Search results for "SUBSTITUTION"
showing 10 items of 536 documents
Synthesis, structure and reaction chemistry of a nucleophilic aluminyl anion.
2018
The reactivity of aluminium compounds is dominated by their electron deficiency and consequent electrophilicity; these compounds are archetypal Lewis acids (electron-pair acceptors). The main industrial roles of aluminium, and classical methods of synthesizing aluminium–element bonds (for example, hydroalumination and metathesis), draw on the electron deficiency of species of the type AlR3 and AlCl31,2. Whereas aluminates, [AlR4]−, are well known, the idea of reversing polarity and using an aluminium reagent as the nucleophilic partner in bond-forming substitution reactions is unprecedented, owing to the fact that low-valent aluminium anions analogous to nitrogen-, carbon- and boron-centred…
Methyl [4-methoxy-3-(methylsulfonyloxy)benzoyl]formate
2005
The crystal structure of the title compound, C11H12O7S, confirms an earlier proposal concerning the regioselectivity of electrophilic substitution reactions of mesyl guaiacol.
Crystal Structure of New Heusler Compounds
2009
Heusler compounds are promising materials in many fields of contemporary research. The spectrum of their possible applications ranges from magnetic and magneto-mechanical materials over semiconductors and thermoelectrics to superconductors. An important feature of the Heusler compounds is the possibility of controlling the valence electron concentration by partial substitution of elements. On the other hand, the properties also depend on the degree of ordering of the the crystal structure. In general, Heusler compounds crystallize in the Cu2MnAl-type structure but in many cases certain types of disorder are observed. In this paper a detailed description of the different types of disordered …
Asymmetric tandem reactions: New synthetic strategies
2010
The use of domino and multicomponent reactions in asymmetric synthesis is constantly increasing nowadays. This allows for the synthesis of complex molecules in a single synthetic sequence, usually with high atom economy. Herein, we report three examples of new asymmetric tandem reactions recently developed in our laboratories, giving rise to new families of enantiomerically enriched fluorinated and nonfluorinated heterocycles. Thus, 1,4-dihydropyridines (1,4-DHPs) bearing fluorinated substituents at C6 were assembled by means of a Hantzsch-type reaction; cyclic β-amino carbonyl derivatives were prepared using a cross-metathesis (CM)–intramolecular aza-Michael sequence; while fluorinated ind…
Carbon Nano-onions: Potassium Intercalation and Reductive Covalent Functionalization
2021
Herein we report the synthesis of covalently functionalized carbon nano-onions (CNOs) via a reductive approach using unprecedented alkali-metal CNO intercalation compounds. For the first time, an in situ Raman study of the controlled intercalation process with potassium has been carried out revealing a Fano resonance in highly doped CNOs. The intercalation was further confirmed by electron energy loss spectroscopy and X-ray diffraction. Moreover, the experimental results have been rationalized with DFT calculations. Covalently functionalized CNO derivatives were synthesized by using phenyl iodide and n-hexyl iodide as electrophiles in model nucleophilic substitution reactions. The functiona…
First Principles Calculations of Atomic and Electronic Structure of TiAl3+- and TiAl2+-Doped YAlO3
2021
In this paper, the density functional theory accompanied with linear combination of atomic orbitals (LCAO) method is applied to study the atomic and electronic structure of the Ti3+ and Ti2+ ions substituted for the host Al atom in orthorhombic Pbnm bulk YAlO3 crystals. The disordered crystalline structure of YAlO3 was modelled in a large supercell containing 160 atoms, allowing simulation of a substitutional dopant with a concentration of about 3%. In the case of the Ti2+-doped YAlO3, compensated F-center (oxygen vacancy with two trapped electrons) is inserted close to the Ti to make the unit cell neutral. Changes of the interatomic distances and angles between the chemical bonds in the de…
CD8 T Cells Control Cytomegalovirus Latency by Epitope-Specific Sensing of Transcriptional Reactivation
2006
ABSTRACT During murine cytomegalovirus (mCMV) latency in the lungs, most of the viral genomes are transcriptionally silent at the major immediate-early locus, but rare and stochastic episodes of desilencing lead to the expression of IE1 transcripts. This low-frequency but perpetual expression is accompanied by an activation of lung-resident effector-memory CD8 T cells specific for the antigenic peptide 168-YPHFMPTNL-176, which is derivedfrom the IE1 protein. These molecular and immunological findings were combined in the “silencing/desilencing and immune sensing hypothesis” of cytomegalovirus latency and reactivation. This hypothesis proposes that IE1 gene expression proceeds to cell surfac…
Halogen‐Imparted Reactivity in Lithium Carbenoid Mediated Homologations of Imine Surrogates: Direct Assembly of bis‐Trifluoromethyl‐β‐Diketiminates a…
2020
The selective formal insertion (homologation) of a carbon unit bridging the two trifluoroacetamidoyl chlorides (TFAICs) units is reported. The tactic is levered on a highly chemoselective homologation-metalation-acyl nucleophilic substitution sequence which precisely enables to assemble novel trifluoromethylated β-diketiminates within a single synthetic operation. Unlike previous homologations conducted with LiCH2Cl furnishing aziridines, herein we exploit the unique capability of iodomethyllithium to act contemporaneously as a C1 source (homologating effect) and metalating agent. The mechanistic rationale grounded on experimental evidences supports the hypothesized proposal and, the struct…
Los espacios de mayor inmigración en los centros históricos: algunos ejemplos en las grandes ciudades españolas
2008
La inmigración reciente ha transformado de forma radical la estructura demográfica de numerosos sectores de los centros históricos de las ciudades, casi siempre los más degradados, pero también algunos en proceso de rehabilitación. Este artículo analiza los cambios producidos en menos de cuatro años –los que van del último Censo al Padrón de 2005– en las secciones censales con mayor porcentaje de extranjeros en 2001. Se estudian los ritmos de llegada, la singularidad respecto a otras áreas de la ciudad, el radical cambio en la composición por edades de dichas secciones, la concentración en ellas de grupos concretos y las diferencias existentes entre las ciudades. Con ello, se intentará cara…
The effect of cooperative infrastructure fees on high-speed rail and airline competition
2021
Abstract This paper explores the effects of cooperation between rail and air infrastructures in setting per-passenger fees prior to competition among airlines and high-speed rail (HSR) in a transport network. It is shown that, for a sufficiently low degree of substitution, cooperation results in lower fees and greater HSR traffic than under competition. Besides, it leads to more connecting passengers. An empirical application allows for a quantitative assessment of cooperation. Gains to passengers and operators are sizeable when cooperation either involves all infrastructure managers or the rail and the hub airport managers. Welfare gains are in the range of 10.4–11.1%. Our contribution off…