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81.
Kentaro Okuma Jun-ichi Sakata Yuji Tachibana Takumi Honda Hiroshi Ohta 《Tetrahedron letters》1987,28(52):6649-6652
Wittig reagents were successfully changed to symmetrical olefins when treated with elemental selenium. The reaction proceeds through a selenocarbonyl intermediate, which existence was confirmed by Diels-Alder reaction. 相似文献
82.
83.
A 1,3,5-substituted benzene platform has been widely used in the fields of supramolecular chemistry and molecular recognition. Here, we show that 1,3,5-tris(2-benzyl-o-carboran-1-yl)benzene 6 exhibits solvent-dependent conformation in the crystalline state. Recrystallization from dichloromethane-n-pentane gave the anti conformation 6-anti, while recrystallization from methanol-acetone gave the syn conformation 6-syn, in which the three benzyl-o-carboranyl moieties are located to one side of the central benzene ring. Interestingly, one acetone molecule is captured in the π-rich space of 6-syn and two complexes facing each other encapsulate two acetone molecules in a π-rich container formed by the eight benzene rings. The inclusion involves several weak interactions, that is, T-shaped C-H···π interactions, and C-H···O and C-H···π interactions. Two C-H···O interactions involving benzylic C-H hydrogens activated by the electron-withdrawing character of the o-carborane cage and the oxygen atom of the acetone seem to be the most important. DFT calculations indicate that the binding energy for entrapment of acetone is 6.6 kcal/mol. Inclusion of acetone is achieved through not only multiple C-H···O interactions but also a number of C-H···π interactions. The third benzyl-o-carborane moiety is fixed in the syn conformation by intramolecular and intermolecular C-H···π interactions. 相似文献
84.
Synthesis of a highly luminescent three-dimensional pyrene dye based on the spirobifluorene skeleton
We have synthesized a highly luminescent (log e > 5.0, F > 0.9) pyrene dye based on a spirobifluorene skeleton [2,2',7,7'-tetrakis(7-tert-butyl-1-pyrenyl)-9,9'-spirobi[9H-fluorene; 4-PySBF]. The use of spirobifluorene prevents fluorescence quenching by intramolecular energy transfer and/or electron transfer among the chromophores in the excited state. The emission spectra of 4-PySBF exhibited a red shift of 20 nm in comparison to a model compound [9,9'-dioctyl-2,7-bis(7-tert-butyl-1-pyrenyl)-9H-fluorene; 2-PyF], but its UV-Vis spectrum remained unchanged. 相似文献
85.
Bending tests and X-ray diffraction studies were conducted on oven-dried wood samples (Picea jezoensis Carr.) treated with various concentrations of aqueous NaOH solution to investigate the influence of alkali treatment on the
longitudinal contraction, bending properties, and cellulose structure. The length of the wood samples decreased and the density
increased at NaOH concentrations greater than 10%. The Young’s modulus and the specific Young’s modulus decreased and the
strain at yield increased for the same concentration range. However, the stress at yield was almost constant for all concentration
ranges. X-ray diffraction analysis showed that lattice transformation from cellulose I to cellulose II did not occur during
alkali treatment and the crystallinity index decreased at NaOH concentrations greater than 10%. The crystallinity index was
linearly correlated with the changes in longitudinal contraction and the bending properties, which indicates that the increase
in the proportion of amorphous components of the cellulose influences the longitudinal contraction and the bending properties
of wood samples during alkali treatment. 相似文献
86.
This study examined the relationship between the functions of plant cells and the characteristics of cellulose microfibril
aggregates in the cell walls. For this purpose, the mature bamboo (Phyllostachys pubescens) culm was separated into fiber and parenchyma cells, and then the morphological and physical properties of the cellulose
microfibril aggregates isolated from both cells were compared. SEM observations revealed that both fiber and parenchyma cells
consist of similar microfibril aggregates approximately 15–20 nm in width. Moreover, X-ray analysis and the tensile tests
of the sheets prepared from the microfibril aggregates showed that the cellulose microfibrils isolated from fiber and parenchyma
cells had almost the same cellulose crystallinity and longitudinal Young’s modulus in the dry state. These results suggest
that all the cellulose microfibrils synthesized in the same individual exhibit the same characteristics in the dry state regardless
of cell function. 相似文献
87.
Kentaro Hatsumi Dolors Berga Shigehiro Serizawa 《International Journal of Game Theory》2014,43(1):153-168
Following “Barberà et al. (1991, Econometrica 59:595–609)”, we study rules (or social choice functions) through which agents select a subset from a set of objects. We investigate domains on which there exist nontrivial strategy-proof rules. We establish that the set of separable preferences is a maximal domain for the existence of rules satisfying strategy-proofness and no-vetoer. 相似文献
88.
We highlight that the connection of well-foundedness and recursive definitions is more than just convenience. While the consequences of making well-foundedness a sufficient condition for the existence of hierarchies (of various complexity) have been extensively studied, we point out that (if parameters are allowed) well-foundedness is a necessary condition for the existence of hierarchies e.g. that even in an intuitionistic setting \({(\Pi_1^0-\mathsf{CA}_0)_\alpha \vdash \mathsf{wf}(\alpha)\, {\rm where}\, (\Pi_1^0-\mathsf{CA}_0)_\alpha}\) stands for the iteration of \({\Pi^0_1}\) comprehension (with parameters) along some ordinal \({\alpha}\) and \({\mathsf{wf}(\alpha)}\) stands for the well-foundedness of \({\alpha}\) . 相似文献
89.
90.
Kentaro Kojima 《Applied mathematics and computation》2010,217(8):4047-4050
This paper extends two existent methods, called the blockability relation and the viability relation, for simple games to compare influence of coalitions, to those for games in characteristic function form, and shows that the newly defined relations satisfy transitivity and completeness. It is shown in this paper that for every game in characteristic function form the blockability relation and the viability relation have a complementary interrelationship. 相似文献