Comparing the stability of tribenzo[ b , n , pqr ]perylene and tribenzo[ b , k , pqr ]perylene

Two isomeric benzenoid hydrocarbons – tribenzo[b,n,pqr]perylene and tribenzo[b,k,pqr]perylene played a crucial role in the formulation of the Clar aromatic sextet theory. The basic assumption of this theory is that tribenzo[b,n,pqr]perylene is more stable than tribenzo[b,k,pqr]perylene because the former has five, whereas the latter only four aromatic sextets. We now approach this stability problem from a different direction. By means of a recently developed molecular-orbital-based method it is possible to estimate the energy effects of individual cycles, as well as pairs, triplets, etc. of cycles in polycyclic conjugated molecules. From these energy-effects one can better understand which structural details are responsible for the thermodynamic stability of the underlying molecule. In particular, it is possible to rationalize (in a quantitative manner) the causes of differences in the thermodynamic stability of isomers. Our analysis corroborates the conclusion of Clar theory, but points out a number of hitherto overlooked structure-stability connections. Correspondence: Ivan Gutman, Faculty of Science, University of Kragujevac, P.O. Box 60, 34000 Kragujevac, Serbia.     

Comparing the stability of tribenzo[ b , n , pqr ]perylene and tribenzo[ b , k , pqr ]perylene

Two isomeric benzenoid hydrocarbons – tribenzo[b,n,pqr]perylene and tribenzo[b,k,pqr]perylene played a crucial role in the formulation of the Clar aromatic sextet theory. The basic assumption of this theory is that tribenzo[b,n,pqr]perylene is more stable than tribenzo[b,k,pqr]perylene because the former has five, whereas the latter only four aromatic sextets. We now approach this stability problem from a different direction. By means of a recently developed molecular-orbital-based method it is possible to estimate the energy effects of individual cycles, as well as pairs, triplets, etc. of cycles in polycyclic conjugated molecules. From these energy-effects one can better understand which structural details are responsible for the thermodynamic stability of the underlying molecule. In particular, it is possible to rationalize (in a quantitative manner) the causes of differences in the thermodynamic stability of isomers. Our analysis corroborates the conclusion of Clar theory, but points out a number of hitherto overlooked structure-stability connections.     

Ab Initio Study of Conformational Properties of ( Z, Z)-, ( E, Z)-, and ( E, E)-Cyclonona-1,5-dienes

Ab initio calculations at the HF/6-31G^* level of theory for geometry optimization and MP2/6-31G^*//HF/6-31G^* for a single point total energy calculation are reported for the important energy-minimum conformations and transition-state geometries of (Z,Z)-, (E,Z)-, and (E,E)-cyclonona-1,5-dienes. The C₂ symmetric chair conformation of (Z,Z)-cyclonona-1,5-diene is calculated to be the most stable form; the calculated energy barrier for ring inversion of the chair conformation via the C_s symmetric boat-chair geometry is 58.3kJmol^–1. Interconversion between chair and twist-boat-chair (C₁) conformations takes place via the twist (C₁) as intermediate. The unsymmetrical twist conformation of (E,Z)-cyclonona-1,5-diene is the most stable form. Ring inversion of this conformation takes place via the unsymmetrical chair and boat-chair geometries. The calculated strain energy for this process is 63.5kJmol^–1. The interconversion between twist and the boat-chair conformations can take place by swiveling of the trans double bond with respect to the cis double bond and requires 115.6kJmol^–1. The most stable conformation of (E,E)-cyclonona-1,5-diene is the C₂ symmetric twist-boat conformation of the crossed family, which is 5.3kJmol^–1 more stable than the C_s symmetric chair–chair geometry of the parallel family. Interconversion of the crossed and parallel families can take place by swiveling of one of the double bonds and requires 142.0kJmol^–1.     

Ab Initio Study of Conformational Properties of ( Z, Z)-, ( E, Z)-, and ( E, E)-Cyclonona-1,5-dienes

