α-氰基丙烯酸乙酯阴离子聚合的密度泛函理论研究

运用密度泛函理论DFT-B3LYP方法,在6-31G^*基组水平上,首次全优化计算了α-氰基丙烯酸乙酯与羟基反应势能面上的反应物、过渡态的分子几何、电子结构、能量、IR光谱和热力学性质,求得气相中反应的活化能为13.83 kJ·mol^-1,引发速率常数数量级为10¹⁰ s^-1,从热力学和动力学两方面阐明了阴离子聚合机理.通过自洽反应场(SCRF) B3LYP/6-31G^*计算,系统研究了相对介电常数分别为2.02, 2.38, 7.58和12.3的溶剂对反应物和过渡态的结构和反应机理的影响,发现溶剂效应使过渡态的活化能随极性增大而下降,并使引发反应在极性溶剂中接近于无垒反应.     

顺-8-三甲基锡烷基-6-辛烯醛分子内环化反应立体选择性的理论研究

用密度泛函方法在B3LYP/6-31G^*水平上研究了顺-8-三甲基锡烷基-6-辛烯醛分子内环化反应的机理,通过振动分析和内禀反应坐标对过渡态进行了确认,解析了三种反应途径.结果表明,反应具有很强的立体选择性,虽然-OSn(CH₃)₃和-C₂H₃基团均处于环的平伏位,是最稳定的产物构型,但是主要产物是经过活化能最低,且具有两个六元环椅式构象的过渡态形成的,主要产物中-OSn(CH₃)₃基团处于环的直立位.该结果与实验事实一致.     

过氧亚硝酸与苯酚的反应机理理论研究

采用量子化学密度泛函理论(DFT)研究了过氧亚硝酸分解产生的自由基(•OH和•NO2)与苯酚的反应机理. 在B3LYP/6-311++G(d, p)//B3LYP/6-311G(d, p)水平上对该反应体系的反应物、中间体、过渡态及产物进行了几何构型优化并计算了振动频率和能量. 计算结果表明, 过氧亚硝酸与苯酚的反应生成两种主要产物, 分别为邻羟基苯酚和对羟基苯酚, 这一结论与实验结果一致. 此外在同一计算水平上采用SCRF(PCM)方法计算了溶剂化效应, 结果表明, 极性溶剂可以降低各反应通道的活化能, 有利于反应的进行.     

白藜芦醇清理羟基自由基夺氢机理的量子化学研究

在DFT方法的B3LYP/6-31G水平下, 对反式白藜芦醇分子的所有可能构象进行了优化, 并对最稳定构象进行了自然键轨道分析. 键级数据表明, 白藜芦醇清理羟基自由基最活泼反应位点应为其单羟基环上的羟基, 对产物白藜芦醇自由基的优化结果表明, 单羟基环氧自由基的稳定性最高. 在B3LYP/6-31G水平下寻找白藜芦醇单羟基环羟基清理羟基自由基的过渡态, 频率分析结果表明只存在一个虚频. 对该过渡态结构进行内禀反应坐标反应路径解析(IRC), 结果表明, 过渡态沿反应坐标方向分别指向反应物络合物和产物络合物, 反应通道各个能量驻点显示反应物与反应物络合物的能量差为E1=173.5193 kJ/mol, 反应物络合物与过渡态、反应物络合物与产物的能量差分别为Ea=16.5143 kJ/mol, E2=51.8799 kJ/mol. 可见反应物的能量远高于过渡态及产物, 因此, 反应物络合物的形成应是整个反应的驱动力.     

醚溶液中烯烃硼氢化反应机理的理论模拟

在B₃LYP/6-31G^*水平上以二甲醚(Me₂O)模拟四氢呋喃(THF)对烯烃在THF溶液中硼氢化反应的机理进行了研究.计算结果发现,烯烃通过类似SN₂的交换过程从醚与BH₃构成的配合物获得BH₃结合成π配合物中间体,这一交换是整个硼氢化反应的决速步骤.     

