Surface Area Study of High Area Cobalt Aluminate Particles Prepared by the Sol-Gel Method

Cobalt aluminate particles were prepared by the sol-gel method, starting from aluminum sec-butoxide and cobalt salts with a Co:Al ratio of 1:3. Samples with the same composition were also prepared by the citrate-gel method from cobalt and aluminum nitrates and citric acid. The particles were calcined to temperatures between 400 and 1000°C, for the formation of the mixed oxide having spinel structure. The surface properties of the different samples (BET surface area and pore size distribution) were measured. The highest BET surface area obtained (about 339 m²/g) corresponds to a sample prepared by cobalt acetate and aluminum sec-butoxide, calcined at 400°C. The surface area of the sample is reduced progressively as the sample is calcined to higher temperatures (to about 65 m²/g at 1000°C). Narrow pore size distributions were observed with average pore radius ranging from 17–20 Å, for samples heated to 400°C, to about 55–65 Å, for samples heated to 1000°C. The different surface areas and porosities obtained for particles prepared by different methods, different precursors or calcination temperatures, are discussed.     

An ab initio study of the geometries and rotational barriers of 1-, 2-, and 5-phenylimidazole

The torsional barrier was calculated in the 3-21G basis set for 1-, 2-, and 5-phenylimidazole. Full geometry optimization was carried out at inter-ring torsional angles of 0°, 30°, 60°, 90°, 120°, 150°, 180°, and additional intermediate angles. All torsional potential energies were found to be symmetric with respect to the 90° conformation. The 2-phenylimidazole torsional energy exhibits a minimum at 0° (and 180°) and a maximum at 90° with a barrier height of 5.83 kcal/mol relative to the 0° conformation. The minima in the 1- and 5-phenylimidazole torsional potential energies correspond to non-planar conformations, resulting in a double-well potential with maxima at 0° (180°) and 90°. The 1-phenylimidazole minima are located at 46.5 and 133.5°; the 5-phenylimidazole minima, at 35.3 and 144.7°. In the 0° (180°) and 90° conformations, 1-phenylimidazole exhibits torsional barriers of 1.84 and 0.75 kcal/mol, respectively, relative to the energy of the 46.5° conformation. For 5-phenylimidazole, these barriers are 0.94 and 1.89 kcal/mol, relative to the energy of the 35.3° conformation. The energy of 5-phenylimidazole in the 35.3° conformation corresponds to a relative tautomeric energy difference of 1.80 kcal/mol compared to the 0° conformer of the 4-phenylimidazole tautomer.     

Active centers on the surface of thermoactivated silica. Their reactivity toward organoaluminum compounds

Interaction between organoaluminum compounds (triethylaluminum, ethoxydiethylaluminum, and diethoxyethylaluminum) and the surface of silica activated at various temperatures (200–800 °C) was studied by IR spectroscopy, mass spectrometry, and quantum chemistry. Formation of structural silanon defects on the surface of silica activated at 800 °C was considered. It was established that the fraction of terminal silanol groups involved in the interaction with organoaluminum compounds on the surface of silica thermoactivated above 600 °C is low, and siloxane bonds and structural surface defects play a determining role. The thermodynamic favorability of coordination of organoaluminum compounds on these active surface centers is shown. The structure and routes of decomposition of aluminum-containing surface intermediates were studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1906–1911, October, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-08847).     

Phase equilibria in the CdI2-Ag2Se system

The phase diagram of the system CdI₂-Ag₂Se is studied by means of X-ray diffraction, differential thermal analysis and measurements of the density of the material. The unit cell parameters of the intermediate phase 2CdI₂·3Ag₂Se were determined a = 0.6387 Å, b = 4.311 Å, c = 4.044 Å; α = 113.72°, β = 90.27° and γ = 94.85°. The intermediate phase 2CdI₂·3Ag₂Se has a polymorphic transition at 125 °C. It melts incongruently at 660 °C.     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

Synthesis and characterization of Zn1−xNixFe2O4 spinels prepared by a citrate precursor

