Chloral as a formylating agent for some bridge heterosystems

The interaction of condensed nitrogen-containing bridge systems with chloral has been studied and the high sensitivity of the reaction to the -excess of the initial heteroaromatic system has been established. It has been shown that chloral is a convenient formylating agent for systems with a moderate -excess —imidazo[l,2-a]imidazole, 9H-imidazo[1,2-a]benzimidazole, imidazo[1,2-a]pyridine, imidazo[1,2-a]naphtho[2,3-d]imidazole. Heterocycles with a high -excess (indolizine, pyrrolo[1,2-a]benzimidazole) form cyanine dyes under the action of chloral. Systems with a lowered -excess (1H-imidazo[1,2-a]benzimidazole, imidazo[1,2-a]quinoline, imidazo[2,1-a]isoquinoline, imidazo[1,2-a]perimidine, imidazo[5,1-b]benzoxazole, imidazo[1,2-a]benzothiazole, and imidazo[1,2-a]pyrimidine) do not react with chloral in a neutral medium. However, in a number of cases their foraylation can be carried out in an acid medium.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 528–537, April, 1980.     

Electronic Structure, Aromaticity, and Physicochemical Characteristics of Carbene, Radical, and Ionic Forms of Compounds of the Imidazole Series, and their Oxo and Thio Analogs

The effects of benzannellation, phenyl substitution at the nitrogen atom, protonation at the carbene carbon, ionization, and the state of the carbene center (² or ²) on the electronic structure, diamagnetic susceptibility, induced -electron ring currents, the ¹H, ¹³C, and ¹⁴N chemical shifts, and the energies of the lowest electronic transitions of imidazol-2-ylidenes and their oxo and thio analogs were examined in the bound version of -electron perturbation theory. The calculated and experimental data are compared.     

Electron structures of azoloisoindoles with a nodal nitrogen atom. 1. Derivatives of isoindolobenzimidazole and imidazo- and pyrazoloisoindoles

N-Methyl-substituted 1H-imidazo[2,1-a]isoindole, 5H-isoindolo[2,1-a]benzimidazole, and 3H-pyrazolo[5,1-a]isoindole were calculated by the PPP and CNDO/2 methods. On the basis of the canonical and localized MO it was concluded that the examined compounds can, to a first approximation, be regarded as 1,2-disubstituted iso-indoles, i.e., 10-electron systems. The calculated data are in good agreement with the experimental UV spectra and the chemical properties of the investigated compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 646–652, May, 1987.     

Homodimerization of spiro{bicyclo[2.2.1]Hepta-2,5-Diene-7,1′-cyclopropane}, catalyzed by group VIII transition metal complexes

Conclusions The homodimerization of spiro{bicyclo[2.2.1]hepta-2,5-diene-7,1-cyclopropane} (I) has been investigated in the presence of Ni-, Fe-, Co-, Rh-, and Ir-based metal complex catalysts. Depending on the nature of the metal and its ligand environment cyclodimerization of (I) can take place via [2+2]-, [2+2+2]-, and [4+4]-cycloaddition schemes, to give high yields of hepta-, octa-, and nonacyclic strained hydrocarbons.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2592–2599, November, 1988.     

Theory of the anisotropic diamagnetic susceptibility of aromatic compounds caused by ring currents,with allowance for π-electron interaction

Perturbation theory is used in a method for calculating the anisotropy in the diamagnetic susceptibility of an aromatic hydrocarbon consequent on currents between atoms, with allowance being made for -electron interaction in the multiconfiguration approximation. The method is applied to pentalene, heptalene, biphenylene, and naphthalene. The theoretical result differs greatly from that given by London's method in the case of a molecule whose anisotropy is anomalous in sign. If the anisotropy is normal in sign, allowance for -electron interaction somewhat reduces the anisotropy.We are indebted to T. K. Rebane for valuable advice and discussions.     

