RCH=CH2与过氧甲酸反应的量子化学研究

本文用MINDO/3方法研究了烯烃RCH=CH2(R=H, CH3, CHO和NO2)与过氧甲酸反应的机理。研究结果表明, RCH=CH2与过氧甲酸反应是亲电反应, 在加热条件下较容易进行。乙烯与过氧甲酸反应的过渡态具有局部对称结构; 若R为取代基时, 这种对称性不复存在, 对于R为给电子基, 过氧基的氧偏向与取代基相连的乙烯碳原子, R为吸电子基, 过氧基氧偏向乙烯的另一碳原子; 取代基的给、吸电子能力越强, 过渡态偏离对称结构越显著, 活化势垒降低或升高也越大。     

取代基对有机金属钽化合物中分子内α-H转移势垒的影响

运用B3LYP方法研究了有机钽化合物中分子内α-氢转移反应, 探讨了不同取代基对α-氢转移反应势垒的影响. 确定了反应物、过渡态和产物的几何构型和反应势垒. 结果表明, 过渡金属钽有机化合物中, 发生α-氢转移的碳原子在过渡态中采用sp2杂化. 取代基对α-氢转移势垒的影响取决于取代基对过渡态中碳原子的未参与杂化的pz轨道上单电子的离域作用. Ta(CH3)4CH(SiMe3)2的α-氢转移反应势垒最低.     

取代基结构-活性关系对电化学降解取代苯胺的影响

以Na2SO4为支持电解质, 使用Ti/PbO2电极, 研究了带有推电子基(—CH3)和吸电子基(—NO2, —Cl)的邻或对位取代基苯胺类化合物的电催化氧化降解过程. 研究结果表明, 带有取代基苯胺类化合物的氧化降解是在羟基自由基进攻下生成氨基酚类化合物, 然后在电极表面失去电子生成苯醌继续氧化的过程. 带有推电子基团苯胺的电催化降解速度比带有吸电子基团的苯胺降解速度快, 这是因为推电子基团使苯环电子云密度提高, 有利于羟基自由基的进攻; 吸电子基团使苯环电子云密度降低, 不利于羟基自由基的进攻. 由于阴极还原反应的作用, 化学反应活性和电化学反应活性并不完全一致. 氯代苯胺在羟基自由基进攻下—Cl离去, 以Cl-离子形式进入溶液中, 被氧化生成有效氯, 加快降解反应速度. 硝基虽然是强吸电子基, 但是可以转化为对苯二胺, 进一步活化苯环, 其降解速度较快.     

钯催化下肟醚导向的sp~2 C—H键邻位酰氧化反应(英文)

使用醋酸钯作为催化剂,过硫酸钠和氧化银为氧化剂,使肟醚导向的底物与苯甲酰甲酸发生sp2C—H键的邻位酰氧化反应,从而得到芳香酮类化合物.该方法对带吸电子基和给电子基的反应物都有很好的适应性,最高产率可达98%.     

取代基对有机钨化合物中α-氢转移势垒的影响

使用密度泛函理论的B3LYP方法,以有机过渡金属钨化合物中的α-氢转移反应为研究对象,探讨不同位置上不同的取代基对α-氢转移反应势垒影响.确定了反应物、产物和过渡态的几何构型和反应势垒.研究结果表明,过渡金属钨有机化合物中,发生α-氢转移的碳原子在过渡态中采用sp²杂化.取代基对α-氢转移势垒的影响取决于取代基对过渡态中碳原子的未参与sp²杂化的pz轨道上单电子的离域作用.R¹,R²位置上为氢原子时,由于H的s轨道与过渡态中单电子所占领的碳原子的Pz轨道对称性不匹配,没有有效的成键作用,所以此时α-氢转移反应有最大的反应势垒.当R¹,R²位置是Me基团时,由于碳原子的Pz轨道与甲基的一个C-H键轨道对称性匹配,存在强的超共轭效应,从而可以最大程度地降低α-氢转移过程的反应势垒.对于R³,R⁴位置,相比于本研究中的其他基团,SiH₃与金属原子轨道间的有效成键作用最大,所以当R³,R⁴位置是SiH3基团时,可以最大程度地降低α-氢转移过程的反应势垒.     