Nanocrystalline single-phase samples of Zn_1−xNi_xFe₂O₄ ferrites (0<x<1) have been obtained via a soft-chemistry method based on citrate-ethylene glycol precursors, at a relatively low temperature (650 °C). The influence of the nickel and zinc contents as well as that of heat treatments were investigated by means of X-ray powder diffraction, Brunauer-Emmett-Teller (BET) surface area, scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) Spectroscopy. Higher Ni content increases the surface areas, the largest one (∼20 m²/g) being obtained for NiFe₂O₄ annealed at 650 °C for 15 h. For all compositions, the surface area decreases for prolonged annealing at 650 °C and for higher annealing temperatures. Those results were correlated to the particle size evolution; the smallest particles (∼50 nm) observed in the NiFe₂O₄ sample (650 °C, 15 h) steadily increase as Ni ions were replaced by Zn, reaching ∼100 nm in the ZnFe₂O₄ sample (650 °C, 15 h). For all the Zn_1−xNi_xFe₂O₄ samples and, whatever the heat treatments was, the FTIR spectra show two fundamental absorption bands in the range 650-400 cm⁻¹, characteristics of metal vibrations, without any superstructure stating for cation ordering. The highest ν₁-tetrahedral stretching, observed at ∼615 cm⁻¹ in NiFe₂O₄, shifts towards lower values with increasing Zn, whereas the ν₂-octahedral vibration, observed at 408 cm⁻¹ in NiFe₂O₄, moves towards higher wavenumbers, reaching 453 cm⁻¹ in ZnFe₂O₄.     

Formation of Superhydrophobic-Superhydrophilic Pattern on Flowerlike Alumina Thin Film by the Sol-Gel Method

We have prepared superhydrophobic surfaces which become superhydrophilic by heat-treatment at 500°C or irradiation of UV-light. When hydrolyzed fluoroalkyltrimethoxysilane (FAS) was coated on Al₂O₃ gel film with a roughness of 20 to 50 nm, the films showed superhydrophobicity and high transparency; the contact angle for water of the film was 165° and the transmittance for the visible light was higher than 92%. When the FAS-coated thin films were heat-treated at temperatures higher than 500°C, the films became superhydrophilic; the contact angle for water on the films was smaller than 5°. Thin films of amorphous TiO₂ or anatase TiO₂ were coated between Al₂O₃ gel and FAS layer, and the contact angle for water was also about 160°. UV irradiation using high-pressure mercury lamp on these films resulted in the contact angle to be smaller than 5°. When UV light was irradiated through a photomask, superhydrophobic-superhydrophilic micropatterns applicable as a stamper for printing or a substrate of micro-optical components were successfully obtained on the films.     

Researches on 2, 1, 3-thia- and selenadiazole

4-Hydroxy-, 4-hydroxy-5-methyl-, 4-hydroxy-7-methylbenzo-2,1,3-thiadiazoles are polymorphous.4-Hydroxybenzo-2,1,3-thiadiazole (I), 4-hydroxy-5-methyl- and 4-hydroxy-7-methylbenzo-2, 1, 3-thiadiazoles (II and III) melt at 114–115°, 110–112°, 100–102° C, respectively, after recrystallization from water [2–4], but after recrystallization from petrol ether [5] they melt at 128–129°, 124–125°, and 119–120° C [5]. In this connection we recrystallized these phenols repeatedly from petrol ether after recrystallizing them from water, and their melting points rose as expected [5]. On the other hand, the compounds with melting points 128–129°, 124–125°, 119–120° C (ex petrol ether), after repeated crystallization from water melted at 114–115°, 110–112°, 100–102° C, respectively.For Part XXXVIII see [1].     

Effect of lithium oxide dopants on electrophysical and sorption properties of zinc oxide

The effects of lithium oxide dopants (0.5–0.8 at. % Li) on the electrophysical and sorption properties of ZnO were studied in the temperature range from 150 °C to 410 °C. The introduction of lithium increases the activation energy of the conductivity of ZnO, decreases its conductivity, and increases the amount of S0₂ sorbed. Two forms of chemisorbed SO₂ (donor and acceptor) are observed on the surface.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1096–1100, May, 1996.     

