Dipole moments and electronic structure of some xanthine and thioxanthine derivatives

1970 ◽  
pp. 596 ◽  
Author(s):  
H. Weiler-Feilchenfeld ◽  
Z. Neiman
Keyword(s):  
Electronic Structure ◽  
Dipole Moments

Conformation and electronic structure of aromatic chloroformates

1987 ◽  
Vol 52 (4) ◽  
pp. 970-979 ◽  
Author(s):  
Otto Exner ◽  
Pavel Fiedler
Keyword(s):  
Electronic Structure ◽  
Oxygen Atom ◽  
Strong Interaction ◽  
Electron Distribution ◽  
Room Temperature ◽  
Functional Group ◽  
Dipole Moments ◽  
Carbonyl Oxygen ◽  
Nonpolar Solvents ◽  
Single Method

Aromatic chloroformates Ib-Ie were shown to exist in the ap conformation, in agreement with aliphatic chloroformates, i.e. the alkyl group is situated cis to the carbonyl oxygen atom as it is the case in all esters. While 4-nitrophenyl chloroformate (Ie) is in this conformation in crystal, in solution at most several tenths of percent of the sp conformation may be populated at room temperature and in nonpolar solvents only. A new analysis of dipole moments explained the previous puzzling results and demonstrated the impossibility to determine the conformation by this single method, in consequence of the strong interaction of adjoining bonds. If, however, the ap conformation is once proven, the dipole moments reveal some features of the electron distribution on the functional group, characterized by the enhanced polarity of the C-Cl bond and reduced polarity of the C=O bond. This is in agreement with the observed bond lengths and angles.

Electronic structure and properties of alkoxymethylenemalonic acid derivatives

1979 ◽  
Vol 44 (5) ◽  
pp. 1423-1433 ◽  
Author(s):  
Dušan Ilavský ◽  
Jiří Krechl ◽  
Petr Trška ◽  
Josef Kuthan
Keyword(s):  
Electronic Structure ◽  
Quantum Chemical ◽  
Chemical Reactivity ◽  
Dipole Moments ◽  
Structure And Properties ◽  
Geometrical Isomers ◽  
H Nmr ◽  
Geometrical Isomerism ◽  
Pmr Spectra ◽  
Insight Into

Six compounds RO(H)C=C(X)CN with R = CH3 or C2H5 and X = CO2CH3, CO2C2H5 or CN are characterized by some spectral data (IR, UV, 1H NMR - solvent effect). The PMR spectra did not confirm the presence of two geometrical isomers. Employing the quantum chemical calculations of the substance with R = CH3 and X = CO2CH3 based on EHT, PPP, HMO and CNDO/2, the geometrical isomerism is discussed in relation to the experimental dipole moments. The HMO indices of chemical reactivity agree with our present synthetic insight into nucleophilic substitution of the derivatives under study.

A study of dipole moments of substituted isothiocyanates of 1,3-diphenyl-2-propen-1-one

1984 ◽  
Vol 49 (10) ◽  
pp. 2382-2386 ◽  
Author(s):  
Gejza Suchár ◽  
Milan Dzurilla ◽  
Pavol Kristian
Keyword(s):  
Electronic Structure ◽  
Benzene Solution ◽  
Dipole Moments ◽  
Vector Addition

The dipole moments have been measured of various substituted isothiocyanates of 1,3-diphenyl-2-propen-1-one in benzene solution. The measured values have been compared with the dipole moments obtained by the vector addition of the bond dipole moments, and the comparison has been used for a discussion of their electronic structure and interactions of the NCS group.

Benchmarking Electronic Structure Methods for Accurate Fixed-Charge Electrostatic Models

2019 ◽  
Author(s):  
Alex Zhou ◽  
Michael Schauperl ◽  
Paul Nerenberg
Keyword(s):  
Electronic Structure ◽  
Gas Phase ◽  
Condensed Phase ◽  
Force Fields ◽  
Dipole Moments ◽  
Fixed Charge ◽  
Basis Set ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Partial Atomic Charges

<p>The accuracy of classical molecular mechanics (MM) force fields used for condensed phase molecular simulations depends strongly on the accuracy of modeling nonbonded interactions between atoms, such as electrostatic interactions. Some popular fixed-charge MM force fields use partial atomic charges derived from gas phase electronic structure calculations using the Hartree-Fock method with the relatively small 6-31G* basis set (HF/6-31G*). It is generally believed that HF/6-31G* generates fortuitously overpolarized electron distributions, as would be expected in the higher dielectric environment of the condensed phase. Using a benchmark set of 47 molecules we show that HF/6-31G* overpolarizes molecules by just under 10% on average with respect to experimental gas phase dipole moments. The overpolarization of this method/basis set combination varies significantly though and, in some cases, even leads to molecular dipole moments that are lower than experimental gas phase measurements. We further demonstrate that using computationally inexpensive density functional theory (DFT) methods, together with appropriate augmented basis sets and a continuum solvent model, can yield molecular dipole moments that are both more strongly and more uniformly overpolarized. These data suggest that these methods – or ones similar to them – should be adopted for the derivation of accurate partial atomic charges for next-generation MM force fields.<br></p>

