螺旋结构和旋光性

旋光性是由分子结构决定的。各种类型的光活性分子内都存在螺旋结构。左螺旋为左旋的，右螺旋为右旋的。分子内含有多少个螺旋时，则所有螺旋旋光度的代数和为正是右旋的，为负是左旋的。因此，由旋光方向可预测分子的构型和构象。     

螺旋结构与旋光性——2.脂族链状化合物的螺旋结构和旋光性

利用弯曲键理论,详细讨论了旋光性的脂肪族链状化合物分子内存在的螺旋结构,同样是右螺是右旋的,左螺旋是左旋的。从螺旋方向可以推断旋光方向,知道旋光方向也可以推断构型。     

旋光性与分子结构关系的新发展

本文以1860年Pasteur提出的旋光性与手性分子所含螺旋结构有关联的设想为模型,剖析了某些光学活性分子。表明Pasteur的设想是符合实际情况的,即右螺旋呈现右旋光性,左螺旋呈现左旋光性。同时,通过螺旋模型和旋光方向与Brewster的基团可极化性序列相结合,则可以推导出手性碳原子的构型。介绍了螺苯类化合物、联苯类化合物、聚积二烯类化合物及含手性碳原子的化合物所含螺旋结构的剖析和与旋光方向的关系。为阐明结构与旋光性的关系提出了一种可供参考的论点。     

导致旋光性根本原因的探讨

旋光性是由结构决定的，手性是一种抽象概念，抽象概念不能决定旋光性，旋光性具有明确的方向性，它必然是由具有明确方向性的结构特征所决定。螺旋结构是具有明确方向性的结构，它是实体不是抽象概念，它与旋光方向和旋光度大小可以联系在一起，螺旋结构才是导致旋光性的根本原因。     

单糖结构及其旋光度的计算

根据螺旋理论的规律，对常见单糖及其甲甙的旋光度进行了计算。计算结果和测定值相当接近，在旋光方向上完全一致，旋光度数值也都在可接受的误差范围之内。证明单糖及其甙的立体结构和旋光性的关系是十分密切的。根据糖和糖甙的立体结构，可以推断旋光方向和旋光度的大小，反之，从旋光性也可以推断单糖及其甲甙的立体结构。     

S-(-)-2, 2'-联二萘酚衍生物的合成及其螺旋结构与旋光性的关系

以S-(-)-2,2'-联二萘酚为手性模板分子,合成出了它的两个七元环衍生物。通过对它们的旋光值、X衍射结构及构象的研究,找出了它们的螺旋结构与旋光性的关系,并对其旋光大小进行了比较。此外,首次提出我们建立的螺旋片段判定规则及我们定义的ω值。     

S-(-)-2, 2'-联二萘酚衍生物的合成及其螺旋结构与旋光性的关系

以S-(-)-2,2'-联二萘酚为手性模板分子,合成出了它的两个七元环衍生物。通过对它们的旋光值、X衍射结构及构象的研究,找出了它们的螺旋结构与旋光性的关系,并对其旋光大小进行了比较。此外,首次提出我们建立的螺旋片段判定规则及我们定义的ω值。     

S-(-)-2,2′-联二萘酚衍生物的合成及其螺旋结构与旋光性的关系

以S-(-)-2,2’-联二萘酚为手性模板分子,合成出了它的两个七元环衍生物.通过对它们的旋光值、X衍射结构及构象的研究,找出了它们的螺旋结构与旋光性的关系,并对其族光大小进行了比较.此外,首次提出我们建立的螺旋片段判定规则及我们定义的ω值.     

甲基取代的手性环酯化合物的螺旋结构与旋光性分析

利用螺旋片段判定规则,结合X射线衍射结构图及模型结构,对4个大环酯类化合物及甲基取代产物的螺旋结构与旋光性进行了定量分析,检测结果证明了理论分析的正确性;对旋光值变化规律给予了合理解释.     

