Topology of density difference and force analysis

The density difference (r) of a molecule A-B is defined as the difference of the density (r) of the molecule A-B and the density _A(r) + _B(r) put at the position of the atoms A and B. We investigate here the topological features of the density difference and define electron density flow (EDF) as representing the direction and the amount of the electron density flow in the course of the nuclear displacement processes. As such examples, we study H₂ molecule formation reaction and the interaction of two He atoms. By the topological analysis of (r), and by using the Hellmann-Feynman force and its partition into the AD, EC, and EGC forces, the characteristic behaviors of the (r) map are clarified. In particular, the electron cloud preceding and incomplete following are represented by using the concept of the EDF. The natures of the covalent bond are clarified based on the topological properties of the difference density (r) rather than that of the total density (r).On leave from the Department of Chemistry, Hebei Teachers' College, Shijiazhuang, Hebei, 050091, China     

Transmission of influence of substituent in 2-arylpyrrole-5-carboxylic acids

Research on the influence of substituenis on the reaction centers of molecules, through various bridge groups, is still an urgent task in theoretical organic chemistry. This problem is usually solved using the Hammett equation f= + a, by comparing the coefficient of the particular series of compounds under investigation with the coefficient ₀ of a reference series of compounds. The ratio of coefficients / ₀=, which is called the transmission factor, characterizes structural changes of the bridge group [1, 2].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, 1182–1186, September, 1992.     

Upper bounds to atomic electron densities in position and momentum spaces

Modified functions r ^–(r) and p ^–(p) of the spherically averaged electron densities (r) in position space and (p) in momentum space are found to be convex (i.e., the second derivatives are nonnegative everywhere) for all the 103 ground-state atoms from hydrogen (atomic number Z=1) to lawrencium (Z=103), if the parameters are chosen to be 0.6 and 1.4. The convex property of r ^–(r) and p ^–(p) is used to derive upper bounds to the density functions (r) and (p) in terms of their radial moments r ^s and p ^s or frequency moments ^t and ^t . In most cases, the present bounds are shown to be more general and more accurate than those reported in the literature.     

Mechanism of oxygen effect on hyrogenation rate of CO over palladium catalysts

Acceleration of CO hydrogenation by oxygen over palladium catalysts can be accounted for by competing reactions taking place in the CO-H₂O₂ system.

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, CO O₂ , CO–H₂–O₂.

     

Acid — Base properties of 3(5)-azido-1,2,4-triazoles

The pK_a and values of a series of 3(5)-azido-1,2,4-triazoles are correlated with the _I and _C constants according to the equation pK =_II + _CC + pK_o. The high _I values in both cases are due to the closeness of the substituent to the reaction center. The _C/_I ratio attests to different contributions of the inductive and mesomeric effects of a substituent during transmission of its effect from the 5-position to the N₁ and N₄ heteroatoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1288–1291, September, 1974.     

Crystal Structures of [Ni(Phen)(i‐Bu2PS2)2] and [Ni(Phen)3](i‐Bu2PS2)2 Complexes and Interaction between Coordinated 1,10‐Phenanthroline Molecules

Single crystals of [Ni(Phen)(iBu₂PS₂)₂] (I) and [Ni(Phen)₃](iBu₂PS₂)₂ (III) compounds were grown, and their structures were determined by Xray diffraction analysis (CAD4 diffractometer, MoK radiation, 3336 F _hkl , R = 0.0373 for I and 2575 F _hkl for III). The crystals of complex I have a triclinic unit cell with the following parameters: a = 11.097(1) , b = 14.903(2) , c = 22.650(3); = 75.18(1)°, = 80.50(1)°, = 75.07(1)°, V = 3479.2(7)³, Z = 4, _calc = 1.255 g/cm³, and space group 1; the crystals of III have a monoclinic unit cell with the following parameters: a = 19.010(3), b = 15.481(1) , c = 17.940(3); = 97.58(1)°, V = 5233.5(12)³, Z = 4, _calc = 1.292 g/cm³, and space group C2/c. The structure of complex I is built from mononuclear molecules, and the structure of III, from [Ni(Phen)₃]²⁺ complex cations and i Bu₂PS₂ ^- outersphere anions. The NiN₂S₄ coordination polyhedra in the structure of I and NiN₆ in the structure of III are distorted octahedra. Based on structural data, the interaction between the coordinated Phen molecules of complexes I, [Ni(Phen)₂(iBu₂PS₂)](iBu₂PS₂) (II), and III is considered, as well as the packing modes of these complexes.     

