Temperature dependence of the volumetric properties of binary mixtures containing oxaalkane +n-heptane

Excess molar volumes of mixtures of n-heptane + 2,5-dioxahexane and n-heptane + 2,5,8-trioxanonane were determined from density measurentents at 5, 15, 25 and 35°C. These results allowed the following mixing quantities to be reported in all range of concentrations: , (v ^E /T) _P and (h ^E /P) _T , at 25°C. The obtained values were then compared with the calculated values by using the Flory theory and the Nitta-Chao theory of liquid mixtures. The results are discussed in terms of order or disorder creation.     

A simplified View of δ → δ* Transition Energies in Compounds with multiple metal-metal bonds: The isolated δ — δ* manifold model

The energetics of the * transition in quadruply bonded complexes are investigated using a very simple valence-bond formalism, called the isolated * manifold (IDDM) model. In this model all electrons except for those that occupy the or * molecular orbitals are ignored, as are explicit metal-ligand interactions. The resulting equations allow the calculation of transition energies very inexpensively, albeit with poor quantitative agreement: the * transition in prototypical quadruple-bond systems is predicted to occur at energies greater than 70,000 cm¹. The model incorporates configuration interaction between the two¹ A _1g configurations (|| and |**|) to roughly the same extent as do correlated all-electron calculations. The application of the method to systems that involve relative changes in * transition energies, such as the torsional twisting of quadruple bonds, is more successful quantitatively.     

Theoretical and Empirical Relationships Between the Redox Potentials and <Superscript>1</Superscript>(<Emphasis Type="Italic">δ</Emphasis>→<Emphasis Type="Italic">δ</Emphasis>*) Transition Energies of Quadruply Bonded Complexes

An analysis of the available electrochemical and electronic-sectroscopic data for quadruply metal–metal bonded complexes reveals that the ¹(*) transition energy is an approximately linear function of the difference between the electrode potentials at which they are reduced and oxidized to the bond-order 3. 5 complexes. A theoretical framework for interpreting this correlation is provided by extending to the redox potentials a simple zero-differential-overlap model previously applied to ¹(*) transition energies. It is suggested on the basis of this model that the simplicity of the empirical relationship between ¹(*) energies and redox potentials is a consequence of the particular one- and two-electron energy terms that characterize these complexes; a linear relationship is not required by theory.     

What are the relative steric demands of carboxyl and methyl groups?

The relative steric demands of carboxyl and methyl groups are compared by contrasting the difference quantity H _f ^o (g, ArCOOH) — H _f ^o (g, ArCH₃) for a collection of alkylated benzoic acids and toluenes with the value for Ar=C₆H₅, the archetypical (i.e., unsubstituted) benzoic acid and toluene. We conclude that carboxyl and methyl groups are nearly the same size.     

Free and Sulfated Sterols of Two Far-East Leptasterias Starfish

NMR spectroscopy, capillary GLC, and GLC-MS are used to study the composition of free and sulfated sterols from the far-east starfishLeptasterias alaskensis asiatica(Fischer) andL. Fisheri(Djakonov). The total free sterols of both species are shown to have similar qualitative and quantitative compositions and contain mainly⁷ -sterols. Sterol sulfate fractions contain cholesterol sulfate as the main component but differ in the ratios of⁵ :⁰ :⁷ -sterol derivatives. Possible reasons for these differences are discussed. A new steroid, 3-hydroxycholest-5-en-7-one sulfate, was isolated.     

Ammoxidation of 3- and 4-picolines over V2O5?SnO2/γ?Al2O3 catalyst

The ammoxidation of 3- and 4-picolines has been studied over V₂O₅–SnO₂/–Al₂O₃ catalysts prepared by surface impregnation technique. Best results were obtained for the generation of cyanopyridines in the temperature range 400–450°C and sub-stoichiometric value with respect to O₂. Catalysts that were calcined above 700°C showed no activity.

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3- 4- V₂O₅–SnO₂/–Al₂O₃, . 400–450°C O₂. , 700 K, .

