Role of nucleophilic solvation and the mechanism of covalent bond heterolysis

2004 ◽  
Vol 17 (10) ◽  
pp. 825-836 ◽  
Author(s):  
Genrih F. Dvorko ◽  
Engelsine A. Ponomareva ◽  
Mykola E. Ponomarev
Keyword(s):  
Covalent Bond ◽  
Nucleophilic Solvation

Role of Nucleophilic Solvation and the Mechanism of Covalent Bond Heterolysis

ChemInform ◽  
2005 ◽  
Vol 36 (6) ◽  
Author(s):  
Genrih F. Dvorko ◽  
Engelsine A. Ponomareva ◽  
Mykola E. Ponomarev
Keyword(s):  
Covalent Bond ◽  
Nucleophilic Solvation

scholarly journals Role of Chemistry and Crystal Structure on the Electronic Defect States in Cs-Based Halide Perovskites

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1032
Author(s):  
Anirban Naskar ◽  
Rabi Khanal ◽  
Samrat Choudhury
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Covalent Bond ◽  
Density Functional Theory Calculations ◽  
Antisite Defect ◽  
Defect States ◽  
Functional Theory ◽  
Electronic Defect ◽  
Constituent Elements

The electronic structure of a series perovskites ABX3 (A = Cs; B = Ca, Sr, and Ba; X = F, Cl, Br, and I) in the presence and absence of antisite defect XB were systematically investigated based on density-functional-theory calculations. Both cubic and orthorhombic perovskites were considered. It was observed that for certain perovskite compositions and crystal structure, presence of antisite point defect leads to the formation of electronic defect state(s) within the band gap. We showed that both the type of electronic defect states and their individual energy level location within the bandgap can be predicted based on easily available intrinsic properties of the constituent elements, such as the bond-dissociation energy of the B–X and X–X bond, the X–X covalent bond length, and the atomic size of halide (X) as well as structural characteristic such as B–X–B bond angle. Overall, this work provides a science-based generic principle to design the electronic states within the band structure in Cs-based perovskites in presence of point defects such as antisite defect.

Insight into structure, stability and hydrogen bond in complexes of guanine and thymine at the molecular level using computational chemical method

2021 ◽  
Vol 11 (1) ◽  
pp. 127-134
Author(s):  
Nhung Ngo Thi Hong ◽  
Huong Dau Thi Thu ◽  
Trung Nguyen Tien
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Energy Surface ◽  
Covalent Bond ◽  
Electrostatic Energy ◽  
Substantial Contribution ◽  
Structure Stability ◽  
Dispersion Terms ◽  
Insight Into

Nine stable structures of complexes formed by interaction of guanine with thymine were located on potential energy surface at B3LYP/6-311++G(2d,2p). The complexes are quite stable with interaction energy from -5,8 to -17,7 kcal.mol-1. Strength of complexes are contributed by hydrogen bonds, in which a pivotal role of N−H×××O/N overcoming C−H×××O/N hydrogen bond, up to to 3.5 times, determines stabilization of complexes investigated. It is found that polarity of N/C−H covalent bond over proton affinity of N/O site governs stability of hydrogen bond in the complexes. The obtained results show that the N/C−H×××O/N red-shifting hydrogen bonds occur in all complexes, and a larger magnitude of an elongation of N−H compared C-H bond length accompanied by a decrease of its stretching frequency is detected in the N/C−H×××O/N hydrogen bond upon complexation. The SAPT2+ analysis indicates the substantial contribution of attractive electrostatic energy versus the induction and dispersion terms in stabilizing the complexes.

