1,720,976 research outputs found
A Rational Approach Towards a New Ferrocenyl Pyrrolidine for Stereoselective Enamine Catalysis
No full textProline and pyrrolidine derivatives (Hayashi– Jørgensen catalysts) are considered “work horses” in organocatalysis. This report describes a new effective ferrocenyl pyrrolidine catalyst that is able to perform well in benchmark organocatalytic reactions (see figure). The ferrocene moiety controls the conformational space and a simple alkyl group effectively covers a face of the derived enamine. This new framework can find applications in organocatalysis, and in general, in new ligand desig
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A novel approach to the evaluation of the importance of steric and electronic effects in SNAr reactions: a computational, thermodynamic and 1H and 13C NMR study of "Meisenheimer-type" adducts in the benzo[b]thiophene series
No full textThe synthetically useful nucleophilic attack on nitrobenzo[b]thiophenes, a starting point for ring-opening/ring-closure pathways to different heterocyclic systems, has been investigated in detail. 3-Nitrobenzo[b]thiophene (9) and 2 nitrobenzo[b]thiophene (10) react with sodium methoxide in either DMSO or methanol to give the relevant “Meisenheimer-type” adducts 9’ and 10’, identified by NMR spectroscopy. A UV study indicated that the equilibrium constants for the formation of 9’ at 293 K are 10.1 and 40700 Lmol–1 in methanol and in DMSO, respectively. Competition reactions showed that the stability constant of 10’ is lower than that of 9’: accordingly, DFT [B3LYP/6-31+G(d,p)] calculations indicate that the formation of 9’ is thermodynamically more favoured than that of 10’ both in the gas phase and in DMSO. The reason for the opposite sequence in the stability constants previously found for the corresponding gem-dimethoxy Meisenheimer adducts 7’ and 8’ was therefore investigated in depth and appears to be a consequence of different steric interactions in the starting compounds, 2-methoxy-3-nitro- (7) and 3-methoxy-2-nitrobenzo[b]thiophene (8), respectively. A study of 13C NMR chemical shift changes accompanying the formation of adducts 9’ and 10’ confirms that the formation of the adduct exhibiting the larger stability constant is accompanied by a smaller π electron density redistribution, as we have previously found in other cases all governed by electronic effects. The opposite behaviour is observed in the formation of the gem-dimethoxy adducts 7’ and 8’, which is a consequence of the predominance of steric effects. Further outcomes of more general interest deal with the aromatic character of benzo[b]thiophenes. NMR spectroscopic data and calculated bond lengths show that in the studied reactions the benzene ring, unlike the thiophene one, is scarcely affected by methoxide addition, retaining its nearly “full” aromatic character. Benzocondensation increases the stability constants of σ-adducts mainly because of a marked reduction in the aromatic character of the thiophene ring in the substrates
ortho-Substituted (aryl)(3-nitrobenzo[b]thiophen-2-yl)amines: study of the electrochemical behavior
No full textA novel approach to the evaluation of the importance of steric and electronic effects in SNAr reactions: a computational, thermodynamic, 1H and 13C NMR study of “Meisenheimer-type” adducts in the benzo[b]thiophene series
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