this reaction. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Theoretical study on the mechanism of cycloaddition reaction between dimethyl germylidene and formaldehyde

The cycloaddition mechanism of the reaction between singlet dimethyl germylidene and formaldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated with CCSD (T)//MP2/6-31G* method. From the potential energy profile, we predict that the cycloaddition reaction between singlet dimethyl germylidene and formaldehyde has two dominant reaction pathways. First dominant reaction pathway consists of three steps: (1) the two reactants (R1, R2) firstly form an intermediate INT1a through a barrier-free exothermic reaction of 43.0 kJ/mol; (2) INT1a then isomerizes to a four-membered ring compound P1 via a transition state TS1a with an energy barrier of 24.5 kJ/mol; (3) P1 further reacts with formaldehyde(R2) to form a germanic heterocyclic compound INT3, which is also a barrier-free exothermic reaction of 52.7 kJ/mol; Second dominant reaction pathway is as following: (1) the two reactants (R1, R2) firstly form a planar four-membered ring intermediate INT1b through a barrier-free exothermic reaction of 50.8 kJ/mol; (2) INT1b then isomerizes to a twist four-membered ring intermediate INT1.1b via a transition state TS1b with an energy barrier of 4.3 kJ/mol; (3) INT1.1b further reacts with formaldehyde(R2) to form an intermediate INT4, which is also a barrier-free exothermic reaction of 46.9 kJ/mol; (4) INT4 isomerizes to a germanic bis-heterocyclic product P4 via a transition state TS4 with an energy barrier of 54.1 kJ/mol.     

HS+HO2气相反应机理及主通道速率常数的理论研究

采用CCSD(T)/6-311++G(3df, 2pd)//B3LYP/6-311+G(2df, 2p)双水平计算方法构建了HO₂+HS反应体系的单、三重态反应势能面,并对该反应主通道的速率常数进行了研究。研究结果表明,标题反应经历了八条反应通道,其中三重态反应通道R1是标题反应主通道。此通道包含路径Path 1 (R → ³IM1 → ³TS1 → P1(³O₂+H₂S))和Path 1a (R → ³IM1a → ³TS1a → P1(³O₂+H₂S))两条路径。利用经典过渡态理论(TST)与变分过渡态理论(CVT)并结合小曲率隧道效应模型(SCT),分别计算了主路径Path 1和Path 1a在200-800 K温度范围内的速率常数k^TST、k^CVT和k^CVT/SCT,在此温度区间内路径Path 1和Path 1a具有负温度系数效应。速率常数计算结果显示,对主路径Path 1和Path 1a而言,变分效应在计算温度段内有一定影响,与此同时量子力学隧道效应在低温段有显著影响。路径Path 1和Path 1a的CVT/SCT速率常数的三参数表达式分别为k₁^CVT/SCT(200-800 K) = 1.54×10^-5T^-2.70exp(1154/T) cm³ ·molecule^-1·s^-1和k_1a^CVT/SCT(200-800 K) = 5.82×10^-8T^-1.84exp(1388/T) cm³·molecule^-1·s^-1。     

Ab initio Study on Mechanism of Forming a Silicic Bis-Heterocyclic Compound Between Dimethylmethylenesilylene and Ethene

The mechanism of the cycloaddition reaction of forming a silicic bis-heterocyclic compound between singlet dimethylmethylenesilylene (Me₂C=Si:) and ethene has been investigated with the CCSD(T)//MP2/6-31G^* method. From the potential energy profile, it can be predicted that, this reaction has one dominant channel. The presented rule of this dominant channel: the 3p unoccupied orbital of Si in dimethylmethylenesilylene and the π orbital of ethene forming the π→p donor-acceptor bond, resulting in the formation of three-membered ring intermediate (INT1); INT1 then isomerizes to a four-membered ring silylene (P2), which is driven by ring-enlargement effect; due to sp³ hybridization of Si atom in P2, P2 further combines with ethene to form a silicic bis-heterocyclic compound.     

自由基HO2与C2H2反应势能面的理论研究

应用量子化学从头计算和密度泛函理论(DFT)对HO2+C2H2反应体系的反应机理进行了研究.在B3LYP/6-311G**和CCSD(T)/6-311G**水平上计算了HO2+ C2H2反应的二重态反应势能面.计算结果表明,主要反应方式为自由基HO2的H原子和C2H2分子中的C原子结合,经过一系列异构化,最后分解得到主要产物P1 (CH2O+ HCO).此反应是放热反应,化学反应热为-321.99 kJ·mol-1.次要产物为P2 (CO2 +CH3),也是放热反应.     

