Protonation of 4 H-Pyran-4-one and its Sulfur Analogues. MNDO Study

1984 ◽  
Vol 39 (3) ◽  
pp. 267-275 ◽  
Author(s):  
Mirjana Eckert-Maksić
Keyword(s):  
Electronic Structure ◽  
Experimental Evidence ◽  
Electron Density ◽  
Structural Features ◽  
Electron Drift ◽  
Strong Polarization ◽  
Appreciable Increase ◽  
Cyclic Conjugation ◽  
Molecular And Electronic Structure ◽  
Good Agreement

AbstractThe molecular and electronic structure of 4H-pyran-4-one and its mono- and disubstituted sulfur analogues (1-4) are studied by the MNDO method. The salient structural features are qualitatively reproduced and the trend of changes of geometric parameters is in good agreement with experiment. The charge distributions exhibit strong polarization due to the large π-electron drift toward the exo-heteroatom. The protonated conjugated acids are considered too. It is found that exo-heteroatom protonation is favoured by 60-80 kcal/mol over the attachment of the proton to the intraring heteroatom. This is in accordance with experimental evidence. It is rationalized by the higher electron density centered on the exo-heteroatom and the appreciable increase in aromatic cyclic conjugation taking place upon the exo-protonation.

Molecular and electronic structure of ozone and thiozone from LCAO local density calculations

1985 ◽  
Vol 63 (7) ◽  
pp. 1982-1987 ◽  
Author(s):  
Mario Morin ◽  
Aniko E. Foti ◽  
Dennis R. Salahub
Keyword(s):  
Electronic Structure ◽  
Ground State ◽  
Local Minimum ◽  
Local Density ◽  
Molecular And Electronic Structure ◽  
Ground State Geometry ◽  
Good Agreement

LCAO local density calculations for ozone yield a ground state geometry in good agreement with experiment (R = 1.27 Å vs. 1.278 Å (exp.), θ = 117.5° vs. 116.8° (exp.)). A second local minimum is found about 45 kcal/mol higher for a cyclic geometry (R = 1.44 Å, θ = 60°). For S3 the calculations predict a bent ground state (R = 2.00 Å, θ = 116°) with the cyclic geometry (R = 2.125 Å, θ = 58°) about 15 kcal/mol higher.

Partition Coefficients of Methylated DNA Bases Obtained from Free Energy Calculations with Molecular Electron Density Derived Atomic Charges.

2018 ◽  
Author(s):  
Alejandro Lara ◽  
Maximiliano Riquelme ◽  
Esteban Vöhringer-Martinez
Keyword(s):  
Electron Density ◽  
Partition Coefficients ◽  
Dna Bases ◽  
Atomic Charges ◽  
Free Energies ◽  
Solvation Model ◽  
Minimal Basis ◽  
Methylated Dna ◽  
Implicit Solvation Model ◽  
Good Agreement

<div> <div> <div> <p>Partition coefficients serve in various areas as pharmacology and environmental sciences to predict the hydrophobicity of different substances. Recently, they have been also used to address the accuracy of force fields for various organic compounds and specifically the methylated DNA bases. In this study atomic charges were derived by different partitioning methods (Hirshfeld and Minimal Basis Iterative Stockholder) directly from the electron density obtained by electronic structure calculations in vac- uum, with an implicit solvation model or with explicit solvation taking the dynamics of the solute and the solvent into account. To test the ability of these charges to describe electrostatic interactions in force fields for condensed phases the original atomic charges of the AMBER99 force field were replaced with the new atomic charges and combined with different solvent models to obtain the hydration and chloroform solvation free energies by molecular dynamics simulations. Chloroform-water partition coefficients derived from the obtained free energies were compared to experimental and previously reported values obtained with the GAFF or the AMBER-99 force field. The results show that good agreement with experimental data is obtained when the polarization of the electron density by the solvent has been taken into account deriving the atomic charges of polar DNA bases and when the energy needed to polarize the electron den- sity of the solute has been considered in the transfer free energy. These results were further confirmed by hydration free energies of polar and aromatic amino acid side chain analogues. Comparison of the two partitioning methods Hirsheld-I and Minimal Basis Iterative Stockholder (MBIS) revealed some deficiencies in the Hirshfeld-I method related to nonexistent isolated anionic nitrogen pro-atoms used in the method. Hydration free energies and partitioning coefficients obtained with atomic charges from the MBIS partitioning method accounting for polarization by the implicit solvation model are in good agreement with the experimental values. </p> </div> </div> </div>

scholarly journals Influence of Copper(I) Halides on the Reactivity of Aliphatic Carbodiimides

