甲基重氮烷阳离子(CH_3N_2~ )与DNA碱基的甲基化反应

在B3LYP/6-31G**和MP2/6-311G**水平上,计算了终致癌物甲基重氮烷阳离子(CH3N2 )在气相和水溶剂中与四种DNA碱基上10个亲核位发生甲基化过程的反应机理.结果表明:在气相和溶剂中,终致癌物CH3N2 对碱基上相应亲核位的甲基化反应过程,活化能都比较小(<33.5kJ/mol),是容易进行的放热反应.所以,二甲基亚硝胺一旦形成终致癌物,则很容易与碱基形成癌变物.     

己烷催化异构化反应中氢溢流机理的理论研究

采用密度泛函理论(DFT)在B3LYP/6-311++ G**//B3LYP/6-311G*水平下, 对正己烷(C6H14)催化异构化反应中的氢溢流机理进行了理论探讨. 通过对振动模式分析和内禀反应坐标(IRC)计算确认了各可能反应的过渡态. 同时在MP2/6-311++G**水平上对各驻点做了单点能计算和零点能校正, 计算出各反应通道的活化能, 进而确定了该反应的主反应通道, 其活化能为42.52 kJ/mol.     

3-甲基环状乙撑磷酸二酯醇解的反应途径的理论研究

采用密度泛函理论和MP2方法研究了3-甲基环状乙撑磷酸二酯(MEP)与甲醇的反应途径:(Ⅰ)CH3O-+MEP;(Ⅱ)CH3OH+MEP;(Ⅲ)CH3O-+HMEP(MEP的质子化形式);(Ⅳ)CH3OH+HMEP.在B3LYP/6-31++G(d,p)水平上优化了四条反应途径的反应物、中间体、过渡态及产物的几何构型,并在同水平上进行了自然电荷分析,然后在MP2/6-311++G(3df,2p)水平上计算了各驻点的单点能.采用极化连续介质模型(PCM)研究了各途径在苯、甲醇和水溶液中的溶剂化效应.计算结果表明,溶剂效应使途径(Ⅰ)的自由能垒降低,而使途径(Ⅱ)和(Ⅳ)的决速步骤的自由能垒升高.在气相和苯溶剂中途径(Ⅳ)是反应的优势途径,在甲醇和水溶剂中途径(Ⅰ)则成为最优.研究结果进一步表明实验条件下途径(Ⅱ)与(Ⅳ)对总醇解反应的贡献相当.     

锗烯与异硫氰酸反应机理的量子化学研究

采用密度泛函理论B3LYP方法研究了GeH2自由基与HNCS的反应机理,并在B3LYP/6-311++G**水平上对反应物,中间体,过渡态进行了全几何参数优化,通过频率分析和IRC确定中间体和过渡态。为了得到更精确的能量值,用QCISD(T)/6-311++G**方法计算了各个驻点的单点能,计算结果表明单重态的锗烯与异硫氰酸的反应有抽提硫、插入N-H键、抽提亚氨基的路径,而经由三元环中间体的抽提硫反应GeH2+HNCS→IM3→TS2→IM4→TS3→IM5→GeH2S+HNC(P1),反应能垒最低,为主反应通道,甲锗硫醛和异氰氢酸为主产物。锗烯经由四元环中间体抽提硫的反应为竞争反应通道。     

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.     

6-烷基鸟嘌呤与DNA碱基间氢键作用的理论研究

用密度泛函B3LYP方法在6-311＋G**基组水平上对鸟嘌呤及顺(cis-)、反式(anti-)-6-烷基鸟嘌呤(O⁶-AlkylG)与DNA碱基(胸腺嘧啶T、胞嘧啶C、腺嘌呤A、鸟嘌呤G)的氢键二聚体结构进行了优化. 在MP2/cc-pVXZ(X＝D,T)// B3LYP/6-311＋G**水平上, 采用完全基组外推方法校正了氢键二聚体的相互作用能, 并用完全均衡校正法(CP)校正了基组重叠误差(BSSE). 在B3LYP/6-311＋G**水平上计算了各氢键碱基对的全电子波函数, 并用分子中的原子理论(AIM)分析了碱基间的弱相互作用. 计算结果显示, 鸟嘌呤6-O烷基化改变了碱基间的氢键作用模式, 使碱基对发生了明显的螺旋桨式扭转和不同程度的位移, 碱基间的电子密度分布和氢键作用能明显减小. O⁶-AlkylG对DNA碱基间的氢键作用是去稳定化的, 去稳定化影响的顺序为GC＞GG＞GA≈GT. 计算结果与文献给出的实验结论基本一致.     

