从轨道对称守恒原理看Diels-Alder反应区域选择性

根据轨道对称守恒原理(PCOS),推断出决定Diels-Alder反应的区域选择性的轨道相互作用是双烯体与亲双烯体各自最稳定的价轨道之间的相互作用,这种相互作用形成的是反应产物的两根新σ键中能量更低的σ键,即σ1键。在过渡态中具有更稳定的σ1键的那个区域异构体将是反应的优势产物,本文将这个规则称为σ1规则。本文的量子化学计算结果既证实了σ1规则预测Diels-Alder反应区域选择性主产物的正确性,也证实了σ1键的确来自于双烯体与亲双烯体各自最稳定的价轨道之间的相互作用。     

类卡宾CH2ClLi和甲醛加成反应机理的从头算

以HF/6-31G*基组研究了类卡宾CH2ClLi和甲醛在四氢呋喃溶液中的加成反应机理.CH2ClLi和甲醛,首先生成一个初期络合物,并伴有明显放热.络合物经一个平面双环结构的过渡态到达产物,仅需要一个很小的活化能(14.6 kJ/mol).在这个羰基加成过程中,甲醛羰基碳的亲电进攻较类卡宾碳的亲核进攻表现得更加活跃.整个反应放热效应达216.5 kJ/mol.     

硫脲催化硝基烯与硫叶立德的不对称Michael加成反应

基于密度泛函理论研究了氯代苯基硫脲催化的硝基苯乙烯与硫叶立德的Michael加成反应,确定了控制反应立体选择性的C―C键形成步骤的过渡态结构,计算了过渡态的相对能量和反应势垒,弄清了硫脲催化的微观反应机理,探讨了硫脲催化性能的微观本质.结果表明,反应有利于反式Michael加成产物的形成,硫脲在反应中作为质子给体,首先与质子受体硝基苯乙烯形成双氢键配合物,通过授受体间的电荷转移活化硝基苯乙烯的β-C原子增强其亲电性,有利于硫叶立德的亲核进攻.     

C60加成反应的理论研究

用AM1方法研究了C₆₀与醌并二烯加成反应的机理,并对反应的过渡态及加成产物的构型进行了优化.研究发现,醌并二烯与C₆₀的加成是协同进行的,反应的活化能较低;而氧取代的醌并二烯与C₆₀的加成是协同进行但不同步,反应的活化能较高.前线轨道理论的研究表明反应是由亲二烯体C₆₀的LUMO控制的.     

利用结构相关性方法研究碳氢键活化反应C-H+M■的机理

本文利用结构相关(?)方法对碳氢键活化反应的氧化加成反应机理进行了研究.建立了反应的过渡态,并对反应途径进行了描述.根据所得到的反应途径对碳氢键活化研究中的一些问题进行了解释.     

化学反应的内禀反应坐标法——Ⅲ.乙炔与氢化锂二聚体加成反应的反应路径解析

本文利用量子化学从头计算法(内禀反应坐标法)在3-21G基组上对乙炔与氢化锂二聚体的加成反应作了反应路径解析。确定了过渡态的结构、反应势能曲线、活化能、反应热以及沿着IRC的一些物理量的变化。研究结果表明:在乙炔与氢化锂二聚体的加成反应途径上,靠近孤立反应物存在一个准稳定的分子复合物状态,并且这个分子复合物经单分子重排生成产物的基元过程构成了该反应的定速步骤。根据RRKM理论还估算出相应于单分子重排过程的频率因子和活化熵值。对反应过渡态的前线分子轨道分析表明:在过渡态的形成过程中,反应物系分子之间的HOMO-LUMO和HOMO-HOMO相互作用都起了重要作用。通过比较乙炔与氢化锂单体和二聚体两个加成反应的活化能、活化熵和反应频率因子,指出了这两个反应发生相互竞争的可能性。     

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.     

褐煤模型化合物与异丙醇进行醇解的反应性研究

采用密度泛函理论对褐煤模型化合物与异丙醇醇解的反应特性进行了研究。估算了醇解反应的热力学参数。提出一种将希什菲尔德电荷分布和福井函数相结合的改良方法,用以确定反应物的初始构型。将线性协同转化方法和二次同步转变法相结合用于搜索过渡态,并同时对反应物和产物的构型进行优化。经过计算发现,反应焓随温度升高而降低;反应过程中出现亲核基团;异丙醇是常用醇类中最活泼的醇解剂。因此可认为褐煤醇解反应是放热反应,反应机理为亲核加成机理。     

1,2-联烯亚砜和1,2-联烯砜的反应

1,2-联烯亚砜和1,2-联烯砜是重要的含硫联烯化合物.综述了1,2-联烯亚砜和1,2-联烯砜的亲核加成、亲电加成、Diels-Alder反应、1,3-偶极加成、[2+2]环加成等反应以及在天然产物中的应用.     

