Topological electron density properties at critical points along aromatic rings as reactivity and regioselectivity descriptors in electrophilic substitutions

2021 ◽  
Author(s):  
Natieli Alves Da Silva ◽  
Roy Edward Bruns ◽  
Roberto Luiz Andrade Haiduke
Keyword(s):  
Electron Density ◽  
Critical Points ◽  
Aromatic Rings ◽  
Electrophilic Substitutions

On the transferability of electron density in binary vanadium borides VB, V3B4 and VB2

2015 ◽  
Vol 71 (6) ◽  
pp. 777-787 ◽  
Author(s):  
Bürgehan Terlan ◽  
Lev Akselrud ◽  
Alexey I. Baranov ◽  
Horst Borrmann ◽  
Yuri Grin
Keyword(s):  
Quantum Theory ◽  
Crystal Structures ◽  
Electron Density ◽  
Critical Points ◽  
Atoms In Molecules ◽  
Model Systems ◽  
Suitable Model ◽  
Interatomic Distances ◽  
Systematic Analysis ◽  
A Charge

Binary vanadium borides are suitable model systems for a systematic analysis of the transferability concept in intermetallic compounds due to chemical intergrowth in their crystal structures. In order to underline this structural relationship, topological properties of the electron density in VB, V3B4 and VB2 reconstructed from high-resolution single-crystal X-ray diffraction data as well as derived from quantum chemical calculations, are analysed in terms of Bader's Quantum Theory of Atoms in Molecules [Bader (1990). Atoms in Molecules: A Quantum Theory, 1st ed. Oxford: Clarendon Press]. The compounds VB, V3B4 and VB2 are characterized by a charge transfer from the metal to boron together with two predominant atomic interactions, the shared covalent B—B interactions and the polar covalent B—M interactions. The resembling features of the crystal structures are well reflected by the respective B—B interatomic distances as well as by ρ(r) values at the B—B bond critical points. The latter decrease with an increase in the corresponding interatomic distances. The B—B bonds show transferable electron density properties at bond critical points depending on the respective bond distances.

A topological analysis of the interion interactions of tetraphenylphosphonium squarate

2006 ◽  
Vol 84 (5) ◽  
pp. 804-811 ◽  
Author(s):  
David Wolstenholme ◽  
Manuel AS Aquino ◽  
T Stanley Cameron ◽  
Joseph D Ferrara ◽  
Katherine N Robertson
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Electron Density ◽  
Intermolecular Interactions ◽  
Critical Points ◽  
Topological Analysis ◽  
Van Der Waals ◽  
Van Der Waals Interactions ◽  
Multipole Refinement ◽  
Diverse Interactions

The tetraphenylphosphonium squarate salt crystallizes with a number of diverse interactions, which all have the potential to be classified as hydrogen bonds. The squarate anions are found as dimers linked by O-H···O interactions. The multipole refinement of the tetraphenylphosphonium squarate was performed using the Hansen–Coppens model followed by topological analysis of its intermolecular interactions. A total of 28 interactions were found among the symmetry related molecules, which include a number of C-H···Cπ, C-H···O, and C-H···H-C interactions, along with the O-H···O interaction. With the criteria for hydrogen bonding proposed by Popelier and Koch, it is possible to determine which of these interactions are hydrogen bonds and which are van der Waals interactions. Both linear and exponentially dependent correlations can be seen for the properties of the bond critical points involving the intermolecular interactions that fulfill these criteria. All this leads to a better understanding of the role that hydrogen bonds play in the formation of small organic compounds.Key words: electron density, multiple refinement, hydrogen bonds.

Weak interactions in chain polymers [M(μ-X)2 L 2]∞ (M = Zn, Cd; X = Cl, Br; L = substituted pyridine) – an electron density study

2009 ◽  
Vol 65 (5) ◽  
pp. 600-611 ◽  
Author(s):  
Ruimin Wang ◽  
Christian W. Lehmann ◽  
Ulli Englert
Keyword(s):  
Hydrogen Bonds ◽  
Electron Density ◽  
Critical Points ◽  
Weak Interactions ◽  
Data Sets ◽  
X Ray Diffraction ◽  
Density Distributions ◽  
The One ◽  
Experimental Electron Density ◽  
Density Study

The experimental electron-density distributions in crystals of five chain polymers [M(μ-X)2(py)2] (M = Zn, Cd; X = Cl, Br; py = 3,5-substituted pyridine) have been obtained from high-resolution X-ray diffraction data sets (sin θ/λ > 1.1 Å−1) at 100 K. Topological analyses following Bader's `Atoms in Molecules' approach not only confirmed the existence of (3, −1) critical points for the chemically reasonable and presumably strong covalent and coordinative bonds, but also for four different secondary interactions which are expected to play a role in stabilizing the polymeric structures which are unusual for Zn as the metal center. These weaker contacts comprise intra- and inter-strand C—H...X—M hydrogen bonds on the one hand and C—X...X—C interhalogen contacts on the other hand. According to the experimental electron-density studies, the non-classical hydrogen bonds are associated with higher electron density in the (3, −1) critical points than the halogen bonds and hence are the dominant interactions both with respect to intra- and inter-chain contacts.