Mikroskopische Untersuchungen an polymorphen Substanzen

Zusammenfassung Es wird darauf hingewiesen, daß die Polymorphie bei organischen Verbindungen durchaus keine Seltenheit ist, daß sie vielmehr eine auch in der organischen Chemie sehr weit verbreitete Erscheinung darstellt.Die mikroskopische Arbeitsweise ist bei der Untersuchung polymorpher Substanzen geradezu unersetzlich.Die bei polymorphen Substanzen auftretenden Umwandlungserscheinungen werden kurz beschrieben.Durch die neu vorliegenden Untersuchungen konnte bei folgenden Substanzen Polymorphie festgestellt werden:Benzoesäurephenylester. Drei Modifikationen: Fp. 69°, 56,5° und 51 bis 52°.Benzoyl-l-ecgonin. Vier Modifikationen: Fp. etwa 202 bis 203°, etwa 179 bis 181°, etwa 130 bis 135°, etwa 100 bis 105°.Chinizarin. Enantiotrop. Modifikation I, orange: Fp. 195°; Modifikation II, rot: Fp. 201°.Chrysophansäure. Zwei Modifikationen: Fp. 195° und 190°.Cumarin. Drei Modifikationen: Fp. 68,5°, 64,5°, 55°.Gallussäure: Zwei Modifikationen: Fp. etwa 258 bis 265° und etwa 225 bis 230°.Hydrochinon. Zwei Modifikationen mit demselben Fp. 172,5°.Morphinhydrochlorid. Zwei Modifikationen: Fp. etwa 295 bis 300° und 280 bis 284°.Nipagin. Sechs Modifikationen: Fp. 127°, 116°, 110°, 110°, 109° und 106°.o-Nitrobenzaldehyd. Zwei Modifikationen: Fp. 42 bis 42,5° und 39°.m-Nitrobenzaldehyd. Zwei Modifikationen: Fp. 56 bis 57° und ungefähr 51°.p-Nitrobenzaldehyd. Zwei Modifikationen: Fp. 105° und 104 bis 104,5°.Phenanthrenchinon. Zwei Modifikationen: 210 bis 211° und 207°.Veronal. Vier Modifikationen: Fp. 190°, > 183° < 190°, 183°, 176°.m-Xylenol. Zwei Modifikationen: Fp. 62 bis 63° und ungefähr 55°.

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Summary It is pointed out that polymorphism in organic compounds is not rare, but is a widely-occurring phenomenon in organic chemistry. The use of the microscope is indispensable in the investigation of polymorphous substances.A brief account is given of the transition phenomena occurring in the case of such substances.By means of the present new investigations, the existence of polymorphism among the following substances has been established:Phenyl benzoate: 3 forms, m. p. 69°, 56,5°, and 51° to 52°.Benzoyl-l-ecgonine: 4 forms, m. p. ca. 202° to 203°, 179° to 181°, 130° to 135°, and 100° to 105°.Quinizarine: enantiotropic. Modification 1, orange, m. p. 195°; modification 2, red, m. p. 201°.Chrysophanic acid: 2 forms, m. p. 195° and 190°.Coumarine: 3 forms, m. p. 68,5°, 64,5°, and 55°.Gallic acid: 2 forms, m. p. ca. 258° to 265° and 225° to 230°.Hydroquinone: 2 forms, with identical m. p. 172,5°.Morphine hydrochloride: 2 forms, m. p. ca. 295° to 300° and 280° to 284°.Nipagine: 6 forms, m. p. 127°, 116°, 110°, 110°, 109°, and 106°.o-Nitrobenzaldehyde: 2 forms, m. p. 42° to 42,5° and 39°.m-Nitrobenzaldehyde: 2 forms, m. p. 56° to 57° and ca. 51°.p-Nitrobenzaldehyde: 2 forms, m. p. 105° and 104° to 104,5°.Phenanthrenequinone: 2 forms, m. p. 210° to 211° and 207°.Veronal: 4 forms, m. p. 190°, > 183° < 190°, 183°, and 176°.m-Xylenol: 2 forms, m. p. 62° to 63° and approx. 55°.