螺旋结构与旋光性 4.螺旋理论对旋光度大小的预测

本文分析了影响旋光度的各种因素,并列举了各类型的大量化合物的旋光数据,证明螺旋理论可以预测旋光度大小。     

膦手性丙炔胺脯氨酸磷酸酯螺旋聚合物的合成与表征

通过添加对映体拆分剂,合成了4种含膦手性的丙炔胺磷酸酯单体[HC帒CC H2NH(PO)R1R2].单体1,R1=OPh,R2=NC4H7COOCH3;单体2,R1=OPh,R2=NC4H7COOCH2CH3;单体3,R1=OPh,R2=NC4H7-COOC(CH3)3;单体4,R1=Ph,R2=NC4H7COOC(CH3)3].1H-NMR和31P-NMR表征可知对映体(单体1)不能被拆分剂拆分,而单体2、单体3、单体4通过拆分剂可以制得单一手性的磷化合物.以(nbd)Rh+[η6-C6H5B--(C6H5)3]为催化剂,以三氯甲烷为溶剂成功得到聚合物分子量范围在0.4×10-4～0.7×10-4,分子量分布在1.26～1.98范围的3种含手性膦侧基的丙炔胺类聚合物.比旋光度([α]D)、圆二色谱(CD)对聚合物的不同侧基及温度对光学活性的影响表明,聚合物具有良好的光学活性且能够形成单一方向的螺旋构象,说明膦手性在构建螺旋聚合物具有重要作用.     

Optically Active Polysilylenes: State‐of‐the‐Art Chiroptical Polymers

Controlled synthesis, chiroptical characterization, and manipulation of artificial helical polymers are challenging issues in modern polymer stereochemistry. Although many artificial polymers adopting a preferential screw‐sense helical structure have been investigated, optically active polysilylenes bearing chiral side chains may be among the most suitable to elucidate the inherent nature of the helical structure, since these polymers offer powerful spectroscopic probes as a result of their ideal chromophoric and fluorophoric main chain properties around 300–330 nm. The present paper will review comprehensively the helix‐property‐functionality relationship between side chain structure, global and local main chain conformation, (chir)optical properties, electronic properties, several helical cooperative phenomena, the effects of temperature and solvent polarity, and molecular imaging. This knowledge and understanding of the nature of the polysilylene helix might constitute a bridge between artificial polymers and biopolymers and will assist in designing and controlling new types of helical polymers directed to diverse screw‐sense‐related properties and applications in the future.     

Manifestation of chiral asymmetry of ferroelectric liquid crystals induced by optically active dipole dopants in a linear electrooptic effect

The existence of eight combinations of absolute spatial configuration, helix handedness and handedness of director tilt has been shown for ferroelectric liquid crystals induced by optically active dipole dopants (optically active diesters of 4,4'-terphenyl dicarboxylic acid). As in the case of individual ferroelectrics alternation of the helix handedness is observed depending on absolute configuration of the C*-atom and its position relative to the rigid core of the molecule. However for these induced ferroelectric liquid crystals the helix handedness does not depend on the inductive effect of the substituent adjacent to the C* atom, e.g. the helix handedness of all the (S)-2-chlorine substituted materials coincides with that of the (S)-2-methyl-butyl derivative. Substitution of a chlorine atom by a cyano group followed by conversion of absolute spatial configuration of the C* atom results in the opposite helical sense. Thus asymmetric parameters of the induced ferroelectric liquid crystals helix handedness and the handedness of director tilt (or the sign of P_s) do not depend directly on the absolute configuration of C* atom and its position in a molecule. For the substances investigated within all of the temperature range of the induced smetic C* phase no reversal of the tilt direction handedness was observed.     

Asymmetric polymerization of methacrylates

The syntheses of optically active polymers having helical conformation from bulky methacrylates are reviewed focusing on selected topics. The monomers include triphenylmethyl methacrylate and its analogues. Asymmetric anionic polymerization of the monomers gives isotactic, optically active polymers having a helical structure with excess helicity. The isotactic content and the extent of helical‐sense excess depend on the monomer structure and the reaction conditions. In the case of methacrylates, completely isotactic and single‐handed helical polymers can be produced by asymmetric anionic polymerization (helix‐sense‐selective polymerization). Asymmetric radical polymerization is also possible for this class of monomer. Some of the helical polymers show chiral recognition ability toward a wide range of racemic compounds. Polymers having main‐chain configurational chirality are also discussed.     

