Search results for "electron density"
showing 10 items of 428 documents
Inter- and intramolecular bonding in 1,3,5-triamino-2,4,6-trinitrobenzene: An experimental and theoretical quantum theory of atoms in molecules (QTAI…
2017
Chemical bonding in the triclinic phase of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) has been analyzed based on the experimental electron density derived from X-ray diffraction data obtained at 20 K. The results have been compared with those from solid state theoretical calculations. The total electron density has been analyzed in terms of the Quantum Theory of Atoms in Molecules (QTAIM). Features of the covalent bonds demonstrate the presence of multiple bonds of various order. Strong intramolecular hydrogen bonds and weaker intermolecular bonds within the layer structure are characterized by the properties of their (3, −1) critical points. Weaker interactions, predominantly O···O, betwe…
Hydrogen-Bond Cooperative Effects in Small Cyclic Water Clusters as Revealed by the Interacting Quantum Atoms Approach
2013
The cooperative effects of hydrogen bonding in small water clus- ters (H2O)n (n = 3-6) have been studied by using the partition of the electronic energy in accordance with the interact- ing quantum atoms (IQA) approach. The IQA energy splitting is comple- mented by a topological analysis of the electron density (1(r)) compliant with the quantum theory of atoms-in-mole- cules (QTAIM) and the calculation of electrostatic interactions by using one- and two-electron integrals, thereby avoiding convergence issues inherent to a multipolar expansion. The results show that the cooperative effects of hy- drogen bonding in small water clusters arise from a compromise between: 1) the deformation energ…
Theoretical Multipolar Atom Model Transfer in Nitro-Derivatives of N-Methylaniline
2014
The nitroanilines are an example of compounds in which the coexistence of electron-rich and electron-deficient substituents, connected through a conjugated π-electronic system, makes their molecular second-order hyperpolarizability and second-harmonic generation efficiency particularly high. This property makes them extremely interesting from the point of view of charge density distribution analysis. The electron density of three isomeric molecules, i.e., N-methyl-2-nitroaniline, N-methyl-3-nitroaniline, and N-methyl-4-nitroaniline, was calculated theoretically through the multipolar atom model transfer. Two types of refinement models, i.e., multipolar atom model (MAM) and independent atom …
Unravelling the strain-promoted [3+2] cycloaddition reactions of phenyl azide with cycloalkynes from the molecular electron density theory perspective
2020
The strain-promoted [3+2] cycloaddition (SP-32CA) reactions of phenyl azide with a series of five strained cycloalkynes C5–C9 have been studied within molecular electron density theory (MEDT) at the MPWB1K/6-311G(d,p) computational level. These zwitterionic type SP-32CA reactions take place through a one-step mechanism, with activation enthalpies in acetonitrile between −4.2 and 19.9 kcal mol−1. An excellent linear correlation between the decrease in activation enthalpies and the ring size of this series of cycloalkynes can be established. The present study shows that the highly strained cycloalkynes C5 and C6 experience a different chemical reactivity than less strained cycloalkynes C7–C9,…
The adhesion nature of the Ag/MgO(100) interface: an ab initio study
1998
The atomic and electronic structure of the Ag/MgO(100) interface are calculated by means of the ab initio Hartree-Fock approach combined with a supercell model. The electronic density distribution and the interface binding energy/distance are analyzed for different Ag adsorption positions, slabs of different thicknesses and varying Ag surface coverage. It is demonstrated that the adhesion energy arises mainly due to the electrostatic interaction of substrate atoms with a complicated charge redistribution in the metal layer(s), characterized by large quadrupole moments as well as electron density redistribution towards bridge and hollow positions between the nearest and next-nearest Ag atoms…
Unveiling the high reactivity of strained dibenzocyclooctyne in [3 + 2] cycloaddition reactions with diazoalkanes through the molecular electron dens…
2020
A molecular electron density theory study of the Grignard reagent‐mediated regioselective direct synthesis of 1,5‐disubstituted‐1,2,3‐triazoles
2020
Studies of plasma breakdown and electron heating on a 14 GHz ECR ion source through measurement of plasma bremsstrahlung
2011
Temporal evolution of plasma bremsstrahlung emitted by a 14?GHz electron cyclotron resonance ion source (ECRIS) operated in pulsed mode is presented in the energy range 1.5?400?keV with 100??s resolution. Such a high temporal resolution together with this energy range has never been measured before with an ECRIS. Data are presented as a function of microwave power, neutral gas pressure, magnetic field configuration and seed electron density. The saturation time of the bremsstrahlung count rate is almost independent of the photon energy up to 100?keV and exhibits similar characteristics with the neutral gas balance. The average photon energy during the plasma breakdown is significantly highe…
A molecular electron density theory study of the [3 + 2] cycloaddition reaction of nitrones with strained allenes
2017
Indexación: Scopus. The [3 + 2] cycloaddition (32CA) reaction of C-phenyl-N-tert-butylnitrone with 1,2-cyclohexadiene (CHDE), a strained allene, has been studied within Molecular Electron Density Theory (MEDT) at the DFT B3LYP/6-311G(d,p) computational level. This non-polar 32CA reaction, which takes place through a non-concerted two-stage one-step mechanism, proceeds with a moderate Gibbs free activation energy of 22.7 kcal mol-1, and presents low stereo- and regioselectivities. The reaction begins by the creation of a pseudoradical center at the central carbon of the strained allene with a relatively low energy cost, which immediately promotes the formation the first C-C single bond. This…
The structural aspects of the transformation of 3-nitroisoxazoline-2-oxide to 1-aza-2,8-dioxabicyclo[3.3.0]octane derivatives: Experimental and MEDT …
2019
Abstract Reaction of 3-nitroisoxazoline-2-oxide with monosubstituted ethenes, first time documented fifty years ago, have been reviewed. Structures of phenyl and cyano derivatives of 1-aza-2,8-dioxabicyclo[3.3.0]octane produced in [3 + 2] cycloaddition (32CA) between styrene and acrylonitrile with 3-nitroisoxazoline-2-oxide were determined through single crystal XRD analysis. The molecular mechanism of the title 32CA has been also analyzed within the Molecular Electron Density Theory (MEDT) based on the M06-2X(PCM)/6-311 + G(d,p) calculations.