Diels-Alder反应活性的量子化学计算研究

通过HF/6-31G*方法对Diels-Alder反应的一些双烯体及亲双烯体分子进行了结构优化和能量计算。对分子的LUMO、HOMO轨道能量的分析发现,给电子取代基双烯体与吸电子取代基亲双烯体、吸电子取代基双烯体与给电子取代基亲双烯体的Diels-Alder反应较易进行,只是反应开始第一步两者电子流向相反。计算结果表明,反应进行的可能性与一个反应分子LUMO轨道和另一个反应分子HOMO轨道能量之差呈正相关。     

巯基化合物结构对巯基/乙烯基共聚体系紫外光固化反应活性的影响

运用FTIR原位跟踪方法, 以巯基和碳碳双键官能团转化率做为检测指标, 研究了巯基化合物的结构对紫外光固化巯基/乙烯基共聚体系固化行为的影响. 在相同的反应条件下, 苯硫酚的反应活性明显低于硫醇的反应活性; 巯基化合物中吸电子基团(酯基)会使反应活性降低, 而推电子基团(异丙撑基)会使反应活性提高. 采用量子化学中密度函数理论B3LYP/6-31G*的方法和基组对巯基化合物中S与H的净电荷和键长计算结果表明：吸电子基团使S上的净电荷减少, 其与H的共价键键长缩短; 而推电子基团的作用则相反. 此结果佐证了FTIR的实验结果, 揭示了巯基化合物结构对巯基/乙烯基共聚体系紫外光固化反应活性的影响机理.     

锗苯与腈氧化物1,3偶极环加成反应理论研究

采用密度泛函理论(DFT)方法在B3LYP/6-311G**水平研究了锗苯与腈氧化物的1,3偶极环加成反应的微观机理、势能剖面,考察取代基和四氢呋喃溶剂对反应势能剖面的影响.计算结果表明,所研究反应均以协同但非同步的方式进行,且总是Ge—O键先于C—C键形成.锗苯分子中Ge原子上的给电子和吸电子取代基均有利于反应的进行,而腈氧化物C原子上的2,4,6-三甲苯基取代基在热力学上对反应很不利.四氢呋喃溶剂对所研究反应的势能剖面影响不大.     

锰配合物催化CO2加氢生成甲酸的理论研究

采用密度泛函理论(DFT)对锰配合物催化二氧化碳加氢生成甲酸的反应进行了理论研究. 整个催化循环主要包括氢气活化和二氧化碳氢化2个阶段. 计算结果表明, 甲酸的参与明显降低了氢气活化的反应能垒; 二氧化碳的氢化过程遵循外层机理并且氢转移是分步进行的, 决速步骤为氢负离子的转移过程, 自由能垒为21.0 kJ/mol. 对配合物中硫原子上的取代基R进行了调变, 研究结果表明, 当R为吸电子基团时能降低氢气裂解和二氧化碳氢化过程中质子转移的能垒, 而当R为推电子基团时有利于氢负离子的转移,当R=CF₃时整个反应的能量跨度(80.4 kJ/mol)最小.     

CH3S与CO反应机理的理论研究

在G3(MP2)//B3LYP/6-311 G(d,p)水平上,对CH3S自由基与CO气相反应的微观机理进行了理论研究.结果表明:该反应共存在3个反应通道,产物分别为CH3 OCS,CH2S HCO和CH2S HOC.由于形成产物CH3 OCS的活化势垒较低,因此为主要反应通道,这与实验观察到的结果是一致的.     

