Cl原子与CH2SH自由基反应机理及电子密度拓扑研究

采用MP2(Full)/6-311G(d,p)和B3LYP/6-311G(d,p)找到了反应Cl＋CH₂SH→HCl＋CH₂S的两个可能的反应通道, 得到了各反应通道的反应物、中间体、过渡态和产物的优化构型、谐振频率. 对反应进程中若干关键点进行了电子密度拓扑分析, 讨论了反应进程中键的断裂、生成和化学键的变化规律, 找到了该反应的结构过渡区(结构过渡态)和能量过渡态, 发现了反应热与结构过渡区之间的关系.     

CH3SH与CN·自由基的反应机理及电子密度拓扑分析

在B3LYP/6-311++G(d,p)水平上研究了CH3SH与CN·自由基的反应机理. 找到了三个可能的反应通道, 得到了各反应通道的反应物、中间体、过渡态和产物的优化构型、谐振频率. 通过内禀反应坐标(IRC)跟踪确认了稳定点与过渡态的连接关系. 在CCSD/6-311++G(d,p)水平上进行能量校正, 成功地解释了Brian等的实验结论. 通过对反应进程中一些重要点的电子密度拓扑分析, 讨论了反应进程中化学键的变化规律, 发现了六元环状过渡结构.     

Kinetics of the hydrogen abstraction reactions of 1,1‐ and 1,2‐difluoroethane with hydroxyl radical: an ab initio study

The hydrogen abstraction reactions of 1,1‐ and 1,2‐difluoroethane with the OH radical have been investigated by the ab initio molecular orbital theory. The geometries of the reactants, products, and transition states have been optimized at the (U)MP2=full level of theory in conjunction with 6‐311G(d,p) basis functions. Single‐point (U)MP2=full with larger basis set, such as 6‐311G(3d,2p), and QCISD(T)=full/6‐311G(d,p) calculations have also been carried out to observe the effects of basis sets utilized and higher order electron correlation. Three and four reaction channels have been identified for 1,1‐ and 1,2‐difluoroethane, respectively. In the case of 1,1‐difluoroethane, hydrogen abstraction from the α‐carbon has been found to be easier than that from the β‐carbon. The barriers of the four reaction channels for 1,2‐difluoroethane are close to each other. Weak hydrogen bonding interactions have been observed between hydroxyl hydrogen and a fluorine atom in the transition states. Rate constants for the reactions of 1,1‐ and 1,2‐difluoroethane with the OH radical have been calculated using the standard transition state theory and found to be in good agreement with the experimental results. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1305–1318, 2000     

CH2NH与O(3P)反应的量子化学及电子密度拓扑研究

采用B3LYP、MP2(full)和 QCISD 三种方法在6-311G(d, p)和aug-cc-pVDZ基组水平上对三线态O(3P)原子与CH2NH(s)的反应进行了详细的理论研究. 采用B3LYP和MP2(full)方法对反应势能面上的各驻点进行了几何构型优化, 通过振动频率分析证实了过渡态的真实性, 内禀反应坐标(IRC)跟踪验证了过渡态与反应物和产物的连接关系, 用上述三种方法计算得到了各反应通道的反应势垒. 对反应过程中的一些重要点进行了电子密度拓扑分析研究. 研究结果表明, O(3P)原子进攻CH2NH(s)中的N2原子和C1原子生成CH2NHO(t)和OCH2NH(t), CH2NHO(t)中N2上的H5可迁移到C1上异构化为CH3NO(t).     

氮原子与卤代甲烷反应的直接氢抽提过程研究

利用B3LYP理论研究了N(~4S)+CH_3X(X = H, F, Cl)反应体系的直接氢抽提过 程,分别得到了各反应物、产物和过渡态的优化构型和谐振频率。同时应用了6- 31G(d), 6-311+G(d,p)和6-311+ + G(2d,2p)基组,考察其大小对反应体系中各物 种构型及能量的影响。理论计算表明,随着基组的增加,反应势垒逐渐降低,反应 吸热减少。对比取代甲烷的情形,结果表明反应过程中卤素原子具有典型的诱导效 应,降低了抽提势垒。     

