共查询到17条相似文献,搜索用时 266 毫秒
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直链共轭多烯的模糊ta/2对称性 总被引:1,自引:0,他引:1
近年来关于分子模糊对称性的工作多属于模糊点对称性的研究.关于模糊空间对称性探讨较少.只曾对线状一维模糊周期分子进行过一些分析.本文在此基础上进一步对于较复杂的平面一维模糊周期分子——直链共轭多烯(简称为共轭多烯)分子进行了较仔细的探讨.除模糊平移变换外,这里还将涉及模糊的螺旋旋转和滑移反映等空间变换.此外,还讨论了存在其中的其他模糊点对称变换.对于点对称元素的变动导致的模糊对称性特征,往往和某种空间对称变换的模糊对称性特征相关.对于分子轨道,除模糊对称变换的隶属函数外,分析了所属不可约表示成分.对这些分子的某些性质和其模糊对称性特征之间的相关性进行探讨. 相似文献
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一般来说,点群理论认为M(o)bius带环分子最高的对称性只能是C2.本文讨论了由18个苯环组成的环并苯的异构体分子,包括柱面的Hückel型分子(HC-[18])和扭转180°的M(o)bius带环分子(MC-[18]).结果表明除了点对称性外,M(o)bius带环分子还存在一种可称为环面螺旋旋转(TSR)变换的对称性,为此还引用了环面正交曲线坐标系.此外,还讨论了这些分子关于TSR对称性匹配的原子集和原子轨道(AO)集.根据TSR对称性的循环群特征,可以建立此类群的不可约表示及有关特征标.这类分子的分子轨道(MO)关于TSR群的不可约表示是纯的,然而所含的相应的原子轨道对称性匹配的线性组合(SALC-AO)成分可以是多种的. 相似文献
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一般来说, 点群理论认为Möbius带环分子最高的对称性只能是C2. 本文讨论了由18个苯环组成的环并苯的异构体分子, 包括柱面的Hückel型分子(HC-[18])和扭转180°的Möbius带环分子(MC-[18]). 结果表明除了点对称性外, Möbius带环分子还存在一种可称为环面螺旋旋转(TSR)变换的对称性, 为此还引用了环面正交曲线坐标系. 此外, 还讨论了这些分子关于TSR对称性匹配的原子集和原子轨道(AO)集. 根据TSR对称性的循环群特征, 可以建立此类群的不可约表示及有关特征标. 这类分子的分子轨道(MO)关于TSR群的不可约表示是纯的, 然而所含的相应的原子轨道对称性匹配的线性组合(SALC-AO)成分可以是多种的. 相似文献
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丙二烯分子的模糊对称性 总被引:1,自引:0,他引:1
利用作者提出的探讨分子及其轨道模糊对称性的方法分析了丙二烯在内旋转过程中模糊对称性特征. 考虑到此过程中经历不同状态所属的对称点群, 即D2h、D2d与D2. 利用包含这些点群中所有元素的最小点群D4h进行分析. 将D4h中的元素分为四组: (i) G0——包含在D2点群中的元素, 也是所有上述点群中都存在的元素; (ii) G1——包含在D2h点群中, 但不包含在D2d点群中的元素; (iii) G2——包含在D2d点群中, 但不包含在D2h点群中的元素; (iv) G3——包含在D4h点群中, 但不包含在D2h与D2d点群中的元素. 分别分析在内旋转过程中各个分子轨道(MO)相应每一组元素的隶属函数的共性变化规律性. 相似文献
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单环多烯烃的离域π分子轨道波函数表达式不是唯一的 总被引:1,自引:0,他引:1
探讨了单环多烯烃(CnHn)的π分子轨道(πMO)波函数ψi表达式与分子对称性的相互关系,用HMO法处理单环多烯烃,其离域πMO由于有简并能级出现,相应的波函数ψi的组合系数(Ci)不是惟一的,Ci值的取得与分子的对称面选择密切相关,使得同一分子体系会有不同的波函数表达式出现。 相似文献
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合成了一系列苯炔化合物, 并对它们的紫外吸收和荧光发射性质进行了研究. 通过HOMO和LUMO轨道能量差ΔE、分子轨道图及相关碳原子上的电荷密度讨论了分子结构和大小对这些化合物紫外吸收和荧光发光性质的影响. 在间位苯炔化合物及间位苯炔树枝大分子(dendrimer)中, 紫外吸收峰不随苯炔分枝数和dendrimer阶数增加而红移, 共轭被中心苯环隔断. 而在邻或对位取代的苯炔化合物中, 共轭则不受中心苯环的影响而延伸至整个分子. 其原因可能和中心苯环上与苯炔分枝相连的碳原子的电荷密度有关. 在激发态下, 间位苯炔化合物中苯炔分枝间存在耦合作用, 荧光发射随苯炔分枝数增加而红移. 但这种耦合作用只发生在与同一苯环相连的分枝间, 因此荧光发射不随dendrimer阶数增加而红移. 相似文献
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本文讨论了用能量梯度法,在用MINDO/3自洽场方法计算得到的位能面上,分別优化得到线型和三员环型重氮甲烷以及这个单分子反应的过渡态的几何构型。研究了体系在过渡态的九种振动模式和反应途径。体系在反应途径上的每一点都保持C_S点群的对称性。轨道相关图表明反应是对称性允许的。 相似文献
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本文利用唐敖庆等人所提出的化学反应局部对称性的新概念,对螯变反应的局部对称性进行了分析;并按照控制反应全过程的局部对称性操作群,运用量子化学方法,第一次建立了有局部对称性标志的螯变反应的分子轨道能量相关图。从而,从反应体系的局部对称性这一本质上揭示了Woodward-Hoffmann所提出的螯变反应选择定则。 相似文献
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Xiufang Xu Guichang Wang Xuezhuang Zhao Yinming Pan Yunxiao Liang Zhenfeng Shang 《Journal of mathematical chemistry》2007,41(2):143-160
In this paper, the fuzzy symmetry of some prototypical linear molecules has been analyzed. The results show that some molecular
orbitals (MOs) are less symmetrical but some others are more symmetrical than the molecular skeleton, which the MOs correspond
to. The membership functions of space inversion for MOs are closely related to the chemical characteristics of the MOs. Sometimes,
although the symmetry of a molecular skeleton is not obvious, however that of some MO is quite obvious. The membership functions
of the fuzzy inversion symmetry depend on the choice of the position of the center of inversion. As compared to those of diatomic
molecules and linear tri-atomic molecules, the linear polyatomic molecules in which a distinctive fuzzy symmetry of space
translation may exist, and thus a significant effect on their properties can be expected. 相似文献
