Search results for "transition"

Hyperconjugative Control by Remote Substituents of Diastereoselectivity in the Oxygenation of Hydrocarbons.

2000

The oxidation of 2-substituted adamantanes (2) with TFDO (1) is reported. The data show a stereodifferentiation of the chemical environments induced by remote electron-withdrawing substituents which produces remarkable Z/E diastereoselectivity in the oxidation of the tertiary C(5)-H and C(7)-H bonds. The results show a bell-shaped correlation between the Z/E stereoselectivity and the substituent constant sigma(I), which is interpreted in terms of hyperconjugative stabilization of the diastereomeric transition states.

1992

Inelastic Neutron Scattering Experiments on Van der Waals Glasses - A Test of Recent Microscopic Theories of the Glass Transition

1989

Etude realisee sur un verre d'o-terphenyle afin de montrer l'existence d'une relaxation secondaire presentant des caracteristiques inhabituelles et le comportement Kohbrausch de la fonction de correlation de densite decrivant la relaxation structurale

ChemInform Abstract: Unique Reactivity of Fluorinated Molecules with Transition Metals

2015

Organofluorine and organometallic chemistry by themselves constitute two potent areas in organic synthesis. Thus, the combination of both offers many chemical possibilities and represents a powerful tool for the design and development of new synthetic methodologies leading to diverse molecular structures in an efficient manner. Given the importance of the selective introduction of fluorine atoms into organic molecules and the effectiveness of transition metals in C-C and C-heteroatom bond formation, this review represents an interesting read for this aim.

Applications and stereoselective syntheses of P-chirogenic phosphorus compounds.

2016

International audience; Phosphorus compounds bearing chirality on the P-center are usually qualified as P-chirogenic or P-stereogenic. This chemical class concerns natural products, agrochemistry, molecular materials, biology and pharmacy, although it is certainly in coordination chemistry and in asymmetric catalysis using chiral transition metal complexes that P-chirogenic phosphorus compounds are the most used. The chiral phosphine ligands and their uses in asymmetric metal-catalyzed reactions have been widely reviewed in literature. However, an overview covering the applications as well as the stereoselective syntheses of all classes of phosphorus compounds has not yet been provided. Thi…

Structure and phase transition in (C2H5NH3)3Sb2Cl 9•(C2H5NH3)SbCl4; x-ray, DSC and dielectric studies

2000

Abstract The structure of (C2H5NH3)3Sb2Cl9 • (C2H5NH3)SbCl4 at 295 K has been determined. The crystals are orthorhombic, space group Pna21 (a -16.925(3), b = 24.703(5), c = 7.956(2) Å, V = 3326.4(12) Å3 , Z = 4, dc= 2.018, dm= 2.01(1) Mg m-3). They consist of an anionic sublattice composed of two different polymeric zig-zag chains. One is built of Sb2Cl9 3- units (corner sharing octahedra) and the other one is made of corner sharing SbCl5 2-square pyramids. In the cavites between the polyanionic chains four non-equivalent ethylammonium cations are located. Three of them are disordered. The cations are connected to the anions by weak N-H...Cl hydrogen bonds. A first order phase transition of…

Phase transitions and distortion of [BiCl6]3– octahedra in (C3H5NH3)3[BiCl6] – DSC and single-crystal X-Ray diffraction studies

2004

The DSC diagram of tris(allylammonium) hexachlorobismuthate(III), (C3H5NH3)3[BiCl6], revealed three anomalies at 152, 191 and 299 K. The structure of the salt was determined at 200 and 315 K, below and above the high-temperature phase transition at 299 K. In both phases the crystals are monoclinic. At 200 K the space group is C2/c whereas at 315 K it is C2/m. The structures, at both temperatures, are composed of [BiCl6]3− octahedra and allylammonium cations. The organic and inorganic moieties are attracted to each other by a network of the N-H. . .Cl hydrogen bonds. The relationship between corresponding parameters of the unit cells has been found. The phase transition at 299 K, of the orde…

Emergent ultrafast phenomena in correlated oxides and heterostructures

2017

The possibility of investigating the dynamics of solids on timescales faster than the thermalization of the internal degrees of freedom has disclosed novel non-equilibrium phenomena that have no counterpart at equilibrium. Transition metal oxides (TMOs) provide an interesting playground in which the correlations among the charges in the metal $d$-orbitals give rise to a wealth of intriguing electronic and thermodynamic properties involving the spin, charge, lattice and orbital orders. Furthermore, the physical properties of TMOs can be engineered at the atomic level, thus providing the platform to investigate the transport phenomena on timescales of the order of the intrinsic decoherence ti…

Transition démocratique, restauration républicaine, violence politique et populaire à la Libération : le rôle des comités départementaux de Libératio…

2022

National audience

Using Contextual Action Theory for conceptualization and research on adolescent development

2019

Recently, scholars’ calls for psychology to move beyond traditional ways of conceptualizing and researching human behaviour have increased. Contextual Action Theory (CAT) is a conceptual, methodological, and practical framework that is consistent with these calls. In CAT action is conceptualized as a complex, dynamic, and multidimensional system that can be comprehended from multiple levels of organization and from multiple perspectives. The Action-Project Method (A-PM) is the research method that emerged from CAT. It is a qualitative, naturalistic, process-oriented, longitudinal methodology that has been used to study joint, goal-directed actions and projects. The focus of data gathering a…