Quantum chemical computations on rotational isomers of hydrogen nitrite and nitritomethane

1982 ◽  
Vol 381 (1781) ◽  
pp. 443-455 ◽  
Keyword(s):  
Excited States ◽  
Quantum Chemical ◽  
Dipole Moments ◽  
Basis Set ◽  
Electronic Transitions ◽  
Rotational Isomers ◽  
Transition Structures ◽  
Quantum Chemical Computations ◽  
Split Valence ◽  
Good Agreement

Ab initio molecular-orbital computations with a split-valence 4-31G basis set have been carried out on syn- and antiperiplanar conformers of both HONO and H 3 CONO, and on the transition structures in the unimolecular isomerization process. Calculated values of geometric structural and rotational parameters, dipole moments, wavenumbers of vibrational transitions, energies of vertical electronic transitions to both neutral and ionized excited states, and thermodynamic properties are compared with experimental data; generally good agreement is found. No explanation of the anomalous stability of antiperiplanar HONO has been discovered.

Vibronic absorption spectra and excited states of acridine red dye in aqueous solution: TD-DFT/DFT study

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Victor V. Kostjukov
Keyword(s):  
Aqueous Solution ◽  
Absorption Spectrum ◽  
Hydrogen Bonds ◽  
Absorption Spectra ◽  
Excited States ◽  
Dipole Moments ◽  
Basis Set ◽  
Calculated Spectrum ◽  
Solvent Model ◽  
Acridine Red

Abstract The vibronic absorption spectra of acridine red (AR) xanthene dye in an aqueous solution using 40 hybrid functionals, the 6-31++G(d,p) basis set, and the IEFPCM solvent model were calculated. It turned out that the O3LYP functional provided the best agreement with the experiment in the positions of the main maximum and the short-wavelength subband (shoulder). The calculations showed that this shoulder is vibronic. At the same time, the shoulder intensity in the calculated spectrum turned out to be lower than in the experimental one. Apparently, insignificant dimerization, which occurs even at low concentrations of the dye in solution, contributes to the shoulder of the experimental absorption spectrum. Various parameters of the AR cation in the ground and excited states (IR spectra, atomic charges, dipole moments, and transition moment) were calculated. Maps of the distribution of electron density and electrostatic potential have been built. The influence of the strong hydrogen bonds of the dye with three water molecules on the absorption spectrum was analyzed. It has been shown that these bonds are strengthened upon AR excitation. The strengthening of two hydrogen bonds with water upon excitation leads to a lowering of the potential energy surface of the excited state, which causes a decrease in the excitation energy (i.e., an increase in the wavelength of the absorbed photon) as compared to a purely implicit specification of the water environment. Therefore, explicit assignment of waters strongly bound to the dye leads to spectrum redshift.

scholarly journals Chelating Mechanisms of Transition Metals by Bacterial Metallophores “Pseudopaline and Staphylopine”: A Quantum Chemical Assessment

Computation ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 56 ◽  
Author(s):  
Ghassan Ghssein ◽  
Samir Matar
Keyword(s):  
Excited States ◽  
Quantum Chemical ◽  
Density Functional ◽  
Ionic Species ◽  
Active Centers ◽  
Functional Theory ◽  
Ligand Charge Transfer ◽  
Td Dft ◽  
Vibration Spectroscopy ◽  
Quantum Chemical Computations

In bacterial pathology, metallophores fabricated by bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa are exported to surrounding physiological media via a specific process to sequester and import metals, resulting in enhanced virulence of the bacteria. While these mechanisms are understood at qualitative levels, our investigation presents a complementary original view based on quantum chemical computations. Further understanding of the active centers in particular was provided for pseudopaline and staphylopine metallophores, which were described chemically and with vibration spectroscopy. Then, for complexes formed with a range of transition metal divalent ions (Ni, Cu, and Zn), description and analyses of the frontier molecular orbitals (FMOs) are provided, highlighting a mechanism of metal-to-ligand charge transfer (MLCT), based on excited-states calculations (time-dependent density functional theory (TD-DFT)) at the basis of the delivery of the metallic ionic species to the bacterial medium, leading eventually to its enhanced virulence. Such investigation gains importance especially in view of stepwise syntheses of metallophores in the laboratory, providing significant progress in the understanding of mechanisms underlying the enhancement of bacterial pathologies.

