Search results for "functional"
showing 10 items of 4822 documents
Enantioselective Synthesis of 5-Trifluoromethyl-2-oxazolines under Dual Silver/Organocatalysis.
2019
[EN] The first enantioselective formal [3 + 2] cycloaddition between ¿-isocyanoesters and trifluoromethylketones to give 5-trifluoromethyl-2-oxazolines bearing two contiguous stereogenic centers, one of them being a quaternary stereocenter substituted with a CF3 group, has been developed. The reaction is based upon a multicatalytic approach that combines a bifunctional Brønsted base-squaramide organocatalyst and Ag+ as Lewis acid. The reaction could be achieved with a range of aryl and heteroaryl trifluoromethyl ketones, and the resulting oxazolines were obtained with good to excellent diastereo- and enantioselectivity.
Compressibility and phase stability of iron-rich ankerite
2021
ABSTRACT: The structure of the naturally occurring, iron-rich mineral Ca₁․₀₈(₆)Mg₀.₂₄(₂)Fe₀.₆₄(₄)Mn₀.₆₄(₄)(CO₃)₂ ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch-Murnaghan equation of state yields V₀ = 328.2(3) ų, bulk modulus B₀ = 89(4) GPa, and its first-pressure derivative B'₀ = 5.3(8)-values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO₃)₂ ankerite composition. At 12 GPa, the iron-rich ankerite structure …
Synthesis of a new family of bi- and polycyclic compounds via Pd-catalyzed amination of 1,7-di(3-bromobenzyl)cyclen
2008
Abstract New bicyclic cryptand type compounds are synthesized by reacting 1,7-di(3-bromobenzyl)cyclen with 1 equiv of linear polyamines under dilute conditions using Pd-catalyzed amination. Bis(cyclen) and tris(cyclen) compounds containing linear polyamine linkers between benzylated cyclens are obtained by a similar procedure using different reaction conditions. Cyclization of these species via intramolecular catalytic diamination led to tri- and tetracyclic polyaza compounds.
Synthesis, Characterization, and Properties of Weakly Coordinating Anions Based on tris-Perfluoro-tert-Butoxyborane
2017
A convenient method for the preparation of strongly Lewis acidic tris-perfluoro-tert-butoxyborane B(ORF)3 (1), (ORF = OC(CF3)3) was developed, and its X-ray structure was determined. 1 was used as a precursor, guided by density functional theory (DFT) calculations and volume-based thermodynamics, for the synthesis of [NEt4][NCB(ORF)3] (3) and [NMe4][FB(ORF)3] (5) and the novel large and weakly coordinating anion salts [Li 15-Crown-5][B(ORF)4] (2) and [NEt4][CN{B(ORF)3}2] (4). The stability of [B(ORF)4]− was compared with that of some related known weakly coordinating anions by appropriate DFT calculations.
Stark ionization of atoms and molecules within density functional resonance theory
2013
We show that the energetics and lifetimes of resonances of finite systems under an external electric field can be captured by Kohn–Sham density functional theory (DFT) within the formalism of uniform complex scaling. Properties of resonances are calculated self-consistently in terms of complex densities, potentials, and wave functions using adapted versions of the known algorithms from DFT. We illustrate this new formalism by calculating ionization rates using the complex-scaled local density approximation and exact exchange. We consider a variety of atoms (H, He, Li, and Be) as well as the H2 molecule. Extensions are briefly discussed.
The role of the economic crisis on the competitiveness of the agri-food sector in the main Mediterranean countries
2014
Th e world economic crisis that, since 2008 has also struck the real economy, cannot be attributed only to the United States bubble which in 2007 involved the mortgage credit market, but it is the result of a series of factors among which the imbalance of the fi nancial market, of the public accounts of the main economies and the real sector. Also agricul- ture, which has always been considered an anti-cyclic sector, has seen a strong slowdown with a plunge in the trade fl ows. Th is paper analyses the changes which happened to the competitive position in the world market of some Mediterranean countries and of France, Italy, Spain and Turkey in particular trying, moreover, to understand the…
L’èxtasi poètic de Fontanella: metateatre i música a la Lloa per la Tragicomèdia pastoral d’amor, firmesa i porfia
2018
Resum: En absència d’estudis monogràfics sobre la Lloa de Fontanella, aquest article n’ analitza l’estructura dramàtica, començant amb una reflexió sobre llur classificació dintre del gènere i sobre l’espai de la Barcelona del segle XVII que podria haver-la escenificat. La importància funcional que el poeta barceloní atorga a la música i al metateatre condueixen a una interpretació de la Lloa des d’un punt de vista poeticomusical, la qual cosa permet una nova lectura de certs passatges i una valoració crítica que afecta, no només a la peça en qüestió sinó a tota la Tragicomèdia pastoral d’amor, firmesa i porfia i al caràcter d’avantguarda del teatre català de l’Edat Moderna
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The language-(in)dependence of writing skills: translation as a tool in writing process research and writing instruction
2014
A pilot study was conducted in which 6 students with L1 German had to produce a German version of a text they had composed in their L2 English. The goals were to explore (a) in what respects the ability of advanced university English students to express themselves in their L2 English differs from their ability to do so in their L1 German, and (b) for which aspects of writing the implementation of translation exercises is useful as a tool to improve writing skills. The methods of data collection used were think-aloud and keystroke logging. In the analysis, special emphasis was placed on text-level errors as opposed to formal, lexical and grammatical errors. In their L1 versions, students wer…
Vagueness expressions in Italian, Spanish and English task-oriented dialogues
2017
In this article, we present a corpus-based analysis on the use of Vagueness Expressions (VEs) in Italian, Spanish and English in Task-oriented Dialogues. Following the distinction among informational, relational and discourse vagueness (Voghera 2012), we compare the width of the functional space of the most frequent VEs. In particular we investigate whether and to what extent the VEs cover all the types of vagueness in the three languages. Quantitative and qualitative analysis brings evidence about a high convergence in the vagueness functions expressed by the VEs of the three languages.
Aportaciones documentales sobre cruces de orfebrería valencianas. Siglos XIV y XV
2020
The article intends to make a contribution of new documentary references, from the notarial funds of the Valencian archives, in which news about parish crosses and Lignum Crucis from the silversmith center of Valencia during the fourteenth and fifteenth centuries are collected. The importance of these typologies lies in being the main elements of Christian worship, so it was an essential piece in each parish that allowed the provision in them of models of varied typology and functionality; for that reason they are conserved from altar crosses, cross-shaped reliquaries ?known as Lignum Crucis or Veracruz ?to processional crosses, larger and representative of the parish community to which it …