Relationships between the lengths,orders, hybridization of the atoms,and force constants of carbon—nitrogen and carbon—oxygen bonds

The bond order—bond length, bond length—average percentage s-character, and bond order—bond -shortening relationships have been obtained for CN and CO bonds. It has been shown that the differences in bond lengths are due chiefly to the specific features of the -bonds. The observed relationship between the length of the -bond and the average percentage s-character is linear. It has been noted that the bond lengths are most sensitive to the -order when it changes in the range 0.3–1.0. For CC, CN, and CO bonds, relationships have been obtained between the -order and the force constants, and for the single bonds the relationship between the average percentage s-character and the force constants has been obtained.     

Preparation and properties of high dispersity palladium catalysts

Preparation methods for monodisperse sols of palladium with 9, 15, 30 and 75 Å particles are suggested. It has been revealed that with decreasing size of palladium particles (d25 Å), the dissolved hydrogen species disappear. As a result, their behavior in dimethyl ethynyl carbinol hydrogenation is close to the platinum properties.

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9, 15, 30, 75 Å. , (d25 Å) , .

     

Temperature-programmed desorption (TPD) of hydrogen from a NiNaY zeolite after reduction

By TPD it could be shown that hydrogen desorption of a reduced NiY-zeolite stoichiometrically corresponds to the decrease of reduction degree. Therefore, the reason for hydrogen abstraction should be a partial reoxidation of Ni⁰.

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, NiY- . Ni⁰.

     

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.     

Contribution to the kinetics of the process of dissolution

Some characteristics of the kinetic equation of dissolution are discussed, bearing in mind that in the course of the process, along with the concentration of the solution, the surface of the soluble substance is also changed. The opportunity for the appication of an exponential kinetic equation is pointed out. Methods are proposed for calculating the solubility and also for using the integral forms of the exponential equation. The meaning of the coefficient of proportionality is explained.

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, , ◹ . . , . .

     

Ein Beitrag zur thermischen Stabilität der Clathratverbindungen der Doppelcyanide in Abhängigkeit von ihrer Struktur

Zusammenfassung Die thermische Zersetzung zweier Hofmann'scher Clathratverbindungen, sowie der Verbindung Cd(NH₃)₂Hg(CN)₄·2 C₆H₆ wurde mittels des Derivatographen untersucht. Diese Clathratverbindungen sind bezüglich ihrer Struktur verschieden. Die Clathrate des Hofmann'schen Typs sind von höherer Stabilität. Die Gründe hierfür werden erörtert.

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The thermal decompositions of two Hofmann's clathrate compounds and the compound Cd(NH₃)₂Hg(CN)₄ · 2 C₆H₆ have been investigated by means of the derivatograph. These clathrate compounds are, as for their structure, different. Clathrate of the Hofmann's types represent the higher stability. The reasons are discussed in this paper.

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Résumé On a étudié, à l'aide d'un Derivatograph, la décomposition thermique de deux clathrates de type Hofmann ainsi que du composé Cd(NH₃)₂Hg(CN)₄·2 C₆H₆. Les clathrates étudiés possèdent des structures différentes. Les clathrates de type Hofmann sont les plus stables. Les raisons en sont discutées dans la présente communication.

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, 1,3,5,7--1,3,5,7- (), 1,5--3,7--1,3,5,7- (DADN), 1,5--3,7- -1,3,5,7- (D), 1,3,5--1,3,5- (-) 1,5--3,7- -1,3,5,7- (DNPT). , , DADN RDX . , R- DNPT, , . DPT.

     

Coupling of thermometric titrimetry and constant-current coulometry: Study and applications

Two systems involving the coupling of thermometric and coulometry are presented. In the first assembly, the two electrodes were in the same compartment. Bromocoulometry was used to test the possibilities of this coupling in the sequential titration of a vitamin C+ aspirin mixture about (10^–4 M) and the determination of enthalpy changes. In a second coupling system, the anodic and cathodic compartments were separated by a sintered-glass disc of porosity 3. The conditions for obtaining an electrochemical cell which is also a good calorimeter are discussed. Examples of applications are given, such as analytical measurements, the study of an electrochemically catalysed reaction and of the thermal effects of electrode reactions.