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Résumé On indique que la polymorphie des combinaisons organiques n'est absolument pas une rarité mais qu'elle est plutôt un phénomène très répandu aussi dans la chimie organique.La méthode microscopique est inévitable pour la recherche des substances polymorphes.On décrit aussi les phénomènes de transformation en cas de polymorphie.Par ces recherches nouvelles on trouva la polymorphie chez les substances suivantes:Benzoate de phényle: 3 modifications: p. f. 69°, p. f. 56,5°, p. f. 51 à 52°.Benzoyle-l-ecgonine: 4 modifications: p. f. ca. 202 à 203°, p. f. ca. 179 à 181°, p. f. ca. 130 à 135°, p. f. ca. 100 à 105°.Quinizarine: modification énantiotrope (orangé) I: p. f. 195°; modification énantiotrope (rouge) II: p. f. 201°.Acide chrysophanique: 2 modifications: p. f. 195°, p. f. 190°.Coumarine: 3 modifications: p. f. 68,5°, p. f. 64,5°, p. f. 55°.Acide gallique: 2 modifications: p. f. ca. 258 à 265°, p. f. ca. 225 à 230°.Hydroquinone: 2 modifications: p. f. (pour les 2 modifications le même) 172,5°.Chlorhydrate de morphine: 2 modifications: p. f. ca. 295 à 300°, p. f. 280 à 284°.Nipaguine: 6 modifications: p. f. 127°, 116°, 110°, 110°, 109°, 106°.1,2-Nitrobenzaldéhyde: 2 modifications: p. f. 42 à 42,5°, 39°.1,3-Nitrobenzaldéhyde: 2 modifications: p. f. 56 à 57°, ca. 51°.1,4-Nitrobenzaldéhyde: 2 modifications: p. f. 105°, 104 à 104,5°.Phénanthrène-quinone: 2 modifications: p. f. 210 à 211°, 207°.Véronal: 4 modifications: p. f. 190°, > 183° < 190°, 183°, 176°.1,3-Xylénole: 2 modifications: p. f. 62 à 63°, 55° (à peu près).

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(Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.)     

New fluorinated polymers bearing pendant phosphonic groups for fuel cell membranes: Part 1 synthesis and characterizations of the fluorinated polymeric backbone

Radical copolymerizations of chlorotrifluoroethylene (CTFE) with vinyl ethers such as 2-chloroethyl vinyl ether (CEVE) and ethyl vinyl ether (EVE) were performed at 75 °C in the presence of peroxide initiator. Three copolymers were obtained and characterized by means of both NMR and elemental analysis. Then, the chlorine atoms in the side chains were converted into iodine atoms by nucleophilic substitution, which was monitored by ¹H NMR spectroscopy. A series of five copolymers with different amounts of iodine atoms in the side chains were thus obtained. These copolymers exhibited molecular weight values of about 25,000 g mol⁻¹, and the thermal analysis of the copolymers showed a starting degradation from about 220 °C. The T_g values were in the range of 34-41 °C and showed a linear dependence versus the content of iodine atoms.     

A molecular orbital study of the rotation about the C-C bond in 1,3-butadiene

The geometry and energy of 1,3-butadiene have been calculated using the 6-311G** basis set as a function of the CCCC dihedral angle-0 ° (trans), 30 °, 60 °, 75 °, 90 °, 120 °, 135 °, 150 °, 165 ° and 180 ° (cis)-assuming that the vinyl groups remain planar. Potential minima are located at 0 ° and 141.4 °, with the trans structure more stable than the gauche by 13.2 kJ mol^–1. Potential maxima are located at 76.7 °, giving a barrier height of 25.4 kJ mol^–1 relative to the trans structure, and at 180 ° giving a barrier height of 3.0 kJ mol^–1 relative to the 141.4 °-gauche structure. Using the 6-31G* basis set the inclusion of electron correlation, accounting for about 52% of the correlation energy, was found to produce no significant change in the shape of the potential energy curve. The magnitude of the expectation energy differences is such that both barriers with respect to the 14l.4 °-gauche maximum structure can be categorized unequivocally as attractive-dominant, whereas the values for the energy barrier with respect to the trans structure, although characteristic of a repulsive-dominant barrier at the 6–311G** level, are sufficiently small that higher level calculations might give the opposite result. Analysis of V _nn for the conversion reactions cis 150 °-gauche, trans 60 °-gauche, and trans 90 °-gauche in terms of the individual contributions from the various internuclear interactions shows that nonbonded interactions are important, not only in initiating the destabilization of the crowded cis structure, but also through-out the entire range of CCCC dihedral angles, 0 ° to 180 °.     