2020 ◽  
Vol 3 (1) ◽  
pp. 20
Author(s):  
Valentina Ferraro ◽  
Marco Bortoluzzi
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
General Formula ◽  
Electron Density ◽  
Density Functional ◽  
Functional Theory ◽  
Fukui Functions ◽  
Bond Lengths ◽  
Linear Complexes ◽  
Nitrogen Bond

The influence of copper(I) halides CuX (X = Cl, Br, I) on the electronic structure of N,N′-diisopropylcarbodiimide (DICDI) and N,N′-dicyclohexylcarbodiimide (DCC) was investigated by means of computational DFT (density functional theory) methods. The coordination of the considered carbodiimides occurs by one of the nitrogen atoms, with the formation of linear complexes having a general formula of [CuX(carbodiimide)]. Besides varying the carbon–nitrogen bond lengths, the thermodynamically favourable interaction with Cu(I) reduces the electron density on the carbodiimides and alters the energies of the (NCN)-centred, unoccupied orbitals. A small dependence of these effects on the choice of the halide was observable. The computed Fukui functions suggested negligible interaction of Cu(I) with incoming nucleophiles, and the reactivity of carbodiimides was altered by coordination mainly because of the increased electrophilicity of the {NCN} fragments.

Synthesis of uranium complexes incorporating extended azo-imine ligands: Molecular and electronic structure

2021 ◽  
pp. 100049
Author(s):  
Poulami Pattanayak ◽  
Sankar Prasad Parua ◽  
Debprasad Patra ◽  
Ashoke Prasun Chattopadhyay ◽  
Surajit Chattopadhyay
Keyword(s):  
Electronic Structure ◽  
Uranium Complexes ◽  
Imine Ligands ◽  
Molecular And Electronic Structure

scholarly journals Molecular and Electronic Structure of Dinuclear Uranium Bis-μ-Oxo Complexes with Diamond Core Structural Motifs

2014 ◽  
Vol 136 (34) ◽  
pp. 11980-11993 ◽  
Author(s):  
Anna-Corina Schmidt ◽  
Frank W. Heinemann ◽  
Wayne W. Lukens ◽  
Karsten Meyer
Keyword(s):  
Electronic Structure ◽  
Structural Motifs ◽  
Oxo Complexes ◽  
Molecular And Electronic Structure

The Structural Framework of Pictorial Balance

Perception ◽  
1996 ◽  
Vol 25 (12) ◽  
pp. 1419-1436 ◽  
Author(s):  
Paul Locher ◽  
Sharon Gray ◽  
Calvin Nodine
Keyword(s):  
Visual Arts ◽  
Structural Features ◽  
Original Compositions ◽  
The Other ◽  
Global Integration ◽  
Artistic Style ◽  
Structural Framework ◽  
Museum Professionals ◽  
Balance Structure ◽  
Good Agreement

Two experiments were performed to examine how the subjective balance of a painting is created by its structural features and to determine if balance influences the way people look at paintings. Stimuli consisted of sixteen reproductions of twentieth-century paintings varying in artistic style and a reconstructed less-balanced version of each. Participants in experiment 1 determined the location of the balance center of each composition, assigned ‘weights’ to the pictorial features which contributed to the location of the balance center, and rated the picture for balance. It was found that design and museum professionals and individuals untrained in the visual arts were in good agreement as to the structural framework underlying the balance organization of a painting. For all participants, disruption of the balanced organizations of the original compositions led to reliable shifts in the location of the perceived balance centers of the originals compared with their less-balanced perturbations. Additionally, it was observed that particular features as such were not the origin of the balance phenomenon; rather, judgments concerning the balance structure and its center were dependent on the global integration of information across a wide area of the display field, but especially from its central region. Last, the subtle changes in balance structure between versions resulted in lower ratings of balance being assigned to the less-balanced perturbations by the design professionals only; the other two participant groups evaluated overall balance of the versions as comparable. In experiment 2, eye movements of a different group of untrained individuals were recorded as they performed similar tasks on the art stimuli. It was found that disruption of the balance structure of the original representational but not abstract compositions resulted in different regions of the original and perturbed versions being visually explored. Findings of both experiments are related to theoretical notions of balance.

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