应用分子形貌理论研究类SN2反应

应用分子形貌理论, 研究了类SN2反应过程中的沿着IRC路径上固定点的分子形貌的特征, 计算给出了形状和电子密度特征参数以及各键的Dpb值. 应用Matlab程序绘制了分子特征边界轮廓上的电子密度分布的三维图像, 即分子形貌像, 给出了这类反应的动态变化过程.     

惰性气体原子与HF分子相互作用的分子形貌动态研究

研究了惰性气体原子(Rg=He,Ne,Ar和Kr)分别向HF分子两端原子接近过程中分子形貌的动态变化,使用MELD精密从头算方法中的CISD/6-311++G(2d,2p)方法,计算了FH-Rg和HF-Rg2个二聚体的单电子作用势、分子平面的边界轮廓以及相应界面上的电子密度.研究表明,惰性气体原子Rg分别向HF的两端接近时,双方的外形在接近的方向上均有伸手欢迎的表示,分子的前沿电子密度也相应的发生变化,对惰性键提供了一种新的认识.     

HF分子与惰性气体二聚体的分子形貌的理论研究

采用Gaussian-03程序中的MP2/6-311++G(2d,2p)方法,优化了FH- Rg(Rg=He,Ne,Ar)二聚体的结构.使用MELD精密从头计算中的CISD方法,结合我们自编的程序,计算了这些二聚体的单电子作用势(PAEM),并绘出了它们的分子形貌图象.分子形貌所提供的形貌特征、前沿电子密度的特征等,可以直观地揭示He,Ne和Ar等原子与HF分子相互作用时2种相互作用的差别,即共价相互作用与非共价相互作用区分的直观形象的表征.从二聚体的内禀特征信息可以看出,F,H和Rg原子都发生了不同程度的变形,HF分子对惰性气体原子有一定影响,而惰性气体原子对HF分子的影响较小.     

多反应离子的质子转移反应质谱

在无放射性辉光放电离子源内, 采用不同试剂气体进行放电, 为质子转移反应质谱(PTR-MS)新增了强度在10⁵ cps量级的3种反应离子NH₄⁺, NO⁺和O₂⁺, 纯度大于95%; 测试了这3种反应离子的离子-分子反应特征. 采用H₃O⁺, NH₄⁺, NO⁺和O₂⁺等4种反应离子对同分异构体丙醛/丙酮进行检测发现, H₃O⁺和NH₄⁺均不能区分的丙醛/丙酮可采用NO⁺或O₂⁺进行区分. 结果表明, 增加反应离子不仅使PTR-MS的可检测有机物范围不再局限于质子亲和势(PA)大于H₂O的有机物, 还提高了PTR-MS区分同分异构体的能力.     

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。     

3—羟基吡啶酰胺激发态质子转移反应的理论研究

用AMl+INDO/SDCI方法对3-羟基吡啶酰胺的激发态质子转移反应进行了理论研究,求得基态和激发态反应位能面、势垒和过渡态.对有关化合物的吸收和荧光光谱进行了理论指认,所有理论计算结果均与实验结果吻合较好.在此基础上对光化学反应机理和应用前景进行了讨论.     

水杨酸激发态质子转移反应及其溶剂效应的理论研究

用AMI和INDO/CI方法对水杨酸的激发态质子转移反应进行了理论研究,求得反应的位能曲线、势垒和过渡态,对有关化合物的吸收和荧光光谱进行了理论指认,计算与实验结果符合较好。对光化学反应机理和应用前景进行了讨论,最后以乙醚作为氢键溶剂的例子研究了影响水杨酸激发态质子转移反应的溶剂效应。     

2—（2‘—羟基苯基）苯并咪唑的质子转移反应和光谱性质的…

用ＡＭ１和ＩＮＤＯ／Ｓ－ＣＩ方法对２－（２＇－羟基苯基）苯并咪唑的基态和激发态分子内质子转移反应进行了理论研究，求得基态和激发态反应的势能曲线、势垒和过渡态，并研究了此分子的一些异构体、阴离了的相对稳定性，估算了氢键能。进行了实验光谱的理论指认，所得结果与实验值符合较好。在此基础上对光化学反应机理和光谱性质进行了探讨。     

关于分子特征形状的理论

借助于分子中电子运动的经典转折点, 定义了分子的内禀特征轮廓. 文中以甲烷、甲醇和甲酸为例, 详细介绍了分子内禀特征轮廓理论方法. 对分子轮廓的特征截面的具体分析, 可以给出形成分子过程中原子的空间变化信息. 首次计算和绘出了上述分子轮廓上的电子密度分布图, 它与分子的化学性质密切相关, 给出了对分子边界的新认识.     

