Search results for "Reactivity"

Quantum chemistry calculations on the effect of electron confinement upon the frontier molecular orbitals of ethylene and benzene in sodalite. Implic…

1997

Abstract Quantum chemistry calculations using HF / STO-3G, CEP-41G, and 3-21G basis sets have been carried out in order to study the effect of the electron confinement of ethylene and benzene in the microporous environment existing in a sodalite cage. The electron confinement produces an increase of 1.06 and 1.31 eV at the 3-21G level in the energy of the HOMO of ethylene and benzene, respectively, when placed in the centre of the cavity with respect to the HOMO energy in the gas phase. There is an increase in the energy of the HOMO when the molecules approach the walls of the zeolite.

A dft analysis of the participation of zwitterionic tacs in polar [3+2] cycloaddition reactions

2014

A set of seven non-substituted tri-atom-components (TACs) participating in [3+2] cycloaddition (32CA) reactions has been studied using the reactivity indices defined within the conceptual DFT at the B3LYP/6-31G(d) level of theory. This series of TACs shows a zwitterionic structure and low reactivity towards ethylene. The general characteristic of these TACs is their high nucleophilic and a low electrophilic behaviour. Activation energies computed at the MPWB1K/6-311G(d) level in dichloromethane point to that non-substituted TACs react quickly toward dicyanoethylene showing their ability to react towards electron-deficient ethylenes. However, when the TACs are electrophilically activated by …

Studies on the microstructure of ethylene/1-hexene copolymers prepared over heterogeneous Ziegler - Natta catalysts

2000

Three MgCl 2(THF) 2-supported, AlEt 2Cl-activated VOCl 3, VCl 4 and TiCl 4 Ziegler - Natta catalysts were used to copolymerize ethylene with 1-hexene in the presence of hydrogen to prepare low-M well-soluble copolymers that could be analyzed by 13C-NMR. The spectra (Fig. 1) showed resonance signals due to ethylene and 1-hexene units in positions unaffected by catalyst type and with intensities related to the degree of comonomer incorporation into the copolymer. The triad sequence distribution and comonomer reactivity ratios (r) were calculated by the Randall method [11] and Bernoulli statistics based on the known copolymer composition. The latter appeared to be the more valid in predicting …

The carbenoid-type reactivity of simplest nitrile imine from a molecular electron density theory perspective

2019

Abstract The [3 + 2] cycloaddition (32CA) reactions of the simplest nitrile imine with ethylene and electrophilic dicyanoethylene have been studied within the Molecular Electron Density Theory (MEDT) with the aim of characterising its reactivity. Topological analysis of the electron localisation function of NI shows that it has a carbenoid structure. The activation energy of the 32CA reaction of the simplest nitrile imine with dicyanoethylene is 5.6 kcal mol−1 lower than that involving ethylene, in agreement with the high polar character of the former reaction. Bonding Evolution Theory accounts for the cb-type reactivity of nitrile imine. Along the more favourable ortho regioisomeric path a…

Understanding the mechanisms of [3+2] cycloaddition reactions. The pseudoradical versus the zwitterionic mechanism

2014

Abstract Analysis of 12 three-atom-components (TACs) participating in [3+2] cycloaddition (32CA) reactions towards ethylene and acetylene allows establishing good correlations between the pseudodiradical character, the hardness η, and the nucleophilicity N index of the TAC with the feasibility of these non-polar reaction. These results allow the introduction of the pr index, which comprises the two aforementioned DFT reactivity indices. The increase of the pr index for an allylic-type TAC goes accompanied by a linear decrease of the activation enthalpy of the reaction. The present study makes it possible to establish a useful classification of 32CA reactions into zw-type reactions involving…

Understanding the domino reaction between 3-chloroindoles and methyl coumalate yielding carbazoles. A DFT study.

2014

The molecular mechanism of the reaction between N-methyl-3-chloroindole and methyl coumalate yielding carbazole has been studied using DFT methods at the MPWB1K/6-311G(d,p) level in toluene. This reaction is a domino process that comprises three consecutive reactions: (i) a polar Diels-Alder (P-DA) reaction between indole and methyl coumalate yielding two stereoisomeric [2 + 4] cycloadducts (CAs); (ii) the elimination of HCl from these CAs affording two stereoisomeric intermediates; and (iii) the extrusion of CO2 in these intermediates, finally yielding the carbazole. This P-DA reaction proceeds in a completely regioselective and slightly exo selective fashion. In spite of the highly polar …

2020

Abstract Trait anxiety refers to the stable tendency to attend to threats and experience fears and worries across many situations. According to the widely noticed, pioneering investigation by Etkin et al. (2004) trait anxiety is strongly associated with reactivity in the right basolateral amygdala to non-conscious threat. Although this observation was based on a sample of only 17 individuals, no replication effort has been reported yet. We reexamined automatic amygdala responsiveness as a function of anxiety in a large sample of 107 participants. Besides self-report instruments, we administered an indirect test to assess implicit anxiety. To assess early, automatic stages of emotion process…

General Principles for the Detection of Modified Nucleotides in RNA by Specific Reagents.

2021

Epitranscriptomics heavily rely on chemical reagents for the detection, quantification, and localization of modified nucleotides in transcriptomes. Recent years have seen a surge in mapping methods that use innovative and rediscovered organic chemistry in high throughput approaches. While this has brought about a leap of progress in this young field, it has also become clear that the different chemistries feature variegated specificity and selectivity. The associated error rates, e.g., in terms of false positives and false negatives, are in large part inherent to the chemistry employed. This means that even assuming technically perfect execution, the interpretation of mapping results issuin…

Catalytic oxidation and reduction of polycyclic aromatic hydrocarbons (PAHs) present as mixtures in hydrothermal media

2012

Author's version of an article in the journal: Polycyclic Aromatic Compounds. Also available from the publisher at: http://dx.doi.org/10.1080/10406638.2012.663451 The reactivity of fluorene, anthracene, and fluoranthene under oxidation and reduction conditions were investigated in this study. This project looks at catalytic and green approaches of converting PAHs to less toxic and/or less stable derivatives that are amenable to further degradation. Hydrothermal reactions have been performed at 300°C with pure H2O and Nafion-SiO2 catalyst for oxidation, and pure H2O, HCOOH, Pd-C, and Nafion-SiO2 catalysts for reductive hydrogenation. Time series has been performed for both the oxidation and …

The Reduction Pathway of End-on Coordinated Dinitrogen. II. Electronic Structure and Reactivity of Mo/W−N2, −NNH, and −NNH2 Complexes

2001

DFT calculations (B3LYP/LanL2DZ) of simplified models of [Mo(N(2))(2)(dppe)(2)] and the two protonated derivatives [MoF(NNH)(dppe)(2)] and [MoF(NNH(2))(dppe)(2)](+) (dppe = 1,2-bis(diphenylphosphino)ethane) provide quantitative insight into the reduction and protonation of dinitrogen bound end-on terminally to transition metals. This "asymmetric" reduction pathway is characterized by a stepwise increase of covalency and a concomitant charge donation from the metal center during each protonation reaction. The major part of metal-to-ligand charge transfer occurs after the first protonation leading to coordinated diazenido(-). In contrast, addition of the second proton is accompanied by a mino…