Pyridopyridazines. II. Some reactions of Pyrido[2,3-d]- and Pyrido[3,4-d]-pyridazine

1969 ◽  
Vol 22 (8) ◽  
pp. 1745 ◽  
Author(s):  
DB Paul ◽  
HJ Rodda
Keyword(s):  
Electron Densities ◽  
Charge Densities ◽  
Bond Lengths ◽  
Alkaline Conditions ◽  
Chlorous Acid

Pyridopyridazines have been oxidized under acid and alkaline conditions and the sites of oxidation have been rationalized on the basis of charge densities. Pyrido-[2,3-d]pyridazine has been brominated, aminated, and made to react with hypo-chlorous acid and with peracids. The positions of substitution and addition are discussed in relation to calculated π-electron densities and bond lengths. Attention is drawn to some unusual features of the N.M.R. spectra of 1,2-diazine N-oxides.

scholarly journals Frozen-density embedding theory with average solvent charge densities from explicit atomistic simulations

2016 ◽  
Vol 18 (31) ◽  
pp. 21069-21078 ◽  
Author(s):  
Andrey Laktionov ◽  
Emilie Chemineau-Chalaye ◽  
Tomasz A. Wesolowski
Keyword(s):  
Atomistic Simulations ◽  
Electron Densities ◽  
Charge Densities ◽  
Embedding Theory ◽  
Molecular Electron ◽  
Oppenheimer Approximation

Besides molecular electron densities obtained within the Born–Oppenheimer approximation (ρB(r)) to represent the environment, the ensemble averaged density (〈ρB〉(r)) is also admissible in frozen-density embedding theory (FDET) [Wesolowski, Phys. Rev. A, 2008, 77, 11444].

SEMIEMPIRICAL SCF CALCULATIONS ON AZULENE AND ITS SINGLY CHARGED IONS

1965 ◽  
Vol 43 (11) ◽  
pp. 3026-3038 ◽  
Author(s):  
J. E. Bloor
Keyword(s):  
Dipole Moment ◽  
Excited States ◽  
Ground State ◽  
Basis Set ◽  
Bond Orders ◽  
Electron Charge Density ◽  
Charge Densities ◽  
Bond Lengths ◽  
Set Agreement ◽  
Singly Charged

SCF MOs for azulene have been obtained by the semiempirical Pariser, Parr, Pople procedure using the Nishimoto–Mataga method of calculating repulsion integrals and the assumption that nearest neighbor resonance integrals are independent of interatomic distance. Excited states calculated from these MOs by a CI calculation are in very good agreement with experiment. Ground state charge densities, bond orders, and the dipole moment are similar to other SCFMO calculations and reveal no disadvantage in adopting a constant resonance integral for all bonds. It is shown that estimates of the π-electron charge density by n.m.r. methods are not compatible with direct dipole moment measurements and it is suggested that the interpretation of the n.m.r. measurements suffers from inaccuracies in estimating ring currents. Doubt is also thrown on the use of simple relationships between calculated π-bond orders and bond lengths obtained by X-ray crystallographic measurements on the solid state, particularly since all the bond lengths in azulene are predicted to be longer than in benzene whereas experiment shows some to be shorter. Calculations on spin densities and charge densities of the singly charged azulene anion and cation have been performed by a restricted Hartree–Fock perturbation method in which the matrix elements for the interaction between singly excited states and the ground state are calculated using the closed shell SCFMOs of azulene as the basis set. Agreement with experiment for the anion is fairly good. For the cation our results are in severe disagreement with recent VB calculations, but there are no experimental results available to decide between the two methods.

scholarly journals Atomic radii from electron densities.

