CH2F自由基与HNCO反应机理的理论研究

采用密度泛函理论的B3LYP方法,在6-311 G(d,p)基组水平上研究了CH2F自由基与HNCO的微观反应机理,优化了反应过程中的反应物、中间体、过渡态和产物的几何构型,通过振动分析验证了所有可能的过渡态;并且还在QCISD(T)/6- 311 G**//B3LYP/6-311 G(d,p)机组水平上计算了相应单点能．找到了CH2F自由基与HNCO反应的7条可行的反应通道,对结果的分析表明,CH2F HNCO→TS8→IM5→TS9→IM4通道的控制步骤活化能最低,是该反应的主要通道．     

吡喃木糖热裂解机理的密度泛函理论研究

采用密度泛函理论理论方法 M062X/6-311++G(d,p),对吡喃木糖的热解反应机理进行了理论计算分析.针对吡喃木糖热解可能发生的化学反应共设计了九条可能的热解路径,并对各路径中的反应物、中间体和过渡态的几何结构进行了能量梯度全优化,并在梯度全优化的基础上计算了各热解反应路径的热力学和动力学参数.文中以两大类方式来设计反应路径:1)木糖首先经过过渡态TS1发生开环反应生成链状中间体2,该步的反应能垒为188.7 kJ/mol,对于中间体2共设计了五种可能的热解反应路径;2)考虑双键同时断裂的情况,木糖先发生脱水反应,接着按C-C和C-O键同时断裂的情况发生开环反应,针于这种情况共设计了四条可能的热解路径.计算结果表明,吡喃木糖热解的主要反应产物有乙醇、乙醛、糠醛、丙酮、酸类、CO_2和CO等小分子化合物.     

吡喃木糖热裂解机理的密度泛函理论研究

采用密度泛函理论理论方法M062X/6-311++G(d,p)，对吡喃木糖的热解反应机理进行了理论计算分析。针对吡喃木糖热解可能发生的化学反应共设计了九条可能的热解路径，并对各路径中的反应物、中间体和过渡态的几何结构进行了能量梯度全优化，并在梯度全优化的基础上计算了各热解反应路径的热力学和动力学参数。文中以两大类方式来设计反应路径：1）木糖首先经过过渡态TS1发生开环反应生成链状中间体2，该步的反应能垒为188.7 kJ/mol，对于中间体2共设计了五种可能的热解反应路径；2）考虑双键同时断裂的情况，木糖先发生脱水反应，接着按C-C和C-O键同时断裂的情况发生开环反应，针于这种情况共设计了四条可能的热解路径。计算结果表明，吡喃木糖热解的主要反应产物有乙醇、乙醛、糠醛、丙酮、酸类、CO2和CO等小分子化合物。     

氟原子与反式1,3-丁二烯分子反应动力学的理论研究

在CCSD(T)／6-311g(d,p)／B3LYP／6-311g(d,p)的基础上对F原子与反式的1,3-丁二烯的反应体系进行了理论研究．计算中发现,这个反应体系有两个形成中间复合物的通道．同时,理论计算结果表明,在交叉分子束的实验中探测到的H原子是通过这两个形成长寿命的中间复合物的通道产生的．而通过同一个复合物通道,生成C2H3 C2H3F的速率要比生成氢原子的低,在交叉分子束实验中要探测到C2H3 C2H3F通道也是很困难的．理论分析的结果还表明, HF也可能是反应中的一个产物,它主要是通过直接抽取反应产生的．     

CH3CH2+N(4S)反应机理的理论研究

利用abinitio方法对CH3CH2+N(4S)反应进行了理论研究,在MP2/6-311+G(d,p)水平上优化得到了反应途径上的反应物、中间体、过渡态和产物的几何构型和谐振频率,并在QCISD(T)/6-311+G(d,p)水平上进行单点能计算.计算结果表明,CH2CH2+3NH和H2CN+CH3是此反应主要产物,CH3CHN+H是此反应次要产物.产物CH2CH2+3NH主要来自直接氢抽提反应通道,H2CN+CH3来自加成-解离反应通道,CH3CHN+H来自加成-解离反应通道.     

