1,721,063 research outputs found
High-pressure single crystal X-ray diffraction study of the linear metal chain compound Co-3(dpa)(4)Br-2 center dot CH2Cl2
No full textThe crystal structure of the linear metal chain compound Co-3(dpa)(4)Br-2 center dot CH2Cl2 (1) has been investigated up to a pressure of 13.6(2) GPa in a diamond anvil cell (DAC) using single crystal X-ray diffraction. The structure remains orthorhombic as the unit cell volume is reduced by 30% at 12.8 GPa. At 13.6(2) GPa the diffraction pattern is of very poor quality and not even reliable unit cell parameters can be determined. Peak broadening resulting from non-hydrostatic conditions was avoided by annealing the loaded DAC prior to data collection, allowing reliable structural models to be refined up to a pressure of 11.8(2) GPa. On increasing pressure, the disordered CH2Cl2 crystal solvent molecule gradually becomes redistributed from one site to another. Hirshfeld surface analysis suggests that the redistribution is a result of repulsive H center dot center dot center dot H interactions. Pressure also affects the molecular geometry, in particular the Co-Co and Co-Br bond lengths which decrease by 4% and 12%, respectively, at 11.8(2) GPa
Amine thiourea catalysed double Michael reaction: an approach for the asymmetric synthesis of spiro[pyrazolone-4,3'-tetrahydrothiophenes]
No full textA domino reaction, based on an organocatalyzed sulfa-Michael-Michael sequence, demonstrated to be useful for the asymmetric synthesis of spiro[pyrazolone-4,3’-tetrahydrothiophenes], bearing three consecutive stereocenters. This new class of spirocyclic compounds has been synthesized in good yield, fairly good diastereo- and enantioselectivity by reacting alpha-unsaturated pyrazolones and trans-tert-butyl 4-mercapto-2-butenoate in the presence of a readily available secondary amine thiourea derived from (R,R)-1,2-diphenyl ethylenediamine
Tunable Cinchona-Based Thioureas-Catalysed Asymmetric Epoxidation to Synthetically Important Glycidic Ester Derivatives
No full textA novel class of synthetically important
glycidic esters has been obtained via an asymmetric
epoxidation of trans-alpha-cyano-alpha,beta-unsaturated esters
catalysed by a multifunctional Cinchona alkaloidderived
thiourea/tert-butyl hydroperoxide (TBHP)
system. The glycidic esters, isolated in excellent
yield with complete trans-diastereocontrol and high
enantioselectivity, proved to be versatile building
blocks to access challenging small targets bearing
a quaternary stereocenter
The Quest for Optimal 3 d Orbital Splitting in Tetrahedral Cobalt Single‐Molecule Magnets Featuring Colossal Anisotropy and Hysteresis
No full textDiastereodivergent and Enantioselective Access to Spiroepoxides via Organocatalytic Epoxidation of Unsaturated Pyrazolones
No full textReadily available chiral amine−thioureas are effective catalysts for the first diastereo- and enantioselective epoxidation of unsaturated pyrazolones. The trans- or cis-spiroepoxides are preferentially obtained in good yield and high to excellent enantioselectivity using an appropriate organocatalyst and tert-butyl hydroperoxide as the oxidant. The epoxidation appears applicable to highly challenging β,β′-substituted unsaturated pyrazolones, giving access to spiroepoxides bearing two vicinal quaternary stereocenters. The reaction represents a unique example of Weitz−Scheffer epoxidation, where the catalystcontrolled ring-closure step is usefully exploited to prepare both enantioenriched diastereomeric epoxides
Experimental and theoretical charge density studies of tetrafluorophthalonitrile and tetrafluoroisophthalonitrile
No full textThe experimental electron density distributions (EDD) in tetrafluorophthalonitrile and tetrafluoroisophthalonitrile have been determined from a multipole refinement with use of accurate X-ray diffraction data collected at 100 K. As hydrogen atoms pose a serious challenge to a successful X-ray based EDD determination due to their diminishing diffraction power, the absence of any such atoms in the studied complexes is an important advantage. The experimental EDD is compared with theoretical densities resulting from high-level ab initio and DFT calculations using the atoms in molecules theory. Topological analysis of the electron density was used to compare the two different isomers and to estimate the similarity of identical functional groups in different crystalline environments. Comparison with theoretical results reveals subtle differences in C-F bonds. The experimental molecular electrostatic potential satisfactorily explains the observed differences in the patterns of weak intermolecular interactions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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