scholarly journals The σ-hole revisited

2017 ◽  
Vol 19 (48) ◽  
pp. 32166-32178 ◽  
Author(s):  
Peter Politzer ◽  
Jane S. Murray ◽  
Timothy Clark ◽  
Giuseppe Resnati
Keyword(s):  
Electrostatic Potential ◽  
Electronic Density ◽  
Covalently Bonded ◽  
Positive Electrostatic Potential

A covalently-bonded atom typically has a region of lower electronic density, a “σ-hole,” on the side of the atom opposite to the bond, approximately along its extension. There is often a positive electrostatic potential (strongest shown in red) associated with a σ-hole, although it may deviate from the extension of the bond.

scholarly journals σ-Holes vs. Buildups of Electronic Density on the Extensions of Bonds to Halogen Atoms

Inorganics ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 71 ◽  
Author(s):  
Peter Politzer ◽  
Jane S. Murray
Keyword(s):  
Electrostatic Potential ◽  
Local Minimum ◽  
Halogen Atom ◽  
Local Maximum ◽  
Outer Side ◽  
Electronic Density ◽  
Halogen Atoms ◽  
Positive Electrostatic Potential

Our discussion focuses upon three possible features that a bonded halogen atom may exhibit on its outer side, on the extension of the bond. These are (1) a region of lower electronic density (a σ-hole) accompanied by a positive electrostatic potential with a local maximum, (2) a region of lower electronic density (a σ-hole) accompanied by a negative electrostatic potential that also has a local maximum, and (3) a buildup of electronic density accompanied by a negative electrostatic potential that has a local minimum. In the last case, there is no σ-hole. We show that for diatomic halides and halogen-substituted hydrides, the signs and magnitudes of these maxima and minima can be expressed quite well in terms of the differences in the electronegativities of the halogen atoms and their bonding partners, and the polarizabilities of both. We suggest that the buildup of electronic density and absence of a σ-hole on the extension of the bond to the halogen may be an operational indication of ionicity.

Halogen bonds as a tool in the design of high energetic materials: evidence from crystal structures and quantum chemical calculations

CrystEngComm ◽  
2021 ◽  
Author(s):  
Aleksandra B. Đunović ◽  
Dušan Ž Veljković
Keyword(s):  
Crystal Structures ◽  
Quantum Chemical Calculations ◽  
Electrostatic Potential ◽  
Energetic Materials ◽  
Quantum Chemical ◽  
Central Area ◽  
Molecular Surface ◽  
Halogen Bonds ◽  
Positive Electrostatic Potential

Positive electrostatic potential over the central area of the molecular surface is one of the main characteristics of high energetic materials (HEM) that determines their sensitivity towards detonation. The influence...

The Molecular Electrostatic Potential: A Tool for Understanding and Predicting Molecular Interactions

1998 ◽  
Author(s):  
Jane S. Murray ◽  
Peter Politzer
Keyword(s):  
Physical Properties ◽  
Density Function ◽  
Molecular Interactions ◽  
Electrostatic Potential ◽  
Chemical Species ◽  
Quantitative Measure ◽  
Theoretical Chemistry ◽  
Electronic Density ◽  
Reactive Behavior ◽  
Improved Methods

The quest for improved methods for elucidating and predicting the reactive behavior of molecules and other chemical species is a continuing theme of theoretical chemistry. This has led to the introduction of a variety of indices of reactivity; some are rather arbitrary, while others are more or less directly related to real physical properties. They have been designed and are used to provide some quantitative measure of the chemical activities of various sites and/or regions of the molecule. In this chapter our focus is on one of these indices, the electrostatic potential V(r) that is created in the space around a molecule by its nuclei and electrons. V(r) can be computed rigorously, given the electronic density function ρ(r), by Eq. (3.1).

Caractérisation physicochimique et électronique de la structure Pt–a-Si: H–c-Si(n)

1991 ◽  
Vol 69 (3-4) ◽  
pp. 357-360 ◽  
Author(s):  
S. Belkouch ◽  
L. Paquin ◽  
A. Deneuville ◽  
E. Gheeraert
Keyword(s):  
Infrared Absorption ◽  
Electrostatic Potential ◽  
Potential Drop ◽  
Localized States ◽  
Electrical Measurements ◽  
Potential Barriers ◽  
Infrared Absorption Spectra ◽  
Hydrogenated Amorphous ◽  
Positive Electrostatic Potential ◽  
Absorption Measurements

Infrared absorption spectra, and electrical measurements I(V, T) and C(V) at 100 Hz of the Pt–a-Si:H–c-Si structure are presented. The thickness, d, of the hydrogenated amorphous silicium, a-Si:H, varies between 4800 and 180 Å(1 Å = 10−10 m). Infrared absorption measurements on a-Si:H show that with the decrease in d there is an increase in the number of defects and the hydrogen concentration on Si-H sites. The electrical results I(V, T) show a Schottky-like structure whose ideality factor increases with decreasing T, but remains limited even for small values of d (1.4 at 300 K for d = 180 Å). Two potential barriers are also deduced: at high temperature [Formula: see text] and is independent of d. This barrier is attributed to the Pt–a-Si:H interface. At low temperature, [Formula: see text] increases from 0.23 to 0.5 eV as d decreases from 2400 to 180 Å. This barrier is attributed to the a-Si = H–c-Si, interface, the transport in a-Si:H taking place by tunnelling between localized states. The C(V) measurements allow the separation between the c-Si and the a-Si:H responses. Above 100 kHz, there is no response from a-Si:H, which behaves then as a dielectric. The electrostatic potential drop in c-Si is deduced as a function of the applied voltage V for each value of d. A positive electrostatic potential is found when V = 0 for d ≤ 500 Å.[Journal translation]

scholarly journals How aromatic system size affects the sensitivities of highly energetic molecules?