Substituent effect on redox potential of nitrido technetium complexes with Schiff base ligand: Theoretical calculations

Theoretical calculations based on the density functional theory (DFT) were performed to understand the effect of substituents on the molecular and electronic structures of technetium nitrido complexes with salen type Schiff base ligands. Optimized structures of these complexes are square pyramidal. The electron density on a Tc atom of the complex with electron withdrawing substituents is lower than that of the complex with electron donating substituents. The HOMO energy is lower in the complex with electron withdrawing substituents than that in the complex with electron donating substituents. The charge on Tc atoms is a good measure that reflects the redox potential of [TcN(L)] complex.     

环状聚茚并茚及其取代衍生物电子结构和磁性研究

采用半经验的AM1法，对环状聚茚并茚及其取代物的电子结构进行了计算研究 ，探讨了其磁性和取代基效应．计算得到，环状聚茚并茚及其取代物皆表现半导体 性质且发现其中一种异构体可能具有磁性．取代基效应表明，吸电子基团的取代使 聚合物的电子亲合势增大，而给电子基团的取代则导致电离势减少，但取代基效应 不能改变聚合物的半导体性质．此外，无论吸电子基团还是给电子基团的取代都不 能改变聚合物的磁性特征．     

Synthesis of Tetrasubstituted Alkenes through a Palladium‐Catalyzed Domino Carbopalladation/C?H‐Activation Reaction

Helical tetrasubstituted alkenes ( 7 ) were obtained in a highly efficient way through a palladium‐catalyzed domino‐carbopalladation/CH‐activation reaction of propargylic alcohols 6 in good to excellent yields. Electron‐withdrawing‐ and electron‐donating substituents can be introduced onto the upper and lower aromatic rings. The substrates ( 6 ) for the domino process were synthesized by addition of the lithiated alkyne ( 20 ) to various aldehydes ( 19 ); moreover, the substrates were accessible enantioselectively (in 95 % ee) by reduction of the corresponding ketone using the Noyori procedure.     

Preparation of 5,5′‐pyrilidene and 5,5′‐quinolidene bis‐barbituric acid derivatives

NMR reaction following experiments were used to find optimal conditions for the barbituric acid double addition to aromatic and heteroaromatic carboxaldehydes. It was established that aromatic aldehydes with electron‐donating substituents such as hydroxy, methoxy, and dimethylamino produce only the single addition barbituric acid adduct (barbituric acid benzylidenes). If these electron‐donating substituents are transformed into electron‐withdrawing substituents by virtue of protonation (NMe₂ to NHMe₂⁺) then the double barbituric acid adduct becomes the sole product of the reaction. This is also true regardless of the reaction media if strong electron‐withdrawing substituents (such as a nitro group) are present. Considering that the reactive species for nitrogen containing aromatic heterocycles are actually the conjugated acids (electron deficient molecule) only the double barbituric acid adducts are isolated. All synthetic procedures presented are applicable to multi‐gram scale preparations of double barbituric acid adducts.     

Substituent Effect on the π Linkers in Triphenylamine Dyes for Sensitized Solar Cells: A DFT/TDDFT Study

A series of metal‐free organic donor–π bridge–acceptor dyes are studied computationally using density functional theory (DFT) and time‐dependent DFT (TDDFT) approaches to explore their potential performances in dye‐sensitized solar cells (DSSCs). Taking triphenylamine (TPA) and cyanoacrylic acid moieties as donor and acceptor units, respectively, the effects of different substituents of the π linkers in the TPA‐based dyes on the energy conversion efficiency of the DSSCs are theoretically evaluated through optimized geometries, charge distributions, electronic structures, simulated absorption spectra, and free energies of injection. The results show that the molecular orbital energy levels and electron‐injection driving forces of the TPA dyes can be tuned by the introduction of substituents with different electron‐withdrawing or ‐donating abilities. The electron‐withdrawing substituent always lowers the energies of both frontier orbitals, while the electron‐donating one heightens them simultaneously. The efficiency trend of these TPA derivatives as sensitizers in DSSCs is also predicted by analyzing the light‐harvesting efficiencies and the free energies of injection. The following substituents are shown to increase the efficiency of the dye: OMe, OEt, OHe, and OH.     

