1,721,178 research outputs found
Observation of a Direct SnLi Bond; The Crystal and Molecular Structure of Monomeric [Ph3SnLi · PMDETA] and the Detection of 119, 117Sn7Li NMR Coupling in Solution
No full textGeneral equations for determining species involved in solution equilibria and equilibrium constants from solution molecular mass measurements
No full textA simple way by which equilibrium species can be identified with reasonable certainty, and equilibrium constants and thermodynamic data can be thereby extracted, from variable-concentration cryoscopic molecular mass measurements in solution is reported. The method relies on the assumption that the individual molecular species involved in such solution equilibria exert independent and additive contributions to the depression in freezing point from that of the pure solvent. Given this assumption, individual equations can be developed for a given dynamic equilibrium, relating the equilibrium constant (K,)to the molecular mass (Mr) and hence to the degree of association (n)o f the species involved. The measurements will fit best one such equation and can thereby be used to pinpoint the equilibrium species present. To fmt illustrate this method, the variation of the degree of association (n) has been examined over arange of concentrations (up to ca. 0.1 mol L-l) for two lithium-containing complexes in benzene solutions; the inorganic complex, lithium bromide pentamethyldiethylenetriamine, (LiBr-PMDETA), (1) [PMDETA = MeN(CH2CH2NMe2)21, and the amidolithium reagent, (dicyclohexy1amido)lithium hexamethylphosphoramide, [(C6H11)2NLi HMPAIn (2) [HMPA = (MezN)+O]. While both complexes have known dimeric structures in the solid state, the cryoscopic work presented here, and ita fitting to specific equations, implies that both 1 and 2 are involved in essentially dimer + monomer equilibria in such solutions. On this basis, the equilibrium constanta for both complexes were determined [for 1, K, = 1.41 X le2 mol L-l, AGO = 9.8 kJ mol-'; and for 2, K, = 4.0 X le3 mol L-l, AGO = 12.8 kJ mol-']
Nucleophile Substitution an Bis(cyclopentadieny1)- zinn(rr); Synthese, Struktur und dynamisches Verhalten in Lösung von trans-[ (3-Cp)Sn{2-N=C(NMe2)2}]2
No full text‐Cp)Na · PMDETA], a Compound with a Trigonal‐Planar “Paddle Wheel” Triorganostannate Ion
No full textAn organotin(II) anion with three 5-Cp ligands and a p. atom in a trigonal-planar environment are found in the title compound 1 (see diagram), obtained from the reaction of CpNa, [Cp2Sn], and PMDETA (mol ratio 1:1:1). This [Cp3Sn]- ion is linked to the Na+ ion by a -5-Cp bridge. Compound 1 is a polymeric array in the solid state due to intermolecular C(H) Na interactions. PMDETA = (Me2NCH2CH2)2NMe
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
Isolation, structure and MO calculational investigations of a highly stable, hydrogen-bonded primary amine–phosphine oxide adduct, 2-aminobenzothiazole–HMPA, C6H4SC(N)NH2OP(NMe2)3; a possible model to explain the carcinogenicity of HMPA (HMPA = hexamethylphosphoramide)
No full textColourless needles of the 1 : 1 primary amine-phosphine oxide adduct CsH4SC(=N)NH2.0=P(NMe2)a3r e obtained in high yield simply by chilling a toluene solution of the two components; the solid-state structure of the highly stable adduct (which can be prepared in water, and which sublimes easily) consists essentially of dimers held by (amine) N-H...O and (amine)N-H...(heterocyclic) N hydrogen bonds
The observation of a Pb–Li bond; synthesis, structure and model molecular orbital (MO) calculations on the monomeric Ph3Pb–Li·(pmdeta) complex [pmdeta =(Me2NCH2CH2)2NMe]
No full textThe title compound has been synthesised by the cleavage reaction of Ph3Pb–PbPh3 with BunLi and has been shown to have a monomeric Pb–Li bonded structure in the solid state; ab initio calculations have been used to probe the nature of the early main group metal/heavy p block metal bonding involved
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