1,720,962 research outputs found
A systematic study into the influence of aromatic stacking interactions and fluorine substituent effects on molecular organic crystal assembly
No full textThis thesis reports the aromatic stacking interactions observed within a system of related fluorinated organic compounds, fluorinated benzylideneanilines (or fluoroanilines). A comprehensive library of fluoroaniline structures was assembled to systematically study the effect of fluorine substitution primarily on the aromatic stacking interactions, but also the complementarity with any other non-covalent intermolecular interactions. Through controlled, iterative changes to the number and position of fluorine substituents in the molecule, it is possible to examine the shifting preference for different aromatic interaction configurations. The entire library of structures was structurally characterised through single crystal X-ray diffraction analysis. The structures are categorised into groups based on their crystal assembly, intermolecular geometry and spatial packing similarity. A subset of these structures was selected for quantitative analysis of the intermolecular interactions by high resolution data collection and quantum crystallographic methods. Topological analysis of the experimental electron density field gradient using Quantum Theory of Atoms in Molecules and complementary theoretical calculations using the interaction energy approach reveal the nature of these interactions. These analyses compute energies for intermolecular interactions from which the observed crystal structure assembly can be rationalised. The primary results of this study characterise the influence of fluorine substituents on the molecular packing in the crystal. Significantly, these findings show that contrary to popular belief, this influence is not necessarily due to atom-atom intermolecular interactions, but rather to dipole-dipole direct substituent interactions between stacked aromatic rings. This study also generated many more results which characterise the nature of these interactions and when combined with the categorisation of packing motifs this provides a framework within which molecular assembly in this system can be rationalised. From this it is possible to identify the nature of interactions which are clearly dominant and provide a means for characterising other interactions which are not structure-directing
Crystallographic Structures, Structural Similarity Parameters, PIXEL Calculations and Charge Density Data for a Set of Fluoroanilines
No full textAdditional appendices for the Doctoral thesis "A Systematic Study into the Influence of Aromatic Stacking Interactions and Fluorine Substituent Effects on Molecular Organic Crystal Assembly" submitted by Eleanor Dodd April 2020</span
<i>N,N′</i>-Dibutyloxamide
No full textN,N′-dibutyloxamide (1) was prepared by reacting diethyloxalate with n-butylamine in ethyl alcohol and characterized by microanalytical techniques, FT-IR, and NMR spectroscopy. Crystals suitable for single crystal X-ray diffraction (SC-XRD) were obtained from an acetonitrile solution of 1, and the structural characterization showed the presence of intermolecular hydrogen bonding interactions.</p
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
Insertion of degradable thioester linkages into styrene and methacrylate polymers: insights into the reactivity of thionolactones
No full textThe thionolactone 3,3-dimethyl-2,3-dihydro-5H-benzo[e][1,4]dioxepine-5-thione (DBT) is shown to radically homopolymerize, copolymerize rapidly with acrylates and styrene, and, for the first time, copolymerize with methacrylates, introducing a degradable thioester backbone functionality. Surprisingly, the aminolysis of DBT homopolymers was accompanied by the intramolecular ether cleavage, leading to the formation of 2,2-dimethylthiirane and salicylamides. The rapid copolymerization with styrene was exploited to produce degradable copolymers through free-radical polymerization in a starve-fed semibatch setup. The higher reactivity of DBT compared to the current benchmark thionolactone dibenzo[c,e]oxepine-5(7H)-thione (DOT) was inconsistent with the expected electron-donating effect of the alkoxy substituent in DBT. Using single-crystal XRD structure analysis and DFT modeling, this study rationalized the higher reactivity of DBT by (i) better stabilization of the intermediate radical in DBT by means of a better overlap with the adjacent aromatic, which shifts the addition equilibrium to the right; (ii) an increased ring strain in DBT compared to DOT, which drives the ring-opening; and (iii) better reinitiating efficiency of the tertiary alkyl open-ring radical of DBT compared to the benzylic radical of DOT. These insights are expected to facilitate the development of further thionolactone monomers with tailored copolymerization behavior.</p
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
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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