VESCF-MO studies of molecules containing atoms from the second row of the Periodic Table. II. Properties of the fluorides of silicon, phosphorus, sulphur, and chlorine for a minimal basis set excluding 3d-orbitals

1968 ◽  
Vol 21 (11) ◽  
pp. 2605 ◽  
Author(s):  
RD Brown ◽  
JB Peel
Keyword(s):  
Electronic Structure ◽  
Electronic Structures ◽  
Periodic Table ◽  
Central Atom ◽  
Dipole Moments ◽  
Coulomb Repulsion ◽  
Basis Set ◽  
Orbital Method ◽  
Molecular Orbital Method ◽  
Minimal Basis

A study has been made of the electronic structures of the fluorides of silicon, phosphorus, sulphur, and chlorine by the VESCF molecular-orbital method with a minimal basis set, not including 3d-orbitals on the central atom. It proves possible to understand variations in bond lengths and charges on fluorine ligands, dipole moments, force constants, and some n.q.r. data. The calculations are found to be sensitive to assumptions about scaling factors for monocentric coulomb repulsion integrals and penetration integrals. We have not discovered any justification for including 3d-orbitals in the description of the electronic structure of these molecules.

scholarly journals Molecular structure of calcium, magnesium, strontium and barium m-nitrobenzoates

2010 ◽  
Vol 24 (3-4) ◽  
pp. 433-437 ◽  
Author(s):  
Mariola Samsonowicz
Keyword(s):  
Molecular Structure ◽  
Electronic Structure ◽  
Ir Spectra ◽  
Dipole Moments ◽  
Atomic Charges ◽  
Barium Ions ◽  
Nitrobenzoic Acid ◽  
Calcium Magnesium ◽  
Ft Ir

The effect of calcium, magnesium, strontium and barium ions on the electronic structure of m-nitrobenzoates was studied. The FT-IR spectra of m-nitrobenzoic acid and its salts were registered, assigned and analyzed. Characteristic shifts and changes in intensities of bands along the metal series were observed. The structures of m-nitrobenzoic acid and its calcium, magnesium, strontium and barium salts were optimized at the B3LYP/LANL2DZ level. Geometric aromaticity indices, atomic charges, dipole moments and energies were also calculated.

Calculation of the electronic structure and dipole moments of 4-substituted tetrabromopyridines

1981 ◽  
Vol 17 (7) ◽  
pp. 684-689
Author(s):  
A. A. Kisilenko ◽  
A. A. Zeikan' ◽  
S. I. Vdovenko ◽  
V. P. Kukhar'
Keyword(s):  
Electronic Structure ◽  
Dipole Moments

scholarly journals Nonlinear Optical Rectification in a Polar Molecule-Plasmonic Nanoparticle Structure

2020 ◽  
Vol 4 (1) ◽  
pp. 8
Author(s):  
Natalia Domenikou ◽  
Ioannis Thanopulos ◽  
Vassilios Yannopapas ◽  
Emmanuel Paspalakis
Keyword(s):  
Electronic Structure ◽  
Nonlinear Optical ◽  
Dipole Moments ◽  
Quantum Systems ◽  
Optical Rectification ◽  
Plasmonic Nanostructures ◽  
Metallic Nanoparticle ◽  
Plasmonic Nanoparticle ◽  
Rectification Coefficient ◽  
Nonlinear Optical Rectification

The study of nonlinear optical properties of quantum systems, such as quantum dots and molecules, near plasmonic nanostructures, has attracted significant interest in the past decade. Several nonlinear phenomena have been studied in quantum systems next to plasmonic nanostructures, such as second and third harmonic generations, Kerr nonlinearity, four-wave mixing, optical bistability, and nonlinear optical rectification. The latter occurs in asymmetric quantum systems and it can be strongly influenced, enhanced, or suppressed, depending on the particular plasmonic nanostructure used. In this work, we theoretically studied the nonlinear optical rectification of a polar two-level quantum system, a specific molecule, the zinc–phalocyanine molecular complex, interacting with an optical field near a gold nanoparticle. Initially, we used the steady-state solution of the density matrix equations for determining the correct form of the nonlinear optical rectification coefficient. We then used ab initio electronic structure calculations for determining the electronic structure of the molecule under study, i.e., the necessary energy differences and the induced and permanent electric dipole moments. We also used classical electromagnetic calculations for calculating the influence of the metallic nanoparticle on the decay rates of the molecule due to the Purcell effect and on the electric field applied in the molecule in the presence of the metallic nanoparticle. We then used the above to investigate the form of the corresponding nonlinear coefficient in the absence and presence of the plasmonic nanoparticle for various parameters. We found that the nonlinear optical rectification coefficient can be enhanced for specific field polarization and for suitable distance between the molecule and the plasmonic nanoparticle. Additionally, we observed that high efficiency of this process was obtained for weak field intensity, zero pure dephasing rates, and for small values of the transition dipole moments.

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