RSC Advances ◽  
2021 ◽  
Vol 11 (51) ◽  
pp. 31933-31940
Author(s):  
Ivana S. Veljković ◽  
Jelena I. Radovanović ◽  
Dušan Ž. Veljković
Keyword(s):  
Dft Calculations ◽  
Electrostatic Potential ◽  
System Size ◽  
Aromatic System ◽  
Positive Electrostatic Potential

DFT calculations showed that with the increase of the aromatic system size, values of positive electrostatic potential above the central areas of energetic molecules decrease, leading to the decrease in the sensitivities towards detonation.

Synthesis and Characterization of Azobenzene-Containing Polydiacetylene Polymers

2014 ◽  
Vol 976 ◽  
pp. 46-51
Author(s):  
Esthela Albarrán Preza ◽  
Enrique Vigueras-Santiago ◽  
Susana Hernández López
Keyword(s):  
Dielectric Constant ◽  
Room Temperature ◽  
Main Chain ◽  
Dielectric Constants ◽  
Electronic Density ◽  
Polar Species ◽  
Acceptor Group ◽  
Covalently Bonded ◽  
Donor Acceptor

Polydiacetylenes are a type of highly conjugated polymers, and highly polar species are obtained when these polymers contain donor-acceptor azobenzene entities. In this paper the synthesis, characterization and evaluation of the dielectric constant of two polydiacetylenes containing azobenzenes as pendant groups are discussed. The Azobenzene chromophores are covalently bonded to the main chain, and their polarity is defined by an electro-donor (amine) and an electro-acceptor group (nitro or chlorine) bonded to the ends of a conjugated azobenzene structure. Both polymers were processed into plates of 1cm diameter x 0.674 mm thickness using a thermo mechanic technique. Their dielectric constants were evaluated respect to the temperature in a range of frequency of 110 MHz-1.32 GHz, from room temperature to close to their respective Tg. The dielectric constant for the polymer containing the nitro group was higher than it for polymer containing the chloride atom at all temperatures. It is discussed in terms of the ability to nitro and chloride to attract electronic density.

Increased Positive Electrostatic Potential inp-Hydroxybenzoate Hydroxylase Accelerates Hydroxylation but Slows Turnover†

Biochemistry ◽  
2004 ◽  
Vol 43 (6) ◽  
pp. 1569-1579 ◽  
Author(s):  
Mariliz Ortiz-Maldonado ◽  
Lindsay J. Cole ◽  
Sara M. Dumas ◽  
Barrie Entsch ◽  
David P. Ballou
Keyword(s):  
Electrostatic Potential ◽  
Hydroxybenzoate Hydroxylase ◽  
Positive Electrostatic Potential

scholarly journals Can the sensitivity of energetic materials be tuned by using hydrogen bonds? Another look at the role of hydrogen bonding in the design of high energetic compounds.

2021 ◽  
Author(s):  
Danijela S. Kretić ◽  
Jelena I. Radovanović ◽  
Dušan Ž Veljković
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Electrostatic Potential ◽  
Energetic Materials ◽  
Energetic Compounds ◽  
Positive Electrostatic Potential

Strongly positive electrostatic potential in the central areas of molecules of the energetic materials is one of the most important factors that determine the sensitivity of these molecules towards detonation....

scholarly journals Insight into the surface activity of defect structure in α-MnO2 nanorod: first-principles research

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Pengsen Zhao ◽  
Guifa Li ◽  
Haizhong Zheng ◽  
Shiqiang Lu ◽  
Ping Peng
Keyword(s):  
Electrostatic Potential ◽  
First Principles ◽  
Defect Structure ◽  
Dipole Moments ◽  
Chemical Activity ◽  
First Principles Calculation ◽  
Density Of State ◽  
Electronic Density ◽  
Bulk Surface ◽  
Excellent Chemical

AbstractThe contribution of defect structure to the catalytic property of α-MnO2 nanorod still keeps mysterious right now. Using microfacet models representing defect structure and bulk models with high Miller index, several parameters, such as cohesive energy, surface energy, density of state, electrostatic potential, et al., have been used to investigate the internal mechanism of their chemical activities by first-principles calculation. The results show that the trend in surface energies of microfacet models follows as Esurface[(112 × 211)] > Esurface[(110 × 211)] > Esurface[(100 × 211)] > Esurface[(111 × 211)] > Esurface[(112 × 112)] > Esurface[(111 × 112)], wherein all of them are larger than that of bulk models. So the chemical activity of defect structure is much more powerful than that of bulk surface. Deep researches on electronic structure show that the excellent chemical activity of microfacet structure has larger value in dipole moments and electrostatic potential than that of bulk surface layer. And the microfacet models possess much more peaks of valent electrons in deformantion electronic density and molecular orbital. Density of state indicates that the excellent chemical activity of defect structure comes from their proper hybridization in p and d orbitals.

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