Hydroformylation is the transformation of an alkene to an aldehyde via the addition of both hydrogen and carbon monoxide. The final aldehyde has one more carbon atom than the precursor alkene. Two isomeric products can result. The regiochemistry of the hydroformylation reaction is believed to be controlled by the olefin insertion step. A reaction mechanism is usually studied by finding the reactants, products, intermediates, and transition states. Alternatively, a chemical reaction can be studied from the redistribution of the electron density along the reaction path connecting the stationary points. The aim of this work is to describe the reaction mechanism of the insertion process by the structural evolution defined by the changes in the electron density during the reaction.
El trastorno de ansiedad social (TAS) es uno de los trastornos más frecuentes a nivel mundial. El objetivo de este estudio fue comprobar la eficacia del nuevo programa “Intervención multidimensional para la ansiedad social” (IMAS) para el tratamiento del TAS. Participaron 67 personas diagnosticadas con TAS, según el DSM-5, evaluadas mediante una entrevista semiestructurada (Salazar y Caballo, 2018) y dos medidas de autoinforme para la ansiedad social, el CASO (Caballo, Salazar, Arias, et al., 2010) y la LSAS-SR (Liebowitz, 1987). Diferentes terapeutas llevaron a cabo el tratamiento en Ecuador, España, Paraguay y Puerto Rico. Los resultados mostraron importantes mejoras del pretratamiento al postratamiento, que se mantenían a los seis meses. El tamaño del efecto estaba entre 1 y 2 y, en muchas ocasiones, fue superior a 2. Aunque se comparó con un grupo de terapia cognitivo conductual y otro de tratamiento farmacológico, con resultados favorables para el programa IMAS, el bajo número de sujetos de estos últimos grupos no permite llegar a deducciones claras. En conclusión, este nuevo programa para el tratamiento de la ansiedad social parece altamente eficaz a corto y medio plazo y sus resultados positivos parecen generalizables a diferentes países
Theoretical studies about reaction mechanisms are usually limited to the determination of the energetic paths that connect reactants, transition states, and products. Recently, our group proposed the structural evolution, which has provided insights about the molecular structure changes occurring along a reaction path. Structural evolution may be defined as the development of a chemical reaction system across the partitioning of the nuclear configuration space into a finite number of structural regions defined on account of the topology of a scalar field, e.g., the electron density. In this paper, we present a tool to investigate within the framework of the Quantum Theory of Atoms in Molecules the evolvement of the Valence Shell Charge Concentration, the VSCC evolution, which is the description of the changes of electron density concentrations and depletions around the bonding area of an atom. The VSCC evolution provides supplementary information to the structural evolution because it allows the analysis of valence shells within a structural region, i.e., a subset of R(Q) with the same connectivity among the atoms forming a molecule. This new approach constitutes also a complement to the Valence-Shell Electron Pair Repulsion (VSEPR) model because it gives an account of the adjustments of electron pairs in the valence shell of an atom across a chemical reaction. The insertion reaction in the hydroformylation reaction of ethylene, the reduction of cyclohexanone with lithium aluminum hydride, the oxidation of methanol with chlorochromate, and the bimolecular nucleophilic substitution of CH(3)F with F(-) are used as representatives examples of the application of the VSCC evolution. Overall, this paper shows how the VSCC evolution through an analysis of the modifications of local charge concentrations and depletions in individual steps of a chemical reaction gives new insights about these processes.
This work describes the conformational behavior and the activation mechanism of timoprazole and substituted prazoles from the most stable conformation to the sulphenic acid. The stability of the conformers can be explained by the presence of hydrogen bonds, stereoelectronic effect because of the lone pair of sulfur atom and the N … C and N … S interactions. The first step of the Smile rearrangement is a nucleophilic addition to benzimidazole by pyridine moiety, which depends on the difference of the electron population of the atoms involved in the attack. The second step produces sulphenic acid by a concerted reaction where breaking of the S-C bond goes along with a proton migration, and is determined by the electron population of the sulfur atom. Figure 7. (A) Correlation between Electron population difference ΔN = N(N25) -N(C2) with the energy barrier of the first step of the Smile reaction. (B) Correlation between N(S) with the energy barrier of the second step of the Smile reaction. Energy in kcal/mol and electron population in electrons
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