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Xuezhuang Zhao Guichang Wang Xiufang Xu Yinming Pan Ruifang Li Zhengfeng Shang Zucheng Li 《Journal of mathematical chemistry》2008,43(2):485-507
Based on our previous study on the elementary characterization of fuzzy symmetry, we inquire into the fuzzy symmetries of
some simple linear and plane molecules. These systems belong to point groups that include the identity and twofold symmetry
elements, but not include higher multi-fold symmetry ones, and their molecular orbitals (MOs) only belong to one-dimension
irreducible representations. In this paper, we take the azines as a typical model to examine the fuzzy symmetry in relation
to the D6h point group. As this group includes multi-fold symmetry elements such as a sixfold rotation axis, some of the MOs may belong
to two-dimensional irreducible representations. We inquire into the fuzzy symmetry of these molecules and their MOs in terms
of membership functions, representation components and correlation diagrams. In addition to these neutral closed shell molecules,
pyridine hydride radical, anion, and cation are also analyzed. 相似文献
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Xuezhuang Zhao Xiufang Xu Guichang Wang Yinming Pan Zhenfeng Shang Ruifang Li 《Journal of mathematical chemistry》2007,42(2):265-288
Based on our study in relation to the fuzzy symmetry characterization and the application to linear molecule, the fuzzy symmetry
of the planar molecules have been analyzed. The prototypical planer molecules we have chosen to study are the C2F3X (X = Cl, Br, and I) and three kinds of C2F2Cl2 isomers. These molecules relate to the fuzzy symmetry in connection with the
D2h point group. As we known, the D2h point group includes an identity transformation and seven twofold symmetry transformations
but without higher-fold ones. Meanwhile, it is related only to some one-dimensional irreducible representations, but there
is not to multi-dimensional irreducible representation. In this paper, the fuzzy symmetries of these molecules and their molecular
orbital(MO)s have been studied, such as the membership functions, the representation compositions, the fuzzy correlation diagrams
and so on have been analyzed. These analysis methods can be used to analyze the molecular fuzzy symmetries of some other molecule
systems, no difficulty. 相似文献
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The fuzzy symmetries for linear tri-atomic $${\rm B} \cdots {\rm A} \cdots {\rm C}$$ dynamic systems
Xuezhuang Zhao Zhenfeng Shang Zucheng Li Hongwei Sun Lan Chen Guichang Wang Xiufang Xu Ruifang Li Yinming Pan 《Journal of mathematical chemistry》2008,44(1):46-74
Based on our previous study on the elementary characterization of the fuzzy symmetry, we inquired the static state fuzzy symmetry
of some molecules and their molecular orbitals (MO). Now we will analyze the fuzzy symmetry of some simple linear tri-atomic
dynamic systems in connection with the reaction. Three related transformations will mainly be studied in detail. These three
transformations are (1) the space inversion transformation about the mid-atom as the center, (2) the reaction reversal transformation
in relation to the reaction B + AC→BA + C and (3) the joint transformation of the above two. We examined the variation for
the internal configuration of these systems owing to the operation of above three transformations, and then establish methods
to calculate the fuzzy symmetry characterization, such as the membership functions for the MOs of such linear tri-atomic dynamic
systems in relation to these transformations. We examined the variation regularity in relation to the fuzzy symmetry characterization