2-磷酸甘油酸脱水反应机理的理论研究

采用密度泛函理论B3LYP方法研究了蛋白质和水环境下2-磷酸甘油酸脱水生成磷酸烯醇式丙酮酸的反应机理. 优化得到了反应物、过渡态及产物的几何构型并计算了反应势垒. 研究结果表明: 没有H₂O参与时, 反应需要通过四元环过渡态完成, 反应势垒高达287.7 kJ/mol, 常温下难以进行|有H₂O参与时, 反应可以通过六元环过渡态完成, 反应势垒大为降低|Mg^2＋的参与可使反应势垒进一步降低|蛋白质环境下两个Mg^2＋和一个H₂O的共同作用可使反应势垒降低至91.2 kJ/mol, 从而使反应在常温下容易进行.     

C2H与HO2双自由基反应的密度泛函理论研究

应用量子化学从头算和密度泛函理论(DFT)对C₂H与HO₂双自由基的单重态反应进行了研究.在UB3LYP/6-311G水平上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CCSD(T)/6-311G^{**水平上计算了各物种的单点能,并对总能量进行了零点能校正.研究结果表明,反应物中自由基C₂H的边端C进攻自由基HO₂的边端O是主要的进攻方式.首先形成了中间体1(HCCOOH),由此经过不同的反应通道可以得到主要产物P1,次要产物P2,P3和P5.生成P1的反应热为-814.40kJ/mol.自由基C₂H的中间C进攻自由基HO₂的边端O是次要的进攻方式,可以得到产物P4和P6.根据势能面分析,所有反应均是放热反应.}     

ClONO2与H的反应机理

在密度泛函理论B3LYP/6-31G^*基组下,研究ClONO₂+H→HONO₂+Cl和ClONO₂+H→OH+ClONO(cis)及ClONO₂+H→OH+ClONO(trans)的反应机理.计算得到各可能反应途径的过渡态,并经过内禀反应坐标(IRC)分析加以证实.三个反应的活化能垒(分别为19.5,20.0和23.2kJ·mol^-1)相差不大,可认为同时发生.但第一个反应放出的热量较多,可以看成是反应的主通道.     

鸟嘌呤受羟基自由基损伤反应机理的量子化学研究

用密度泛函理论(DFT)研究羟基自由基与鸟嘌呤分子加成反应的过渡态, 并进行内禀反应坐标(IRC)反应路径解析, 结果表明, 羟基自由基加成到鸟嘌呤碳碳双键上. 利用B3LYP/6-31++G**对反应物、反应物络合物、过渡态以及产物络合物等反应通道上各个能量驻点的能量进行了计算, 得到反应活化能E_a=28.0867 kJ/mol. AIM计算结果显示, 过渡态结构中鸟嘌呤分子碳碳双键结构被削弱, 羟基自由基氧原子与鸟嘌呤分子碳碳双键中的C4原子具有较强的相互作用, 双键中剩余的π电子离域到了环体系中.     

DFT法研究3-羟基丙烯醛的双键旋转异构反应机理

利用密度泛函理论(DFT)分别在B3LYP/6-31G**和B3LYP/6-311＋＋G**的计算水平上优化了基态3-羟基丙烯醛分子在双键旋转异构反应过程中的平衡态以及过渡态的几何构型，分析了反应过程中键参数的变化，计算了该反应的内禀反应坐标(IRC)，发现在重排反应途径上存在一个四元环骨架的中间体.通过振动分析对平衡态和过渡态进行了确认，并得到了零点能.计算结果表明，基态3-羟基丙烯醛分子的双键旋转异构反应经过两步完成，第一步反应位垒稍高，第二步反应位垒较低，存在着发生重排反应的可能性.     