New Approach to Analysis of the Nonlinearity of the Brønsted Relationship: II. An Empirical Procedure Combining the σρ Correlation Method with the Concept of Hard and Soft Acids and Bases,as Applied to Pseudo CH Acids

A comparative systematic analysis of the features of Brönsted behavior of pseudo CH acids(according to Eigen's classification) is made. The analysis is based on combined use of experimental data onpK _a, Ggas, logk _D of CH acids (Ggas is the free energy of acid ionization in the gas phase, logk _D isthe logarithm of the rate constant of hydrogen exchange in a protic solvent). The modified nucleophilicKabachnik constants ^- are applicable to correlations for all the three kinds of acidity of pseudo CH acids. The electrostatic solvation makes an insignificant contribution to variation of pK _a and weakening of the substituent effect in going from the gas phase to dimethyl sulfoxide, and also to differentiation of the kinetic acidity. The coefficient in the Brönsted equation and the ratio between the rate constants in the correlations, which characterize the degree of proton transfer in the reaction transition state, have much in common from the physical viewpoint. The results of correlation analysis, demonstrating intramolecular uniformity of the interactions, are fully consistent with the conclusion made in the previous part of this work about the solvation uniformity of the interactions, resulting in the absence of thermodynamic deviations from the Brönsted relationship.     

Laser Sintering of SnO2 : Sb Sol-Gel Coatings

Sb doped sol-gel SnO2 single layers (thickness 100 nm) were prepared from alcoholic solution and deposited via a dip coating process on fused silica substrates. The coatings have been sintered at a typical rate of 10–15 cm2/s by CO2 laser irradiation. The laser spot was scanned in one direction at a speed of 15,000 cm/s and the sample was moved in a perpendicular one at a speed up to 250 mm/s. The temperature of the topmost 10 m layer was monitored by a fast pyrometer (s resolution). The following properties of the coatings have been determined: the electrical resistivity , the carrier density n, and mobility , the structure, the thickness, the mesoscopic and micromorphology and the density. The sintering by CO2 laser radiation is mainly a thermal driven process. At T 500°C it allows to obtain coatings with a smaller resistivity (6.8×10–3 cm) than those produced by conventional furnace firing (el2.9×10–2 cm). The results are discussed in terms of particle size and packing density.     

Bestimmung der HMO-Parameter von Nitrogruppen aus den UV-Absorptionsspektren von Nitroaromaten

Zusammenfassung Unter Benutzung der experimentellen Werte derK-Banden von Nitro-, m- und p-Dinitro- und sym-Trinitrobenzol wurden die Parameter der Resonanzintegrale der Nitrogruppe zu _CN=1,1 und _NO=1,6 bestimmt, die Parameter der Coulombintegrale auf Grund von Plausibilitätsbetrachtungen zu _O=1,5, _N=1,8 und _C=0,25 abgeschätzt. Die UV-Spektren der vier genannten Verbindungen wurden in Cyclohexan vermessen.Die erhaltenen Parameter werden zur Berechnung der Moleküldiagramme und Energieniveaus der vier Strukturen benutzt. Die Rechendaten stehen in guter Übereinstimmung mit den experimentellen Befunden, vor allem dann, wenn den weiterreichenden induktiven Effekten der Nitrogruppe in geeigneter Weise Rechnung getragen wird.