Theoretical investigation of the oxidation pathways of the Cl-initiated reaction of 2-methyl-3-buten-2-ol

The mechanism and products of the reaction of 2-methyl-3-buten-2-ol (MBO232) with Cl atoms in the presence of O₂ have been elucidated by performing high-level quantum chemistry calculations. The geometries of the reactants, intermediates, transition states, and products are optimized at the MP2(full)/6-311G(d,?p) level, and their single-point energies are refined at the CCSD(T)/6-311?+?G(d,?p) level. The potential energy surface profiles have been constructed at the CCSD(T)/6-311?+?G(d,?p)//MP2(full)/6-311G(d,?p)?+?0.95?×?ZPE level of theory, and the possible channels involved in the reaction are also discussed. The calculations indicate that the reaction predominantly proceeds via the addition of Cl atoms to the double bond rather than the direct abstraction of the H atoms in MBO232. The nascent adducts (CH₃)₂C(OH)CHCH₂Cl (IM1) and (CH₃)₂C(OH)CHClCH₂ (IM2) do not undergo subsequent isomerization and dissociation reactions, but rather react with O₂. The theoretical results show that the major products are CH₂ClCHO and CH₃C(O)CH₃ for the reaction of MBO232?+?Cl in the presence of O₂, which is in good agreement with the experimental finding.     

聚对苯二甲酸丁二醇酯二聚体键离能的理论研究

采用密度泛函理论方法对聚对苯二甲酸丁二醇酯(PBT)二聚体的键离能进行了计算.为了选取较为精确的方法来计算PBT各个键的键离能,以与PBT具有相同的酯基官能团的乙酸乙酯为模型参照物.采用M062X, B3P86, M06, PBE0, wB97xD方法分别在基组6-31G(d), 6-311G(d), 6-311+G(d, p), 6-311++G(d, p), cc-pVDZ, cc-pVTZ水平下对乙酸乙酯的键离能进行计算.通过对比计算结果与iBonD数据库的乙酸乙酯实验测定值可知,M062X在基组6-311G(d)水平下计算结果与实验值最为接近.因此,本研究采用M062X方法在基组6-311G(d)水平下对聚对苯二甲酸丁二醇酯(PBT)二聚体的键离能进行计算.计算结果表明：在PBT的各键中C-C_arcmatic键的键离能最大,主链上的C-C键离能最小,为370.9 kJ/mol.其次就是C-O键,为404.6 kJ/mol.基于PBT键离能的计算结果,设计了3条PBT二聚体热降解过程可能形成的反应路径,分析了热解产物的形成机理.结果表明PBT二聚体热解过程可...     

Reaction of C2HCl2+O2: Combined TR-FTIR Spectroscopy and Electronic Structure

用时间分辨傅立叶变换红外发射光谱(TR-FTIR)和G3MP2//B3LYP/6-311G(d,p)水平的电子结构计算研究了环境化学中重要的二氯代乙烯自由基C₂HCl₂和O₂分子的基元反应通道和机理. 通过0.5 cm^-1高分辨的TR-FTIR发射光谱观察到三种振动激发态产物CO₂、CO和HCl,由光谱拟合得到CO和HCl的振动态分布,结合电子结构计算的反应势能曲线,提出反应机理和能量上最可能的反     

