1,721,049 research outputs found
Photocyclisations of o-iodobenzyl-indanonesand tetralones infer the intermediacyof triplet aryl cations
No full textPhotocyclisations of aryl iodides to 2-indanones and 2-tetralones give different outcomes to analogous radical reactions implicating the intermediacy of triplet aryl cations. Additions to 2-indanones genereally give dibenzoisochromenones by sequential cyclisation, CO extrusion and electrocyclisation. By contrast, 2-tetralones produce benzo[a]phenalenones by ortho-cyclisation
Predictive TDDFT Methodology for Aromatic Molecules UV-Vis properties: from Benchmark to Applications
No full textThe absorption and emission properties of a series of 44 aromatic molecules have been investigated in Time Dependent Density Functional Theory (TDDFT) using different exchange-correlation functionals. Solvent effects have been included within linear response (LR) and state specific (SS) polarisable continuum model (PCM). The comparison with experimental UV-Vis data showed reasonable agreement for all the aromatic molecules when ωB97XD with SS-PCM is used. In particular, we found an accurate linear correlation between experimental and theoretical results which is revealed in an equation for absorption and another equation for emission derived from a linear fitting between theoretical and experimental data. Through these linear equations we propose a simple, pragmatic and effective approach able to describe and predict the absorption and the emission of aromatic molecules with a reasonable computational cost.</p
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
Dearomatization of electron-poor arenes by (4+2) cycloaddition reactions
No full textLes composés aromatiques sont largement accessibles, que ce soit à partir de la pétrochimie, ou de molécules naturelles. Ainsi, des efforts importants ont été faits pour convertir ces molécules simples et facilement disponibles en structures 3D complexes d’intérêts synthétiques tels que des polycycles possédant des centres tétrasubstitués, utiles par exemple dans la synthèse de produits naturels ou pharmaceutiques. Même si plusieurs méthodes efficaces de désaromatisation ont été décrites, le développement de méthodologies complémentaires reste nécessaire. Dans ce contexte, les cycloadditions (4+2) représentent une approche attrayante pour obtenir des composés polycycliques complexes à partir de substrats aromatiques simples. Au cours de ce travail, nous avons examiné la réactivité de différents composés nitroaromatiques vis-à-vis des des silyloxydiènes lors de cycloadditions de Diels-Alder à demande électronique normale. Ces réactions se font sous pression ambiante pour les dérivés du nitroindole ; tandis qu'une pression élevée est nécessaire pour les nitroaromatiques moins réactifs. Une méthodologie complémentaire basée sur l'activation nucléophile du diène, par la formation de son énolate de lithium, a été développée. La désaromatisation des nitroarènes par des énolates lithiés peut également avoir lieu dans un processus formel de cycloaddition (4+2).Aromatic compounds are common substrates, obtained either from the petrochemical industry or from natural products. Thus, important efforts have been made to convert these simple and easily available molecules into complex 3D structures of synthetic interest such as polycycles featuring tetrasubstituted centers, for example, useful in the synthesis of natural or pharmaceutical products. Even if several efficient dearomatizing methods have been reported, the development of complementary methodologies is still needed. In this context, (4+2) cycloadditions represent an attractive approach to obtain complex polycyclic compounds from simple aromatic substrates. In the course of this work, we have examined the reactivity of different nitroaromatics towards silyloxydienes in Normal Electron Demand Diels-Alder cycloadditions. These reactions showed to proceed under ambient pressure for nitroindole derivatives, while high pressure conditions were needed for more challenging nitroaromatics. A complementary methodology based on the nucleophilic activation of the diene, through the formation of its lithium enolate has been developed. The dearomatization of nitroarenes by lithiated enolates can also take place following a formal (4+2) cycloaddition process
Development of recyclable elastomers from tire waste through olefin metathesis and Diels-Alder reactions
No full textLes travaux présentés dans ce manuscrit portent sur le développement d’un procédé de valorisation chimique des déchets pneumatiques pour la préparation de matériaux élastomères. Dans un premier temps, la synthèse de polydiènes fonctionnalisés avec des groupements furane via la réaction de métathèse croisée d’oléfines catalysée au ruthénium, entre un polydiène et un alcène symétrique porteur de fonctions furane (agent de transfert de chaîne, CTA). Après une optimisation de la réaction sur le polyisoprène, comme polydiène modèle, elle a été étendue aux granulats de déchets pneumatiques, permettant d’obtenir des polydiènes à haute valeur ajoutée avec des masses molaires contrôlées, de faibles dispersités, des bons taux de fonctionnalisation et de très bons rendements.Dans une seconde étape, les polydiènes obtenus ont été réticulés par réaction de Diels-Alder avec des agents de réticulation multifonctionnels contenant des motifs maléimide, soit pétrosourcés, soit issus de déchets pneumatiques. La réaction de Diels-Alder a été activée thermiquement et par micro-ondes pour former des réseaux élastomères thermoréversibles. Ces derniers ont été analysés, leurs propriétés thermomécaniques modulées en fonction de la nature des polydiènes et agents de réticulation utilisés, et de leur ratio molaire.Enfin, ces réseaux élastomères ont été recyclés avec succès par des cycles Diels-Alder/rétro-Diels-Alder, et conservent leurs propriétés thermomécaniques même après plusieurs cycles, démontrant ainsi leur potentiel pour des applications durables.The work presented in this manuscript focuses on the development of a chemical valorization process for tire waste to prepare elastomeric materials. Initially, the synthesis of functionalized polydienes with furan groups was carried out via the cross-metathesis reaction of olefins catalyzed by ruthenium, involving a polydiene and a symmetrical alkene bearing furan functions (chain transfer agent, CTA). After optimizing the reaction on polyisoprene as a polydiene model, the method was extended to tire waste granulates, resulting in high-value poly dienes with controlled molar masses, low dispersities, good functionalization rates, and very high yields.In a second step, the obtained polydienes were crosslinked through a Diels-Alder reaction with multifunctional crosslinking agents containing maleimide moieties, derived from petrochemical sources or from tire waste. The Diels-Alder reaction was thermally activated and also activated by microwaves to form thermoreversible elastomer networks. These networks were analyzed, and their thermomechanical properties were modulated based on the nature of the poly dienes and crosslinking agents used, as well as their molar ratio.Finally, these elastomeric networks have been successfully recycled through Diels-Alder/retro-Diels-Alder cycles, maintaining their thermomechanical properties even after several cycles, thereby demonstrating their potential for sustainable applications
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
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