Substituenteneffekte in den13C-NMR-Spektren von diastereomeren Chalkondihalogeniden, 10. Mitt.: Erste Synthese und Konfigurationsbestimmung vonthreo-Chalkonbromhydrinen

Summary The first synthesis ofthreo chalcone bromohydrins was realized by reaction oftrans chalcone epoxides with SnBr₄ in molar ratios from 1:1 to 2:1. The compounds were obtained in high yields and isomeric purity. Their configuration was determined asthreo by different methods based on¹³C-NMR shifts of C- and C- atoms.

     

Graph edge colorings and their chemical applications

A general method is outlined to enumerate the edge-colorings of graphs under group action. The symmetry group of the graph acting on the vertices induces permutation of the edges. The edge-colorings are enumerated using the edge-permutation group. A number of chemical applications especially to multiple quantum NMR spectroscopy, statistical mechanics, enumeration of unsaturated isomers, etc. are considered.Alfred P. Sloan fellow; Camille and Henry Dreyfus teacher-scholar     

SCF-CI studies of the equilibrium structure and the proton transfer barrier H3O 2 −

Large-scale configuration interaction (CI) calculations have been performed in order to study the effect of the correlation energy on the equilibrium geometrical structure, the stability, and on the energy barrier of the proton transfer reaction in the hydrogen bonded system HO^– · HOH. An extended Gaussian basis set including polarization functions on each nuclear centre has been employed to approximate the molecular Orbitals. All possible single and double replacements resulting from a single determinant Hartree-Fock reference state have been taken into account in the CI wavefunction. Compared to the SCF results the equilibrium oxygen/oxygen distance has been obtained from the CI calculations to be smaller by about 0.08 Å and the correlation energy has been found to stabilize the composed system by 3.6 kcal/mole. An almost symmetric equilibrium structure with the hydrogen bonding H-atom midway between the two oxygen centres has been obtained in the CI treatment, whereas SCF calculations yield an asymmetric geometrical configuration with a small energy barrier of 1.4 kcal/mole for the proton transfer process.     

A programmable spin-free method for configuration interaction

In this note a method is presented for quick implementation of configuration interaction (CI) calculations in molecules. A spin-free Hamiltonian for anN electron system in a spin stateS, expressed in terms of the generators for the unitary group algebra, is diagonalized over orbital configurations forming a basis for the irreducible representation [2^1/2N-S 1^2S ] of the permutation group S _N . It has been found that the basic algebraic expressions necessary for the CI calculation involve a limited category of permutations. These have been displayed explicitly. On leave from the Indian Institute of Technology, Bombay, India.     

New Cembrane-Type Diterpenoids from the South China Sea Soft Coral Sinularia nanolobata

In the present study,nine new cembrane-type diterpenoids,namely ximaonanolobatins A—I(1—9),together with six related known analogs(10—15)and four known tetraprenylated alkaloids malonganenones D,E,H,and K(16—19)were isolated from the soft coral Sinularia nanolobata collected off the Ximao Island in the South China Sea.The structures of 1—9 were robustly established by a combination of detailed spectroscopic analyses,chemical reactions,quantum mechanical(QM)-NMR methods,biogenetic consideration,and the comparison with those literature data.The absolute configuration of 1 was confirmed by X-ray diffraction analysis,and the absolute configuration of 2 was determined by QM-NMR calculations and chemical transformation.In addition,the absolute configuration of 3 was determined using the modified Mosher's method.All these isolates were evaluated for their anti-inflammatory and anti-tumor activities.The results showed that only compound 15 exhibited potential anti-inflammatory effect against LPS-induced TNF-αrelease in RAW264.7 macrophages with an IC50 value of 12.6μmol/L.     

足球分子的电子结构和UV谱的研究

用INDO/2和INDO/CI方法研究了足球分子的电子结构和UV谱。几何构型优化后得到2种键长:R_(5-6)=1.4507,R_(6-6)=1.3979,相应的键序为1.1356和1.4385。SCF计算得到120个成键轨道和120个反键轨道,符合我们建议的结构规则。足球分子的光谱计算结果是振子强度不为零的跃迁只有一个,其值为386.0 nm,和实测的UV谱符合得较好。     

取代基间电荷转移对分子二阶非线性极化系数的影响

计算了苯胺、硝基苯、邻硝基苯胺、间硝基苯胺、对硝基苯胺及2,4-二硝基苯胺的二阶非线性光学系数β_2,讨论了取代基间电荷转移对分子二阶非线性光学系数的影响。得知β′=β_(add)+β_(ct)不是很好的计算公式,但考虑取代基间的电荷转移对β的贡献仍有其价值。     

配位氧原子对7—氯—4—喹啉醇结构单元电子结构的影响

7-氯-4-喹啉醇氮氧化合物(Ⅰ)已被临床证明是一种抗癌新药,而7-氯-4-喹啉醇(Ⅱ)则不具有抗癌活性,二者在结构上只差1个配位氧原子,本文试图通过电子结构的比较分析阐明配位氧原子引起的7-氯-4-喹啉醇结构单元的电子结构变化,MINDO/3构型优化计算表明,化合物Ⅰ、Ⅱ皆为平面结构的几何构型,在此基础上进行了INDO/1+CI计算。     

Boosting Benzene Oxidation with a Spin-State-Controlled Nuclearity Effect on Iron Sub-Nanocatalysts

A fundamental understanding of the nature of nuclearity effects is important for the rational design of superior sub-nanocatalysts with low nuclearity, but remains a long-standing challenge. Using atomic layer deposition, we precisely synthesized Fe sub-nanocatalysts with tunable nuclearity (Fe₁–Fe₄) anchored on N,O-co-doped carbon nanorods (NOC). The electronic properties and spin configuration of the Fe sub-nanocatalysts were nuclearity dependent and dominated the H₂O₂ activation modes and adsorption strength of active O species on Fe sites toward C−H oxidation. The Fe₁-NOC single atom catalyst exhibits state-of-the-art activity for benzene oxidation to phenol, which is ascribed to its unique coordination environment (Fe₁N₂O₃) and medium spin state (t_2g⁴e_g¹); turnover frequencies of 407 h⁻¹ at 25 °C and 1869 h⁻¹ at 60 °C were obtained, which is 3.4, 5.7, and 13.6 times higher than those of Fe dimer, trimer, and tetramer catalysts, respectively.     

锗烯X2Ge与环硫乙烷硫转移反应的密度泛函研究

利用量子化学密度泛函理论(DFT)的B3LYP方法, 在6-311++G(d, p)的水平上对锗烯X2Ge(X=H、CH3、F、Cl、Br、OH、OCH3)与SC2H4的硫转移反应进行了计算研究. 结果表明, 锗烯的基态是单重态, 取代基的电负性越强, 单-三态的能量差越大; 反应的活化能越高, 放热越少; 控制反应的因素是电子效应, 而不是立体效应; 该硫转移反应由两步组成, 第一步生成中间配合物, 是一个无势垒的放热过程, 第二步经过渡态生成产物. 并用组态混合模型对反应机理和势垒进行了解释. 同时讨论了该反应中环硫乙烷的C—S键解离过程.