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Zusammenfassung Zwei Systeme werden beschrieben, die eine Kombination von thermometrischer Titrimetrie und Coulometrie darstellen. Bei der ersten Vorrichtung sind die Elektroden im gleichen Raum Untergebracht. Die Bromocoulometric wurde zur Testung der durch diese Kombination für die aufeinanderfolgende Titration von Vitamin C/Aspirin Gemischen (ungefähr 10^–4 M) und für die Bestimmung der Enthalpieänderungen gebotenen Möglichkeiten angewandt. In einem zweiten kombinierten System waren Anoden- und Kathodenraum durch ein Sinterglasfilter der Porosität 3 voneinander getrennt. Es werden die Bedingungen diskutiert, die notwendig sind, um eine elektrochemische Zelle zu erhalten, die zugleich auch ein gutes Kalorimeter ist. Anwendungsbeispiele sind angegeben, wie analytische Messungen und elektrochemische Untersuchungen katalysierter Reaktionen oder thermischer Effekte von Elektrodenreaktionen.

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, . . — 10^–4 M . — N^o3. , . , , .

     

Chemical algebra. II: Discriminating pairing products

The algebra of stereogenic pairing equlibria is presented in a very general context. Starting from the notions of fuzzy subgroup and conjugacy link, chemical pairing constants between molecular speciesu andv having a skeletal symmetry groupG are formulated as pairing products on aG-Hilbert space. Discriminating pairing productsK are defined by the conditions: K 1 and K = 1 the representative vectors of the paired species areG-equivalent. WhenG has only two elements, the pairing product is always discriminating. For several skeletal symmetries, if the vectors are enantiomorphic (v = u, ² =e, G), thenK is greater than 1 and reaches 1 only ifu is achiral: chirality indexes and general permutational indexes are then defined fromK(u u). The general model is illustrated by some examples.     

Chemical stability and reactivity of the 1∶1 and 2:1 halobis(N,N-dialkyldithiocarbamato)iron(III): Molecular halogen loose associations

EHMO-SCCC calculations have been used to probe the molecular orbital interactions of 1:1 and 21 charge-transfer complexes of halobis(N,N-dialkyldithiocarbamato)iron(III) complexes with molecular halogens, treated as super molecules. The molecular orbital structure of the compounds is being described in essentially the same way to that successfully applied in the cases of-, -gs, and n- CT complexes. It is found that all types of orbital interactions (- and/or type) have a destabilizing effect on the complexes; hence, the forces of attachment have to be of the charge-transfer and van der Waals type, to offset this molecular orbital-based repulsion. The relative stability of the compounds is broadly discussed in terms of the calculated binding energies, which are found to depend on the nature of both constituent molecules. Moreover, orbital populations, two-center energy terms, and computed atomic charges of the super molecules, as compared to those of the constituent molecules, provide adequate information on the mechanism of the charge-transfer processes occurring upon complexation. It is important that weak bonding interactions between the constituent molecules do exist, but surprisingly directly, between the molecular halogens and the iron(III) central atoms, and not via the apical halogeno ligands. These bonding interactions, although not responsible for the stability of the compounds, account well for the observed magnetic behavior of the dimeric (21) complexes and are of key importance in promoting intramolecular electron-transfer reactions responsible for the oxidation of half of the dithio ligands into the thiuram disulfides observed in some of the reactions of the iron(III) halobisdithiocarbamates with molecular halogens.     

Critical evaluation and experimental determination of the nuclear activation and decay parameters for the reactions:6 4Zn(n, γ)6 5Zn,1 1 2Sn(n, γ)1 1 3 (m)Sn (E. C.)1 1 3mIn,1 7 4Yb(n, γ)1 7 5(m)Yb

A best choice from literature was made of the isotopic abundance values for⁶⁴zn,¹¹²Sn and¹⁷⁴Yb, and of the absolute gamma-intensities for⁶⁵Zn,^113mIn and¹⁷⁵Yb. From these data and from activation method experiments, the following 2200 m·s^–1 cross sections were determined:⁶⁵Zn(n, )⁶⁵Zn; ₀=(0.726±0.0007) barn [cf. literature 0.76–0.78 barn];¹¹²Sn(n,)¹¹³(m)Sn; ₀(0.91 m⁺g)=(0.539±0.011) barn [cf. literature 1 barn];¹⁷⁴Yb(n,)¹⁷⁵(m)Yb; ₀(m⁺g)=(130+4) barn [cf. literature 65 barn].     