Summary. Ab initio calculations at the HF/6-31G^* level of theory for geometry optimization and MP2/6-31G^*//HF/6-31G^* for a single point total energy calculation are reported for the important energy-minimum conformations and transition-state geometries of (Z,Z)-, (E,Z)-, and (E,E)-cyclonona-1,5-dienes. The C₂ symmetric chair conformation of (Z,Z)-cyclonona-1,5-diene is calculated to be the most stable form; the calculated energy barrier for ring inversion of the chair conformation via the C_s symmetric boat-chair geometry is 58.3kJmol^–1. Interconversion between chair and twist-boat-chair (C₁) conformations takes place via the twist (C₁) as intermediate. The unsymmetrical twist conformation of (E,Z)-cyclonona-1,5-diene is the most stable form. Ring inversion of this conformation takes place via the unsymmetrical chair and boat-chair geometries. The calculated strain energy for this process is 63.5kJmol^–1. The interconversion between twist and the boat-chair conformations can take place by swiveling of the trans double bond with respect to the cis double bond and requires 115.6kJmol^–1. The most stable conformation of (E,E)-cyclonona-1,5-diene is the C₂ symmetric twist-boat conformation of the crossed family, which is 5.3kJmol^–1 more stable than the C_s symmetric chair–chair geometry of the parallel family. Interconversion of the crossed and parallel families can take place by swiveling of one of the double bonds and requires 142.0kJmol^–1.     

冻地银莲花中三萜皂苷的HPLC/MSn分析

药用植物冻地银莲花(Anemone rupestris ssp. gelida)的全草中含有丰富的三萜皂苷, 经HPLC-MSⁿ分析, 发现其总皂苷中共含有10余个三萜皂苷成分. 除由总离子流色谱图给出各皂苷成分的相对含量外, 从每个色谱峰的正负离子ESI-MS获得相应皂苷的分子量, 进而由多级质谱给出糖链连接的信息, 结合文献报道, 将11个主要三萜皂苷成分分别鉴定为革叶常春藤皂苷F (1), 牡丹草皂苷D (2), 刺楸皂苷B (3), 革叶常春藤皂苷E (4), 红毛七皂苷D (5), 常春藤皂苷B(6), 刺五加皂苷C₃ (7), 牡丹草皂苷B (8), 刺楸皂苷A (9), 木通皂苷D (10)和齐墩果酸-3-鼠李糖基-(12)-[葡萄糖基-(14)]-阿拉伯糖苷(11). 其中微量成分2, 5, 7, 10和11为首次从冻地银莲花中分离鉴定. 最后通过与标准品的HPLC保留时间对照证实了他们的存在.     

Lipids of the biomass ofRuta graveolens, grownin vivo andin vitro

A lower content of chlorophylls, phospholipids, and linolenic acid and a higher content of rutin, carotenoids, and xanthophylls in the biomass ofRuta graveolens L. obtainedin vitro has been found as compared with these indices from the epigeal part of the plant grownin vivo.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Institute of Botany, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 651–655, September–October, 1993.     

Steroid compounds ofErysimum XI. Sterols ofErysimum diffusum andE. cuspidatum

Summary It has been shown that the unsaponifiable fraction of the oil ofErysimum cuspidatum contains -sitosterol and campesterol, and the oil ofErysimum diffusum contains -sitosterol.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 821–823, November–December, 1977.     

On functionalized fullerenes C 60 X n

Optimal configurations of functionalized fullerenes C ₆₀ X _n for n = 2, 4, 6, 8 have been determined by application of three topological stability measures. It has been found that the optimal configurations with higher n contain optimal configurations with lower values of n. Two stability measures prefer configurations in which functional groups Xs are crowded while the third one points to configurations with isolated pairs of Xs.     

P(VAc-MMA)为基体的聚合物电解质研究

以醋酸乙烯酯(VAc)和甲基丙烯酸甲酯(MMA)为单体, 采用半连续种子乳液聚合法制备了无规共聚物聚(醋酸乙烯酯-甲基丙烯酸甲酯)[P(VAc-MMA)], 并以此聚合物为基体制备了聚合物电解质. 用红外光谱(FTIR)、核磁共振氢谱(¹H NMR)、扫描电镜(SEM)、差热/热重分析(DSC/TG)、X射线衍射(XRD)、机械性能测试和电化学交流阻抗等方法对聚合物和聚合物电解质的性质进行了研究. 测试结果表明: VAc和MMA聚合生成P(VAc-MMA); 聚合物膜含有大量微孔结构, 利于离子传输; 聚合物电解质膜具有优良的热稳定性和机械强度; 25 ℃下, 最高的离子电导率达到了1.27× 10^－3 S•cm^－1; 离子电导率随着温度的升高而迅速增加, 电导率-温度曲线符合Arrhenius方程.     

Cardenolides ofCoronilla glauca andC. scorpioides

The cardenolide glycosides glucocorotoxigenin, scorpioside, and coronillobioside and a new compound which has been called glucocoroglaucigenin have been isolated from the seeds ofCoronilla glauca L. for the first time. The new glycoside has the structure of 3-(-D-glucopyranosyloxy)-14,19-dihydroxy-5-card-20(22)-enolide. This glycoside has also been isolated from the seeds ofC. scorpioides.Khar'kov Pharmaceutical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 676–679, September–October, 1985.