The low temperature thermal decomposition of ammonium perchlorate: nitryl perchlorate as the reaction intermediate

1984 ◽  
Vol 396 (1811) ◽  
pp. 425-440 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Low Temperature ◽  
Ammonium Perchlorate ◽  
Bond Formation ◽  
Covalent Bond ◽  
Subsequent Reaction ◽  
Temperature Decomposition ◽  
Covalent Bond Formation ◽  
Localized Reaction

We identify nitryl perchlorate as the essential intermediate in the low temperature thermal decomposition of ammonium perchlorate AP. Evidence supporting this identification includes the analytical detection of an oxidized nitrogenous species in partly reacted AP and the ability of ammonium nitrate and several other nitrates to markedly reduce the induction period to decomposition of AP and to accelerate the subsequent reaction. It is also shown that the measured rate of the reaction of pure AP is in very satisfactory agreement with that estimated to result from this amount of NO 2 ClO 4 present. This mechanism differs from those currently accepted, in which the controlling process is believed to involve the transfer of either a proton or an electron. Our proposal is based on the known instability of NO 2 ClO 4 at reaction temperature ( ca . 500 K), the enhanced reactivity compared to the ionic alkali perchlorates being ascribed to covalent bond formation O 2 NO─ClO 3 . Subsequent reactions of the products of breakdown of this species, NO + , ClO 3 - and 2O or O 2 , are regarded as capable of oxidizing reactant NH 4 + (→NO 2 + ), thus regenerating the intermediate. Localized reaction in migrating ‘particles’ of fluid NO 2 ClO 4 , advancing through the reactant and leaving a residue of porous NH 4 ClO 4 , explains the unusual, incomplete low temperature decomposition that is characteristic of AP. The article reports comparative kinetic data for the decomposition of pure AP and the reaction initiated by various added nitrates. Rate studies are complemented by scanning electron microscope examinations of the geometry of interface development and the structure of the decomposed salt. From these and analytical results the role of nitryl perchlorate in AP decomposition is discussed.

scholarly journals Bond orders for intermolecular interactions in crystals: charge transfer, ionicity and the effect on intramolecular bonds

IUCrJ ◽  
2018 ◽  
Vol 5 (5) ◽  
pp. 635-646 ◽  
Author(s):  
Khidhir Alhameedi ◽  
Amir Karton ◽  
Dylan Jayatilaka ◽  
Sajesh P. Thomas
Keyword(s):  
Charge Transfer ◽  
Intermolecular Interactions ◽  
Covalent Bond ◽  
Halogen Bonding ◽  
Close Packing ◽  
Bond Orders ◽  
Binding Motifs ◽  
Bond Indices ◽  
Interaction Regions

The question of whether intermolecular interactions in crystals originate from localized atom...atom interactions or as a result of holistic molecule...molecule close packing is a matter of continuing debate. In this context, the newly introduced Roby–Gould bond indices are reported for intermolecular `σ-hole' interactions, such as halogen bonding and chalcogen bonding, and compared with those for hydrogen bonds. A series of 97 crystal systems exhibiting these interaction motifs obtained from the Cambridge Structural Database (CSD) has been analysed. In contrast with conventional bond-order estimations, the new method separately estimates the ionic and covalent bond indices for atom...atom and molecule...molecule bond orders, which shed light on the nature of these interactions. A consistent trend in charge transfer from halogen/chalcogen bond-acceptor to bond-donor groups has been found in these intermolecular interaction regionsviaHirshfeld atomic partitioning of the electron populations. These results, along with the `conservation of bond orders' tested in the interaction regions, establish the significant role of localized atom...atom interactions in the formation of these intermolecular binding motifs.

First-principles Investigation of Edged Ferroelectric PbTiO3 Nanowires and the Role of Axial Strain

2009 ◽  
Vol 1199 ◽  
Author(s):  
Takahiro Shimada ◽  
Shogo Tomoda ◽  
Takayuki Kitamura
Keyword(s):  
Cross Section ◽  
First Principles ◽  
Electronic Structures ◽  
Axial Strain ◽  
Covalent Bond ◽  
First Principles Calculations ◽  
Significant Suppression ◽  
Axial Tension ◽  
Sharp Edges

