Excited Π states of divinyl chalcogenides and chalcophenes

Electron transitions in divinyl chalcogenides (CH₂=CHXCH=CH₂, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: ^* < ^* < ^* < ^* for Te and ^* < ^* < ^* < ^* for S and Se. For chalcophenes, a correlation between the energy of the excited state (E ^*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E ^*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited ^* states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994.     

Infrared spectra of vinyl compounds and the effects of conjugation involving the π-electrons of the vinyl group

Conclusions The frequencies of the =CH₂ group wagging vibration in CH₂=CH-X compounds reflects both the inductive effect of the substituents X, and the effects of, -, ,p- and (d-p)-conjugation in which these substituents take part.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.l, pp. 152–154, January 1970.     

The Exciton Model and the Circular Dichroism of Polypeptides

Summary. Exciton coupling of the 190nm ^* transition is an important factor in the CD spectrum of peptides and proteins. The CD spectrum of the -helix is dominated by the exciton effect. The spectrum is sensitive to the direction of the ^* transition dipole moment, especially for short helices. Exciton theory is much less successful in accounting for the CD spectrum of the poly(proline)II (PPII) conformation, an important conformer in collagen and in unordered peptides. Mixing of the ^* transition with high-energy transitions in the peptide backbone and in side chains must be considered to explain the strong negative CD band near 200nm of PPII.     

A 2pπ, 3dπ valence bond wave function for the 1B1u state of ethylene

A 2p, 3d valence bond wave function for the lowest ¹ B _1u state of the -system of ethylene is variationally optimized with respect to the atomic orbital exponents using a non-empirical -approximation. The resulting energy compares favourably with previous calculations and leads to a satisfactory value for the lowest ¹ A _1g-¹ B _1u transition energy. The optimized exponent for the 2p orbital is close to the Slater value whereas the exponent for the 3d orbital is found to be nearly hydrogenic. The implications of this result are discussed in some detail.

---

Zusammenfassung Für den tiefsten ¹ B _1u -Zustand des -Elektronensystems des Äthylens wird nach der Variations-methode eine 2p, 3d-Valenzbindungs-Wellenfunktion bezüglich der Orbitalkoeffizienten optimiert, wobei eine nicht-empirische -Approximation zugrunde gelegt wird. Die berechnete Energie stimmt gut mit den Ergebnissen vorausgegangener Rechnungen überein. Für den tiefsten ¹ A _1g ¹ B _1u -Übergang ergibt sich ein befriedigender Energiewert. Der optimierte Orbitalkoeffizient für das 2p-Orbital stimmt gut mit dem nach der Slaterschen Regel bestimmten Koeffizient überein, während man für den 3d-Orbitalkoeffizienten einen Wert findet, der dem des Wasserstoffs ähnlich ist.

---

Résumé Une founction d'onde V.B.(2p , 3d ) est optimée pour l'état ¹ B _1u d'aethylen. L'energie calculé aussi que l'energie de transition la plus basse ¹ A _1g -¹ B _1u est en bon accord avec des valeurs connues.

     

Reactivity of pyrrole pigments,XXI: Structure and reactivity of Cu(II) and Zn(II) bilindione chelates

Summary Several Mn, Cu, and Zn chelates of etiobiliverdin-IV-, mesobiliverdin-IX, and its dimethyl ester are studied. The results show that the chemical constitution of the Cu biliverdin chelate corresponds to a formal metal oxidation state of (II) coordinated to a neutral radical of the NH trideprotonated biliverdin. The reactivity of the Cu(II) bilindione chelates in nucleophilic solvents agrees with that expected for a neutral radical structure of the ligand; in CH₃OH, they undergo oxidation towards dimethoxybilipurpurins. The magnetic behaviour of Cu(II) etiobiliverdinate-IV- in the solid state shows an intramolecular weak antiferromagnetic coupling d⁹Cu-to--radical (J=–23 cm^–1) and an intermolecular weak antiferromagnetic coupling -radical-to--radical (J=–45 cm^–1). The analogy of this magnetic behaviour to that of the cation radical of metalloporphyrins is discussed.