CH2SH与NO2双自由基反应机理的理论研究

在B3LYP/6-311＋＋G(2df,p)水平上优化了标题反应驻点物种的几何构型, 并在相同水平上通过频率计算和内禀反应坐标(IRC)分析对过渡态结构及连接性进行了验证. 采用双水平计算方法HL//B3LYP/6-311＋＋G(2df,p)对所有驻点及部分选择点进行了单点能校正, 构建了CH2SH＋NO2反应体系的单重态反应势能剖面. 研究结果表明, CH2SH与NO2反应体系存在4条主要反应通道, 两个自由基中的C与N首先进行单重态耦合, 形成稳定的中间体HSCH2NO2 (a). 中间体a经过C—N键断裂和H(1)—O(2)形成过程生成主要产物P1 (CH2S＋trans-HONO), 此过程需克服124.1 kJ•mol－1的能垒. 中间体a也可以经过C—N键断裂及C—O键形成转化为中间体HSCH2ONO (b), 此过程的能垒高达238.34 kJ•mol－1. b再经过一系列的重排异构转化得到产物P2 (CH2S＋cis-HONO), P3 (CH2S＋HNO2)和P4 (SCH2OH＋NO). 所有通道均为放热反应, 反应能分别为－150.37, －148.53, －114.42和－131.56 kJ•mol－1. 标题反应主通道R→a→TSa/P1→P1的表观活化能为－91.82 kJ•mol－1, 此通道在200～3000 K温度区间内表观反应速率常数三参数表达式为kCVT/SCT＝8.3×10－40T4.4 exp(12789.3/T) cm3•molecule－1•s－1.     

Ab initio direct dynamics studies on the reactions of chlorine atom with CH3-nFnCH2OH (n = 1-3)

The hydrogen abstraction reactions of Cl atom with a series of fluorinated alcohols, i.e., CH(3-n)F(n)CH(2)OH + Cl (n = 1-3) (R1-R3) have been studied systematically by ab initio direct dynamics method and the canonical variational transition state theory (CVT). The potential energy surface information is calculated at the MP2/6-311G(d,p) level. Energies along the minimum energy paths are improved by a series of single-point calculations at the higher modified GAUSSIAN-2 (G2M) level of theory. Theoretical analysis shows that three kinds of hydrogen atoms can be abstracted from the reactants CH(2)FCH(2)OH and CHF(2)CH(2)OH, and for CF(3)CH(2)OH, two possible pathways are found. The rate constants for each reaction channel are evaluated by CVT with the small-curvature tunneling correction (SCT) over a wide range of temperature from 200 to 2000 K. The calculated CVT/SCT rate constants are in good agreement with the available experimental values for the reactions CHF(2)CH(2)OH + Cl and CF(3)CH(2)OH + Cl. However, for the reaction CH(2)FCH(2)OH + Cl, there is negative temperature dependence below 500 K, which is different from the experimental fitted. It is shown that in the low temperature ranges, the three reactions all proceed predominantly via H-abstraction from the methylene positions, and with the increase of the temperature the H-abstraction channels from the fluorinated-methyl positions should be taken into account, while the H-abstraction channels from the hydroxyl groups are negligible over the whole temperature ranges. Also, the reactivity decreases substantially with fluorine substitution at the methyl position of alcohol.     

Quantum study on the electrocyclic reactions of CH2CHCHCHX (XH,F, Cl)

The microscopic mechanisms of the electrocyclic reactions for cis‐1,3‐butadiene and its monofluoro‐, monochloroderivatives have been studied by density functional theory (DFT), using the B3LYP method and 6‐311++G** basis sets. We optimized the geometric configurations of reactants, transition states, and products; verified all the probable transition states through vibrational analysis; and calculated the relative single‐point energies at the QCISD(T)/6‐311++G**//B3LYP/6‐311++G**. The results show that the monofluoro‐, monochloroderivatives of cis‐1,3‐butadiene both have two conformers; the reactant favors the electrocyclic reaction when one outboard hydrogen atom of the CH₂ groups is substituted by the fluorine or chlorine atom. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Theoretical investigations on thermal rearrangement reactions of (aminomethyl)silane