吡咯喹啉醌模型化合物与氨亲核加成的理论探讨

为了揭示辅酶PQQ结构与反应性的关系,在B3LYP/D95(d, p)水平上对一系列PQQ模型化合物及其类似物与氨的亲核加成进行了理论计算.结果表明:对单羰基体系,羰基碳的亲电性对反应能垒有重要的影响;对双羰基体系,过渡态中邻位羰基氧与亲核试剂氨上的H形成的氢键对反应的活化能起着关键的作用;稠合芳香环本身对反应的能垒影响不大,但当稠合杂环的1-位为可提供氢键受体的N原子时,由于N1与氨上H原子间可形成氢键而进一步降低反应的活化能.发现过渡态中被进攻羰基与氨上N原子之间形成的夹角(OCN)与活化能有良好的线性关系.     

硼氢化反应机理Ⅴ——HOMO-HOMO相互作用对有机腈类硼氢化反应的影响(英文)

利用量子化学从头计算法ＲＨＦ／ＳＴＯ－３Ｇ基组对甲基腈和氢氰酸硼氢化反应进行了理论研究。微扰分子轨道理论分析表明：在甲基腈硼氢化反应中,过渡态的ＨＯＭＯ是由ＨＯＭＯ－ＬＵＭＯ相互作用和ＨＯＭＯ－ＨＯＭＯ相互作用形成的。通过与氢氰酸硼氢化反应的比较,即考虑甲基对ＨＯＭＯ－ＨＯＭＯ相互作用的影响,可知供电子基团能提升ＨＯＭＯ的能级进而增加了有机腈类硼氢化反应的速度     

The basis for the consistency between the woodward-hoffmann rule and fukui's frontier orbital theory

The Woodward-Hoffmann rule and Fukui's Frontier orbital theory are based on two rather different concepts, yet the two selection rules generally yield consistent conclusions concerning the feasibility of a concerted reaction. This paper suggests that their consistency can be understood in terms of the HOMO-HOMO interaction. First, one can show that the result of the HOMO-HOMO interaction reinforces that of the HOMO-LUMO interaction. Therefore it can be viewed that the HOMO-HOMO interaction is actually taken into account implicitly when the selection rule based solely on the HOMO-LUMO interaction is applied. Secondly, one can make an explicit interpretation of the Woodward-Hoffmann scheme in terms of the HOMO-HOMO interaction.     

Reaction ergodography for the additions of HLi and its dimer to acetylene

The ab initio calculation has been performed with the addition pathways of HLi and its dimer to acetylene at the RHF/3-21G basis set. It shows that the reaction mechanisms of these two reactions are rather similar. In either of two reaction pathways, there is a meta-stable molecular complex near the isolated reactant state. This kind of addition can be treated approximately as the unimolecular reaction in which the molecular complex rearranges into the product. We have estimated the activation entropies and the statistical A factors of these two reactions by the use of RRKM theory. Frontier molecular orbital analysis of these two transition states reveals their HOMOS to be formed from both HOMO-LUMO and HOMO-HOMO interactions.     

The IRC method in chemical reactions: Reaction ergodography for the addition of LiH to acetylene

The ab initio calculation have been performed on the addition of LiH to acetylene at RHF/3-21G basis set. The geometries and energies of the isolated reactant, molecular complex, transition state and product have been determined on the singlet potential energy surface of the ground state. Our results indicate that there is a meta stable molecular complex near the isolated reactant in the reaction pathway. The process from isolated reactant to molecular complex is a non-bonding-exchanging reaction process, and the process from molecular complex to product is the rate-controlling step of the reaction. We also estimate the activated entropy and the frequency factor of the rate-controlling step by using the RRKM theory. The FMO analysis for the transition state reveals the HOMO of transition state to be formed from both HOMO-LUMO and HOMO-HOMO interactions.     

