1,720,997 research outputs found
Molecular structure and benzene ring deformation of three cyanobenzenes from gas-phase electron diffraction and quantum chemical calculations
No full textTransmission of Electronic Substituent Effects through a Benzene Framework: A Computational Study of 4-Substituted Biphenyls Based on Structural Variation
No full textStructural variations and electronic substituent effects in phenylcubane derivatives: a quantum chemical study
No full textPolar Effects and Structural Variation in 4-Substituted 1-Phenylbicyclo[2.2.2]octane Derivatives: A Quantum Chemical Study
No full textElectronic Substituent Effects in Bicyclo[1.1.1]pentane and [n]Staffane Derivatives: A Quantum Chemical Study Based on Structural Variation
No full textThe transmission of electronic substituent effects through one or more bicyclo[1.1.1]pentane units has been
investigated by ascertaining how a variable substituent at a bridgehead position perturbs the geometry of a
phenyl group at the opposite end of the molecule. We have analyzed the molecular structures of many
bicyclo[1.1.1]pentane and [n]staffane derivatives of general formula Ph-[C(CH2)3C]n-X (n ) 1-5), as
obtained from molecular orbital calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory.
When n ) 1, the structural variation of the benzene ring is controlled primarily by the long-range polar effect
of X, with significant contributions from electronegativity and π-transfer effects. The capability of the
bicyclo[1.1.1]pentane framework to transmit these short-range effects originates from the rather high electron
density inside the cage and the hyperconjugative interactions occurring between substituent and framework.
A set of at least two bicyclo[1.1.1]pentane units appears to be necessary to remove most of the electronegativity
and π-transfer effects. In higher [n]staffanes (n g 3), the very small variation of the benzene ring geometry
is controlled entirely by the long-range polar effect of X. With charged groups and for n g 2, the potential
energy of the ring deformation decreases linearly with n-3. In Ph-C(CH2)3C-X molecules, the relatively
large deformation of the bicyclo[1.1.1]pentane cage is determined primarily by the electronegativity of X,
similar to the electronegativity distortion of the benzene ring in Ph-X molecules. Transfer of π electrons
from substituent to cage or vice versa also plays a role in determining the cage deformation
Molecular structure and conformation of triphenylsilane from gas-phase electron diffraction and theoretical calculations, and structural variations in H4−nSiPhn molecules (n = 1–4)
No full textElectronegativity and resonance parameters from the geometry of monosubstituted benzene rings
No full text
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
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