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Using the experimental values for theK bands of nitro-, m-and p-dinitro- and sym-trinitrobenzene, the parameters of the resonance integrals of the nitro group were calculated to be _CN=1,1 and _NO=1,6, and the parameters of the Coulomb integrals estimated as _O=1,5,_N=1,8 and _C=0,25 on the basis of plausibility considerations. The UV-spectra of the above compounds were measured in cyclohexane.The parameters obtained are used to calculate the molecular diagrams and energy levels. The calculated data are in good agreement with the experimental findings, above all when the more extensive inductive effects of the nitro group are suitably taken into account.

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Mit 7 Abbildungen     

On the Interaction of Two Finite-Dimensional Quantum Systems

Interaction of quantum system S ^a described by the generalised × eigenvalue equation A| _s =E _s S ^a | _s (s=1,...,) with quantum system S ^b described by the generalised n×n eigenvalue equation B| _i = _i S ^b | _i (i=1,...,n) is considered. With the system S ^a is associated -dimensional space X ^a and with the system S ^b is associated an n-dimensional space X _n ^b that is orthogonal to X ^a . Combined system S is described by the generalised (+n)×(+n) eigenvalue equation [A+B+V]| _k = _k [S ^a +S ^b +P]| _k (k=1,...,n+) where operators V and P represent interaction between those two systems. All operators are Hermitian, while operators S ^a ,S ^b and S=S ^a +S ^b +P are, in addition, positive definite. It is shown that each eigenvalue _{k i} of the combined system is the eigenvalue of the × eigenvalue equation . Operator in this equation is expressed in terms of the eigenvalues _i of the system S ^b and in terms of matrix elements _s |V| _i and _s |P| _i where vectors | _s form a base in X ^a . Eigenstate | _k ^a of this equation is the projection of the eigenstate | _k of the combined system on the space X ^a . Projection | _k ^b of | _k on the space X _n ^b is given by | _k ^b =( _k S ^b –B)^–1(V– _k P})| _k ^a where ( _k S ^b –B)^–1 is inverse of ( _k S ^b –B) in X _n ^b . Hence, if the solution to the system S ^b is known, one can obtain all eigenvalues _{k i} } and all the corresponding eigenstates | _k of the combined system as a solution of the above × eigenvalue equation that refers to the system S ^a alone. Slightly more complicated expressions are obtained for the eigenvalues _{k i} } and the corresponding eigenstates, provided such eigenvalues and eigenstates exist.     

Charakterordnungen undBrownsche p-Lokalisierungsenergien linearer Polyacene

Zusammenfassung Die mit der Zahl der anellierten Ringe abnehmende Stabilität linearer Polyacene wird durch die Benzol-Charakterordnungen erklärt. DieBrownschen p-Lokalisierungsenergien und die Benzol-Charakterordnungen werden für den mittleren Ring (=0,800,L _p=3,12 ) und für die randständigen Ringe (=0,885,L _p=3,61 ) eines unendlich langen Polyacens berechnet. Diese Berechnung erfolgt auf Grund der Energieeigenwerte und Bindungsordnungen und führt auf elliptische Integrale.

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The well known fact that the stability of linear polyacenes decreases with the number of anellated rings is explained by the benzene character orders.Brown's p-localisation energies and the benzene character orders for the middle ring (=0,800,L _p=3,12 ) and for the endpositioned rings (=0,885,L _p=3,61 ) of a polyacene with an infinite number of rings are calculated. This calculation, based on the energy eigenvalues and the bond orders, leads to elliptical integrals.

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Mit 2 Abbildungen

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H. S.: Institut für Physikalische Chemie der Technischen Hochschule Wien, A-1060;G. D.: dzt. Institut für Statistik an der Universität Wien, A-1010.     

Peculiarities of formation of ZnO and CuO-based solid solutions

Low-temperature (623 K) treatment of hydroxocarbonate compounds of copper-zinc and copper-zinc-aluminium leads to the formation of phases with CuO and ZnO structures, which are solid solutions of the promoter ions. The formation of solid solutions is attributed to structural distortions (uniform or local) in the oxide lattice due to the incomplete removal of OH^– and CO ₃ ^2– groups at low temperatures.

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, (623 ) - -- CuO ZnO, . , ( ) - OH ₃ ^–– - .