去氢抗坏血酸分子振动光谱的理论研究

采用RHF, MP2, DFT(B3LYP)方法, 以6-311++G**为基组研究了去氢抗坏血酸分子(DHA)的平衡几何构型和振动光谱. 计算结果表明, 采用RHF, B3LYP以及MP2 方法优化得到的几何结构以及频率值是一致的. 采用B3LYP/6-311++G**计算了DHA分子平衡构型下的谐振动力场﹑振动频率和振动强度. 使用Wilson的GF矩阵方法对DHA分子进行了简正坐标分析, 依据所得的势能分布对DHA分子的振动基频进行了合理的理论归属.     

CH3CHF自由基与HNCO反应机理的理论

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CH3CHF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, 在QCISD(T)/6- 311++G(d, p)水平上计算体系在反应通道各驻点的能量. 振动分析结果和IRC分析结果证实了中间体和过渡态的真实性, 计算所得的成键临界点电荷密度变化也确认了该反应过程, 并找到了七条反应通道. 其中生成氟代烷基酰亚胺稳定分子的通道活化能垒最低, 在该反应体系中是与氢迁移平行竞争较易发生的一条反应通道.     

L-缬氨酸旋光异构的两种光反应可能途径

利用密度泛函理论(DFT)和从头算分子轨道理论对L-缬氨酸的旋光异构光反应机理进行了研究. 分别用B3LYP和MP2方法在6-311++G(d, p)基组级别上全优化得到了S₀和T₁态反应路径上的反应物、产物、中间体以及过渡态结构的几何构型, 给出了反应能垒, 利用含时密度泛函理论(TD-DFT)中的B3LYP/6-311++G(d, p)方法优化得到了S₁态反应路径上的平衡态几何构型. 通过分析反应途径上各个驻点的几何构型特征, 确定了L-缬氨酸在激发态可能通过手性碳上的氢原子以羰基氧或氨基氮为中转媒介发生质子迁移来完成旋光异构反应. 进一步用自洽反应场理论中的极化连续模型(PCM)方法探讨了溶剂化效应对旋光异构反应机理的影响.     

D-苯丙氨酸与Cu＋(1S0, 3d10)气相反应理论研究

用量子化学密度泛函(DFT)方法研究D-苯丙氨酸与一价基态金属阳离子Cu^＋在气相中反应的机理. 在B3LYP/6-31G*水平上, 优化了反应包含的4个反应通道的反应物、中间体、过渡态和产物的几何构型, 并采用B3LYP/DZVP, B3LYP/[6-311＋G**(C,H,O)＋Lanl2dz(Cu)], B3LYP/6-311＋G**, MP2/6-311＋G** 等方法对各驻点进行了单点能计算. 通过对计算结果的分析, 获得了其单重态反应势能面的一般轮廓、各驻点几何构型优化参数, 明确了其反应机理.     

An ab initio study of intermolecular interactions of nitromethane dimer and nitromethane trimer

Different geometries of nitromethane dimer and nitromethane trimer have been fully optimized employing the density functional theory B3LYP method and the 6-31++G** basis set. Three-body interaction energy has been obtained with the ab initio supermolecular approach at the levels of MP2/6-31++G**//B3LYP/6-31++G** and MP2/aug-cc-pVDZ//B3LYP/6-31++G**. The internal rotation of methyl group induced by intermolecular interaction has been observed theoretically. For the optimized structures of nitromethane dimer, the strength of C--H...O--N H-bond ranges from -9.0 to -12.4 kJ mol(-1) at the MP2/aug-cc-pVDZ//B3LYP/6-31++G** level, and the B3LYP method underestimates the interaction strength compared with the MP2 method, while MP2/6-31++G**//B3LYP/6-31++G** calculated DeltaE(C) is within 2.5 kJ mol(-1) of the corresponding value at the MP4(SDTQ)/6-31G**//B3LYP/6-31++G** level. The analytic atom-atom intermolecular potential has been successfully regressed by using the MP2/6-31++G**//B3LYP/6-31++G** calculated interaction energies of nitromethane dimer. For the optimized structures of nitromethane trimer the three-body interaction energies occupy small percentage of corresponding total binding energies, but become important for the compressed nitromethane explosive. In addition, it has been discovered that the three-body interaction energy in the cyclic nitromethane trimer is more and more negative as intermolecular distances decrease from 2.2 to 1.7 A.     