Investigation of Pd?Pb/Al2O3 catalysts by temperature-programmed reduction

Temperature-programmed reduction has been used to characterize, a series of Pd–Pb/Al₂O₃ catalysts. Oxidation and thermal decomposition of bimetallic Pb–Pb/Al₂O₃ catalysts in a stream of argon leads to segregation of individual oxides. Reduction of PdO–PbO/Al₂O₃ occurs at the same temperature as that found for PdO/Al₂O₃ and PbO/Al₂O₃. TPR measurement after isothermal reduction at 823 K and reoxidation point to bimetallic interaction between palladium and lead atoms only for small percentages of palladium.

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- () Pd–Pb/Al₂O₃. PdO–Pb/Al₂O₃ . PdO–PbO/Al₂O₃ PdO/Al₂O₃ PbO/Al₂O₃. - 823 — .

     

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.

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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.

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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.

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

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

Quantum-chemical study of allylstannanes

It has been shown by the MNDO method that in allyl compounds of tin, the atomic orbitals of the heteroatom interact with the -orbital through the bridge group, but interact with the ^*-orbital mainly through space. The position and intensity of the long-wave electronic transitions for methylvinylstannane should not depend on the conformation, with the ,- and , pseudo--conjugation effects being approximately identical, whereas for allylstannane, the ,-conjugation is considerably stronger. In molecules containing several allyl fragments bonded to heavy atoms, ,-conjugation is far weaker than ,-conjugation in polyenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2071–2076, September, 1991.     

Exchange kernel of density functional response theory from the common energy denominator approximation (CEDA) for the Kohn–Sham Green's function

A complete and explicit expression for the exchange kernel f _x of density functional response theory (DFRT) is derived in terms of the occupied Kohn-Sham (KS) orbitals _i. It is based on the common energy denominator approximation (CEDA) for the KS Green's function (O. V. Gritsenko and E. J. Baerends, Phys. Rev. A 64, 042506 (2001)). The kernel f _x ^CEDA is naturally subdivided into the Slater f _S ^CEDA and the 'response' f _resp ^CEDA parts, which are the derivatives of the Slater _S and response _resp potentials, respectively. While f _S ^CEDA is obtained with a straightforward differentiation of _S , some terms of f _resp ^CEDA are obtained from the solution of linear equations for the corresponding derivatives. All components of f _x ^CEDA are explicitly expressed in terms of the products _i ^* _j of the occupied KS orbitals taken at the positions r ₁ and r ₂, as well as the potentials of these products at r ₃. The coefficients in these expressions are obtained by inversion of the matrix, associated with the overlap matrix of the products _i ^* _j and _k ^* _l . Terms are indicated, which generate in an external electric field an ultra-nonlocal potential _x , counteracting an external field, and possible approximations to f _x ^CEDA are considered.     

Diffusion Conductivity of Electrode Processes under Conditions of Natural Convection

The diffusion conduction = di/d (where i is the current and is the overvoltage) in reversible system [Fe(CN)₆]^3–/4– is measured by the electrochemical impedance method under isothermal and nonisothermal conditions of natural convection. Platinum disk electrodes 3 mm and 20 m in diameter are used. For a macroelectrode under isothermal conditions, passes through a maximum near equilibrium and tends to zero at 0. Under nonisothermal conditions and for a microelectrode under isothermal conditions, achieves a maximum near equilibrium. These data correlate with the dependence of the diffusion layer thickness and quantitatively agree with theory.     

An interpretation of the nuclear quadrupole coupling constant for the HCl molecule on the basis of an “ab initio” calculation

The results of a LCAO MO SCF calculation of the quadrupole coupling constant of chlorine in the HCl molecule (carried out with a fairly extended set of basic orbitals) are analyzed. Sensible deformations of the internal shells and of the p -bonding, p -lone pair and p type orbitals of the valence shell of chlorine are evidenced.