N-甲硝胺异构化和分解反应机理和动力学的理论研究

The complex potential energy surface and reaction mechanisms for the unimolecular isomerization and decomposition of methyl-nitramine (CH3NHNO2) were theoretically probed at the QCISD(T)/6-311+G*//B3LYP/6-311+G* level of theory. The results demonstrated that there are four low-lying energy channels: (i) the NN bond fission pathway; (ii) a sequence of isomerization reactions via CH3NN(OH)O; (IS2a); (iii) the HONO elimination pathway; (iv) the isomerization and the dissociation reactions via CH3NHONO (IS3). The rate constants of each initial step (rate-determining step) for these channels were calculated using the canonical transition state theory. The Arrhenius expressions of the channels over the temperature range 298-2000 K are k6(T)=1014:8e-46:0=RT , k7(T)=1013:7e-42:1=RT , k8(T)=1013:6e-51:8=RT and k9(T)=1015:6e-54:3=RT s-1, respectively. The calculated overall rate constants is 6.9￡10-4 at 543 K, which is in good agreement with the experimental data. Based on the analysis of the rate constants, the dominant pathway is the isomerization reaction to form CH3NN(OH)O at low temperatures, while the NN bond fission and the isomerization reaction to produce CH3NHONO are expected to be competitive with the isomerization reaction to form CH3NN(OH)O at high temperatures.     

Reaction Mechanism and Product Branching Ratios of OH+C2H3F Reaction: A Theoretical Study

Ab initio CCSD(T)/CBS//B3LYP/6-311G(d, p) calculations of the potential energy surface for possible dissociation channels of HOC\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F, as well as Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of rate constants, were carried out, in order to predict statistical product branching ratios in dissociation of HOC\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F at various internal energies. The most favorable reaction pathway leading to the major CH\begin{document}$_2$\end{document}CHO+HF products is as the following: OH+C\begin{document}$_2$\end{document}H\begin{document}$_3$\end{document}F\begin{document}$\rightarrow$\end{document}i2\begin{document}$\rightarrow$\end{document}TS14\begin{document}$\rightarrow$\end{document}i6\begin{document}$\rightarrow$\end{document}TS9\begin{document}$\rightarrow$\end{document}i3\begin{document}$\rightarrow$\end{document}TS3\begin{document}$\rightarrow$\end{document}CH\begin{document}$_2$\end{document}CHO+HF, where the rate-determining step is HF elimination from the CO bridging position via TS11, lying above the reactants by 3.8 kcal/mol. The CH\begin{document}$_2$\end{document}O+CH\begin{document}$_2$\end{document}F products can be formed by F atom migration from C\begin{document}$_\beta$\end{document} to C\begin{document}$_\alpha$\end{document} position via TS14, then H migration from O to C\begin{document}$_\alpha$\end{document} position via TS16, and C-C breaking to form the products via TS5, which is 1.8 kcal/mol lower in energy than the reactants, and 4.0 kcal/mol lower than TS11.     

Density Functional Theory Study of Mechanism of Cycloaddition Reaction Between Dimethyl-Silylene Carbene and Acetone

The mechanism of the cycloaddition reaction between singlet dimethyl-silylene carbene and acetone has been investigated with density functional theory, From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The presented rule of this reaction: the [2+2] cycloaddition effect between the πorbital of dimethyl-silylene carbene and the π orbital of π-bonded compounds leads to the formation of a twisty four-membered ring intermediate and a planar four-membered ring product; The unsaturated property of C atom from carbene in the planar four-membered ring product,resulting in the generation of CH₃-transfer product and silicic bis-heterocyclic compound.     

Ab initio Study of Mechanism of Forming Germanic Bis-Heterocyclic Compound Between Dichloro-Germylene Carbene (Cl2Ge=C:) and Formaldehyde

The mechanism of the cycloaddition reaction of forming germanic bis-heterocyclic compound between singlet dichloro-germylene carbene and formaldehyde has been investigated with CCSD(T)//MP2/6-31G^* method, from the potential energy profile, we predict that the re-action has two competitive dominant reaction pathways. The presented rule of this reaction: the 2p unoccupied orbital of the C atom in dichloro-germylene carbene insert the π orbital of formaldehyde from oxygen side, resulting in the formation of intermediate. In the interme-diate and between two reactants, because of the two bonding π orbital in dichloro-germylene carbene and formaldehyde have occurred [2+2] cycloaddition reaction, forming two four-membered ring compounds in which Ge and O are in the opposite orientation and in the syn-position, respectively. Because of the unsaturated property of C atom from carbene in the two four-membered ring compounds, they further reacts with formaldehyde, resulting in the generation of two germanic bis-heterocyclic compounds.     

气相中Y^＋活化CS2中的C—S键

以Y+与CS2反应作为第二行前过渡金属离子与CS2反应的范例体系.采用密度泛函UB3LYP方法,对于Y+采用Stuttgart赝势基组,对于CS2采用6-311+G(2d)基组,计算研究了Y+离子在基态和激发态时与CS2气相反应的机理.并用UCCSD(T)方法在相同的基组水平上对各驻点作了单点能量校正.结果表明Y+离子与CS2的反应是插入-消去反应,在反应过程中会发生系间窜越,并且找到了两个势能面的能量最低交义点.