Thermal rearrangement reactions of (aminomethyl)silane H(3)SiCH(2)NH(2) were studied by ab initio calculations at the G3 level. The results show that two dyotropic reactions could happen when H(3)SiCH(2)NH(2) is heated. In one reaction, the silyl group migrates from the carbon to the nitrogen atom while a hydrogen atom shifts from the nitrogen to the carbon atom, forming (methylamino)silane CH(3)NHSiH(3) (reaction A). This reaction can proceed via three paths: a path involving two consecutive steps with two transition states and one intermediate metastable carbene species (A-1); and two concerted paths (A-2 and A-3). In the other reaction, the amino group migrates from the carbon to the silicon atom while a hydrogen atom shifts from the silicon to the carbon atom, via a double three-membered ring transition state, forming aminomethylsilane CH(3)SiH(2)NH(2) (reaction B). Reaction rate constants, changes (DeltaS(#), DeltaH, and DeltaG) in thermodynamic functions and equilibrium constants of the reactions were calculated with the MP2(full)/6-311G(d,p) optimized geometries, harmonic vibrational frequencies and G3 energies of reactants, transition states, intermediates and products with statistical mechanical methods and the conventional transition-state theory (TST) with Wigner tunneling approximation over a temperature range 400-1800 K.     

CH3SH与NO2的反应机理及动力学

在G3B3, CCSD(T)/6-311＋＋G(d,p)//B3LYP/6-311＋＋G(d,p)水平上详细研究了CH3SH与基态NO2的微观反应机理. 在B3LYP/6-311＋＋G(d,p)水平得到了反应势能面上所有反应物、过渡态和产物的优化构型, 通过振动频率分析和内禀反应坐标(IRC)跟踪验证了过渡态与反应物和产物的连接关系. 在CCSD(T)/6-311＋＋G(d,p)和G3B3水平计算了各物种的能量, 得到了反应势能面. 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), 分别计算了在200～3000 K温度范围内的速率常数kTST, kCVT和kCVT/SCT. 研究结果表明, 该反应体系共存在5个反应通道, 其中N进攻巯基上H原子生成CH3S＋HNO2的通道活化势垒较低, 为主要反应通道. 动力学数据也表明, 该通道在200～3000 K计算温度范围内占绝对优势, 拟合得到的速率常数表达式为k1CVT/SCT＝1.93×10－16T0.21exp(－558.2/T) cm3&;#8226;molecule－1&;#8226;s－1.     

HNCX (X＝O,S)和F反应机理及电子密度拓扑分析

采用G3B3//B3LYP/6-311＋＋G(d,p)方法研究了HNCX (X＝O, S)与F原子的反应机理. 找到了六条可能的反应通道, 计算结果表明, 该反应的主产物为HF＋NCX (X＝O, S). 对反应过程进行了电子密度拓扑分析, 讨论了反应过程中化学键的断裂和生成规律, 找到了HNCX (X＝O, S)和F反应过程中的T型结构过渡态、三元环状结构过渡区和四元环状结构过渡区.     

Br＋活化甲烷C—H键反应机理的理论研究

化甲烷催化剂的可能性. 在B3LYP/6-311＋＋G(3df,3p)和MP2/6-311＋＋G(3df,3p)水平下优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型. 在G2M(＋)水平下计算了各物种的能量. 研究结果表明: CH4与Br＋(3P)反应存在三条不同的吸热反应途径, 与Br＋(1D)反应存在二条不同的放热反应通道. 反应更易于通过单重态反应通道进行. 理论结果不仅较好地解释了实验事实, 还说明Br＋有可能成为一种活化甲烷的催化剂.     

硅炔氢加成生成甲硅烷基硅烯的量子化学研究

利用量子化学从头算和密度泛函理论(DFT), 研究了硅炔和氢气分子加成生成甲硅烷基硅烯的反应机理. 在B3LYP/6-311G**水平上, 全参数优化了反应通道上各驻点(反应物、过渡态和产物)的几何构型, 计算出了它们的振动频率和零点振动能(ZPVE), 并对它们进行了振动分析, 以确定过渡态的真实性. 各物质总能量由QCISD(T)/6-311G**// B3LYP/6-311G**给出, 并对能量进行了零点能校正. 计算表明, 硅炔与氢分子加成反应可生成稳定的甲硅烷基硅烯. 热力学与动力学计算表明, 反应过程是一个放热、熵减少而自发趋势和反应程度较大的反应.     