for the MOs of these systems along the intrinsic reaction coordinate (IRC) and dividing line. The variation regularity and
the distribution for the fuzzy symmetry characterization in related internal configuration coordinate space are also analyzed.
An IRC-scale is suggested for internal configuration coordinate space in this paper. 相似文献
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Xuezhuang Zhao Zhengfeng Shang Guichang Wang Xiufang Xu Ruifang Li Yinming Pan Zucheng Li 《Journal of mathematical chemistry》2008,43(3):1141-1162
In our previous papers on the molecular fuzzy symmetry, we analyzed the basic characterization in connection with the fuzzy
point group symmetry. In this paper, polyynes and their cyano-derivatives are chosen as a prototype of linear molecules to
probe the one-dimensional fuzzy space group of parallel translation. It is notable that the space group is an infinite group
whereas the point group is a finite group. For the fuzzy point group, we focus on considering the fuzzy characterization introduced
due to the difference of atomic types in the monomer through point symmetry transformation in the beginning; and then we consider
the difference between the infinity of space group and the finite size of real molecules. The difference between the point
group and the space group lies in the translation symmetry transformation. This is the theme of this work. Starting with a
simple case, we will only analyze the one-dimensional translation transformation and space fuzzy inversion symmetry transformation
in this paper. The theory of the space group is often used in solid state physics; and some of its conclusions will be referred
to. More complicated fuzzy space groups will be discussed in our future papers. 相似文献
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Yun Li XueZhuang Zhao XiuFang Xu ZhenFeng Shang Zhen Zhou ZunSheng Cai GuiChang Wang RuiFang Li 《中国科学B辑(英文版)》2009,52(11):1892-1910
On the basis of our recent studies on the molecular fuzzy point group symmetry, we further probe into the more complicated
planar one-dimensional fuzzy periodic molecules—straight chain conjugate polyene. Except for the fuzzy translation transformation,
the space transformation of the fuzzy screw rotation and the glide plane will be referred to. In addition, other fuzzy point
symmetry transformation lain in the space transformation is discussed. Usually there is a correlation between the fuzzy symmetry
characterization caused by the transition of the point symmetry elements and by certain space symmetry transformation. For
the molecular orbital, the irreducible representation component is analyzed besides the membership function of the fuzzy symmetry
transformation. Also, we inquire into the relativity between some molecular property and the fuzzy symmetry characterization. 相似文献
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Shengkai Xing Yun Li Xuezhuang Zhao Zunsheng Cai Zhenfeng Shang Xiufang Xu Ruifang Li Guichang Wang 《Journal of mathematical chemistry》2012,50(5):1309-1332
In this paper, we will investigate the fuzzy layer group symmetries of two-dimensional (2D) periodic molecules. Here, we select several graphene molecules as typical examples to discuss. For these two-dimensional graphene molecules, their MO energies, symmetries and fuzzy symmetries are preliminarily studied. In addition, we especially make a detailed comparison between the zigzag and armchair graphene molecules. These studies will develop a theoretical framework that will help us to investigate the fuzzy symmetries of various layer group molecules as well as molecules with 3D periodic structure. 相似文献