Electron density distribution in heterocyclic systems with two adjacent nitrogen atoms

Dipole moments found are compared with those calculated vectoran ially. Bis(3, 5-dimethylpyrazol-4-yl) has a constant dipole moment, which indicates inequality of nitrogen atoms in the pyrazole ring. Dipole moments of condensed pyrazolopyridines can be found by adding vectorially the dipole moments of pyridine and pyrazole. Involvement of a nitrogen atom and formation of two aromatic rings does not significantly alter the dipole moment of pyrazolo[2, 3-a]-pyridine as compared with pyrazole.For Part V see [1].     

Electron density distribution in heterocyclic systems with two adjacent nitrogen atoms

A comparison is given between the dipole moments found experimentally for 1, 2, 4-triazole and its derivatives and those computed vectorially. In 1, 2, 4-triazoles unsubstituted on nitrogen, the hydrogen is attached at N₁ in the majority of cases. The 1, 2, 4-triazoles undergo acylation on N₁. Under the influence of a strong electron acceptor (a p-nitrophenyl substituent), the electron cloud of the triazole ring is highly polarized.For communication III see [1].     

Electron density distribution in heterocyclic systems with two vicinal nitrogen atoms. II. Pyrazole dipole moments

The dipole moment of pyrazole is determined and found to agree well with that calculated vectorially. From vector calculation the angle between the dipole moment and the N-H bond is found to be 118° 15.For Part I see [1].The authors wish to express their thanks to Dr, M. E. Vol'pin and G. N. Kartsev, M.sc., for valuable advice.     

Electron density distribution in heterocyclic systems with two vicinal nitrogen atoms. III. Dipole moments of some alkyl,aryl, and nitro pyrazole derivatives

Dipole moments of 13 alkyl and aryl derivatives of pyrazole are determined. It is found that fundamentally it is the pyrazole ring that determines the values of these dipole moments. The phenyl group behaves as a weak electron donor with respect to the pyrazole ring. It is shown that under the action of powerful electron-accepting substituents, such as the nitro group, the electron cloud of the pyrazole ring is polarized toward the electron acceptor.For Part II see [1].     

Condensed heterocyclic systems with a quaternary nitrogen atom

Nitro and amino derivatives of pyrido[1,2-f]phenanthridinium perchlorate were synthesized by the Pschorr method and by photocyclodehydrogenation from N-(nitrophenyl)-or N-(aminophenyl)pyridinium perchlorates. The mechanism of the photoconversion was investigated.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1226–1229, September, 1978.     

Mass spectrometric fragmentation of saturated six membered heterocyclic systems containing two chalcogen family atoms

The mass spectra of six-membered saturated heterocycles containing oxygen, sulphur, selenium and tellurium in the 1,4-positions have been measured. The differing fragmentation modes have been characterized using high resolution, low voltage and metastable ion scan techniques. The important decomposition reactions of the molecular ions involve elimination of C₂H₄ and CH₂X (X is a chalcogen atom) and formation of [C₂H₄X]⁺ and C₂H₅⁺. The propensities of these reactions vary systematically as a function of the ability of the chalcogen to stabilize a positive charge.     

Synthesis of new condensed nitrogen heterocyclic systems

A cotarnine alkaloid-based synthesis was developed for new heptacyclic condensed diisoquinolines via the double intramolecular pseudosalt bis[1,3]dioxolo[4,5-g;4′,5′-g′][1,3,4]oxadiazolo[2,3-a;5,4-a′]diisoquinoline 6. Substitution of the central O atom in 6 by C, S, or N nucleophiles afforded the first representatives of the new ring systems bis[1,3]dioxolo[4,5-g:4,5-g′]pyrazolo[3,2-a:5,1-a′]diisoquinoline (7a-d), bis[1,3]dioxolo[4,5-g:4,5-g′][1,3,4]thiadiazolo[2,3-a:5,4-a′]diisoquinoline (8), and bis[1,3]dioxolo[4,5-g:4,5-g′][1,2,4]triazolo[3,2-a:5,1-a′]diisoquinoline (9a-d) under simple reaction conditions.     

Electronic structure and spectra of fused n/m ring systems with one or two bridgehead nitrogen atoms

Electronic structures and absorption spectra of the quinolizinium cation, all its monoaza-derivatives and the pyridazo(1.2-a)pyridazinium dication, have been computed by using the Pariser-Parr-Pople method, including all singlet mono-excited electronic configurations. The assignment of the observed bands of the quinolizinium cation has been made by comparing its observed transition energies and intensities with those of naphthalene, quinoline and isoquinoline. Discussion is given on reactivity and band interpretation.

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Zusammenfassung Die Elektronenstrukturen und Absorptionsspektren des Quinolizinium Kations und aller seiner Monoazaderivate und des Pyridazo(1,2-a)-pyridazinium Dikations, werden nach der Pariser-Parr-Pople Methode berechnet, wobei alle einzeln angeregten Konfigurationen berücksichtigt werden. Die Banden des Quinolizinium Kations werden durch einen Vergleich der beobachteten Übergangsenergien und Intensitäten mit denen des Naphthalins, Quinolins und Isoquinolins zugeordnet. Reaktivität und Bandeninterpretation werden diskutiert.