Theoretical investigations on removal reactions of ethenol by H atom

Ethenol is a recently identified combustion intermediate. However, its chemistry remains unclear. In present work, the removal reactions of ethenol by H atom are investigated. The geometries of all species involved in the reaction are optimized at B3LYP/6-311++G(d,p), and their single point energies are extrapolated to the infinite-basis-set limit at the level CCSD(T). Energies are also calculated at G3B3, CBS-APNO, and CCSD(T)/6-311++G(3df, 2p) for comparison. A total of six elementary reactions, including four abstractions and two additions, with explicit transition states are investigated. The results show that the reactions are selective: for abstractions, the hydrogen atom, linked to the oxygen atom, is the most reactive; while for additions, the preferred carbon site is the head "CH(2)═". The rate constants are estimated in the temperature range 300-3000 K according to the conventional transition state theory with the Eckart tunneling model. The dominant channels are the two additions in the whole temperature range. The abstractions can be competitive at high temperature but still do not dominate. The calculated rate constants for the reverse reaction of (R6), syn-CH(2)═CHOH + H ? CH(3)·CHOH, are consistent with the available literature values. Finally, the Fukui functions are calculated to analyze the site reactivity.     

单分子水对CH_2SH+NO_2反应机理影响的理论研究

在B3LYP/6-311++G(2df,p)水平下对单分子水参与下的CH_2SH+NO_2反应的微观机理进行了研究.为了获得更准确的能量信息,采用HL复合方法和CCSD(T)/aug-ccpvtz方法进行单点能校正.结果表明,加入单分子水后的CH_2SH+NO_2反应体系,共经过10条不同的反应路径,得到6种反应产物.与裸反应(CH_2SH+NO_2)相比,水分子在反应中起到了明显的正催化作用.不仅使生成产物trans-HONO的能垒(-52.84kJ·mol~(-1))降低了176.94kJ·mol~(-1),而且不需经过复杂的重排和异构化过程便可得到产物cis-HONO.在生成产物cis-HONO通道(Path3和Path4)中,活化能垒分别为143.65和126.70kJ·mol~(-1),而其裸反应的活化能垒却高达238.34kJ·mol~(-1).生成HNO_2的通道中(Path5和Path6)活化能垒分别为295.23和-42.19kJ·mol~(-1).其中Path6的无势垒过程使HNO_2也成为该反应的主要产物.另外,单分子水还可通过氢迁移的方式直接参与CH_2SH+NO_2的反应,活化能垒(TS7-TS10)分别为-10.62,151.03,186.22和155.10kJ·mol~(-1).除直接抽氢通道中的(Path8-Path10)外,其余反应通道均为放热反应,在热力学上是可行的.     

Theoretical study and rate constant calculation for the reactions of SH (SD) with Cl2, Br2, and BrCl

The mechanisms of the SH (SD) radicals with Cl2 (R1), Br2 (R2), and BrCl (R3) are investigated theoretically, and the rate constants are calculated using a dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points are calculated at the MP2/6-311G(d,p) and MPW1K/6-311G(d,p) levels. Higher-level energies are obtained at the approximate QCISD(T)/6-311++G(3df, 2pd) level using the MP2 geometries as well as by the multicoefficient correlation method based on QCISD (MC-QCISD) using the MPW1K geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of these reactions, which indicate that the reactions may proceed via an indirect mechanism. The enthalpies of formation for the species XSH/XSD (X = Cl and Br) are evaluated using hydrogenation working reactions method. By canonical variational transition-state theory (CVT), the rate constants of SH and SD radicals with Cl2, Br2, and BrCl are calculated over a wide temperature range of 200-2000 K at the a-QCISD(T)/6-311++G(3df, 2pd)//MP2/6-311G(d, p) level. Good agreement between the calculated and experimental rate constants is obtained in the measured temperature range. Our calculations show that for SH (SD) + BrCl reaction bromine abstraction (R3a or R3a') leading to the formation of BrSH (BrSD) + Cl in a barrierless process dominants the reaction with the branching ratios for channels 3a and 3a' of 99% at 298 K, which is quite different from the experimental result of k3a'/k3' = 54 +/- 10%. Negative activation energies are found at the higher level for the SH + Br2 and SH + BrCl (Br-abstraction) reactions; as a result, the rate constants show a slightly negative temperature dependence, which is consistent with the determination in the literature. The kinetic isotope effects for the three reactions are "inverse". The values of kH/kD are 0.88, 0.91, and 0.69 at room temperature, respectively, and they increase as the temperature increases.     