Comparative analysis of the electronic structure of positional isomers: Indole-isoindole

On the basis of an analysis of the canonical and localized molecular orbitals of indole and isoindole, calculated in the SCF and CNDO/2 approximations, as well as an x-ray crystallographic investigation of 2-methyl-isoindole, a comparison of the electronic structure of the positional isomers was made. The 10-electronic system of isoindole is more integral than for indole: isoindole is a single 10-electronic system with an appreciable localization of the bonds in the carbocyclic portion of the bicycle; the electronic structure of indole can be represented in a first approximation as the aggregate of three weakly interacting -subsystems: the benzene ring, the double bond between the - and -carbon atoms, and the free electron pair of the nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1497–1503, November, 1984.     

Exact topological π-electron Hamiltonians from ab initio wavefunctions?

A general topological -electron Hamiltonian is defined as an appropriate function of the adjacency matrix. It is shown that any electronic property of a planar benzenoid hydrocarbon, including its all-electron wavefunction, is entirely determined by the topological -electron Hamiltonian describing the hydrocarbon. However, using electronic wavefunctions (calculated at the HF/6-31G^** level) of several such hydrocarbons as examples, it is demonstrated that it is impossible to construct topological Hamiltonians with eigenvectors related by simple universal algebraic formulae to the corresponding occupied Hartree-Fock orbitals of symmetry. This observation casts doubt on the usefulness of the Hückel -electron orbitals in understanding the electronic structures of benzenoid systems.Dedicated to Professor Frank Harary on the occasion of his 70th birthday.     

Partitioning of <Emphasis Type="Italic">π</Emphasis> -electrons in rings of polycyclic conjugated hydrocarbons: Part 6. Comparison with other methods for estimating the local aromaticity of rings in polycyclic benzenoids

By adopting the convention that shared double bonds in polycyclic conjugated hydrocarbons contribute with one -electron and unshared ones with two -electrons, a partition of -electrons in each ring (-electron content, EC) can be obtained by averaging over all Kekulé structures, which are assumed to have equal weights. This affords a simple measure of local aromaticity that is comparable with other such local aromaticity indices in polycyclic benzenoids.     

Tautomerism,electronic structures,and electronic spectra of indolo[2,3-b]quinoxaline and its derivatives

The tautomerism, electronic spectra, and electronic structures of the ground and excited states of indolo [2,3-b]quinoxaline and its 2,3- and 1,4-dibutoxy derivatives were investigated by the Pariser-Parr-Pople (PPP) method. It is shown that these compounds exist primarily in the 6H form; the long-wave s^* transition is due to transfer of charge from the indole fragment to the quinoxaline fragment, and in the first excited state many of the bonds in the quinoxaline fragment are loosened significantly. The effect of butoxy substituents on the first s^* transition of indolo [2,3-b] quinoxaline was analyzed by means of perturbation theory within the framework of the Hückel MO method.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1259–1263, September, 1982.     

Electronic structure of the Fe3S4 cluster and its quasi-aromaticity

The localized molecular orbitals and their energy levels for the clusters [Fe₃S₄(SH)₃]^2–, [(HS)₃Fe₃S₄·Ni(PH₃)]^2–, [Mo₃S₄(OH₂)₉]⁴⁺, and [Mo₃S₄·Ni]⁴⁺ have been calculated by mean of the Edmiston-Ruedenberg energy localization technique under the CNDO/2 approximation in order to reveal the resemblance between [Fe₃S₄]⁺ and [Mo₃S₄]⁴⁺ in the geometrical configurations and the addition reactivities with heterometal atoms. It is shown that in these two cluster species with core {M ₃(₃-S)(-S)₃} of similar structure (M = Mo, Fe) there exist three synergically connected three-centered two-electron (M-S-M) -bonds around the puckered six-membered {M₃S₃} rings on account of delocalization of a lone electron pair on each bridging S atom; these (M-S-M) -bonds are thus capable of forming cubane-like heterometal clusters with intruder metal atoms through the ( M) bonding. It is therefore seen that unlike the [Mo₃S₄]⁴⁺ with appreciable bonding between the Mo atoms, the extra d-electrons on the metal atoms in the [Fe₃S₄]⁺ cluster are localized on the Fe atoms, exhibiting an electronic structure significantly different from that of the [Mo₃S₄]⁴⁺ cluster.     

