亚硝基苯与甲醛的反应机理和溶剂效应的理论研究

采用密度泛函理论方法RB3LYP/6-311＋＋G(d,p)研究了亚硝基苯与甲醛在单重态势能面上分别在气相和溶剂中的反应机理. 找到两条反应通道: 协同机理和分步机理, 均生成实验产物N-苯基氧肟酸C6H5NOHCHO. 计算结果表明: 亚硝基苯与甲醛在气相中分步机理为主要通道. 采用导电极化连续介质模型研究了反应体系在水、乙醇、乙腈、二氯甲烷、四氢呋喃、环己烷溶液中反应的溶剂化效应, 这些溶剂可降低反应的活化能, 但反应对溶剂的极性不敏感. 无论在气相还是溶剂中, 亚硝基苯与甲醛的分步机理为优势通道.     

甲酸苯酯氨解反应的机理和溶剂效应的理论研究

采用密度泛函理论方法B3LYP/6-31G(d,p)研究了甲酸苯酯与氨在气相中的反应机理. 考虑了两条可能的反应途径: 中性协同的和中性分步的机理. 采用自洽反应场极化连续模型(CPCM模型)研究了反应体系在水、乙醇和乙腈溶液中反应的溶剂化效应. 计算结果表明气相和溶液中协同机理均是最优途径. 水、乙醇和乙腈溶剂可降低协同途径的活化能, 溶剂化效应的大小对溶剂的极性不敏感.     

溶剂化效应对6-亚甲基环戊二烯酮与HCN的反应机理影响的理论研究

在B3LYP/6-311+G**计算水平上, 采用导体极化连续模型研究了溶剂化效应对6-亚甲基环戊二烯酮与HCN反应生成主要产物b类酸的反应机理的影响. 计算结果表明, 在溶剂中的反应机理与在气相中的反应机理一致. 溶剂化效应使反应路径中各驻点的自由能降低, 稳定化了各物质. 溶液中的活化自由能与气相相比也有所降低, 反应更容易发生, 其中CC进攻方式的活化自由能降低得更多.     

水溶液中亚硝基甲烷与甲醛肟之间互变异构反应的理论研究

采用超分子-连续介质(PCM)模型,在密度泛函B3LYP/6-311++G^**水平上对水溶液中亚硝基甲烷异构化反应的机理进行了理论研究.结果表明,在水溶液中亚硝基甲烷可以通过两条反应途径(Ⅰ和Ⅱ)经质子迁移得到更稳定的重排产物--反式甲醛肟,但优势反应途径与在气相反应不同.在水溶液中亚硝基甲烷异构化反应最有可能的途径Ⅰ是通过氢迁移先生成顺式甲醛肟,然后绕N-O键旋转生成更稳定的反式甲醛肟.并且由于水分子的催化作用使得反应活化能从气相中240.6和196.2 kJ/mol分别降低至水溶液中的61.7和92.1 kJ/mol.     

钐(II)类卡宾CH_3SmCH_2I与乙烯环丙烷化反应及溶剂化效应(THF)对反应途径影响的理论研究

用密度泛函B3LYP方法研究了过渡金属钐类卡宾与乙烯的环丙烷化反应的机理.对钐类卡宾试剂CH3SmCH2I和CH2CH2反应的反应物、中间体、过渡态和产物构型的全部结构几何参数进行了优化,并计算了THF溶液的溶剂化效应,用内禀反应坐标(IRC)计算和频率分析方法,对过渡态进行了验证.结果表明:CH3SmCH2I与CH2CH2环丙烷化反应按亚甲基转移机理(通道A)和卡宾金属化机理(通道B)都可以进行,与锂类卡宾的反应机理相同,通道A比通道B反应的势垒降低了14.65kJ/mol.溶剂化效应使通道B比通道A的反应势垒大幅度提高,更有利于反应沿通道A进行,而不利于通道B.     