---

Reaktivität von Pyrrolpigmenten, 21. Mitt.: Struktur und Reaktivität von Cu(II)- und Zn(II)-Chelaten von Bilindionen

Zusammenfassung Einige Mn, Cu and Zn Chelate von Etiobiliverdin-IV-, Mesobiliverdin-IX und seinem Dimethylester werden untersucht. Im Komplex koordiniert ein Metallatom (mit der Formalladung II) mit einem Neutralradikal des dreifach NH-deprotonierten Bilindions. Die Reaktivität des Komplexes gegenüber nukleophilen Lösungmitteln entspricht erwartungsgemäß dem eines neutralen -Radikals; in CH₃OH wird er zu Dimethoxybilipurpurin oxidiert. Bei Cu(II)-Etiobiliverdinat-IV beobachtet man im festen Zustand neben schwacher, antiferromagnetischer Kupplung zwischen d⁹Cu und -Radikal (J=–23 cm^–1) auch eine schwache, intermolekulare, antiferromagnetische Wechselwirkung zwischen zwei -Radikalen (J=–45 cm^–1). Dieses magnetische Verhalten wird dem des -Kationradikals von Metalloporphyrinen gegenübergestellt.

     

Ru(II) Chloro-Bis(bipyridyl) Complexes with Substituted Pyridine Ligands: Interpretation of Their Electronic Absorption Spectra

A number of complexes were synthesized with the general formula cis-[Ru(Bipy)₂(L)(Cl)](BF₄), where Bipy is 2,2"-bipyridine, L is pyridyne (Py), 4-aminopyridine (4-NH₂py), 4-picoline (4-Mepy), nicotin-amide (3-CONH₂py), isonicotinamide (4-CONH₂py), 3- and 4-cyanopyridine (3-CNpy, 4-CNpy), 4,4"-bipyridine (4,4"-Bipy), trans-1,2-bis(4-pyridyl)ethylene (Bpe), 4,4"-azopyridine (Azpy), pyrazine (Pyz), imidazole (Imid), and NH₃. The semiempirical CINDO-CI method was used to calculate the energies and intensities of transitions in the electronic absorption spectra. The differences observed in the spectra of these compounds are mainly due to the positions of the charge-transfer transitions d (Ru) *(L). Depending on the positions of these transitions, ligands L can be divided into three groups: 1) transitions Ru L lie in the region of the first long-wavelength band d (Ru) *(Bipy) (L = Azpy, Pyz); 2) transitions Ru L lie between the first and second bands due to the charge transfer to Bipy (L = 3-CONH₂py, 4-CONH₂py, 4,4"-Bipy, Bpe, 4-CNpy), and 3) transitions Ru L lie in the region of the second band d (Ru) *(Bipy) (L = Py, 4-Mepy, 3-CNPy, 4-NH₂py, Imid).     

Configuration mixing involving σ and π orbitals

The effect (on the energy of the different states) of including doubly excited configurations in a - plus -configuration interaction treatment, is studied within the CNDO/2 framework. For moderately large molecules the problem of the choice of the type ( or ) of configurations taken into account is examined. When possible, comparison is made with similar non empirical calculations.

---

Zusammenfassung Im Rahmen der CNDO/2 Methode wird der Einfluß (auf die Energien verschiedener Zustände) des Einschlusses doppelt angeregter Konfigurationen in einer - und -Konfigurationswechsel-wirkungs-Behandlung studiert. Für nicht allzu große Moleküle wird das Problem der Wahl der Art ( oder ) der berücksichtigten Konfigurationen untersucht. Soweit möglich, werden die Resultate mit denen ähnlicher nichtempirischer Rechnungen verglichen.

---

Résumé L'effet (sur l'énergie des différents états) de l'introduction de configurations diexcitées dans une interaction de configuration plus , est étudié dans le cadre de la méthode CNDO/2. Pour des molécules de taille moyenne le problème du choix du type ou des configurations est examiné. Les résultats obtenus sont comparés aux calculs non-empirique similaires disponibles.