Interaction of anions with perfluoro aromatic compounds

The complexes formed by a variety of anions with perfluoro derivatives of benzene, naphthalene, pyridine, thiophene, and furan have been calculated using DFT (B3LYP/6-31++G**) and MP2 (MP2/6-31++G** and MP2/6-311++G**) ab initio methods. The minimum structures show the anion interacting with the pi-cloud of the aromatic compounds. The interaction energies obtained range between -8 and -19 kcal mol(-1). The results obtained at the MP2/6-31++G** and MP2/6-311++G** levels are similar. However, the B3LYP/6-31++G** results provide longer interaction distances and smaller interaction energies than do the MP2 results. The interaction energies have been partitioned using an electrostatic, polarization, and van der Waals scheme. The AIM analysis of the electron density shows a variety of topologies depending on the aromatic system considered.     

Structure of the boronic acid dimer and the relative stabilities of its conformers

Despite the widespread use of boronic acids in materials science and as pharmaceutical agents, many aspects of their structure and reactivity are not well understood. In this research the boronic acid dimer, [HB(OH)(2)](2), was studied by second-order M?ller-Plesset (MP2) perturbation theory and coupled cluster methodology with single and double excitations (CCSD). Pople split-valence 6-31+G*, 6-311G**, and 6-311++G** and Dunning-Woon correlation-consistent cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis sets were employed for the calculations. A doubly hydrogen-bonded conformer (1) of the dimer was consistently found to be lowest in energy; the structure of 1 was planar (C(2h)) at most computational levels employed but was significantly nonplanar (C(2)) at the MP2/6-311++G** and CCSD/6-311++G** levels, the result of an intrinsic problem with Pople-type sp-diffuse basis functions on heavy atoms. The dimerization energy, enthalpy, and free energy for the formation of (1) from the exo-endo conformer of the monomer were -10.8, -9.2, and +1.2 kcal/mol, respectively, at the MP2/aug-cc-pVTZ level. Several other hydrogen-bonded conformers of the dimer were local minima on the potential energy surface (PES) and ranged from 2 to 5 kcal/mol higher in energy than 1. Nine doubly OH-bridged conformers, in which the boron atoms were tetracoordinated, were also local minima on the PES, but they were all greater than 13 kcal/mol higher in energy than 1; doubly H-bridged structures proved to be transition states. MP2 and CCSD results were compared to those from the BLYP, B3LYP, OLYP, O3LYP, PBE1PBE, and TPSS functionals with the 6-311++G** and aug-cc-pVTZ basis sets; the PBE1PBE functional performed best relative to the MP2 and CCSD results. Self-consistent reaction field (SCRF) calculations predict that boronic acid dimerization is less favorable in solution than in vacuo.     

A quantum-chemical study of the LiH + LiH⋅− ⇄ LiH2− + Li⋅ reaction

Parts of the potential energy surface of the title process and related processes have been investigated at the SCF /6-31G **, SCF /6-31++G **, and MP 2/6-31++G ** levels. The investigated reaction is exothermic (?6.23 kcal/mol, MP 4/6-31++G **//MP 2/6–31++G** level, ZPE included): A linear intermediate radical anion, Li? H? Li? H??, is significantly stabilized with respect to LiH + LiH?? (?38.74 kcal/mol, the same level as above). The BSSE at MP 2/6–31++G **//MP 2/6–31++G ** amounts to 1.8 kcal/mol. The title process seems to be suitable for experimental study in molecular beams.     

An ab initio and density functional theory study of keto-enol equilibria of hydroxycyclopropenone in gas and aqueous solution phase