高效液相色谱法同时检测化妆品中两种亚硝基物质

建立了同时测定化妆品中4-亚硝基苯酚和1-甲基-3-硝基-1-亚硝基胍两种亚硝基类禁用物质的高效液相色谱方法。化妆品样品经溶剂超声提取,经Fortis-C18柱分离,二极管阵列检测器(DAD)检测,保留时间定性,外标法定量。实验结果表明:该方法在0.5～10μg/mL浓度范围内,两种物质均具有良好的线性响应,方法对4-亚硝基苯酚和1-甲基-3-硝基-1-亚硝基胍的检出限均为20ng/g,在三个添加水平下的平均回收率分别在94.14%～102.8%和96.3%～104.1%之间,相对标准偏差(RSD)均<3.5%。     

双[1,2-二(三氟甲基)乙烯-1,2-二硫基]镍与丁二烯反应的溶剂效应

采用密度泛函理论(DFT)在B3LYP/6-31G(d)水平上研究了双[1,2-二(三氟甲基)乙烯-1,2-二硫基]镍(Ni[S2C2(CF3)2]2)与丁二烯的反应机理.采用极化连续介质模型(PCM),考察了溶剂对各反应驻点的电荷分布、偶极矩、溶剂化自由能的影响.计算结果表明:Ni[S2C2(CF3)2]2与丁二烯的反应为前线轨道对称性匹配的协同反应,溶剂介电常数的增大有利于稳定各反应驻点.同时在同种溶剂中,过渡态和产物稳定的程度大于反应物,从而反应更加容易进行.     

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.     

5-氯-2-硝基苯胺合成5-氯-苯并氧化呋咱反应的密度泛函研究

利用密度泛函理论(DFT)的B3LYP/6-31G(d,p)计算方法研究了次氯酸钠氧化环化5-氯-2-硝基苯胺合成5-氯-苯并氧化呋咱的反应, 采用连续介质模型(PCM)评估了溶剂效应. 提出两种可能的分步反应通道: (1)氧化、移氢、脱水和环化, (2)移氢、亚氨基氢扭转、氧化、脱水和环化|前者为优势通道. 非极性的CCl₄溶剂有较低的活化能垒, 比极性的乙醇溶剂更有利于5-氯-2-硝基苯胺的合成. 标题反应的机理类似于次氯酸钠氧化邻硝基苯胺合成苯并氧化呋咱, 但其速控步的活化能垒更低, 反应更易进行.     

S→N烷基重排反应的机理和溶剂化效应

采用密度泛函理论的B3LYP方法、从头算的MP2方法和自洽反应场极化连续模型(PCM),在6-311++G(2d,2p)基组水平上研究了N,N’-二甲基-S-异苯并呋喃在气相和溶液中发生S→N烷基重排反应的机理、溶剂效应和取代基效应.结果表明:该反应通过四元环机理和双位迁移机理生成产物,在气相和溶剂水中,双位迁移途径的能垒均比四元环途径低,反应主要通过双位迁移途径生成产物.在气相,苯环上发生-Cl,-NO2和-OCH3取代时,双位迁移途径的能垒在MP2/6-311++G(2d,2p)水平上比没有取代时分别低4.18,7.61,4.96kJ/mol,反应的取代基效应不明显.而在溶剂水中,苯环上发生-Cl,-NO2和-OCH3取代时,双位迁移途径的能垒在PCM-MP2/6-311++G(2d,2p)水平上比气相时分别低37.73,39.96和37.17kJ/mol,反应的溶剂化效应非常明显.理论研究结果与实验观察结果一致.     

Theoretical investigation of isotopic scrambling mechanisms in 2-chloroethyl methyl sulfide

Ab initio and semiempirical molecular orbital calculations have been applied to study the concerted and stepwise isotopic scrambling mechanisms of 2-chloroethyl methyl sulfide in the gas phase and in aqueous solution. The calculations reveal the structural details of the reactants, transition structures, and intermediates involved in this reaction and provide relative energy estimates. The concerted mechanism is found to be competitive with the stepwise mechanism in the gas phase, but the stepwise mechanism is favored in aqueous solution as no true transition structure for the concerted mechanism could be found using the solvation models. A combined approach of evaluating solvation energies with the generalized-Bom-plus-surface-tensions SM _x solvation models of Cramer and Truhlar at ab initio optimized geometries is found to deliver the best agreement with experimentally determined reaction barriers. Together with the recent experimental results of McManus and co-workers, the present study provides insights into the controlling factors involved in the elementary reaction steps of sulfur mustards and a solid foundation for investigations into more complex reactions of related compounds.     

A theoretical study of the ion pair SN2 reaction between lithium isocyanates with methyl fluoride with inversion and retention mechanism

This paper is devoted to a detailed theoretical study of an ion pair S_N2 reaction LiNCO+CH₃F in the gas phase and in solution at the level of MP2(full)/6-31+G**//HF/6-31+G**. Two possible reaction mechanisms, inversion and retention, are discussed. There are eight possible reaction pathways. The inversion mechanism is more favorable no matter in the gas phase or in solution based on analyses of the transition structures. Methyl isocyanate should form preferentially in the gas phase and more stable methyl cyanate is the main product in solution. The retardation of the reaction in solvents was attributed to the difference in solvation in the separated reactants and in the transition state.     

