1,720,958 research outputs found
Synthesis and characterization of isomeric α,α′- bithienyls with β-methylsulfanyl substituents
No full textThe three isomeric bithienyls, 1, 2 and 3, formally related to the dimerization of 3-(methylsulfanyl)-thiophene, have been synthesized by the metal-catalysed coupling between a metallated and a halogenated derivative of thiophene of suitable structure. The 1H and 13C NMR data are discussed
CRYSTAL AND MOLECULAR-STRUCTURE OF CIS-[DICHLOROBIS(METHYL PHENYL SULPHOXIDE)]PLATINUM(II) AND CIS-[DICHLOROBIS(BENZYL METHYL SULPHOXIDE)]PLATINUM(II) - AN X-RAY AND NMR SPECTROSCOPIC STUDY
No full textReactions of (R,S)-methyl phenyl sulphoxide and (R,S)-benzyl methyl sulphoxide with K2PtCl4 give diastereomeric mixtures of cis-L2PtCl2 complexes. The mixtures isolated from the reactions, change their composition when allowed to stand in solution, to give, at equilibrium, ratios of +/- and meso forms which differ as a function of the sulphoxide employed. The crystal structure of one of the diastereoisomers isolated in the case of the complex obtained from (R,S)-methyl phenyl sulphoxide is built up from racemic pairs of discrete molecules with R,R and S,S configurations at chiral sulphur atoms. The crystals of the complex prepared from (S)-benzyl methyl sulphoxide contain two crystallographically independent but chemically equivalent molecules with S,S absolute configuration at sulphur atoms, and one methanol solvate molecule. In both complexes the metal atom shows cis square-planar coordination geometry of the two chlorine and two sulphur atoms from the organic ligands. The complexes show differences in the orientation of the sulphoxide ligands with respect to the co-ordination plane. The NMR parameters obtained at H-1, C-13 and Pt-195 frequencies provide useful indications for recognizing +/- and meso forms of platinum(II) complexes of sulphoxides and also contain information on the relative conformational patterns of the free and complexed ligands
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
CONFORMATIONAL PROPERTIES OF 3,3'-, 3,4'- AND 4,4'-DIMETHYL- AND -BIS(METHYLSULFANYL)-2,2'-BITHIOPHENES
No full textThe conformational properties of the title compounds, which are the basic head-to-head, head-to-tail and tail-to-tail repeat units of regioregular poly(3-methylthiophenes) and poly[3-(methylsulfanyl)thiophenes], are discussed. The paper reports the X-ray structures of the two 4,4'-derivatives, H-1 NMR NOE data on the 3,4'- and 4,4'-derivatives and force field MM2 calculations of the conformation of the three bis(methylsulfanyl) derivatives
Effect of ortho substituents on the internal rotation processes and conformational preferences of 1,2-diaryl-1,1,2,2-tetrachloroethanes: A 1H and 13C NMR variable temperature and x-ray structural study
No full textThe conformational behaviour of 1,2-diaryl-1,1,2,2-tetrachloroethanes, ortho,ortho'-disubstituted with CN (1), F (2) and CO2CH3 (3), and of the mesityl derivative (4), has been studied in solution by variable temperature H-1 and C-13 NMR spectroscopy. The internal rotation processes around the exocyclic C-C and central C-C bonds appear to have similar energy barriers and thus behave differently from the compounds without ortho substituents, studied previously, which have a higher barrier for the interconversion of anti/gauche conformers. At low temperature, compounds 1-3 exist as mixtures of gauche and anti conformers with the former prevailing; compound 4 is almost exclusively in the gauche form. The solid state crystal and molecular structure has been determined for compounds 2 and 3. The molecule of compound 2 has point symmetry () over bar 1, which defines perfect staggering around the central C-C bond with the aromatic rings anti. The structure is affected by statistical disorder due to two alternate orientations of the phenyl rings. The crystal structure of compound 3 indicates one asymmetrical molecule in a gauche conformation. Statistical disorder involves both the methoxycarbonyl substituents at the phenyl rings; these latter display almost the same orientation with respect to the C(sp(3)) carbons, in both compounds
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
Conformational study of substituted methyl phenyl sulphoxides. A multinuclear (1H, 13C, and 17O) approach
No full textA number of ring-substituted methyl phenyl sulphoxides have been examined with a multinuclear n.m.r. approach in order to obtain experimental evidence of the conformational properties of the methylsulphinyl group bonded to an aromatic ring. Measurements were performed of 1H, 13C, and 17O chemical shifts and LIS (lanthanide-induced shifts) on 1H and 13C, long-range 13C 1H coupling constants. Each of these approaches by itself is not fully conclusive in showing the orientation of the SO bond in the different compounds examined, but by using them in combination a sound picture of the conformational behaviour of these molecules in solution can be obtained. The SO bond is thus almost coplanar with the aromatic ring in ortho-substituted compounds and oriented in the opposite direction with respect to the substituent. The twist-angle probably differs slightly as a function of the ortho-group. An increasing degree of distortion from coplanarity is found in parasubstituted derivatives and ortho-disubstituted compounds. As regards 170 chemical shifts, these were found to span a smaller range than in the corresponding acetophenones
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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