scholarly journals Anisotrope Fluoreszenz langgestreckter Moleküle in Lösungen / The Anisotropie Fluorescence of Prolate Molecules in Solutions

1979 ◽  
Vol 34 (9) ◽  
pp. 1066-1069 ◽  
Author(s):  
A. Kawski ◽  
J. Kukielski ◽  
J. Kamiński
Keyword(s):  
Excited States ◽  
Linear Dependence ◽  
Electric Dipole ◽  
Quantum Chemical ◽  
Dipole Moments ◽  
Relaxation Times ◽  
Rotational Relaxation ◽  
Electric Dipole Moments ◽  
Transition Moments ◽  
Non Linear

Abstract Quantum chemical investigations of the electric dipole moments in the ground and excited states and also transition moments of 2,2′-p-phenylenebis (5-phenyloxazole) (POPOP) and 2,2′-p-phenylenebis (4-methvl-5-phenylaxazole) (2MPOPOP) were carried out with the PPP-CI-method. It was established that the transition moments of POPOP and 2MPOPOP are parallel to the long axis, whereas the electric dipole moments are mutually parallel and perpendicular to the long axis of these molecules. Further, the emission anisotropics r of the fluorescence of the prolate molecules POPOP. 2MPOPOP and the non-polar diphenvlenestilbene (DPS) in solvents of different viscosities η were investigated. Also for these substances the non-linear dependence of 1/r on T/η was confirmed. This deviation from the linear dependence is stipulated essentially through the length of the molecule. The effective volumes and the rotational relaxation times in different solvents of the studied molecules were determined.

scholarly journals UV/VIS spectral properties of novel natural products from Turkish lichens

2005 ◽  
Vol 7 (1) ◽  
pp. 27-35 ◽  
Author(s):  
Yevgen Posokhov ◽  
Sule Erten ◽  
Ömer Koz ◽  
H. AnIl ◽  
Süheyla KIrmIzIgül ◽  
...  
Keyword(s):  
Natural Products ◽  
Excited States ◽  
Quantum Chemical ◽  
Spectral Properties ◽  
Dipole Moments ◽  
Spectral Characteristics ◽  
Molecular Geometry ◽  
Biologically Active ◽  
Semiempirical Methods ◽  
Active Natural

UV/VIS spectral characteristics of three new biologically active natural products, isolated from Turkish lichens, have been investigated in solvents of various polarity and proton donating ability. The effect of the solvent on spectral characteristics has been estimated. Quantum chemical calculations with the optimization of molecular geometry were done with the full-valent semiempirical methods AM1 and PM3 for conformational analysis and in order to discuss the charge distributions and dipole moments in the ground and in the excited states.

scholarly journals Energetic Degeneracy and Electronic Structures of Germanium Trimers Doped with Titanium

2020 ◽  
Author(s):  
Le Nhan Pham ◽  
Salvy P. Russo
Keyword(s):  
Experimental Data ◽  
Excited States ◽  
Electronic Structures ◽  
Quantum Chemical ◽  
Electronic Transitions ◽  
Chemical Methods ◽  
Quantum Chemical Methods ◽  
Experimental Group ◽  
Comparison With Experimental Data

Several quantum chemical methods including CASSCF/CASPT2, CCSD(T)-F12, and DFT were used to study electronic structures and excited states of germanium trimers singly doped with titanium. All necessary parameters and calculations process are reported in the text. The conclusion on electronic transitions causing anion photoelectron bands was made by analysis of electronic structures and comparison with experimental data (reported by an experimental group).

scholarly journals THERMOCHEMICAL PARAMETERS OF SOME SMALL PURE AND DOPED SILICON CLUSTERS

2018 ◽  
Vol 55 (6A) ◽  
pp. 18
Author(s):  
Nguyen Minh Tam
Keyword(s):  
Quantum Chemical ◽  
Large Error ◽  
Basis Set ◽  
Coupled Cluster ◽  
Electron Affinities ◽  
Silicon Clusters ◽  
Coupled Cluster Theory ◽  
Doped Silicon ◽  
Thermochemical Parameters ◽  
Quantum Chemical Computations