     

Thermochemical study of aliphatic and phenyl-substituted geminal diacetates

The standard enthalpies of combustion _c H ^o of aliphatic diacetates1 and aromatic diacetates2 were measured calorimetrically. The enthalpies of vaporization _vap H ^o or sublimation _sub H ^o of1 and2 were obtained from the temperature function of the vapor pressure measured in a flow system. From _f H ^o(g) of1 and2 new values of group increments for the estimation of standard enthalpies of formation of these classes of compounds were derived. The geminal interaction energy between the geminal acyloxy groups shows no anomeric stabilization.Geminal Substituent Effects, Part 12, for part 11 see Ref. 7.     

Untersuchung binärer metallischer Systeme mit Hilfe des Amalgamverfahrens. Das System Nickel-Zinn

Zusammenfassung Eine unter Anwendung des Amalgamverfahrens durchgeführte Untersuchung des Systems Nickel-Zinn ergab bis 50 At.-% Zinn sehr gute Übereinstimmung mit dem Schmelzdiagramm. In Legierungen mit höherem Zinngehalt wurden jedoch, abweichend von den Ergebnissen bisheriger Untersuchungen, zwei einander strukturell sehr ähnliche Phasen und ₁ mit schmalem Homogenbereich aufgefunden. Die -Phase ist identisch mit der bereits in Schmelzlegierungen festgestellten monoklinen Kristallart; ihre Zusammensetzung ist aber gegenüber dem Schmelzdiagramm gegen die Nickelseite hin verschoben.Die zinnreichere ₁-Phase ist von der -Phase durch einen heterogenen Bereich von nur 2,5% getrennt. Bei höheren Temperaturen tritt eine Aufweitung des - und eine Verengung des ₁-Gebietes ein, wobei der zwischen diesen Phasen liegende heterogene Bereich noch schmaler wird; er umfaßt bei 600° nur mehr 0,5%.Mit 3 Abbildungen.Herrn Prof. Dr.A. Klemenc zum 70. Geburtstag gewidmet.     

Enthalpy of formation of triphenylphosphine sulfide

The first measurements of the enthalpies of combustion, sublimation, and fusion of an organo-phosphorus sulfide, triphenylphosphine sulfide, are reported: _c H _m ^o (C₁₈H₁₅PS, cr)=–(10752.58 ±2.90), _sub H _m ^o (C₁₈H₁₅PS, 403 K)=(136.80±6.09), and _fus H _m ^o (C₁₈H₁₅PS, T_m=435.92 K) =(30.53±0.21) kJ·mol^–1. Correction of the phase change enthalpies toT=298.15K and p^o =0.1 MPa results in the standard phase change enthalpy values of _sub H _m ^o (298.15 K)=(142.8 ±6.8) and _fus H _m ^o (298.15 K)=(19.28±0.21) kj·mol^–1. Accordingly, the enthalpies of formation of solid, liquid, and gaseous triphenylphosphine sulfide are derived: _f H _m ^o (C₁₈H₁₅PS, cr) =(63.20±2.56), _fH _m ^o (C₁₈H₁₅PS, l)=(82.48±2.57), and _fH _m ^o (C₁₈H₁₅PS, g)=(206.0±7.3) kJ·mol^–1. From these ancillary data, the P=S double-bond enthalpy is 394 kJ-mol^–1 and in good agreement with earlier reaction calorimetry results. These phosphorus sulfide values are compared with those for the arsenic sulfides. Plausibility arguments are given for our results.     

The phenomenon of conglomerate crystallization: XXXVII: The crystallization behavior of the Cr(III) and Co(III) amine carbonates [Cr(en)2CO3]I (I) and NH4{[cis-β-Co(trien)Co3]2}(PF6)3 (II)

[Cr(en)₂CO₃]I (I), ICoO₃N₄C₅H₁₆, crystallizes from water at 21°C in space groupP2₁/c (no. 14), with lattice constantsa=7.298(4),b=8.622(8),c=17.577(6)Å,=91.29(4)°;V=1105.59 ų andd(calc; MW=359.11, Z=4)=2.157 g cm^–3. A total of 2825 data points were collected over the range of 4°250°; of these, 1855 (independent and withI3(I)) were used in the structural analysis. Data were corrected for absorption (=37.657 cm^–1) and the transmission coefficients ranged from 0.4850 to 0.9991. The finalR(F) andR _w(F) residuals were, respectively 0.134 and 0.113. The cations exist in the lattice as the enantiomeric pair () and (). NH₄{[cis--Co(trien)CO₃]₂}(PF₆)₃ (II), Co₂P₃F₁₈O₆N₉C₁₄H₄₀, crystallizes from water at 21 °C in space groupP2₁/c (no. 14), with lattice constantsa=10.397(2),b=20.292(3),c= 27.082(4) Å,=100.30(3)°;V=3545.70 ų andd(calc; MW=983.29, Z=4)=1.842 g cm^–3. A total of 3724 data were collected over the range of 4°250°; of these, 2653 (independent and withI3(I)) were used in the structural analysis. Data were corrected for absorption (=12.031 cm^–1) and the transmission coefficients ranged from 0.8326 to 0.99985. The finalR(F) andR _w (F) residuals were, respectively 0.104 and 0.124. The cations exist in the asymmetric unit as() and()[cis--Co(trien)CO₃]⁺ pairs. The three independent PF₆ ^– anions exhibit the usual high thermal motion typical of these species and the NH₄ ⁺ cation is either disordered or exhibits high thermal motion also (its H atoms could not be found in difference maps).     