羟基加成反应对A-T碱基对结构和质子转移过程的影响

应用密度泛函理论在B3LYP/6-31++G(d,p)//B3LYP/6-31G(d,p)水平上对羟基化碱基对A-T的结构进行了研究,经计算共得到8种稳定的羟基化加成产物,其能量的相对顺序为8OHA-TA-T6OHA-T5OH2OHA-T4OHA-T5OHA-TA-T2OHA-T4OH(数字表示羟基加成进攻的原子在腺嘌呤或胸腺嘧啶中的编号),这与其加成反应前后结构变化的大小密切相关.当羟基对腺嘌呤端进行加成时,A-T间的相互作用能略有增加,而当羟基对胸腺嘧啶进行加成时,A-T之间的相互作用能略有减小.另外,还以能量较低的加成产物8OHA-T和A-T6OH为例对羟基化碱基对中A和T之间的质子转移过程进行了研究,结果表明羟基化产物中A与T之间的质子转移机理由未加成前的分步双质子转移变为协同双质子转移,且其势垒低于未加成的A-T发生第一步(决速步骤)质子转移的势垒.     

New Investigation of Potential Acting on an Electron in a Molecule to Draw Molecular Faces

A new approach to calculate the potential acting on an electron in a molecule(PAEM) has been established for drawing the molecular face(MF) of a macromolecule, according to the classic point charge model and the atom-bond electronegativity equalization method(ABEEMσπ) for one electron in a molecule. We introduced a dynamic charge distribution from the view of a local electron movement in a molecule based on the new approach, and as further direct evidence, we calculated some physical quantities using the original ab initio method and the new method to verify the accuracy of the method, such as the boundary distance(BD), molecular face surface area(MFSA) and molecular reactivities indicated by the MFs for a variety of organic molecules. All the results by the new method are in agreement with the results by ab initio method.     

Investigation of the molecular surface area and volume: Defined and calculated by the molecular face theory

Based on the molecular face (MF) theory, the molecular face surface area (MFSA) and molecular face volume (MFV) are defined. For a variety of organic molecules and several inorganic molecules, the MFSA and MFV have been studied and calculated in terms of an algorithm of our own via the Matlab package. The MFV shows a very good linear relationship with the experimentally measured critical molar volume. It is also found that the MFSA and MFV have significant linear correlations with those of the commonly used hard‐sphere model and the electron density isosurface. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Method and algorithm of obtaining the molecular intrinsic characteristic contours (MICCs) of organic molecules

The molecular intrinsic characteristic contour (MICC) is defined as the set of all the classical turning points of electron movement in a molecule. Studies on the MICCs of some medium organic molecules, such as dimethylether, acetone, and some homologues of alkanes, alkenes, and alkynes, as well as the electron density distributions on the MICCs, are shown for the first time. Results show that the MICC is an intrinsic approach to shape and size of a molecule. Unlike the van der Waals hard-sphere model, the MICC is a smooth contour, and it has a clear physical meaning. Detailed investigations on the cross-sections of MICCs have provided a kind of important information about atomic size changing in the process of forming molecules. Studies on electron density distribution on the MICC not only provide a new insight into molecular shape, but also show that the electron density distribution on the boundary surface relates closely with molecular properties and reactivities. For the homologues of alkanes, Rout(H), Dmin, and Dmax (the minimum and maximum of electron density on the MICC), all have very good linear relationships with minus of the molecular ionization potential. This work may serve as a basis for exploring a new reactivity indicator of chemical reactions and for studying molecular shape properties of large organic and biological molecules.     