AbstractAtomistic and electronic structures of PbTiO3 nanowires with atomically sharp edges consisting of (100)/(010) surfaces using first-principles calculations. Ferroelectricity is enhanced at the PbO-terminated edge in the nanowire because the Pb-O covalent bond that predominates the ferroelectric distortions is partially strengthened. On the other hand, a significant suppression is observed in the TiO2-terminated nanowire. Surprisingly, the smallest (one-unit-cell cross- section) PbO-terminated nanowire can keep ferroelectricity, while ferroelectricity disappears in the TiO2-terminated nanowires with a diameter of smaller than 17 Å. The ferroelectricity is recovered by axial tension, where the thinner nanowire requires the higher critical strain.

scholarly journals The Basics of Covalent Bonding in Terms of Energy and Dynamics

Molecules ◽  
2020 ◽  
Vol 25 (11) ◽  
pp. 2667 ◽  
Author(s):  
Sture Nordholm ◽  
George B. Bacskay
Keyword(s):  
Kinetic Energy ◽  
Covalent Bond ◽  
Covalent Bonding ◽  
Bonding Mechanism ◽  
Physical Origin ◽  
Bonding Analysis ◽  
Molecule Formation ◽  
The Subject ◽  
Modern Form

We address the paradoxical fact that the concept of a covalent bond, a cornerstone of chemistry which is well resolved computationally by the methods of quantum chemistry, is still the subject of debate, disagreement, and ignorance with respect to its physical origin. Our aim here is to unify two seemingly different explanations: one in terms of energy, the other dynamics. We summarize the mechanistic bonding models and the debate over the last 100 years, with specific applications to the simplest molecules: H2+ and H2. In particular, we focus on the bonding analysis of Hellmann (1933) that was brought into modern form by Ruedenberg (from 1962 on). We and many others have helped verify the validity of the Hellmann–Ruedenberg proposal that a decrease in kinetic energy associated with interatomic delocalization of electron motion is the key to covalent bonding but contrary views, confusion or lack of understanding still abound. In order to resolve this impasse we show that quantum mechanics affords us a complementary dynamical perspective on the bonding mechanism, which agrees with that of Hellmann and Ruedenberg, while providing a direct and unifying view of atomic reactivity, molecule formation and the basic role of the kinetic energy, as well as the important but secondary role of electrostatics, in covalent bonding.

scholarly journals The impact of growth stimulators and retardants on the utilization of reserve lipids by sunflower seedlings

2017 ◽  
Vol 8 (3) ◽  
pp. 317-322 ◽  
Author(s):  
V. G. Kuryata ◽  
І. V. Poprotska ◽  
Т. І. Rogach
Keyword(s):  
Linoleic Acid ◽  
Butyric Acid ◽  
Covalent Bond ◽  
Chemical Compounds ◽  
Lipase Hydrolysis ◽  
The Impact ◽  
Hydrolysis Of ◽  
Higher Fatty Acids

Using growth stimulators and anti-gibberillin preparations of different chemical compounds, we created different pressures in the coordinate covalent bond systems during germination of sunflower seeds. Using gibberellin and treptolem growth stimulators and Paclobutrazol and Chlormequat-Chlorid anti-gibberillin preparations is an efficient method of reconstructing coordinate covalent bond during the germination of seeds of oil-bearing crops. It allows determination of the role of the hormone factor in the utilization of reserve lipids over the heterotrophic phase of plant development. Blocking the synthesis of gibberellins by retardants caused decrease in activity of lipase, hydrolysis of reserve lipids and the meristem, which resulted in decrease in the energy of germination. Compared to the control, the impact of gibberellin increased the content of butyric acid, and the impact of Paclobutrazol reduced the content of butyric acid. Linoleic acid showed exactly the opposite changes. In relation to the control, a significant increase in the content of non-saturated linoleic acid was observed in both variants of the experiment. Gibberellic acid stimulated and Paclobutrazol slowed the usage of free higher fatty acids for the process of morphogenesis. 

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