Effect of core substituents on the intramolecular exchange interaction in N,N′‐dioxy‐2,6‐diazaadamantane biradical: DFT studies

Density‐functional theory calculations of a series of organic biradicals on the basis of the N,N′‐dioxy‐2,6‐diazaadamantane core with different substituents at carbon atoms adjacent to the nitroxyl groups have been performed by the UB3LYP/6‐311++G(2d,2p) method. Using the breaking symmetry approach, the values of the exchange interaction parameter, J, between the radical centers are calculated. It is shown that the intramolecular exchange interaction for the most part is ferromagnetic in nature, but the J parameter gradually decreases, changing its sign to antiferromagnetic interaction for the last substituent in the following sequence: CF₃(CH₃)COH > CH₂F(H)COH > CH₂OH > H > CBr₃ > CH₂F > CCl₃ > CF₃ > CH₂Br > CH₂Cl > CH₃ > C₂H₅ > C₃H₇ > i‐C₄H₉ > F > Br > OCH₃ > Cl > CH₂C₆H₅. The calculations at the UHSEH1PBE/6‐311++G(2d,2p) level with the most of substituents show nearly the same variation sequence for the J parameter. It is concluded that spin polarization effects in the diazaadamantane cage and a direct through‐space antiferromagnetic exchange interaction between the nitroxyl groups are the main mechanisms contributing to the exchange interaction parameter value in the studied series of compounds. The exchange coupling constant, J, depends on the electronic effects and geometry of the substituents, as well as on their specific interactions with the nitroxyl radical groups.     

Transition metal catalyzed asymmetric cyclopropanation via diazo decomposition: Ligand architecture defining stereoselectivity

Asymmetric cyclopropanation of alkenes through diazo decomposition mediated by transition metal complexes is a widely investigated catalytic reaction to obtain cyclopropanes where high enantioselectivity is achieved by optimizing metal–ligand combination. Instead of a chronological listing of developments, this review illustrates the existing literature data according to the structural types of ligands in catalytic complexes and attempts to correlate substrate structure and selectivity with ligand design.     

A Note on Symmetries and Generalized W∞ Algebra of the Modified KP Equation

Some remarks on the paper Symmetries and generalized W algebra of the modified KP equation (S. Y. Lou and G. J. Ni, Lett. Math. Phys. 34 (1995), 327–331) are given. It is pointed out that if we consider the inverse operator of a differential operator to be a linear operator, the vector fields nv(f) defined in the above Letter are not certain to be symmetries of the modified KP equation under consideration.     

爆轰波面轮廓及其旋转对称性的同时观测

利用间隙技术并靠一个专用模板,就能仅通过一次试验而对爆轰波面轮廓进行记录,辽河对其不同对称程度和旋转对称性加以详细分析.     

Substitution symmetry

Pólya's enumeration theory and its generalizations are refined to count derivatives of symmetrical parent compounds with any specified subsymmetry. Equivalently, enumeration of orbits of mappings, upon which a group acts by acting on their domain and their range, is refined to count orbits with stabilizers in any specified conjugacy class of subgroups.     

高氯酸锂-乙酰胺新型二元熔盐电解质的谱学研究

高氯酸锂与乙酰胺在适宜摩尔配比范围内可形成热稳定性良好、电化学性能优良的室温熔盐.从分析LiClO4与乙酰胺形成熔盐的作用机制出发,通过红外、拉曼光谱的谱学分析并应用非局部密度泛函理论方法进行量化计算对二者的相互作用进行了讨论.发现乙酰胺通过Li－O键与LiClO4中的Li＋配位而破坏了LiClO4的离子键,形成很大的配位阳离子,削弱了阴阳离子间的库伦作用力;同时Li－O也导致乙酰胺分子间的氢键断裂,因而体系的共熔温度较之纯物质熔点显著降低,部分样品室温下以液体状态稳定存在.     

Useful parameter describing magnetic interactions in extended bis‐bidentate bridged dimers

A useful parameter describing magnetic coupling interactions has been inspected in transition metal dimers, in which two transition metal ions are bridged by extended bis‐bidentate ligands. This parameter is the square of overlap integral between the spatial parts of magnetic orbitals in the broken symmetry state. The oxalato‐bridged Cu (II) dimers, in which the Cu (II) atom is either in tetrahedral or square pyramid coordination environment, have been calculated with the density functional theory coupling the broken symmetry approach. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

溴化顺式-溴•氨•二(乙二胺)合钴(III)绝对不对称合成与拆分机理*

分别用绝对不对称合成和改进的拆分方法制备标题配合物Λ-(+)D-cis-[CoBr(NH3)(en)2]Br2(1)和Δ-(-)D-cis-[CoBr(NH3)(en)2]Br2(2), 以及制备了cis-[CoBr(NH3)(en)2]Br2·2H2O(3)(en=1,2-乙二胺). 用元素分析、差热-热重、旋光度、UV-Vis、CD 光谱等对产物进行了表征.通过CD 光谱法获得了绝对不对称合成Co(III)配合物的产物ee 值分布图援当利用绝对不对称合成得到的手性Co(III)配合物去“逆向拆分”外消旋溴代樟脑磺酸铵[NH4(dl-BCS)]时只获得部分拆分, 初步认为这与交互拆分过程中阴阳离子之间的有效手性识别有关, 对于手性Co(III)配合物的绝对不对称合成还提出了一个新的反应机理,即“催化-结晶诱导”机理.     

The use of site symmetry in constructing symmetry adapted functions

It is shown that the application of a projection operator from a given group to a function is equivalent to the successive application of projection operators from factor groups of the starting group to that function. When used with the factor groups representing the site symmetry of a position and the simplest group of interchanges of positions, this concept provides a very simple method for obtaining symmetry adapted linear combinations of basis functions.