2000 ◽  
Vol 53 (2) ◽  
pp. 317 ◽  
Author(s):  
B. E. Etschmann ◽  
E. N. Maslen
Keyword(s):  
Angular Momentum ◽  
Bond Order ◽  
Free Atom ◽  
Nuclear Region ◽  
Electron Densities ◽  
Bond Lengths ◽  
Valence Electrons ◽  
Exchange Repulsion ◽  
Predicted Values ◽  
Atomic Radii

Bond lengths for diatomic molecules are predicted from atomic radii derived from free atom one-electron densities by postulating shielding factors for their valence electrons that depend on orbital angular momentum and on the bond order. The predicted values are closer to spectroscopically measured bond lengths than those based on earlier atomic radii inferred from a wider range of structural evidence. The bond lengths predicted by the sum of the atomic radii are corrected by a reduction that allows for charge transfer and by an extension associated with exchange repulsion of the overlapping electrons in the inter-nuclear region. Both corrections are related to free atom one-electron densities.

Towards the use of experimental electron densities to estimate reliable lattice energies

CrystEngComm ◽  
2018 ◽  
Vol 20 (36) ◽  
pp. 5340-5347 ◽  
Author(s):  
Mark A. Spackman
Keyword(s):  
Electron Densities ◽  
Charge Densities ◽  
Lattice Energies

Lattice energies derived from experimental charge densities are critically assessed, with a view to encouraging further research of this nature.

scholarly journals Hirshfeld atom refinement

IUCrJ ◽  
2014 ◽  
Vol 1 (5) ◽  
pp. 361-379 ◽  
Author(s):  
Silvia C. Capelli ◽  
Hans-Beat Bürgi ◽  
Birger Dittrich ◽  
Simon Grabowsky ◽  
Dylan Jayatilaka
Keyword(s):  
Hydrogen Atom ◽  
Diffraction Data ◽  
Iterative Procedure ◽  
Structural Parameters ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
Electron Densities ◽  
X Ray ◽  
Bond Lengths ◽  
Better Than

Hirshfeld atom refinement (HAR) is a method which determines structural parameters from single-crystal X-ray diffraction data by using an aspherical atom partitioning of tailor-madeab initioquantum mechanical molecular electron densities without any further approximation. Here the original HAR method is extended by implementing an iterative procedure of successive cycles of electron density calculations, Hirshfeld atom scattering factor calculations and structural least-squares refinements, repeated until convergence. The importance of this iterative procedure is illustratedviathe example of crystalline ammonia. The new HAR method is then applied to X-ray diffraction data of the dipeptide Gly–L-Ala measured at 12, 50, 100, 150, 220 and 295 K, using Hartree–Fock and BLYP density functional theory electron densities and three different basis sets. All positions and anisotropic displacement parameters (ADPs) are freely refined without constraints or restraints – even those for hydrogen atoms. The results are systematically compared with those from neutron diffraction experiments at the temperatures 12, 50, 150 and 295 K. Although non-hydrogen-atom ADPs differ by up to three combined standard uncertainties (csu's), all other structural parameters agree within less than 2 csu's. Using our best calculations (BLYP/cc-pVTZ, recommended for organic molecules), the accuracy of determining bond lengths involving hydrogen atoms from HAR is better than 0.009 Å for temperatures of 150 K or below; for hydrogen-atom ADPs it is better than 0.006 Å2as judged from the mean absolute X-ray minus neutron differences. These results are among the best ever obtained. Remarkably, the precision of determining bond lengths and ADPs for the hydrogen atoms from the HAR procedure is comparable with that from the neutron measurements – an outcome which is obtained with a routinely achievable resolution of the X-ray data of 0.65 Å.

scholarly journals Intermolecular Interactions in Ionic Crystals of Nucleobase Chlorides—Combining Topological Analysis of Electron Densities with Energies of Electrostatic Interactions

Crystals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 668 ◽  
Author(s):  
Prashant Kumar ◽  
Małgorzata Katarzyna Cabaj ◽  
Paulina Maria Dominiak
Keyword(s):  
Intermolecular Interactions ◽  
Critical Points ◽  
Electrostatic Interactions ◽  
Point Of View ◽  
Ionic Crystals ◽  
Interaction Energies ◽  
Electron Densities ◽  
Charge Densities ◽  
Non Covalent Interactions ◽  
Covalent Interactions