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

Correlation between the stereochemistry and optical activity of chiral dimolybdenum tetracarboxylates and related compounds

Sector rules for chiral dimolybdenum tetracarboxylates and related compounds were derived using the one-electron model of optical activity. The correlation between the sign of the Cotton effect (CE) of the ^* transition and the stereochemistry of this type of binuclear clusters is expressed as a rule of 16 in which the positive sign of the EC corresponds to the negative sign of the pseudoscalar function xyz(x²-y²) of the cluster atoms. A negative sign of the CE was predicted for the ^* transition in cis-(L-isoleucine)₂(NCS)₄Mo₂.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1504–1507, July, 1990.We would like to thank M. A. Porai-Koshits and A. A. Levin for becoming acquainted with the research and discussing the results obtained.     

13C-NMR-Untersuchungen von Substituenteneffekten in mehrfach substituierten Benzen-und Naphthalenverbindungen: Inkrementberechnungen der13C-chemischen Verschiebungen

Summary The aryl¹³C chemical shifts of Cl-substituted 4-amino-, 4-diazonium-N,N-dimethylanilines, N,N-dimethylanilines and differently substituted naphthalenes were assigned by means of different NMR methods. The assignments were compared with chemical shifts obtained by using empirical additivity relationship for mono substituted aromatic substances. As a means of substitutent interactions, the chemical shift difference between calculated and experimental values ( _c ⁱ ) has been used. In the presence of remarkable steric and electronic substituent interactions, large deviations from additivity ( _c ⁱ values up to 15.4 ppm) were found. Which originate primarily from steric interactions between the substitutents. In order to account therefore, correction increments have been developed by employing the _c ⁱ values obtained from 1,2-disubstituted benzenes or naphthalenes. The¹³C chemical shifts of more than seventy substituted benzenes and naphthalenes have been predicted. The results corroborate that reasonable calculation of chemical shifts in sterically hindered benzenes is possible by using the extended additivity rule. The _c ⁱ values are much lower and allow reasonable structural assignments.For external users of this incremental system, a computer program for IBM compatible PC/AT was developed. By means of this program, the¹³C chemical shifts for different benzenes and naphthalenes with or without 1,2-disubstituted correction increments will be calculated and the corresponding spectrum displayed. The program can assist the successful assignment of experimental¹³C chemical shifts.

     

Lattice Dynamics in LaTa2-2xNb2xVO9-δ (x=0–0.1) Solid Solutions

The oxygen nonstoichiometry (x) of LaTa_2-2xNb_2xVO₉- (x = 0–0.1) solid solutions was studied using Xray phase analysis, vibrational spectroscopy, and radiospectroscopy. A correlation was found between (x) and the unit cell volume V(x) of the solid solutions. It was shown that the infrared spectra of LaTa₂VO₉- change in passing from = 0 to 0. The structural position of the oxygen vacancy in LaTa_2-2xNb_2xVO₉- is discussed.     

Kinetics of acyl exchange of series of N- and O-acyl salts with 4-(p-dimethylamino)styrylpyridine-N-oxide

A study has been mode of the reaction of acyl exchange between a series of N- or O-acyl salts and 4-(p-dimethylamino)styrylpyridine-N-oxide in acetonitrile solution. Values of the rate constant (k₂) and activation characteristics (E_a, G, S, and H) have been obtained for these systems.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 31, No. 2, pp. 86–89, March–April, 1995.This work was performed with financial support from the State Committee of the Ukraine for Matters of Science and Technology.     

