1,721,018 research outputs found
Structural Motifs in Enantiopure Halogenated Aryl Benzyl Sulfoxides: Effect of Fluorine Substitution
No full textA series of enantiopure crystalline aryl benzyl sulfoxides, bearing different substituents on both the aryl groups, were synthesized by an enantioselective oxidation of the corresponding sulfides. Structural investigations, achieved by means of single-crystal X-ray diffraction, allowed us to recognize the main assembling interactions. The same procedure was repeated for some corresponding fluorinated aryl benzyl sulfoxides. The synthesis of the enantiomers of a new fluorinated compound, which shows unusual structural patterns, prompted us to compare the structural motifs of the two families of sulfoxides (fluorinated and unfluorinated) and to investigate the changes due to the fluorine substitution. Some short contacts involving the fluorine atom were discussed in more details, taking into account the recent interest in these sometimes controversial interactions
ChemInform Abstract: Enantio- or Diastereoselective Oxidation of (Methylthio)methylphosphonates as a Route to Precursors of Chiral Sulfoxides.
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A Study of Factors Affecting Enantioselectivity in the Oxidation of Aryl Benzyl Sulfides in the Presence of Chiral Titanium Catalysts
No full textComparison between the Crystal Structures of Racemic and Enantiopure Aryl Benzyl Sulfoxides
No full textIn literature reports about the comparison between the crystal structures of racemic and enantiopure compounds, minor differences have been observed between the conformations of an enantiopure compound and the conformations of the same enantiomer when they are a part of a racemic compound. In the present investigation, the crystal structures of aryl benzyl sulfoxides show peculiar behaviours, in particular when the choice between anti or gauche-conformers was investigated. In three cases of poly-halogenated molecules, the most frequent anti-conformations remain for the crystal structures of racemic compounds, whereas the corresponding enantiopure compounds arrange in gauche-conformations. Energy calculations confirm the interactions building up the crystal structures and suggest the reasons for the gauche–anti choice
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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