单体结构和聚合条件对大体积乙烯基聚合物旋光性质的影响

合成了3种手性大体积烯类单体——(+)-4,4″-二[(S)-2-甲基丁氧基]-2′-乙烯基对三联苯(p-BMVT)、(+)-3,3″-二[(S)-2-甲基丁氧基]-2′-乙烯基对三联苯(m-BMVT)和(+)-2,2″-二[(S)-2-甲基丁氧基]-2′-乙烯基对三联苯(o-BMVT),其中后两个为新化合物.系统研究了单体结构对其聚合反应活性以及单体结构和反应条件对所得聚合物旋光性质的影响.p-和m-BMVT在合适的条件下可以顺利地进行自由基聚合,形成某一旋向占优的手性二级结构;手性取代基在单体分子上移动一个共价键的距离导致聚合物的旋光方向相反.单体o-BMVT的合成产率低且不能进行自由基聚合.提高芳烃类或者降低非芳烃类聚合溶剂的极性、升高反应温度、减少单体浓度有利于得到旋光度大的聚合物.     

Mechanism of helix induction on a stereoregular Poly((4-carboxyphenyl)acetylene) with chiral amines and memory of the macromolecular helicity assisted by interaction with achiral amines

Cis-transoidal poly((4-carboxyphenyl)acetylene) (poly-1) is an optically inactive polymer but forms an induced one-handed helical structure upon complexation with optically active amines such as (R)-(1-(1-naphthyl)ethyl)amine ((R)-2) in DMSO. The complexes show a characteristic induced circular dichroism (ICD) in the UV-visible region of the polymer backbone. Moreover, the macromolecular helicity of poly-1 induced by (R)-2 can be "memorized" even after complete replacement of (R)-2 by various achiral amines. We now report fully detailed studies on the mechanism of the helicity induction and memory of the helical chirality of poly-1 by means of UV-visible, CD, and infrared spectroscopies. We have found that a one-handed helix is cooperatively induced on poly-1 upon the ion pair formation of the carboxy groups of poly-1 with optically active amines and that the bulkiness of the chiral amines plays a crucial role for inducing an excess of a single-handed helix. On the other hand, the free ion formation was found to be essential for the macromolecular helicity memory of poly-1 after the replacement of the chiral amine by achiral amines, since the intramolecular electrostatic repulsion between the neighboring carboxylate ions of poly-1 significantly contributes to reduce the atropisomerization process of poly-1. On the basis of the mechanism of helicity induction and the memory of the helical chirality drawn from the present studies, we succeeded in creating an almost perfect memory of the induced macromolecular helicity of poly-1 with (R)-2 by using 2-aminoethanol as an achiral chaperoning molecule to assist in maintaining the memory of helical chirality.     

THE STRUCTURE AND OPTICAL PROPERTIES OF COPOLYMER OF CHOLESTERIC ESTER

The structure and switching properties of liquid crystalline side chain copolymers of cholesteric ester of 1,2-hydroxypropyl 2,4-di-isocyanatoluene methylmethacrylate (PHCPM) have been studied in detail. The cholesteric mesophase of PHCPM is shown by polarizing microscopy, X-ray diffraction and selective light reflection. Solution of PHCPM in CHCl_3 is optically anisotropic; its optical properties were determined by specific rotation [α], circular dichroism (CD) and wide-angle hght scattering (WALS) methods.     

A rational design for the directed helicity change of polyacetylene using dynamic rotaxane mobility by means of through-space chirality transfer

Directed helicity control of a polyacetylene dynamic helix was achieved by hybridization with a rotaxane skeleton placed on the side chain. Rotaxane-tethering phenylacetylene monomers were synthesized in good yields by the ester end-capping of pseudorotaxanes that consisted of optically active crown ethers and sec-ammonium salts with an ethynyl benzoic acid. The monomers were polymerized with [{RhCl(nbd)}(2)] (nbd=norbornadiene) to give the corresponding polyacetylenes in high yields. Polymers with optically active wheel components that are far from the main chain show no Cotton effect, thereby indicating the formation of racemic helices. Our proposal that N-acylative neutralization of the sec-ammonium moieties of the side-chain rotaxane moieties enables asymmetric induction of a one-handed helix as the wheel components approach the main chain is strongly supported by observation of the Cotton effect around the main-chain absorption region. A polyacetylene with a side-chain rotaxane that has a shorter axle component shows a Cotton effect despite the ammonium structure of the side-chain rotaxane moiety, thereby suggesting the importance of proximity between the wheel and the main chain for the formation of a one-handed helix. Through-space chirality induction in the present systems proved to be as powerful as through-bond chirality induction for formation of a one-handed helix, as demonstrated in an experiment using non-rotaxane-based polyacetylene that had an optically active binaphthyl group. The present protocol for controlling the helical structure of polyacetylene therefore provides the basis for the rational design of one-handed helical polyacetylenes.