Chemistry of 2-hetarylbenimidazoles. 7. Transformations of trans-1-methyl-2-[Β-(2′-furyl)vinyl] benzimidazole

Electrophilic substitution reactions in the furylvinylbenzimidazole series were studied. In nitration, sulfonation, bromination, acylation, formylation, and hydroxymethylation reactions, the substituent enters at the -position of the furan ring. The presence of a vinylene group reduces the influence of the benzimidazole fragment on the furan ring, and therefore the reactions in the latter proceed considerably more rapidly and under milder conditions than in the case of furylbenzimidazole. Calculated data are given for the -electronic density on the carbon atoms of furyl-vinylbenzimidazole, obtained by the CNDO method.For Communication 6, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1078–1081, August, 1986.The authors wish to express their gratitude to Yu. N. Sheinker for help in the interpretation of the PMR spectra.     

TheSemmler-Wolff aromatization andSchmidt reaction applied to some pyrido[2′,3′:3,4]pyrazolo[5,1-c][1,2,4]benzotriazines

Pyrido[2,3:3,4]pyrazolo[5,1-c][1,2,4]benzotriazin-4(1H)ones were transformed via their oximes in aSemmler-Wolff aromatization process in the tetracyclic heteroaromatic amines4 or bySchmidt reaction into a mixture of the same amine4 and a ring enlarged lactam3. Syntheses of some halo pyrazolo[3,4-b]pyridines and a photochemical transformation of 3-azidopyrazolo[3,4-b]pyridine are also described.

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Über dieSemmler-Wolff- undSchmidt-Reaktion einiger Pyrido[2,3:3,4]pyrazolo[5,1-c][1,2,4]benzotriazine

Zusammenfassung Pyrido[23:3,4]pyrazolo[5,1-c][1,2,4]benzotriazin-4(1H)one werden über Oxime in einerSemmler-Wolff-Reaktion in die tetracyklischen aromatischen Amine4 umgewandelt. In einerSchmidt-Reaktion wurden dieselben Ketone in ein Gemisch aus Amin4 und Lactam3 übergeführt. Synthesen von halogensubstituierten Pyrazolo[3,4-b]pyridinen und photochemische Umwandlung von 3-Azidopyrazolo[3,4-b]pyridin werden beschrieben.

     

Crystal,molecular, and π-electronic structure of 1,3,2-benzodithiazolium chloride

X-Ray diffraction examination and MNDO calculations have shown that 1,3,2-benzodithiazolium chloride (I) is ionic, with a planar heteroaromatic 10-electron cation. The -MO of the cation (I) is isolobal with the p-MO of benzo-2,1,3-thiadiazole. In the cation of (I), as in the latter compound, the p-AO of nitrogen and sulfur contribute for the most part to -MO of differing symmetry (b₁ and a₂, respectively). This has the consequence that although both nitrogen and sulfur participate in the formation of a single -system in the thiazolium cation of (I), there is virtually no -bonding between them. Generally speaking, the -MO of the (I) cation shows a tendency to localization on separate molecular fragments. The charge on the cation is localized at the SNS group, and the five-membered ring is strongly polarized. These features all reduce the heteroaromaticity of the system.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1683–1688, December, 1990.     

A comment on the Hückel 4n + 2 rule

Conclusions The pentalenopentalene molecule has an open (in the Hückel sense) -electron shell, notwithstanding that the number of -electrons forming the -electron system is a number of the form (4n+2).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1185–1186, May, 1969.     

Absorption and luminescence spectra of indolo[2,3-b]quinoxaline

The spectral-luminescence properties of indolo[2,3-b]quinoxaline, which at 77 °K has fluorescence and phosphorescence of the * type, were investigated. Retarded fluorescence and nonexponential quenching of the phosphorescence were observed; this is explained by photochemical processes with subsequent recombination luminescence.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1540–1544, November, 1982.     

Electronic structure and aromaticity of planar singlet π-electron monocyclic π2 carbenes

Induced -electron ring currents and relative diamagnetic susceptibilities of planar singlet -electron monocyclic ² carbenes are calculated in the coupled variant of perturbation theory in the CNO method. It is shown that the parity theorem holds for charged planar ² and ² carbenes formally generated by the detachment of a proton or a hydride ion from alternant hydrocarbons. This leads, in such carbenes, to the same energies of singlet-singlet and singlet-triplet transitions, electric polarizabilities, conjugation energies, -electron ring currents, diamagnetic susceptibilities and current contributions to chemical shifts, whereas the charge contributions to the latter are of opposite signs.Donbas State Academy of Building and Architecture, 1 Derzhavina St., 339023 Makeevka, Donetsk Region, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 157–162, May–June, 1996. Original article submitted December 5, 1994.     