Quantum chemical computations of thermochemical parameters of several series of small pure and doped silicon clusters are reviewed. We analyzed the performance of the coupled-cluster theory with energies extrapolated up to complet basis set, CCSD(T)/CBS and the composite G4 method in determining the total atomization energies (TAE), standard heats of formation (∆fH0), electron affinities (EA) and ionization energies (IE) and other thermochemical parameters with respect to available experimental data. The latter were determined with large error margins.

Abinitio Calculations of the Barriers to Rotation in Some Monosubstituted Benzenes

1986 ◽  
Vol 39 (7) ◽  
pp. 1157 ◽  
Author(s):  
S Marriott ◽  
RD Topsom
Keyword(s):  
Electron Transfer ◽  
Ab Initio ◽  
Benzene Ring ◽  
Theoretical Calculations ◽  
Geometry Optimization ◽  
Basis Set ◽  
Monosubstituted Benzenes ◽  
Split Valence ◽  
Good Agreement ◽  
Abinitio Calculations

Theoretical calculations at the ab initio level have been made of the twofold rotational barriers of some monosubstituted benzenes, and the effects both of basis set and of geometry optimization have been examined. Values at the STO-3G//STO-3G level are in good agreement with experiment. The use of split-valence sets, even with geometry optimization, is much less satisfactory, and this may be related to an overestimation of π-electron transfer between the substituent and the benzene ring.

Experimentelle und Quantenchemische Untersuchungen der Dipolmomente von Substituierten Stilbenen im Ersten Angercgten Singulettzustand / Experimental and Quantum Chemical Investigations of Dipole Moments of Substituted Stilbens in the First Excited Singlet State

1977 ◽  
Vol 32 (5) ◽  
pp. 420-425 ◽  
Author(s):  
A. Kawski ◽  
I. Gryczyński
Keyword(s):  
Dipole Moment ◽  
Excited States ◽  
Ground State ◽  
Quantum Chemical ◽  
Singlet State ◽  
Dipole Moments ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Fluorescent State ◽  
Experimental Values

Abstract The values a/a3 (α = polarizability), the Onsager cavity radii a and the dipole moments μe of six substituted stilbens in the fluorescent state have been determined. It is shown that if the dipole moment of the lowest excited singlet state μe is parallel to the dipole moment in the ground state μg, the values of μe and a can be determined from the solvent effects. Moreover, quantum chemical investigations of the dipole moments in the ground and excited states were carried out with the Pariser-Parr-Pople method and compared with the experimental values.

scholarly journals Theoretical Study of Reaction Between Nitrilimine and 1,4 Oxazine 2 Carboxylate by MP2 and DFT Methods

2018 ◽  
Vol 34 (6) ◽  
pp. 2992-2997
Author(s):  
H. El-Hadki ◽  
F. Hlimi ◽  
M. Salah ◽  
K. Marakchi ◽  
N. Komiha ◽  
...  
Keyword(s):  
Energy Surface ◽  
Theoretical Study ◽  
Basis Set ◽  
Dft Methods ◽  
Reactivity Indices ◽  
B3lyp Method ◽  
Transition Structures ◽  
Potential Energy Surface Calculation ◽  
Good Agreement ◽  
Surface Calculation

The regioselectivity of the reaction between phenyldiazen-1-ium-1-ylidene p-tolyl methanide and ethyl 4-benzoyl-4H-benzo [1,4]oxazine-2-carboxylate were studied by means of the DFT/B3LYP method coupled by the 6-31g(d) basis and MP2 in connection with 6-31G(d) and 6-31G+(d,p) basis set. The mechanism of this regioselectif reaction has performed by transition state optimization, evaluation of the potential energy surface, calculation of IRC and reactivity indices. Location and verification of minima and transition structures have been realized by using the Berny's algorithm. The process of formation of the two regioisomers is achieved through concerted and asynchronous mechanism. The results are in good agreement with the experimental data.

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