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Zusammenfassung Die Ergebnisse einer verhÄltnismÄ\ig ausgedehnten LCAO-MO-SCF-Rechnung zur Bestimmung der Quadrupolkopplungskonstanten für Chlor in HCl werden untersucht. Die Verzerrungen, die der Rumpf und die verschiedenen ZustÄnde der Valenzschale erleiden, werden dabei gesondert wiedergegeben.

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Résumé Les résultats d'un calcul LCAO-MO-SCF (avec un jeu d'orbitales assez étendu) de la constante de couplage quadripolaire du Cl dans la molécule de HCl sont analysés. On trouve que et les couches internes et les orbitales p liante, p libre et p de la couche de valence du chlore sont sensiblement déformées.

     

Calculation of σ→π* and π→σ* transitions in vinylboranes

Calculations are presented of the energies of the ground and excited and electronic states of ethylene and substituted vinylboranes. The Pople-Segal-Santry method was employed throughout. It is concluded that the excited state of lowest energy in ethylene has * character whilst the lowest energy ultra-violet spectral bands of the latter compounds stem from ^* transitions.

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Zusammenfassung Valenzelektronenrechnungen nach Pople-Segal-Santry wurden für Äthylen und Vinylborane durchgeführt. Danach hat der niedrigste angeregte Zustand von Äthylen ^*-Charakter, während die längstwellige UV-Bande der Vinylborane einem ^* -Übergang entspricht.

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Résumé Calculs de l'énergie pour les états fondamentaux et excités et de l'éthylène et des vinylboranes substitués. Utilisation de la méthode de Pople-Ségal-Santry. L'état excité le plus bas pour l'éthylène résulte d'une transition ^* , alors qu'il résulte d'une transition ^* pour les vinylboranes.

     

Asymmetric unbridged nitrogen. 39. Configuration and conformations of N-substituted perhydro-1, 3,2-dioxazines

The stereochemical peculiarities of N-substituted perhydro-1,3,2-dioxazines were analyzed thoroughly on the basis of NMR spectroscopic data, the results of x-ray diffraction analysis, and quantitative MO theory. It is shown that in solutions and in the crystalline state these compounds exist in a chair conformation with an equatorial orientation of the substituents in the 2 and 4 positions; the high degree of crimped character of the heteroring (the angle of inflection along the 0...0 line is 70.3°) is due to repulsion of the unshared electron pairs of the N and 0 atoms and n- interactions. An increase in the n- interaction in dialkoxy amines and acetals on passing from C_s to C₂ symmetry of the molecules was demonstrated.See [1] for communication 38. Communication 39 is also communication 25 of the series Geminal systems. See [2] for communication 24.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1341–1347, October, 1985.     

A new steroidal glycoside phrygioside A and its aglycone from the starfish <Emphasis Type="Italic">Hippasteria phrygiana</Emphasis>

Three polyhydroxylated steroids were isolated from the Far-Eastern starfish Hippasteria phrygiana collected from the Sea of Okhotsk and were characterized as a new glycoside phrygioside A, viz., sodium (20R, 24S)-3,4,7,8,15,24-hexahydroxy-24-O-[3-O-methyl--D-xylopyranosyl-(12)--L-arabinofuranosyl]-5-cholestan-6-yl sulfate, its aglycone, and the already known marthasterone sulfate.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2526–2529, November, 2004.     

Calculation of two-center zero-field splitting integrals

Two-center zero-field splitting (ZFS) integrals have been calculated by numerical integration of Coulomb repulsion integrals which are evaluated over basic charge distributions as defined by Roothaan in terms of Slater atomic orbitals. The method is applied to the calculation of the ZFS integrals for -, - and - electron interactions on C, N and N⁺ centers. Numerical results are given.

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Zusammenfassung Zweizentren ZFS-Integrale sind mittels numerischer Integration von Coulombintegralen berechnet worden, und zwar die -, -- und --Integrale an C-, N- und N⁺-Zentren. Die numerischen Resultate werden mitgeteilt.

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Résumé Les intégrales bi-centriques de séparation à champ nul (ZFS) ont été calculées par intégration numérique des intégrales de répulsion coulombiennes évaluées pour les distributions de charge fondamentales définies par Roothan en termes d'orbitales atomiques de Slater. La méthode est appliquée au calcul des intégrales ZFS pour les interactions -, - et - sur les centres C, N et N⁺. Résultats numériques.