CH3CH2,CH3CHCl,CH3CCl2与NO2反应微观动力学理论研究

运用量子化学密度泛函理论UB3LYP/6-311+G*和高级电子相关校正的偶合簇(CCSD(T)/6-311+G*)方法,对CH3CH2,CH3CHCl和CH3CCl2自由基与NO2反应的机理和动力学进行了理论研究,得到了体系的势能面信息和可能的反应机理.根据计算得到的各反应热力学参数及反应能垒,采用传统过渡态理论计算了各反应在温度T=298 K和T=700 K时的速率常数.研究结果表明,该类反应均通过1个中间体和1个过渡态生成产物,产物分别为CH3CHO+HNO,CH3CHO+ClNO和CH3CClO+ClNO.     

CH2SH与NO2双自由基反应机理的理论研究

在B3LYP/6-311＋＋G(2df,p)水平上优化了标题反应驻点物种的几何构型, 并在相同水平上通过频率计算和内禀反应坐标(IRC)分析对过渡态结构及连接性进行了验证. 采用双水平计算方法HL//B3LYP/6-311＋＋G(2df,p)对所有驻点及部分选择点进行了单点能校正, 构建了CH2SH＋NO2反应体系的单重态反应势能剖面. 研究结果表明, CH2SH与NO2反应体系存在4条主要反应通道, 两个自由基中的C与N首先进行单重态耦合, 形成稳定的中间体HSCH2NO2 (a). 中间体a经过C—N键断裂和H(1)—O(2)形成过程生成主要产物P1 (CH2S＋trans-HONO), 此过程需克服124.1 kJ•mol－1的能垒. 中间体a也可以经过C—N键断裂及C—O键形成转化为中间体HSCH2ONO (b), 此过程的能垒高达238.34 kJ•mol－1. b再经过一系列的重排异构转化得到产物P2 (CH2S＋cis-HONO), P3 (CH2S＋HNO2)和P4 (SCH2OH＋NO). 所有通道均为放热反应, 反应能分别为－150.37, －148.53, －114.42和－131.56 kJ•mol－1. 标题反应主通道R→a→TSa/P1→P1的表观活化能为－91.82 kJ•mol－1, 此通道在200～3000 K温度区间内表观反应速率常数三参数表达式为kCVT/SCT＝8.3×10－40T4.4 exp(12789.3/T) cm3•molecule－1•s－1.     

Dual-level direct dynamics studies for the reactions of OH radical with bromine-substituted ethanes

The dynamic properties of the multichannel hydrogen abstraction reactions of CH(3)CH(2)Br + OH --> products and CH(3)CHBr(2) + OH --> products are studied by dual-level direct dynamics method. For each reaction, three reaction channels, one for alpha-hydrogen abstraction and two for beta-hydrogen abstractions, have been identified. The minimum energy paths (MEPs) of both the reactions are calculated at the Becke's half-and-half (BH&H)-Lee-Yang-Parr (LYP)/6-311G(d, p) level and the energy profiles along the MEPs are further refined with interpolated single-point energies (ISPE) method at the G2M(RCC5)//BH&H-LYP level. There are complexes with energies less than those of the reactants or products located at the entrance or exit channels, which indicates that the reactions may proceed via an indirect mechanism. By canonical variational transition-state theory (CVT) the rate constants are calculated incorporating the small-curvature tunneling (SCT) correction in the temperature range of 220-2000 K. The agreement of the rate constants with available experimental values for two reactions is good in the measured temperature range. The calculated results show that alpha-hydrogen abstraction channel is the major reaction pathway in the lower temperature for two reactions, while the contribution of beta-hydrogen abstraction will increase with the increase in temperature.     

Fe原子活化乙烷的微观反应机理

本文采用密度泛函理论B3LYP方法在6-311 G(d,p)基组水平上研究了Fe原子催化乙烷反应的微观反应机理,优化了反应过程中各反应物、中间体、过渡态和产物的构型,并在同一水平上计算了反应中各驻点的振动频率,运用自然键轨道理论(NBO)方法分析了各物质的成键情况和轨道间相互作用。Fe原子对乙烷的活化过程可分为C-C键活化及C-H键活化,分别释放出CH4和H2。