Configuration of benzoylpyridineoximes studied by 1H and 13C NMR. Effect of protonation of the pyridine nitrogen atom

A simple and convenient method is proposed for determining the configuration of E,Z-isomers of 2-, 3-, and 4-benzoylpyridines. The difference in chemical shifts (, ppm) in the system CCl₄-DMSO-D₆ and CCl₄-DMSO-CF₃COOD for the -H atoms or the , -C atoms of the pyridine ring can be used to determine the configuration. The shift () of the -H signals to weak field is greater for the Z-isomers than for the E-isomers due to protonation of the pyridine nitrogen atom. The reverse dependence is seen in the ¹³C NMR for the E,Z-isomers. The signals of the -C atoms shift to stronger field after protonation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1073–1077, August, 1990.     

Thermoanalytical characterization of amorphous synthetic silicic acids

Due to the various preparation procedures, silicic acid products display differences in dispersity, morphology and structural characteristics.Simultaneous DTA-TG is well suited for the separate determination of water bound adsorptively and chemically in the form of silanol groups, and also the characterization of aftertreated silicic acids. A classification of the different silicic acid types is possible on the basis of the thermoanalytical results.

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Zusammenfassung Nach unterschiedlichen Verfahren hergestellte Kieselsäuren zeigen verschiedene Dispersitäten, Morphologien und strukturelle Charakteristika. Simultane TG-DTA ist gut geeignet zur Bestimmung von adsorptiv oder chemisch-in Form von Silanolgruppen-gebundenem Wasser sowie zur Charakterisierung nachbehandelter Kieselsäuren. Eine Klassifikation der verschiedenen Kieselsäure-Typen ist auf der Grundlage thermoanalytischer Ergebnisse möglich.

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, , . , . .

     

Quadrupole polarizability and hyperpolarizability of carbon monoxide

Summary We report a study of the electric dipole-quadrupole (A _,,), quadrupole-quadrupole (C _,,), dipole-octopole (E _,) polarizability and the dipole-dipole-quadrupole (B _,,) hyperpolarizability of carbon monoxide. All values are obtained from finite-field self-consistent field (SCF) and fourth-order manybody perturbation theory (MP4) calculations. Our best values for the dipole-octopole polarizability areE _z,zzz=60.19 andE _x,xxx=–38.06e ² a ₀ ⁴ E _h ^–1 . For the dipole-dipole-quadrupole hyperpolarizability we reportB _zz,zz=–296,B _xz,xz=–170,B _xx,zz=88 andB _xx,xx=–178e ³ a ₀ ⁴ E _h ^–2 .     

étude thermodynamique de certains médicaments

Two compounds of sulphamide type:p-amino-benzene sulphonamide (I) and 3,4-dimethylisoxazol 5-sulphanylamide (II) were studied by combustion calorimetry and by differential scanning calorimetry (DSC).The enthalpies in solid state at 298,15 K of combustion, _c H _m ^o (I)=-2788,5±1,6 kJ mol^–1, _c H _m ^o (II)=-5036±3,8 kJ mol^–1 and of formation, _f H _m ^o (I)=-458,3±1,6 kJ mol^–1, _fH _m ^o (II)=-180,1±3,8 kJ mol^–1 were determined.The thermal effects concerning the melting and phase transition of this compounds were also measured.

     

Effect of the organic modifier on the retention of retinoids in reversed-phase liquid chromatography

Summary The retention of retinoids in reversed-phase liquid chromatography was studied using aqueous mobile phases of different composition (methanol 94–86% and acetonityrile 92–82%) at five temperatures (40–60 °C). With both organic modifiers the effect of the molecular structure increased as the water content and the polarity of the mobile phase increased. The temperature-dependence increased in the same manner with aqueous acetonitrile mobile phases. The - interactions between the retinoids and acetonitrile diminish when the water content of the mobile phase is increased, as happens also to the hydrophobic interactions with both organic modifiers. The net effect of these changes depends on the composition of the mobile phase. There was excellent correlation of retention with all polarity parameters studied(, P, x_e, x_d, x_n, E _T ^N , _T, , _o and _d), when the calculations were made separately with methanol and acetonitrile. The volume fraction of the organic modifier, , was the only parameter describing the retention well in both organic modifiers simultaneously.