EDMA: a computer program for topological analysis of discrete electron densities

2012 ◽  
Vol 45 (3) ◽  
pp. 575-580 ◽  
Author(s):  
Lukáš Palatinus ◽  
Siriyara Jagannatha Prathapa ◽  
Sander van Smaalen
Keyword(s):  
Computer Program ◽  
Electron Density ◽  
Critical Points ◽  
Topological Analysis ◽  
Three Dimensional ◽  
Real Space ◽  
Principal Curvatures ◽  
Electron Densities ◽  
Structure Solution ◽  
Aperiodic Crystals

EDMAis a computer program for topological analysis of discrete electron densities according to Bader's theory of atoms in molecules. It locates critical points of the electron density and calculates their principal curvatures. Furthermore, it partitions the electron density into atomic basins and integrates the volume and charge of these atomic basins.EDMAcan also assign the type of the chemical element to atomic basins based on their integrated charges. The latter feature can be used for interpretation ofab initioelectron densities obtained in the process of structure solution. A particular feature ofEDMAis that it can handle superspace electron densities of aperiodic crystals in arbitrary dimensions.EDMAfirst generates real-space sections at a selected set of phases of the modulation wave, and subsequently analyzes each section as an ordinary three-dimensional electron density. Applications ofEDMAto model electron densities have shown that the relative accuracy of the positions of the critical points, the electron densities at the critical points and the Laplacian is of the order of 10−4or better.

Electron Density of Paracetamol Metastable Polymorph, Topologycal H-Bonds Analysis

2013 ◽  
Vol 8 (2) ◽  
pp. 109-116
Author(s):  
Dmitriy Druzhbin ◽  
Tatyana Drebushchak ◽  
Elena Boldyreva
Keyword(s):  
Electron Density ◽  
Critical Points ◽  
Experimental Analysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Orthorhombic Modification ◽  
Experimental Electron Density

The experimental electron density of paracetamol metastable polymorph (orthorhombic, Pbca) was derived from highresolution X-ray diffraction at 100 K. The multipole model was used to refine electron density and for experimental analysis of the features of the critical points for orthorhombic modification. Geometrical H-bonds features were obtained from spherical and multipole models. The current study provides topological H-bonds analysis in orthorhombic paracetamol compared with stable monoclinic paracetamol polymorphs in normal conditions

Electron-density critical points analysis and catastrophe theory to forecast structure instability in periodic solids

2018 ◽  
Vol 74 (2) ◽  
pp. 102-111 ◽  
Author(s):  
Marcello Merli ◽  
Alessandro Pavese
Keyword(s):  
Electron Density ◽  
Critical Points ◽  
Catastrophe Theory ◽  
Phase State ◽  
State Transitions ◽  
Mathematical Tool ◽  
Electron Density Topology ◽  
Rutile Structure ◽  
Corundum Structure ◽  
Experimental Pressure

The critical points analysis of electron density,i.e. ρ(x), fromab initiocalculations is used in combination with the catastrophe theory to show a correlation between ρ(x) topology and the appearance of instability that may lead to transformations of crystal structures, as a function of pressure/temperature. In particular, this study focuses on the evolution of coalescing non-degenerate critical points,i.e. such that ∇ρ(xc) = 0 and λ1, λ2, λ3≠ 0 [λ being the eigenvalues of the Hessian of ρ(x) atxc], towards degenerate critical points,i.e. ∇ρ(xc) = 0 and at least one λ equal to zero. The catastrophe theory formalism provides a mathematical tool to model ρ(x) in the neighbourhood ofxcand allows one to rationalize the occurrence of instability in terms of electron-density topology and Gibbs energy. The phase/state transitions that TiO2(rutile structure), MgO (periclase structure) and Al2O3(corundum structure) undergo because of pressure and/or temperature are here discussed. An agreement of 3–5% is observed between the theoretical model and experimental pressure/temperature of transformation.

Grid-based algorithm to search critical points, in the electron density, accelerated by graphics processing units

2014 ◽  
Vol 35 (31) ◽  
pp. 2272-2278 ◽  
Author(s):  
Raymundo Hernández-Esparza ◽  
Sol-Milena Mejía-Chica ◽  
Andy D. Zapata-Escobar ◽  
Alfredo Guevara-García ◽  
Apolinar Martínez-Melchor ◽  
...  
Keyword(s):  
Electron Density ◽  
Critical Points ◽  
Graphics Processing Units ◽  
Graphics Processing ◽  
Grid Based

Nuclear Magnetic Resonance of Compounds Related to DDT: Part II. Aromatic Protons

1968 ◽  
Vol 22 (5) ◽  
pp. 506-512 ◽  
Author(s):  
Norman E. Sharpless ◽  
Robert B. Bradley
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Electron Density ◽  
Chemical Shifts ◽  
Molecular Orbital Calculations ◽  
Aromatic Rings ◽  
Butyl Group ◽  
Nuclear Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The nuclear magnetic resonance spectra of the aromatic protons of DDT and 31 of its analogs and derivatives have been analyzed. Chemical shifts of these molecules are functions of the electronegativities of the substituents on the ring, as well as those in the aliphatic portion, although substitution of the ring chlorine in DDT by either a nitro or a t-butyl group leads to anomalous values. Molecular orbital calculations show that the chemical shift of the proton ortho to the ring substituent depends upon the π electron density at the corresponding carbon, but the chemical shift of the proton meta to this substituent is independent of the π electron density at the corresponding carbon. The data also indicate that the two aromatic rings in DDT are independent of each other.

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