Imidoylketene-alpha-oxoketenimine and alpha-oxoketene-alpha-oxoketene rearrangements. 1,3-shifts of substituted phenyl groups

1,3-phenyl shifts interconvert imidoylketenes 1 and alpha-oxoketenimines 2 and, likewise, alpha-oxoketenes 3 automerize by this 1,3-shift. These rearrangements usually take place in the gas phase under conditions of flash vacuum thermolysis. Energy profiles calculated at the B3LYP/6-31G(d,p) and B3LYP/6311 + G(3df,2p)//B3LYP/6-31G(d,p) levels demonstrate that electron donating substituents (D) in the migrating phenyl group and electron withdrawing ones (W) in the non-migrating phenyl group, can stabilise the transition states TS1 and TS2 to the extent that activation barriers of ca. 100 kJ mol(-1) or less are obtained; i.e. enough to make these reactions potentially observable in solution at ordinary temperatures. The calculated transition state energies DeltaG(TS1) show an excellent correlation with the Hammett constants sigma(p)(W) and sigma(p+)(D).     

Synthesis of unsymmetrical biaryl ureas from N-carbamoylimidazoles: kinetics and application

N-Carbamoylimidazoles dissociate in solution to yield imidazole and an isocyanate that may be reacted with another aryl amine to form an unsymmetrical biaryl urea. This paper investigates the reaction kinetics and the influence of electron withdrawing/donating substituents on the reaction of N-carbamoylimidazoles with aniline. The overall reaction mechanism involves two zwitterionic intermediates, formed during dissociation and upon reaction of the liberated isocyanate with aniline. The rate limiting step for the reaction is a base catalysed proton transfer from the second zwitterionic intermediate. Although electron withdrawing substituents on the aryl group hinder dissociation, they significantly increase reaction rates compared to compounds bearing electron donating substituents. The imidazole liberated upon dissociation catalyses the rate determining step so that reactions of dissociated N-carbamoylimidazoles proceed more rapidly than those involving only isocyanates. In addition, the imidazole eliminates the need for anhydrous reaction conditions. The N-carbamoylimidazole methodology was demonstrated by preparing sorafenib, a biaryl urea kinase inhibitor, in good yield and excellent purity.     

A novel method for the synthesis of dipyrromethanes by metal triflate catalysis

5-Substituted dipyrromethanes were synthesized by the reaction of N-tosyl imines with excess pyrrole in the presence of metal triflates. Tripyrromethane and other oligomeric side products were not observed. High yields of 5-substituted dipyrromethanes were obtained for electron donating and withdrawing substituents by performing the reaction at two different temperatures. The new reaction procedure is simple and anhydrous conditions are not required.     

Effect of Substituents in Catechol Dye Sensitizers on Photovoltaic Performance of Type II Dye‐Sensitized Solar Cells

In order to provide a direction in molecular design of catechol (Cat) dyes for type II dye‐sensitized solar cells (DSSCs), the dye‐to‐TiO₂ charge‐transfer (DTCT) characteristics of Cat dyes with various substituents and their photovoltaic performance in DSSCs are investigated. The Cat dyes with electron‐donating or moderately electron‐withdrawing substituents exhibit a broad absorption band corresponding to DTCT upon binding to TiO₂ films, whereas those with strongly electron‐withdrawing substituents exhibit weak DTCT. This study indicates that the introduction of a moderately electron‐withdrawing substituent on the Cat moiety leads to not only an increase in the DTCT efficiency, but also the retardation of back electron transfer. This results in favorable conditions for the type II electron‐injection pathway from the ground state of the Cat dye to the conduction band of the TiO₂ electrode by the photoexcitation of DTCT bands.