     

Ab initio SCF and CI study of the electronic spectrum of pyridine N-oxide

Configuration interaction (CI) studies of ground, n *, * * electronically excited states are reported for pyridine N-oxide. The transition energy to the lowest * excited ¹ B ₂ state is calculated at 4.35 eV, compared to the experimental spectrum range of 3.67–4.0 eV. This state lies below the lowest n * excited ¹ A ₂ state calculated at 4.81 eV above the ground state. The only experimentally reported triplet state at 2.92 eV above the ground state is predicted to be the ³ A ₁ (*) state. The calculated energy lies at 3.27 eV. Numerous other high-lying singlet states as well as the triplet states have also been calculated. The intramolecular charge transfer character of the ground and the excited states have been studied in terms of the calculated dipole moment and other physical properties.     

A semiempirical method based on geminal functions

An extention is reported of a previously proposed semiempirical approach based on geminal functions and formulas are given for the transition moments and the electronic population analysis.The case of pyridine is considered as an example and used to predict the n ^* or ^* character of its lower transition.This work was carried out with the financial support of the Consiglio Nazionale delle Ricerche (C.N.R.), Roma.     

Electronic absorption spectra of 3-hydroxypyridine and 5-hydroxypyrimidine

The electronic absorption spectra ( ^* type) of the mixture of the enolic and zwitterionic forms of both 3-hydroxypyridine and 5-hydroxypyrimidine are interpreted by means of the Pariser-Parr-Pople type calculations.     

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.     

Thermodynamics of adsorption (as a function of temperature and pressure) of N2 and CO2 on graphites

Summary A quantitative treatment, coupled with critical qualitative considerations, pertaining to the study of thermodynamics of adsorption of N₂ and CO₂ on different graphite samples, through the evaluation of the film pressure, as a function of temperature and pressure, is presented. The . determination of the adsorbent specific surface areas is affected through the graphic manipulation of the Langmuir adsorption equation utilizing data adopted from literature, and the values are then computed by employing the Gibbs adsorption equation by making use of the areas under them-lnP curves. The results deduced are discussed specifically in terms of as related to the nature of the adsorbents, the magnitude of the calculated thermodynamic functions and the specific surface areas for the individual adsorbents.

---

Zusammenfassung Die Arbeit bringt eine thermodynamische Studie der Adsorption von N₂ and CO₂ an verschiedenen Graphitpräparaten. Grundlage der Betrachtung ist der Filmdruck als Funktion der Temperatur und des Druckes. Die Bestimmung der spezifischen Oberfläche des Adsorbens wird beeinflußt durch die graphische Behandlung der Langmuirschen Adsorptionsgleichung. Es wurden Literaturwerte adoptiert und-Werte nach der Gibbsschen Adsorptionsgleichung berechnet. Die abgeleiteten Ergebnisse werden diskutiert und zur Natur des Adsorbens, zur Größenordnung der berechneten thermodynamischen Funktionen und zur spezifischen Oberfläche der einzelnen Adsorbentien in Beziehung gesetzt.

     

The inclusion of non-nearest neighbor ß terms in pariser-parr-pople type S.C.M.O. calculations

The calculation of -electron properties by an S.C.M.O. method including all _core terms has been extended to nitrogen and oxygen containing systems. The singlet ^* electronic transitions and -ionization potentials (where available) are in reasonable agreement with experiment. A comparison is made with the non-empirical all electron calculations of Clementi for pyrrole, pyridine and pyrazine.

---

Zusammenfassung Die Berechnung von -Elektronen-Eigenschaften mittels einer SCMO-Methode, die alle _core-Terme einschließt, wurde auf Systeme mit Stickstoff- und Sauerstoffatomen ausgedehnt. Die Singulett- ^*-Übergänge und -Ionisierungsenergien sind in vernünftiger Übereinstimmung mit dem Experiment. Es wird einen Vergleich mit den nichtempirischen Rechnungen mit allen Elektronen von Clementi an Pyrrol, Pyridin und Pyrazin angestellt.

---

Résumé Le calcul des propriétés des électrons par une méthode S.C.M.O. tenant compte de tous les termes _coeur a été étendu aux systèmes contenant de l'azote et de l'oxygène. Les transitions électroniques singulet ^* et les potentiels d'ionisation (lorsqu'ils sont connus) sont en accord raisonnable avec l'expérience. Les résultats sont comparés aux calculs non-empiriques de tous les électrons effectués par Clémenti pour le pyrrole, la pyridine et la pyrazine.