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Résumé La structure électronique et les spectres d'absorption du cation quinolizinium, de tous ses monoazadérivés et du dication pyridazo(1,2-a)pyridazinium ont été calculés par la méthode de Pariser-Parr-Pople, avec intéraction de toutes les configurations singulets mono-excitées. L'attribution des bandes d'absorption du cation quinolizinium a été faite en comparant ses énergies de transition et intensités observées avec celles du naphthaléne, quinoléine et isoquinoléine. On a aussi discuté la reactivité et l'interprétation des bandes.

     

Electronic structure and spectra of fused n/m ring systems with one or two bridgehead nitrogen atoms

The semiempirical ASMO-SCF-CI method has been applied to study the electronic structures and ultraviolet absorption spectra of the 4-azapentalenyl anion, 4,8-diazapentalene and related azaderivatives. The agreement between observed and calculated transition energies is, in general, satisfactory. Chemical reactivity and assignment of the observed bands are discussed.

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Zusammenfassung Mit Hilfe einer semi-empirischen ASMO-SCF-CI Methode wurden Elektronenstruktur und UV Absorptionsspektren des 4-Azapentalenylanions, des 4,8-Diazapentalens und der entsprechenden Azaderivate studiert. Im allgemeinen ist die Übereinstimmung zwischen experimentellen und theoretischen Übergangsenergien zufriedenstellend. Die Zuordnung der beobachteten Banden und Reaktivitäten werden diskutiert.

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Résumé La méthode semi-empirique ASMO-SCF-CI a été appliquée à l'étude de la structure électronique et des spectres d'absorption U.V. de l'anion 4-azapentalenil, du 4,8-diazapentalene et de composés aza-derivés apparentés. L'accord entre les énergies de transition observées et calculées est, dans l'ensemble, satisfaisant. La reactivité chimique et l'attribution des bandes observées ont été discutées.

     

Electron momentum density distribution in homonuclear diatomic molecules

Individual orbital contributions to the electron momentum densities of first-row homonuclear diatomic molecules are discussed. It is shown that the nodal surfaces in the orbital EMDs arise from a diffraction factor with both geometric and electronic components. The positions of the nodal surfaces convey information on the electronic structure. The results are illustrated with a Hartree-Fock-Slater calculation of the F₂(X¹Σ_g⁺) molecule.     

Electron pair density information measures in atomic systems

Shannon entropies of the pair density, conditional entropies, and mutual information are studied in position and in momentum space for ground state neutral atoms and selected excited states at the Hartree‐Fock level. We show that the mutual information, a measure of correlation, is larger in position space than in momentum space. This result also holds for a mutual information defined in terms of the exchange density; however, these quantities display much more structure than the corresponding ones based on the pair densities. The interpretation of this behavior is that exchange effects are smaller in momentum space than in position space in these systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Diazabicycloalkanes with bridgehead nitrogen atoms

By heating 1-(2-hydroxyethyl)benzo[b]-1-azonium-4-azabicyclo-[2.2.2]octene halides in anhydrous solvents or via thermolysis, opening of the bicycle occurs with formation of the corresponding N-(2-hydroxyethyl)-N-(2-haloethyl)-1, 2,3,4-tetrahydroquinoxalines. In the presence of base, fission of the hydroxyethyl group principally occurs.For Communication 25, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1091–1094, August, 1992.     

Diaza crown ethers bearing heterocyclic ligating groups on nitrogen atoms and their complexing properties with divalent inorganic cations

Two nitrogen-substituted 4,13-diaza-I8-crown-6 compounds, bearing 2-methylquinolyl and 2-methylquinolyl-1-oxide groups, have been prepared. Ionophore-cation selectivities with a range of inorganic divalent cations have been investigated by means of membrane techniques, demonstrating their high selectivity for the Hg(II) cation.     

Computational study of iron(II) systems containing ligands with nitrogen heterocyclic groups

Density functional theory (DFT) calculations show the higher energy HOMO (highest occupied molecular orbital) orbitals of four iron(II) diimine complexes are metal centered and the lower energy LUMO (lowest unoccupied molecular orbitals) are ligand centered. The energy of the orbitals correlates with electrochemical redox potentials of the complexes. Time-dependent density functional theory (TDDFT) calculations reveal ligand centered (LC) and metal-to-ligand charge transfer (MLCT) at higher energy than experimentally observed. TDDFT calculations also reveal the presence of d-d transitions which are buried under the MLCT and LC transitions. The difference in chemical and photophysical behavior of the iron complexes compared to that of their ruthenium analogues is also addressed.     

Electron density distribution in a thiourea pyridinium nitrate inclusion compound

The study presented has been focussed on characterization of electron density distribution in a thiourea pyridinium nitrate inclusion system by quantum chemistry (DFT) calculations. The atomic charges, dipole moments and electrostatic potentials has been calculated for large clusters of two types corresponding to two neighbouring fragments of the host-guest structure cut out in a different way from the low-temperature crystallographic structure. A transfer of electron density from the nitrate anions over to thiourea molecules and pyridinium cations have been revealed. The polarization of the selected species in host-guest system has been analysed.