Understanding intermolecular interactions in crystals of molecular ions continues to be difficult. On the one hand, the analysis of interactions from the point of view of formal charges of molecules, similarly as it is commonly done for inorganic ionic crystals, should be performed. On the other hand, when various functional groups are present in the crystal, it becomes natural to look at the interactions from the point of view of hydrogen bonding, π…π stacking and many other kinds of non-covalent atom–atom bonding. Often, these two approaches seem to lead to conflicting conclusions. On the basis of experimental charge densities of cytosinium chloride, adeninium chloride hemihydrate, and guanine dichloride crystals, with the help of theoretical simulations, we have deeply analysed intermolecular interactions among protonated nucleobases, chloride anions and water molecules. Here, in the second paper of the series of the two (Kumar et al., 2018, IUCrJ 5, 449–469), we focus on applying the above two approaches to the large set of dimers identified in analysed crystals. To understand electrostatic interactions, we analysed electrostatic interaction energies (Ees) computed directly from molecular charge densities and contrasted them with energies computed only from net molecular charges, or from a sum of electric multipolar moments, to find the charge penetration contribution to Ees. To characterize non-covalent interactions we performed topological analyses of crystal electron densities and estimated their interaction energies (EEML) from properties of intermolecular bond critical points. We show that the overall crystal architecture of the studied compounds is governed by the tight packing principle and strong electrostatic attractions and repulsions between ions. Many ions are oriented to each other in a way to strengthen attractive electrostatic interactions or weaken strong repulsion, but not all of them. Numerous bond critical points and bond paths were found between ions, including nucleobase cations despite their overall repulsive interactions. It is clear there is no correlation between EEML and Ees. However, strong relation between EEML and the charge penetration component of Ees is observed. The relation holds regardless of interaction types or whether or not interacting molecules bear the same or opposite charges. Thus, a charge density-based approach for computing intermolecular interaction energies and the atom–atom approach to analyse non-covalent interactions do complement each other, even in ionic systems.

The cytotoxicity of ortho alkyl substituted 4-X-phenols: A QSAR based on theoretical bond lengths and electron densities

2006 ◽  
Vol 16 (5) ◽  
pp. 1249-1254 ◽  
Author(s):  
R.J. Loader ◽  
N. Singh ◽  
P.J. O’Malley ◽  
P.L.A. Popelier
Keyword(s):  
Electron Densities ◽  
Bond Lengths

ELECTRONIC AND STRUCTURAL PROPERTIES OF C36 MOLECULE

1999 ◽  
Vol 13 (12) ◽  
pp. 1513-1523
Author(s):  
XIAOQING YU ◽  
CONGJUN WU ◽  
CHUI-LIN WANG ◽  
ZHAO-BIN SU
Keyword(s):  
Electronic Properties ◽  
Structural Properties ◽  
Coulomb Interaction ◽  
Long Distance ◽  
Charge Densities ◽  
Bond Lengths ◽  
Homo And Lumo ◽  
Spin Triplet ◽  
Electronic And Structural Properties ◽  
Ssh Model

The extended SSH model and Bogoliubov–de–Gennes (BdeG) formalism are applied to investigate the electronic properties and stable lattice configurations of C 36. We focus the problem on the molecule's unusual D6h symmetry. The electronic part of Hamiltonian without Coulomb interaction is solved analytically. We found that the gap between HOMO and LUMO is small due to the long distance hopping between the 2nd and 5th layers. The charge densities of HOMO and LUMO states are mainly distributed in the two layers, that causes a large splitting between the spin triplet and singlet excitons. The differences of bond lengths, angles and charge densities among molecule and polarons are discussed.

A crystalline–amorphous Ni–Ni(OH)2 core–shell catalyst for the alkaline hydrogen evolution reaction

2020 ◽  
Vol 8 (44) ◽  
pp. 23323-23329
Author(s):  
Jing Hu ◽  
Siwei Li ◽  
Yuzhi Li ◽  
Jing Wang ◽  
Yunchen Du ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Electrocatalytic Activity ◽  
Core Shell ◽  
Alkaline Conditions

Crystalline–amorphous Ni–Ni(OH)2 core–shell assembled nanosheets exhibit outstanding electrocatalytic activity and stability for hydrogen evolution under alkaline conditions.

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