Synthesis of pyrrolidine ring-fused metallofullerene derivatives

The azomethine ylide generated from the reaction of sarconsine and formaldehyde adds to Gd@C₈₂ to give the mono- through octo-adducts, while the direct interaction of sarcosine with Gd@C₈₂ yields only the mono-adduct, which is characterized by HPLC, MALDI-TOF MS, UV-Vis-NIR and FT-IR. The reaction mechanism for this reaction is proposed to be a 1,3-dipolar addition.     

The role of the counterion and of silicon chelation in the selective mono(trifluoromethylation) of tartaric acid derived 1,4-diketones

The addition of trifluoromethyl(trimethyl)silane (TFMTMS) to tartaric acid derived aromatic 1,4-diketones was reported to be highly stereoselective but also chemoselective towards a monoaddition product. This chemoselectivity remained unexplained. Complementary experiments and monitoring of the reaction by electrospray ionization mass spectrometry (ESI-MS) show that: i) the countercation (tetrabutylammonium (TBA(+)) or Cs(+)) associated to the initiator and the charged intermediates in the chain reaction plays a crucial role and ii) in the case of a tetrabutylammonium salt initiator, the second addition on the preformed monoadduct does occur but the resulting bis(trifluoromethyl)carbinolate is unable to evolve through the chain-transfer process and it exhibits an intramolecular Si-O interaction.     

Designing Hole Transport Materials with High Hole Mobility and Outstanding Interface Properties for Perovskite Solar Cells

Organic–inorganic halide perovskite solar cells (PSCs) have attracted much attention due to their rapid increase in power conversion efficiencies (PCEs), and many efforts are devoted to further improving the PCEs. Designing highly efficient hole transport materials (HTMs) for PSCs may be one of the effective ways. Herein we theoretically designed three new HTMs (FDT−N, FDT−O, and FDT−S) by introducing a nitrogen-phenyl group, an oxygen atom, and a sulfur atom into the spiro core of an experimentally synthesized HTM (FDT), respectively. And then we performed quantum chemical calculation to study their application potential. The results show that the devices with FDT−O and FDT−S instead of FDT may have higher open circuit voltages owing to their lower highest occupied molecular orbital (HOMO) energy levels. Moreover, FDT−S exhibits the best hole transport performance among the studied HTMs, which may be due to the significant HOMO-HOMO overlap in the hole hopping path with the largest transfer integral. Furthermore, the results on interface properties indicate that introducing oxygen and sulfur atoms can enhance the MAPbI₃/HTM interface interaction. The present work not only offers two promising HTMs (FDT−O and FDT−S) for PSCs but also provides theoretical help for subsequent research on HTMs.     

Catalytic C–H arylation of unactivated heteroaromatics with aryl halides by cobalt porphyrin

Direct C–H arylation of unactivated heteroaromatics with aryl halides catalyzed by cobalt porphyrin is reported. The reaction is proposed to go through a homolytic aromatic substitution reaction. The aryl radical is electrophilic and a SOMO–HOMO interaction is predominant in the aryl radical addition process.     

Protein thermal stability and phospholipid-protein interaction investigated by capillary isoelectric focusing with whole column imaging detection

CIEF with whole column imaging detection (WCID) is an attractive technique for studying protein reaction and protein-ligand interaction due to its fast separation, simple operation, and high efficiency. In this study, two interesting applications by the CIEF-WCID were developed, involving the study of protein thermal stability and phospholipid-protein interaction. Four proteins (beta-lactoglobulin B, trypsin inhibitor, phosphorylase b, and trypsinogen) with different pI, and two types of phospholipids, including phosphatidylcholine (PC) and phosphatidylserine (PS), were used for this purpose. First, the altered CIEF profiles of four proteins were exhibited due to conformational changes resulting from protein denaturation induced by a high incubation temperature at 60 degrees C. It was demonstrated that the addition of a zwitterionic phospholipid (PC) played a crucial role in the thermal stability of targeted proteins, especially for trypsin inhibitor whose thermal stability was promoted with the addition of the PC vesicles at 60 degrees C. Second, the zwitterionic (PC) and acidic (PS) phospholipids displayed completely different interactions with the proteins. The addition of PS vesicles modified the zwitterionic phospholipids to carry negative charges, which correspondingly changed the interaction between the phospholipid and the protein. Our study demonstrates that the CIEF-WCID is a powerful approach to study protein reaction and protein-ligand interaction with high efficiency, high selectivity, and fast separation.