     

New structural aspects of 3-vinyl-1H-indoles for predicting the outcome of Diels-Alder reactions

Summary Some selected 3-vinyl-1H-indoles have been synthesised and the first¹³C-NMR studies performed; in addition He(I) photoelectron spectra and the results of perturbation MO calculations of some examples of this class of compounds are presented. The molecular characteristics obtained thereby can be used to predict the results of [4s+2s]-cycloaddition reactions with 3-vinylindoles.

---

Neue strukturelle Aspekte von 3-Vinylindolen zur Vorhersage der Reaktionsergebnisse bei Diels-Alder-Reaktionen

Zusammenfassung An selektiv synthetisierten 3-Vinyl-1H-indolen werden erstmals¹³C-NMR-spektroskopische Studien durchgeführt und exemplarisch an einigen Vertretern dieser Strukturklasse He(I)-Photoelektronenspektren sowie Ergebnisse von Störungs-MO-Rechnungen vorgestellt. Die daraus gewonnenen Moleküleigenschaften können zur Vorhersage des Reaktionsausganges von [4s+2s]-Cycloadditionen mit 3-Vinylindolen verwendent werden.

     

Intensity of the η(C≡C) Bands in the IR Spectra of Acetylene Derivatives and σR 0 Constants of Organosilicon,Organogermanium, and Organotin Substituents

The integral absorptivities of shape-characteristic (CC) bands in the IR spectra of 66 acetylene derivatives RCCX (R = H, Me₃M; X are inorganic and organic substituents) are related by a common linear equation to the _R ⁰ constants of the R and X substituents. The _R R⁰ constants of 10 Alk₃M substituents were calculated. The _R ⁰, _R , and _R ⁺ constants of Me₃M substituents were analyzed. The positive _R ⁰ values (0.12, 0.06, and 0.04 for R = Si, Ge, and Sn, respectively) suggest that in the ground electronic state of Me₃MCCX molecules the resonance acceptor effect of the Me₃M substituents (d, conjugation) prevails over donor (, conjugation). The first effect attenuates and the second enhances as the atomic number of M increases.     

The Effect of cis-trans Isomerism on the Electronic-vibrational Structure of the Ground and Excited States and Reactivity of 2-(2-Furyl)- and 2-(2-Thienyl)oxazole

The fluorescent properties, structure, and electronic structure of the ground and excited singlet and triplet electronic states of the cis and trans forms of 4,5-dihydro-2-(2-furyl)oxazole, 4,4-dihydro-2-(2-thienyl)oxazole, 2-(2-furyl)oxazole (FO), and 2-(2-thienyl)oxazole (TO) have been studied. The orbital nature of the lower excited singlet and triplet states has been studied by the semiempirical INDO/S (valence approximation) and PPP/S ( approximation) methods. It was shown that for FO and TO molecules the lower triplet state is of the * type, for which delocalization of the electronic excitation on atoms is characteristic. In the singlet excitation state inversion was observed of the energy levels of the delocalized * states and n* states localized over several bonds (for the free TO and FO molecules the lower excited singlet states S₁* were assigned to * and n* types respectively). Owing to the low position of the T * and T _n* levels relative to the singlet level of * type, the rate constant for intercombination conversion is greater than the rate constant for radiative decay. Consequently an efficient population of the triplet states of the molecules occurs under conditions of electronic-vibrational excitation. The direction of reactions during synthesis was compared with the localization indices in the ground state for electrophilic, nucleophilic, and radical substitution, and also with the excitation localization numbers L for a wide selection of electronically excited states. It was concluded that the change in the structure of the azole molecule on replacing an O atom by an S atom, or on changing from a partially hydrogenated to a heteroaromatic system, was the main reason for the change of all the spectral parameters characterizing the electronic-vibrational or the spin-orbital interaction of the most reactive groups of atoms in the molecular structure.     