     

Specificity of hydrogen adsorption on chromia-supported platinum group metal catalysts

Hydrogen adsorption on chromia supported Pd, Rh and Pt was studied under various pretreatment conditions. The reduction temperature influences strongly the hydrogen uptake for all these metals. Platinum supported on chromia shows an unusually high hydrogen adsorption stoichiometry.

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Pd, Rh Pt, Cr₂O₃, . , . Cr₂O₃ .

     

Thermal analysis of 1-Hydroxiethylidenediphosphonic acid and its salts

1-Hydroxyethylidenediphosphonic acid and its tetrasubstitutcd Li, Na, K, Rb, NH₄, Ca and Ba salts were synthcsized and their thermal behaviour was studied under non-isothermal conditions by simultaneous TG-DTG-DTA at 20–1000 C. The following thermal transformations were observed: loss of crystallization water, melting in the case of the acid, and intramolecular dehydration in the case of the salts, leading to the corresponding unsaturated derivatives. From the free acid, its acidic salts and the neutral ammonium salt, long-chain polycondensates are formed through intermolecular dehydration.

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Zusammenfassung 1-Hydroxyethyldiphosphonsäure und ihr Li-, Na-, K-, Rb-, NH₄-, Ca- und Ba-Salz wurden dargestellt. Ihr thermisches Verhalten wurde durch simultane TG-DTG-DTA unter nichtisothermen Bedingungen bei 20–1000 C untersucht. Folgende thermische Umwandlungen wurden beobachtet: Verlust von Kristallwasser, Schmelzen (nur bei der freien Säure), intramolekulare Wasserabspaltung (nur bei den Salzen) zu ungesättigten Verbindungen. Die freie Säure, die sauren Salze und das neutrale Ammoniumsalz bilden unter intermolekularer Wasserabspaltung langkettige Polykondensate.

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1- , , , , , . - . , , , . , , .

     

Catalytic properties of V?Mo?O systems in acrolein oxidation

Catalytic properties of V–Mo–O systems have been studied in acrolein oxidation. When catalysts are activated in reaction mixtures at 673 K, then a solid solution of molybdenum oxides in reduced vanadium oxides is formed, which is responsible for deep oxidation. Also, several compounds are produced, which by their activity and selectivity to acrylic acid formation are arranged in the sequences VMo₃O₁₁VMo₂O_8+x>V₆Mo₄O₂₅, and VMo₃O₁₁>VMo₂O_8+xV₆Mo₄O₂₅, respectively.

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V–Mo–O . 673 K , , , : VMo₃O₁₁VMo₂O_8+x>V₆Mo₄O₂₅, : VMo₃O₁₁>VMo₂O_8+xV₆Mo₄O₂₅.

     

Methanol-based synthesis of hydrocarbons on bifunctional Y-type zeolites

The directions of methanol conversion on Pt, Pd, Zn, Ni metals and Y zeolites and on bifunctional metal-Y-zeolite catalysts have been studied. The increase of the hydrogenation activity of bifunctional catalysts enhances the rate of methanol conversion and decreases the selectivity of hydrocarbon formation.

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- Y, - Y.

     

Thermogravimetric characterization of Quayarah heavy crude oils

Five heavy crude oil samples from the Quayarah field were thermally evaluated using two modes of thermogravimetry (TG): dynamic and programmed TG with heating and hold-up periods at 350 and 550°. The light and medium volatility fraction (L+M) appeared directly proportional to the metal content. In contrast, the heavy fraction (H) (350–550°) was inversely proportional to the metal content. This contradiction was attributed to the autocatalytic degradation of some of the heavy fraction into lighter species, which upgrades the crude with respect to the (L+M) fraction at the expense of the heavy fraction. The crudes were identical with regard to the ratio (L+M) to (H+R), whereR=residue, as a consequence of their identical API gravity and sulphur contents.The rate of degradative volatilization of the heavy fraction was measured by DTG, which indicated a direct correlation with the vanadium content as regards the onset temperatures and the DTG peak maximum.