Isomers of OCS and their reaction with H2O on singlet potential energy surface

The isomers of the carbonyl sulfide (OCS) molecule are investigated in detail at CCSD(T)/cc-pVTZ//MP2/6-311++G(2d,2p) level of theory. One cyclic isomer was identified along with three different linear minima of the OCS molecule. Three interconversion transition states were also located between cyclic and linear forms of OCS. Among these four isomers, the singlet potential energy surface (PES) for the molecule–molecule reaction between the three most energetically favoured isomers of OCS and H₂O has been explored theoretically at the CCSD(T)/cc-pVTZ//MP2/6-311++G(2d,2p) level. This singlet PES comprises of three paths. Path 1 is the reaction of linear OCS molecule with water producing the major product P1 (CO₂?+?H₂S), minor product P2 (S?+?HCOOH) and two isomers via 14 minima and 15 transition states. The Path 2 is an isomerization process in which cyclic isomer of OCS reacts with water molecule via another initial barrierless aduct producing five isomers of the OCS–H₂O system through five interconversion transition states. The reaction of linear COS isomer with water is shown in Path 3. This path produces the radicals SH and COOH from another COS–H₂O complex via a transition state. Among these three products, the product P1 is energetically most favoured. The overall exothermicity of the product channels for the formation of major product P1 on PES is calculated to be about 10.60?kcal/mol possessing initial high entrance barriers of 45.48 and 55.47?kcal/mol in two possible pathways. As the process is favoured thermodynamically but not kinetically, the reaction is expected to be very slow.     

NH_3与CaH_2反应机理的密度泛函理论研究

基于密度泛函理论(DFT)当中的B3LYP(杂化密度泛函)方法,于6-311G(d,p)基组水平上对NH_3与CaH_2的反应机理进行了计算分析,对反应过程中的反应物、中间体、过渡态及产物进行了全几何参数优化,得到其构型和基本参数.对得到的中间体和过渡态进行频率分析和内禀反应坐标(IRC)计算,以证实中间体和过渡态的正确性和相互连接关系.使用QCISD方法在6-311G(d,p)基组水平对各驻点的单点能进行计算,给出能量信息.计算结果表明:CaH_2与NH_3主要以摩尔比为1:2进行反应,分两步氢取代过程,生成产物Ca(NH2)2和2H2.反应所释放的H2中两个H原子分别来源于CaH_2和NH_3,反应的关键是脱氢,主要在于克服N—H键断裂所需能量.相比较而言从NH_3中脱氢比从—NH2中脱氢较易.     

The mechanism of alkaline hydrolysis of amides: a comparative computational and experimental study of the hydrolysis of N‐methylacetamide,N‐methylbenzamide,and acetanilide

Theoretical computations and experimental kinetic measurements were applied in studying the mechanistic pathways for the alkaline hydrolysis of three secondary amides: N‐methylbenzamide, N‐methylacetamide, and acetanilide. Electronic structure methods at the HF/6‐31+G(d,p) and B3LYP/6‐31+G(d,p) levels of theory are employed. The energies of the stationary points along the reaction coordinate were further refined via single point computations at the MP2/6‐31+G(d,p) and MP2/6‐311++G(2d,2p) levels of theory. The role of water in the reaction mechanisms is examined. The theoretical results show that in the cases of N‐methylbenzamide and N‐methylacetamide the process is catalyzed by an ancillary water molecule. The influence of water is further assessed by predicting its role as bulk solvent. The alkaline hydrolysis process in aqueous solution is characterized by two distinct free energy barriers: the formation of a tetrahedral adduct and its breaking to products. The results show that the rate‐determining stage of the process is associated with the second transition state. The entropy terms evaluated from theoretical computations referring to gas‐phase processes are significantly overestimated. The activation barriers for the alkaline hydrolysis of N‐methylbenzamide and acetanilide were experimentally determined. Quite satisfactory agreement between experimental values and computed activation enthalpies was obtained. Copyright © 2008 John Wiley & Sons, Ltd.     

