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Electron-transfer-induced reductive dealkoxylation of alkyl aryl ethers .2. Reductive cleavage of isomeric dimethoxybenzenes
No full textThe reactivity of the three isomeric dimethoxybenzenes in the reduction with potassium metal in THF and iso-octane in the absence of proton donors has been studied. The ortho and meta isomers reacted readily to afford products of both demethoxylation and demethylation, with the former prevailing for the ortho isomer in THF and for both isomers in iso-octane. Furthermore, in iso-octane, particularly at high temperature, significant amounts of benzene, the product of double demethoxylation, were formed. Exclusive demethylation was instead observed under all reaction conditions for the para isomer, which showed to be the least reactive of the three isomers. Labelling experiments have also been carried out in order to shed light on the mechanism of demethoxylation. The results are consistent with a competition between two modes of fragmentation of a radical anion, leading to aryl radical and methoxide anion on one side (demethoxylation) and to phenoxide anion and methyl radical on the other side (demethylation); in a subsequent step, the radicals thus formed abstract a hydrogen atom from components of the reaction medium or are reduced by single electron transfer to the corresponding anions. As concerns demethylation, however, a mechanism involving fragmentation of a dianion cannot be excluded. In light of previous results, a rationalization of the different reactivity of the three isomers is discusse
Regioselective Reductive Electrophilic Substitution of Derivatives of 3,4,5-Trimethoxybenzaldehyde
No full textThe behavior of several protected derivatives of 3,4,5-trimethoxybenzaldehydeh as been investigated under
conditions of electron transfer from alkali metals in aprotic solvents. The 4methosy group can be regioselectively
removed in good to high yield under such conditions, and an appropriate choice of the protecting group, metal,
and solvent allows its substitution with a variety of electrophiles. 3,4,5-"rimethoxybeddehyde dimethyl acetal,
1, is the starting material of choice for a new general synthetic approach to several polysubstituted resorcinol
dimethyl ethers. Inveatigation of the m e d " of demethoxylation, with the aid of labeling experiments, showed
that reductive demethoxylation is strongly influenced by the nature of the aldehyde protective group employe
Electron-Transfer-Induced Reductive Demethoxylation of Anisole: Evidence for Cleavage of a Radical Anion
No full textThe electron-transfer induced cleavage of anieole with alkali metals (mostly potassium) in the absence of proton
donors was studied in solvents of low polarity under a variety of conditions. In THF exclusive demethylation
to phenol was observed, regardleas of the temperature, whereaa in solvents of very low dielectric constant (aliphatic
hydrocarbons, toluene, tributylamine, dioxane) demethoxylation to benzene was the main reaction pathway,
particularly at the lowest temperatures investigated. Inveatigation of the mechanism of demethoxylation, with
the aid of labeling experiments, provided strong evidence for fragmentation of the radical anion of anisole to
methoxide anion and phenyl radical, in a subsequent step, the latter abstracta a hydrogen atom from components
of the reaction medium or undergoes one-eledron reduction to phenyl anion. The influence of solvent and
temperature on the regioselectivity of cleavage is discussed
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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