Theory on the molecular characteristic contour (II)--Molecular intrinsic characteristic contours of several typical organic molecules

The molecular intrinsic characteristic contour (MICC) is defined based on the classical turning point of electron movement in a molecule. Three typical organic molecules, I.e. Methane, methanol and formic acid, were employed as examples for detailed introduction of our method. Investigations on the cross-sections of MICC provide important information about atomic size changing in the process of forming molecules. The electron density distributions on the MICCs of these molecules were calculated and shown for the first time. Results showed that the electron density distribution on the MICC correlates closely with molecular chemical properties, and it provides a new insight into molecular boundary.     

Unveiling the Noncovalent Interaction of Thiazol-2-ylidene and Its Derivatives as N-heterocyclic Carbene with Different Proton Donor Molecules

The importance of noncovalent interaction has gained attention in various domains covering drug and novel catalyst design. The present study mainly characterizes the role of hydrogen bond (H-bond) and other intermolecular interactions in different (1 : 1) complex analogues formed between the N-aryl-thiazol-2-ylidene (YR) and five proton donor (HX) molecules. The analysis of the singlet-triplet energy gap ( ) confirmed the stability of the singlet state for this class of N-aryl-thiazol-2-ylidenes than the triplet state. The interaction energy values of the YR-HX complexes follow the order: YR-NH₃<YR-HCN<YR-H₂O<YR-MeOH<YR-HF. In addition, substituting the H-atom of the N−H bond with bulky groups (−R) leads to an increase in the interaction energy of the YR-HX complexes. Hence, it was found that the replacement of N-atom in N-heterocyclic carbene (NHC) by S-atom forming N-aryl-thiazol-2-ylidene results in comparable intermolecular interactions with proton donor molecules similar to imidazole-2-ylidene (NHC). The current study enlightened the role of noncovalent interactions in carbene complexes with proton donor molecules. We hope that our work on carbene chemistry will pave the way for its application in the designing and synthesis of efficient catalysts.     

Theory on the molecular characteristic contou(II)

The molecular intrinsic characteristic contour (MlCC) is defined based on the classical turning point of electron movement in a molecule. Three typical organic molecules, i.e. methane, methanol and formic acid, were employed as examples for detailed introduction of our method. Investigations on the cross-sections of MlCC provide important information about atomic size changing in the process of forming molecules. The electron density distributions on the MlCCs of these molecules were calculated and shown for the first time. Results showed that the electron density distribution on the MlCC correlates closely with molecular chemical properties, and it provides a new insight into molecular boundary.     

气相质子转移反应中热化学和动力学的关系

质子键合的分子簇的离子－分子反应中的热化学和动力学关系的考察结果表明：对于非烷基锁闭的分子簇,如（C2H5OH）nH＋（5＝1-3）和（CH3OH）3H＋;与中性碱B的质子转移反应,属快速反应,其反应效率r是由总反应的自由能变化△γGm控制,而与反应过渡态的本质无关。那些反应可能存在两个中间体,因电子转移导致质子从分子簇内部转移到中性碱,进而导致二个或三个溶剂分子的直接蒸发;烷基锁闭的质子键合的二聚体,如（CH3CN）2H＋,（CH3OCH3）2H＋,（CH3COCH3）2H＋和（C3COOCH3）2H＋,与中性碱的质子转移反应,其效率远小于1;与总反应的△γGm无关     

酞菁-卟啉超分子的形成及光致电子转移过程

用吸收光谱的方法研究了溶液中四－（４’－Ｎ，Ｎ，Ｎ－三甲基）－苯氧基）酞菁季铵碘盐及它的锌络合物与四－（４’－磺酸基苯基）卟啉及它的锌络合物通过分子间自组装形成的新一类超分子排列的杂聚体，用Ｊｏｂ氏光度滴定的方法确定了它们的组成，为面对面的杂二聚体或三明治式的杂三聚体超分子排列，证实卟啉和酞菁的中心络合金属与溶剂分子之间的轴向配位是决定了卟啉，酞菁杂聚体的组成，发现在超分子体系中卟啉与酞菁能互相猝