1,721,004 research outputs found
Palladium-catalysed synthesis of non symmetrically disubstituted-1,1'-biphenyls from o-substituted aryl iodides through aryl coupling and delayed hydrogenolysis
No full textLavoro in onore di Howard Alpe
The mechanochemical conversion of acetone to methyl isobutyl ketone over Cu-Mg based substrates
No full textSelected results concerning the acetone conversion to methyl isobutyl ketone promoted by mechanical energy are presented. Cu-MgO composites at different Cu contents and amorphous Cu40Mg60, prepared by different ball milling techniques, were employed as solid substrates for the mechanochemical process. The conversion and selectivity values of the acetone transformation were followed under Ar and H-2 reaction atmosphere and as a function of the impact energy. The mechanical treatment under H-2 resulted mainly in acetone hydrogenation leading to 2-propanol, while under Ar, the formation of diacetone alcohol, mesityl oxide and methyl isobutyl ketone (MIBK) was observed. Conversion changes and selectivity shifts were observed depending on the substrates employed, and the largest amount of MIBK; was obtained when amorphous Cu40Mg60 was used. An important structural transformation occurred during the mechanochemical runs. (C) 1999 Elsevier Science S.A. All rights reserved
Rates of the oxidative addition of benzyl halides to a metallacyclic palladium(II) complex and of the reductive elimination from a benzyl-palladium(IV) complex.
No full textPd(II) metallacyclic complexes are key intermediates in sequential reactions in which three new
C−C bonds are formed in an aromatic ring. The Pd(II) metallacyclic complex 10 with
phenanthroline as ligand undergoes oxidative addition to benzyl bromide or chloride in DMF to
generate benzyl-Pd(IV) complexes. The rate constant of the oxidative addition is determined by
means of electrochemical techniques, with the expected reactivity order PhCH2Br (k1Br = 3.6 M−1 s−1)
> PhCH2Cl (k1Cl = 6 × 10−3 M−1 s−1) at 29 °C. When the benzyl-Pd(IV) complex is generated from
PhCH2Br, the oxidative addition is followed by a slow C−C reductive elimination, which gives a
Pd(II) complex. The rate constant of the reductive elimination has been determined in DMF (k2Br = 6
× 10−4 s−1) at 29 °C
Synthesis of selectively substituted ortho-vinylbiphenyls by palladium-catalysed reaction of ortho-substituted aryl iodides with olefins
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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
A new catalytic method for the synthesis of selectively substituted biphenyls containing an oxoalkyl chain
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