二氯亚甲基锗烯与乙烯环加成反应机理的理论研究

The mechanism of a cycloaddition reaction between singlet dichloromethylene germylene and ethylene has been investigated with B3LYP/6-31G＊ method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Energies for the involved conformations were calculated by CCSD（T）//B3LYP/6-31G＊ method. On the basis of the surface energy profile obtained with CCSD（T）// B3LYP/6-31G＊ method for the cycloaddition reaction between singlet dichloromethylene germylene and ethylene, it can be predicted that the dominant reaction pathway is that an intermediate INT1 is firstly formed between the two reactants through a barrier-free exothermic reaction of 61.7 kJ/mol, and the intermediate INT1 then isomerizes to an active four-membered ring product P2.1 via a transition state TS2, an intermediate INT2 and a transition state TS2.1, in which energy barriers are 57.7 and 42.2 kJ/mol, respectively.     

Isomerization study of C5H5NO molecules

The complex potential energy surface (PES) for the isomerization of C₅H₅NO species, including 18 isomers and 23 interconversion transition states, is probed theoretically at the B3LYP/6‐311++G(d,p) and MP2//B3LYP/6‐311++G(d,p) levels of theory. The geometries and relative energies for various stationary points were determined. The zero‐point vibrational energy (ZPVE) corrections have been made to calculate the reliable energy. We predicted a six‐membered ring structure as a global minima isomer I, which is 118.49 and 131.48 kcal · mol^?1 more stable than the least stable, four‐ and three‐membered ring isomer VIII at B3LYP and MP2//B3LYP levels of theory, respectively. The isomers and interconversion transition states have verified by frequency calculation. The intrinsic reaction coordinates (IRC) calculations have been performed to confirm that each transition state is linked by the desired reactants and products. The isomer stability has been studied using relative energies, chemical hardness, and chemical potential. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Relevance of backbiting and beta-scission reactions in the free radical polymerization of Acrylonitrile

Summary: In this work, backbiting and beta-scission reactions are investigated through Quantum Chemistry methods by adopting the Becke 3 parameters and Lee Yang Parr functional (B3LYP) and 6-31G(d,p) basis set. Namely, the 1:3, 1:5 and 1:7 backbiting reactions are studied for acrylonitrile polymerization. It was found that the backbiting 1:5 is the most favorited because this kinetic event leads to the formation of a 6 membered transition state, while the backbiting 1:3 requires high activation energy due to the formation of a highly strained 4 membered ring. 7:3 backbiting reaction was also examined, since it is an alternative pathway that can explain the formation of defects generated by radicals in the third position. Simulations showed that this kinetic step is characterized by high rate constant because of its low activation energy. The right and left beta-scission reactions from the mid chain radicals formed by the considered backbiting reactions are also studied. Computational analysis demonstrated that all beta-scission reactions are endothermic and both the right and left beta-scission reactions have the same activation energy, which seems to be more influenced by the position of the mid chain radical.     

CH2FCF3与O(1D)反应机理的理论研究

用量子化学密度泛函理论(DFT)和G3(MP2)B3方法，对O(1↑D)与CH2FCF3的反应进行了研究．在UB3LYP/6-31G(d)计算水平上，优化了反应势能面上各驻点的几何结构，在G3(MP2)B3水平上进行了单点计算，并利用UB3LYP/6-311 G(3df，3pd)计算的波函数进行了电荷密度分析．通过内禀坐标(IRC)计算和振动分析，对反应过渡态进行了确认，并确定了反应机理．     

尿酸质子转移反应的理论研究I——分子内质子转移研究

使用量子化学中的Hartree-Fock方法和密度泛函理论中的B3LYP方法，分别在3－21G^*和6－31G（d)水平上，计算了尿酸分子从三羰基异构体向三羟基异构体的转化。结果表明，转化过程经历了单羟基和双羟基异构体2种中间物和3种过渡态时的分子内质子转移（IPT），转移中的H原邻近的N，O和C原子形成了具有四元环结构的过渡态。随着IPT的进行，N－H键逐渐被削弱和断裂，O－H键则逐渐生成。3个反应的活化能分别为190.3kJ/mol,181.4kJ/mol和249.9kJ/mol(B3LYP/6-31G(d))。较高的活化能表明在室温下，无催化剂的IPT难以进行。     