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Zusammenfassung Fünf vom Quayarah-Feld stammende schwere Rohöle wurden mittels dynamischer und programmierter TG mit konstanten Perioden bei 350 und 550 °C charakterisiert. Der Anteil der leicht- und mittelflüchtigen Fraktion (L+M) schien proportional, der der schwerflüchtigen Fraktion (H) (350 550°) dagegen umgekehrt proportional dem Metallgehalt zu sein. Dieser Widerspruch wurde dem autokatalytischen Abbau einiger der schwerflüchtigen Komponenten zu leichteren Spezies zugeschrieben, der zu einer Erhöhung des Anteils der (L+M)-Fraktion auf Kosten der schwerflüchtigen Fraktion führt. Die Rohöle waren wegen der gleichen API-Schwere und gleicher Schwcfclgehalle hinsichtlich des Verhältnisses von (L+M) zu (H+R) identisch (R=Rückstand). Die Geschwindigkeit der degradaliven Verflüchtigung der schweren Fraktion wurde mittels DTG gemessen, wobei sich eine direkte Korrelation zwischen dem Vanadingehalt einerseits und der Einsatztemperatur bzw. dem DTG-Peakmaximum andererseits ergab.

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350 550°. (+ ) , () (350–550°) — . , . + +, — , . . , , .

     

Catalytic properties of plantinized polycyanogens

The effect of various inorganic polymers on the catalytic activity and selectivity of platinum in the hydrogenation of 4-chloronitrobenzene and dinitrotoluene has been studied. Platinized iron-containing polycyanogens are less active but more selective catalysts for the hydrogenation of 4-chloronitrobenzene than Pt/C or Pt/BaSO₄.

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4- . , , , 4-, Pt/C Pt/BaSO₄.

     

Thermal treatment and analysis involved in the preparation and investigation of different types of inorganic glasses

The importance of the thermal behaviour of glasses is illustrated. Some procedural characteristics for glass preparation upon quenching are discussed to distinguish the positive effects of increasing cooling rate. The basic thermodynamic quantities, kinetic data and procedural parameters are listed. The glass-transformation interval is treated in detail to demonstrate the temperature-dependences of heat capacity, enthalpy an Gibbs energy for as-quenched and annealed glasses, exemplifying processes of thermally stimulated reordering. Particular attention is paid to DTA measurements, which are of use for the determination of characteristic temperatures and to for the distinction of possible types of processes which occur upon reheating. Most common cases are illustrated by a series of hypothetical H vs. T and T _dta vs. T plots. Different glass formation coefficients based on the onset temperatures are discussed to confirm the general knowledge that their maxima match with concentration regions close to that of invariant melting of the system.

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Zusammenfassung Es wird die Bedeutung des thermischen Verhaltens von Glas verdeutlicht. Einige technologische Kenngrößen der Gasherstellung beim Abschrecken sowie grundlegende thermodynamische Größen, kinetische Daten und technologische Parameter, wurden beschrieben, um bei steigender Abkühlgeschwindigkeit positive Einflüsse erkennen zu können. Zur Unterstreichung thermisch stimulierter Umordnungsprozesse und zur Verdeutlichung der Temperaturabhängigkeit von Wärmekapazität, Enthalpie und freier Enthalpie von abgeschrecktem und kühlgeglühtem Glas wird das Intervall der Glasumformung ausführlich behandelt. Erhöhte Aufmerksamkeit wurde DTA-Messungen geschenkt, um charakteristische Temperaturwerte festzustellen und um eventuelle Typen der Prozesse, die beim Nachhitzen ablaufen, zu erkennen. Die häufigsten Fälle werden durch hypothetische H-T und T _dta -T Diagramme illustriert. Verschiedene Glasformationskoeffizienten für die Anfangstemperatur wurden diskutiert, um den allgemeinen Fakt zu bekräftigen, daß deren Maximum mit den Konzentrationsbereichen nonvariant schmelzender Systeme übereinstimmt.

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. , . , . , , , . , , . H- _a-. , , , .