Full MP2 study of solvent implicit and explicit effect on tautomers of Dithio-Biuret

Dithio biuret conformers were optimised and frequency calculations were performed at MP2/6–311++G(d,p) level of theory. Classification of conformers was done to five different tautomers and the most stable conformer of each tautomer was selected. Tautomer 3 having trans conformation of amino and thiocarbonyl functional group was the most stable tautomer in the gas phase. Optimisation and frequency calculations were also done in four different solvents as follows: benzene, acetonitrile, DMSO and water. Stability of tautomers were compared in these solvents to explore effect of polarity on stabilisation of tautomers. Inter-conversion of selected tautomers was investigated both in the gas phase and in four different media. Results showed that when solvent is used as an implicit media, it has negligible effect on proton transfer. Water-explicit effect was also investigated and the results exhibited high dependency of proton transfer mechanism on water molecules when they participate in breaking and formation of bonds.     

2-(3-巯基-2-吡啶基)苯并咪唑分子内质子转移及溶剂化效应

在B3LYP/6-31G(d,p)和TD B3LYP/6-31++G(d,p)//CIS/6-31G(d,p)水平上,研究了2-(3-巯基-2-吡啶基)苯并咪唑(MPyBI)在气相和七种溶剂(环己烷、苯、三氯甲烷、乙醇、乙腈、二甲亚砜和水)中基态和激发态的分子内质子转移(GSIPT和ESIPT)过程.在基态势能面的研究中发现,该化合物存在分子内双质子转移,其中分步的双质子转移在动力学上具有优势.同时对激发态质子转移势能面及激发态转移过程中的光物理现象进行了研究,结果表明该化合物存在快速的无能垒的激发态分子内质子转移,随着溶剂极性的增强,可以降低基态过渡态的能垒,改变硫醇式与硫酮式互变异构体的比例,从而灵敏地控制荧光的强度.     

Ab initio studies on the pyrolysis mechanism of 2-haloacetic acids in the gas phase

The dehydrohalogenation mechanism of 2-haloacetic acids (XCH2CO2H, X=F, Cl and Br) has been studied theoretically by HF/3-21G and AM1 methods. The results indicate that these reactions are most probably proceeded in terms of a polar five-membered cyclic transition state in the gas phase. Their microscopic processes are beleived to be a stepwise reaction and the rate-determining step is the first one. By comparing the energy barriers of different 2-haloacetic acids, it can be realized that 2-fluoroacetic acid is easier to react than 2-chloroacetic and 2-bromoacetic acids.     

2-溴乙酸气相热消除反应的机理探讨

分别利用密度泛函、从头算分子轨道方法及半经验分子轨道AM 1法对 2 溴乙酸气相热消除反应的机理进行了理论研究 .结果表明 ,虽然用三种不同的方法得到的结果有一定差异 (如反应势能面上各驻点的几何构型、反应的活化能 ) ,但研究得到的反应机理是一致的 ,即反应分两步进行 .其中 ,具有五元环过渡态的第一步反应为速控步骤 ,与实验工作者所建议的机理相符 .     

溶液中类锗烯H2GeClMgCl的结构与异构化反应

用密度泛函理论(DFT)和QCISD(quadratic configuration interaction with single and double excitations)方法研究了类锗烯H2GeClMgCl在气相和五种溶剂中的构型与异构化反应. 结果表明, 类锗烯H2GeClMgCl有三种平衡构型. 其中p-配合物型构型能量最低, 是其存在的主要构型. 讨论了溶剂效应对结构、能量与异构化反应的影响. 计算模拟了最稳定构型的红外光谱.     

Theoretical investigation on structures and isomerizations of the aluminum chlorogermylenoid H2GeClAlCl2

The aluminum chlorogermylenoid H₂GeClAlCl₂ was studied for the first time by using the DFT B3LYP and QCISD methods in gas phase and in C₆H₁₂, THF, DMSO, and H₂O solvents. The theoretical calculations predicted that H₂GeClAlCl₂ has three equilibrium configurations, in which the p-complex is the lowest in energy and is the most stable structure. The isomerization reactions among the three complexes have been investigated. The p-complex is suggested to be the predominant form of H₂GeClAlCl₂ in the gas phase and in solutions thermodynamically and kinetically.