Carbocyclic and nitrogen-containing fused CH-acids with an annelated indenyl fragment. Thermogravimetric and X-ray structural analysis of 6H-indeno[1,2-b]quinoline

Based on thermogravimetric characteristics first obtained for the model 6H-indeno [1,2-b]quinoline, the scheme of thermal conversions of this compound in the temperature range 20–700 °C has been proposed, and the limit of its thermal stability (300 °C) has been determined. This temperature is recommended as the optimum for synthesizing fused benzoaza(diaza)fluorenes. Based on the results of X-ray structural analysis, the molecules of the studied indenoquinoline form centrosymmetric pairs, which are arranged in (110) layers. The molecules are orientationally disordered. The observed self-association of these molecules is similar to the - association of fused heterocyclic systems with-excessive and ****- deficient fragments. It has been suggested that interferon-inducing and antitumor compounds with an annelated indenyl fragment have a common mechanism of action according to the intercalation model of stacking structures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 703–709, April, 1995.     

Research on 1-aza two-ring systems

Reduction of 5-[2-(methoxycarbonyl)ethyl]-1,3-dihydropyrrolizines with lithium aluminum hydride gave 5-(-hydroxypropyl)-1,2-dihydropyrrolizines (in 70–90% yields), which have intramolecular -hydrogen bonds in dilute solutions. The parameters of the -hydrogen bonds were determined in the IR spectra, and their enthalpies were found. The data obtained (_OH 95–99 cm^–1, –H 3.05 kJ·mole^–1) show that among compounds with an aliphatic hydroxyl group and a system of electrons, 5-(-hydroxypropyl)-1,2-dihydropyrrolizines have some of the strongest intramolecular -hydrogen bonds.See [1] for communication XVI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 359–363, March, 1978.     

σ-π separation: Excited H2 as a model system

The low-lying states of H₂ consist of one core () and one valence () electron and afford a direct evaluation of intershell - interaction. After resolution of the electronic energy into only, only, and - parts, it is shown that an electronic change in this model system is due solely to a change in the electrons. Simple Hückel theory is examined. If the molecular core is represented properly, regardless of the wave function the calculated and parameters are in reasonable agreement with the empirical parameters. This agreement appears to be due to a fortuitous cancellation of energy contributions.

---

Zusammenfassung Die niedrig liegenden -Zustände des H₂ bestehen aus einem Rumpfelektron und einem Valenzelektron und ermöglichen eine direkte Auswertung der --Wechselwirkung zwischen zwei Schalen. Nach der Zerlegung der elektronischen Energie in -,- und --Anteile wird gezeigt, daß eine elektronische Veränderung in diesem Modellsystem nur auf eine Veränderung des -Elektronenanteils zurückgeht. Die einfache Hückeltheorie wird untersucht. Wenn der Molekülrumpf geeignet dargestellt wird, so sind, unabhängig von der -Wellenfunktion, die berechneten Parameter und in guter Übereinstimmung mit den empirischen Parametern. Diese Übereinstimmung scheint auf eine starke Auslöschung von Energieanteilen zurückzugehen.

---

Résumé Les états inférieurs de H₂ consistent en un électron de coeur () et un électron de valence () et fournissent une évaluation directe de l'interaction entre couches -. Après expression de l'énergie électronique en parties , et -, on montre qu'une modification électronique de ce système modèle est due seulement à une modification des électrons . La théorie de Hückel simple est examinée. Si le coeur moléculaire est convenablement représenté, quelle que soit la fonction d'onde , les paramètres at calculés sont en accord raisonnable avec les paramètres empiriques. Cet accord apparaît comme le résultat d'une compensation fortuite de contributions énergétiques.

---

---

Work performed in part under the auspices of the U.S. Atomic Energy Commission.

---

Work aided by the U.S. Public Health Service via grant GM 08068.     

The cis-effect in trans-[PtCl2XY] compounds

The cis-influence observed in chlorine NQR data of X, Y affecting the Pt-Cl bonds in compounds of type trans-[PtCl₂XY] is interpreted. -bonding differences in Pt-Cl bonds are suggested to account for the trends in NQR frequencies. Pt-Cl -bonding is negligibly small for both d (Pt)–p (Cl) and p –p (Cl) interactions.