CF4/Ar微波放电与CS2反应的可见化学发光研究

利用交叉分子束-化学发光研究方法,研究了气相条件下不同反应压力时CF4／Ar微波放电的产物与二硫化碳CS的交叉反应在可见区(300～900nm)的化学发光,利用密度泛函B3LYP和二阶微扰MP2理论分别在6-311 G(3df,2pd)和6-311 G(d,p)基组下计算了可能的反应产物电子基态的构型和振动频率,将得到的光谱标识为F2S2电子激发态的发射谱,通过对光谱和产物的分析,认为微波放电得到的亚稳态的Ar原子与CS发生碰撞反应使CS解离为S原子和CS,解离得到的S原子与微波放电产生的F原子发生多步反应得到了F2S2的激发态。     

自由基-分子反应:F+Propene(CH2CHCH3)的从头算研究

采用从头算CCSD(T)/6-311 G(2d,2p)//B3LYP/6-311G(d,p)方法,研究了自由基-分子反应F CH2CHCH3的各种不同的反应通道．该反应主要是通过复合物形成机制进行,即F分别加到碳碳双键的两端形成自由基复合物1和2．这两种亚稳态自由基会解离成三种产物:H C3H5F、CH3 C2H3F和HF C3H5．理论计算结果表明,生成CH3 C2H3F是反应的主要通道,而生成H C3H5F和HF C3H5对产物也有一定的贡献．这一结果和实验符合得很好．     

甲基乙烯醚和OH反应机理的理论研究

利用量子化学从头计算的方法对甲基乙烯醚的两个异构体之间的转化,羟基与顺式-甲基乙烯醚和反式-甲基乙烯醚的加成反应,以及羟基提取甲基上的氢原子的反应机理进行了研究.研究结果表明:顺式-甲基乙烯醚比反式-甲基乙烯醚更加稳定,在QCISD/6-31G(d,P)//BHandHLYP/6.311 G(d,P)理论水平下,OH加到顺式-甲基乙烯醚1号住的碳原子上需要跨越的能垒比其它反应通道需要跨越的能垒少7.5～34 KJ/mol,因此是主要的反应通道,而OH加在反式.甲基乙烯醚2号位的碳原子上所需要跨越的能垒比其它反应路径所需要跨越的能垒少8.3～26.7 kJ/mol,因此是主要的反应路径.利用经典过渡态理论计算了总的速率常数     

NH3与BeH2反应机理的密度泛函理论研究

金属-N-H体系储氢材料在放氢反应过程中往往伴随着NH_3的释放,且NH_3会对材料的储放氢性能产生重要影响.采用密度泛函理论当中的杂化密度泛函(B3LYP)方法,6-311G(d,p)基组水平上对NH_3与BeH_2的微观反应机理进行了理论计算分析,对得到的中间体和过渡态进行频率计算和内禀反应坐标(IRC)分析,以判断中间体和过渡态的正确性和相互连接关系.使用QCISD方法在6-311G(d,p)基组水平对各驻点的单点能进行计算,给出能量信息.计算结果表明:BeH_2与NH_3主要以摩尔比为1:2进行反应,分两步氢取代过程,生成产物Be(NH_2)_2和2H_2.反应所释放的H_2中两个H原子分别来源于BeH_2和NH_3,反应的关键是脱氢,主要在于克服N—H键断裂所需能量.相比较而言从NH_3中脱氢比从—NH_2中脱氢较易.     

Fe(5D/3D)+CH2(1A1)→FeC+H2的理论研究

采用密度泛函理论(DFT)中的UB3LYP方法在6-311 G(2d,2p)水平上研究了五重态和三重态的Fe与单重态CH2反应的机理,在UB3LYP结构优化的基础上用耦合簇理论方法UCCSD(T)在相同水平下对各驻点进行了单点能校正.结果表明,该反应在三重态和五重态上的势能面非常相似,都经过两个过渡态(TS1、TS2)和三个中间体(FeCH2、HFeCH、H2FeC),五重态和三重态势能面在形成中间体FeCH2前发生交叉,整个反应沿三重态路径进行,最后得到三重态的FeC和H2.该反应是一个四步反应,其中由HFeCH到H2FeC的反应步骤为整个反应的速率控制步骤,反应的活化能为176.3 kJ/mol.     