Keto-enol tautomerism in hydroxycyclopropenone (2-hydroxy-2-cyclopropen-1-one) has been studied using ab initio methods, the B3LYP functional of density functional theory, as well as complete basis set (CBS-QB3 and CBS-APNO) and G3 methods. Absolute and relative energies were calculated with each of the methods, whereas computations of geometries and harmonic frequencies for hydroxycyclopropenone and 1,2-cyclopropanedione were computed in the gas phase but were limited to HF, MP2 and CCSD levels of theory, and the B3LYP functional, in combination with the 6-31++G** basis set. Using the MP2/6-31++G** gas phase optimized structure, each species was then optimized fully in aqueous solution by employing the polarizable continuum model (PCM) self-consistent reaction field approach, in which HF, MP2 and B3LYP levels of theory were utilized, with the same 6-31++G** basis set. In both gas and aqueous solution phases, the keto form is higher in energy for all of the model chemistries considered. The presence of the solvent, however, is found to have very little effect on the bond lengths, angles and harmonic frequencies. From the B3LYP/6-31++G** Gibbs free energy, the keto-enol tautomeric equilibrium constant for 2-hydroxy-2-cyclopropen-1-one <==> 1,2-cyclopropanedione is computed to be K(T)(gas) = 2.35 x 10(-6), K(T)(aq) = 5.61 x 10(-14). It is concluded that the enol form is overwhelmingly predominant in both environments, with the effect of the solvent shifting the direction of equilibrium even more strongly in the favor of hydroxycyclopropenone. The almost exclusive nature of this species is attributed to stabilization resulting from aromaticity. Confirmation is provided by comparison of the simulated vibrational spectra of hydroxycyclopropenone with the measured infrared spectrum in an argon matrix.     

气相中O3与HSO自由基间的氢键复合物

气相中O3与HSO自由基之间的相互作用及其反应在大气化学中非常重要.在DFT-B3LYP/6-311++G**和MP2/6-311++G**水平上求得O3+HSO复合物势能面上的稳定构型,B3LYP方法得到了三种构型(复合物Ⅰ,Ⅱ和Ⅲ),而MP2方法只能得到一种构犁(复合物Ⅱ).在复合物Ⅰ和Ⅲ中,HSO单元中的1H原子作为质子供体.与O3分子中的端基O原子作为质子受体相互作用,形成红移氢键复合物;而在复合物Ⅱ中,虽与复合物Ⅰ和Ⅲ中具有相间的质子供体和质子受体,却形成了蓝移氢键复合物.B3LYP/6-311++G**水平上计算的单体间相互作用能的计算考虑了基组重甍误差(BSSE)和零点振动能(ZPVE)校正,其值在-3.37到-4.55 kJ·mol-1之间.采用自然键轨道理论(NBO)对单体间相互作用的本质进行了考查,并通过分子中原子理论(AIM)分析了三种复合物中氢键的电子密度拓扑性质.     

气相中O3与HSO自由基间的氢键复合物

气相中O3与HSO自由基之间的相互作用及其反应在大气化学中非常重要. 在DFT-B3LYP/6-311++G**和MP2/6-311++G**水平上求得O3+HSO复合物势能面上的稳定构型, B3LYP方法得到了三种构型(复合物I, II和III), 而MP2方法只能得到一种构型(复合物II). 在复合物I和III中, HSO单元中的1H原子作为质子供体, 与O3分子中的端基O原子作为质子受体相互作用, 形成红移氢键复合物; 而在复合物II中, 虽与复合物I和III中具有相同的质子供体和质子受体, 却形成了蓝移氢键复合物. B3LYP/6-311++G**水平上计算的单体间相互作用能的计算考虑了基组重叠误差(BSSE)和零点振动能(ZPVE)校正, 其值在-3.37到-4.55 kJ·mol-1之间. 采用自然键轨道理论(NBO)对单体间相互作用的本质进行了考查, 并通过分子中原子理论(AIM)分析了三种复合物中氢键的电子密度拓扑性质.     

2-溴丙酸气相热消除反应的机理

用密度泛函（DFT）方法,在B3LYP/6-31G**水平上对2-溴丙酸气相消除反应机理进行了研究.计算表明,反应主要是通过半极化五元环结构过渡态进行的,羧基上的氢原子协助溴原子离去,羧基氧原子帮助稳定过渡态.在B3LYP/6-311＋＋G(3df,3pd)水平上对B3LYP/6-31G**优化的几何构型进行了单点能计算,计算所得反应的速度控制步骤的活化能为189.461 kJ•mol－1,偏离实验值((180.3±3.4) kJ•mol－1)5.08％.     

FC(O)O自由基与NO2反应的量子化学研究

用量子化学DFT, MP2, G3和G3MP2方法对FC(O)O自由基与NO₂的反应机理进行了理论研究. 优化了反应势能面上各驻点的几何结构, 通过内禀反应坐标(IRC)计算和振动分析, 确认了反应中的过渡态, 并用过渡态理论(TST)计算了相关反应的速率常数.