亚烷基卡宾与丙烯环加成反应机理的理论研究

用二阶微扰理论研究了单重态亚烷基卡宾与丙烯环加成反应的机理，采用 MP2/6-31G~*方法计算了势能面上各驻点的构型参数、振动频率和能量。根据所得 势能面上的能量数据可以预言，反应（1）的a途径和反应（2）的b途径将是单重态 亚烷基卡宾与丙烯环加成反应的两条相互竞争的主反应通道，两反应途径均由两步 组成，(I)两反应物分别生成了富能中间体INT1a和INT2b，它们均是无势垒的放热 反应，放出的能量分别为60.28和26.33kJ·mol~(-1).(II)中间体INT1a和INT2b分 别通过过渡态TS1a和TS2b异构化为三元环产物P1和四元环产物P2，其势垒分别为 16.43和12.73kJ·mol~(-1)。     

Quantum chemical investigation of low-temperature intramolecular hydrogen transfer reactions of hydrocarbons

The B3LYP functional was evaluated as a method to calculate reaction barriers and structure-reactivity relationships for intramolecular hydrogen transfer reactions involving peroxy radicals. Nine different basis sets as well as five other MO/DFT and hybrid methods were used in comparing three reactions to available experimental data. It was shown that B3LYP/6-311+G(d,p) offers a good compromise between speed and accuracy for studies in which thermodynamic and kinetic data of many reactions are required. Sixteen reactions were studied to develop structure-reactivity relationships to correlate the activation energy with the heat of reaction. As long as no structural heterogeneities were present in the transition state ring, a simple Evans-Polanyí relationship was shown to capture the activation energy as a function of heat of reaction for reactions in the 1,5-hydrogen shift family. For peroxy radicals undergoing self-abstraction of a hydrogen atom in the 1,5-position, the activation energy was calculated as E(a) (kcal mol(-1)) = 6.3 + Delta H(rxn) (kcal mol(-1)). For reactions with a carbonyl group embedded in the ring of the transition state, the activation energy of peroxy radicals undergoing self-abstraction was correlated as E(a) (kcal mol(-1)) = 18.1 + 0.74 Delta H(rxn) (kcal mol(-1)). The impact of the size of the transition state ring on the activation energy and pre-exponential factor was also probed, and it was shown that these effects can be described using simple nonlinear and linear fits, respectively.     

On the origin of cis selectivity in the cyclization of N-protected 2-substituted 3-aza-5-hexenyl radicals: a density functional study

Cyclization of the N-dimethylphosphinoyl-2-methyl-3-aza-5-hexenyl radical has been studied at the UB3LYP/6-31+G(d)//UB3LYP/6-31G(d) hybrid density functional level. The corresponding radical precursor has been synthesized and found to give cis/trans ratios of up to 10/1 in reductive radical cyclizations. The relative energies of reactant and transition state conformers were determined. In discord with the Beckwith-Houk model, it has been found that chair-axial transition states, which lead to cis products, are lowest in energy, rationalizing the observed experimental diastereoselectivity.     

气相中Y＋, Zr＋, Nb＋与CO2反应的理论研究

以Y^＋, Zr^＋, Nb^＋与CO₂反应作为第二前过渡金属离子与CO₂反应的范例体系. 采用密度泛函UB3LYP方法, 对于Y, Zr, Nb采用Stuttgart赝势基组, 对于CO₂采用6-311＋G(2d)基组, 计算研究了三种金属离子在基态和激发态时与CO₂气相反应的机理. 结果表明三种金属离子与CO₂反应以高自旋进入反应通道, 在反应过程中发生系间窜越, 以低自旋中间体和最终产物离开反应通道. 用内禀坐标单点垂直激发计算的方法找到了势能面交叉点, 并作了相应的讨论. 因为有金属离子的参与, 使单分子CO₂的强吸热分解反应变为生成CO和MO^＋的放热过程.