FC(O)O自由基与NO反应机理的理论研究

用密度泛函理论(DFT)的B3LYP方法,在6-311G(d,p)基组水平上研究了FC(O)O自由基与NO反应的微观机理,全参数优化了反应过程中各反应物、中间体、过渡态和产物的几何构型,在CCSD(T)水平上计算了它们的能量,振动分析结果证实了中间体和过渡态的真实性,从对FC(O)O与NO的反应机理的研究结果看,FC(O)O与NO反应为4条反应通道多步反应过程,其反应的主要通道是FC(O)O+NO→M3→TS6→M5→FNO+CO₂,其主要产物是自由基FNO和CO_{2关键词： 密度泛函理论 反应机理 反应通道}     

硝酸溴与三重态氧原子反应机理的密度泛函研究

用密度泛函理论方法 (B3LYP) ,在 6 311+G(d ,p)水平上对硝酸溴与三重态氧原子的反应进行了研究 ,计算了反应中各驻点物种的平衡构型、振动频率、总能量和零点能 (ZPE) .对计算得到各可能反应途径的过渡态经内禀反应坐标分析加以了证实 ,对反应途径中的键长和能量的变化作了IRC解析 .在B3LYP优化的基础上利用了耦合簇理论方法 (CCSD(T) )在 6 311+G(d ,p)水平上对各驻点物种的单点能进行了修正 .研究表明 ,存在三种可能的反应途径 ,其产物分别为 :cis BrONO和 3 O2 、trans BrONO和 3 O2 以及BrOO和NO2 .其中第三个通道由于活化能垒较低 ,是主要反应 .     

Reaction mechanism and rate constants of the CH+CH4 reaction: a theoretical study

Ab initio and density functional calculations have been performed to elucidate the mechanism of CH radical insertion into methane. The results show that the reaction can be viewed to occur via two stages. On the first stage, the CH radical approaches methane without large structural changes to acquire proper positioning for the subsequent stage, where H-migration occurs from CH₄ to CH, along with a C–C bond formation. Where the first stage ends and the second begins, a tight transition state was located using the B3LYP/6-311G(d,p) and MP4(SDQ)/6-311++G(d,p) methods. Using a rigid rotor – harmonic oscillator approach within transition state theory, we show that at the MP5/6-311++G(d,p)//MP4(SDQ)/6-311++G(d,p) level the calculated rate constants are in a reasonably good agreement with experiment in a broad temperature range of 145–581 K. Even at low temperatures, the insertion reaction bottleneck is found about the location of the tight transition state, rather than at long separations between the CH and CH₄ reactants. In addition, high level CCSD(T)-F12/CBS calculations of the remainder of the C₂H₅ potential energy surface predict the CH+CH₄ reaction to proceed via the initial insertion step to the ethyl radical which then can emit a hydrogen atom to form highly exothermic C₂H₄+H products.     

Theoretical study of the photo-isomerisation reactions of 1,2-dihydro-1,2-phosphaborine and 1,2-dihydro-1,2-alumazaine

The mechanisms of the photochemical isomerisation reactions are investigated theoretically using the model systems, 1,2-dihydro-1,2-phosphaborine (5) and 1,2-dihydro-1,2-alumazaine (6), using the CAS(6,6)/6-311G(d,p) and MP2-CAS-(6,6)/6-311++G(3df,3pd)//CAS(6,6)/6-311G(d,p) methods. For each model reactant, three reaction pathways, which lead to three kinds of photo-isomers, are examined. The structures of the conical intersections, which play a key role in such photo-rearrangements, are determined. The thermal (or dark) reactions of the reactant species are also examined, using the same level of theory, to provide a qualitative explanation of the reaction pathways. These model investigations demonstrate that the preferred reaction route for these two aromatic heterocyclics is as follows: reactant → Franck–Condon region → conical intersection → photoproduct. The theoretical evidences anticipate that after irradiation of 5, the photoproduct yield of the Dewar BP-isomer, 8, should be larger than that of the Dewar BP-isomer, 7, whereas no Dewar BP-isomer 9 can be observed. Moreover, the present theoretical data predict after irradiation of 6, all three Dewar AlN-isomers (10, 11, and 12) and the starting molecule, 6, are produced.