Electronic structure of long molecules with conjugated bonds

The -electron system in a long molecule of the polyene type was calculated according to the Hartree-Fock self-consistent field method in which electrons with different spins are located on different molecular orbitals. The ground state of the -electron system in a long molecule is found to be antiferromagnetic and possesses a gap in the one-particle excitation spectrum. The calculated value of the first -electron transition as a function of the number of atoms in the polyene chain is in good agreement with experiment.     

First electronic transitions in compounds with the perimeter π-system

In the Pariser-Parr-Pople approximation, an analysis has been made of the first -electron transitions in neutral and charged [N]annulenes with a closed shell. The influence of the ratio of numbers of -electrons and atoms in the annulene on the spectrum of the annulene has been examined critically. A similarity of the spectra of [N]annulenes and polymethine dyes has been noted.Deceased.Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 4, pp. 493–499, July–August, 1991. Original article submitted February 8, 1988.     

MO-Berechnungen an Heterocyclen, 4. Mitt.1: Zum Einfluß der Ladungsterme in den Diagonalelementen derHamilton-Matrix von self-consistent-Verfahren auf die Berechnung von π-Elektronendichten und Bindungslängen

Zusammenfassung Mit SC- und SC_, -MO-Methoden werden die grundlegenden Einflüsse von Ladungstermen in derHamilton-Diagonalmatrix auf -Elektronendichten und Bindungslängen weiter studiert, insbesondere an N-Heterocyclen (Benzologe des Pyrrols und Pyridins). Im Vergleich mit erweiterten -Elektronenansätzen vom SCF—PPP-Typ liefern die einfachen, auf einige wesentliche Terme reduzierten SC-Matrixelemente sehr gute Resultate.

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The influence of charge terms in the hamilton diagonal-Matrix of self-consistent methods on the calculation of -electron densities and bond lengths

SC- and SC_, -MO methods are applied to the study. Subjects of the calculations are N-heterocycles (pyrrole and pyridine series). Simple SC matrix elements, which were found to include the essential terms, give good results in -electron densities and bond lengths.

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3. Mitt.:M. Scholz undD. Heidrich, Mh. Chem.99, 588 (1968).     

The electronic structures of charge-transfer complexes: Application of the semiempirical SCF-MO-Cl method

A method is developed to calculate the electronic structure of a molecular complex composed of a -electron donor and a n-electron acceptor. The complex is treated as a single conjugated system of -electrons, and its -electron states are calculated by the semi-empirical SCF-MO-CI method within the n-electron approximation, by including all terms. The method is applied to the TONE complexes of polycyclic aromatic hydrocarbons. It is shown that the absorption spectra of these complexes are well predicted by this method. Discussions are given on the mixing of the charge-transfer configurations and the locally-excited configurations.

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Zusammenfassung Es wird eine Methode entwickelt, um die Elektronenstruktur eines Molekülkomplexes aus einem -Donor and einem n-Akzeptor zu berechnen, and zwar wird er als einheitliches n-Elektronensystem nach einem SCF-Verfahren unter Einschluß aller /3-Terme behandelt. Das Verfahren wird auf TCNE-Komplexe von polycyclischen aromatischen Kohlenwasserstoffen angewendet, wobei sich die Absorptionsspektren recht gut ergeben. Diskutiert wird schließlich noch die Kombination von CI- mit lokal-angeregten Konfigurationen.

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Résumé Développement d'une méthode pour calculer la structure électronique d'un complexe moléculaire entre un donneur et un accepteur d'électrons. Le complexe est traité comme un système conjugué unique dont les états électroniques sont calculés dans l'approximation par la méthode semi-empirique SCF MO CI, en tenant compte de tons les termes. La méthode est appliquée aux complexes des hydrocarbures aromatiques polycycliques avec TCNE. Cette méthode prévoit bien les spectres d'absorption de ces complexes. Discussion du melange des configurations à transfert de charge avec les configurations localement excitées.