The influence of biotic and abiotic factors on the rate of degradation of poly(lactic) acid (PLA) coupons buried in compost and soil

Poly(lactic) acid (PLA) is a compostable biopolymer and has been commercialised for the for the manufacture of short-shelf life products. As a result, increasing amounts of PLA are entering waste management systems and the environment; however, the degradation mechanism is unclear. While hydrolysis of the polymer occurs abiotically at elevated temperature in the presence of water, potential catalytic role for microbes in this process is yet to be established. In this study, we examined the degradation of PLA coupons from commercial packaging at a range of temperatures (25°, 37°, 45°, 50° and 55 °C) in soil and compost and compared with the degradation rates in sterile aqueous conditions by measuring loss of tensile strength and molecular weight (Mw). In addition, in order to assess the possible influence of abiotic soluble factors in compost and soil on degradation of PLA, degradation rates in microorganism-rich compost and soil were compared with sterile compost and soil extract at 50 °C. Temperature was determined to be the key parameter in PLA degradation and degradation rates in microorganism-rich compost and soil were faster than in sterile water at temperatures 45° and 50 °C determined by tensile strength and Mw loss. Furthermore, all tensile strength was lost faster after 30 and 36 days in microorganism-rich compost and soil, respectively, than in sterile compost and soil extract, 57 and 54 days, respectively at 50 °C. Significantly more Mw, 68% and 64%, was lost in compost and soil, respectively than in compost extract, Mw, 53%; and in soil extract, 57%. Therefore, degradation rates were faster in microorganism-rich compost and soil than in sterile compost and soil extract, which contained the abiotic soluble factors of compost and soil at 50 °C. These comparative studies support a direct role for microorganisms in PLA degradation at elevated temperatures in humid environments. No change in tensile strength or Mw was observed either 25° or 37 °C after 1 year suggesting that accumulation of PLA in the environment may cause future pollution issues.     

Synthesis of N,N-dialkylaminobenzonitriles and halo-(N,N-dialkyl)benzamidines by reaction of halobenzonitriles with lithium amides

3- and 4-N,N-Dialkylaminobenzonitriles and 4-chloro-(N,N-dialkyl)benzamidines were isolated by reacting 4-chlorobenzonitrile with hindered lithium amides under thermodynamic (0 °C) and kinetic control conditions (−78 °C), respectively. As previously reported, a benzyne mechanism seems to be confirmed since N,N-dialkylaminobenzonitriles are formed. Only benzamidines were isolated in fair to high yields at both 0 °C and −78 °C with non-hindered lithium amides. Exploitation and mechanistic rationale of the reaction of different halobenzonitriles are also reported.     

Morphology and mechanical properties of ultrahigh molecular weight polypropylene prepared by gelation/crystallization at various temperatures

Films of ultrahigh molecular weight (5.4×10⁶) polypropylene were produced by gelation/crystallization at various temperatures from dilute decalin solutions according to the method of Smith and Lemstra. The temperatures chosen were 20°, 30°, 50°, and 60°C. With increasing the temperature, the long period and crystallinity of the resultant gel film increased. By contrast, when the films were stretched up to 50 } 60 times, the increases in Young's modulus and crystallinity become more significant, as the temperature of the gelation/crystallization became lower. This interesting phenomenon is thought to be due to the dependence of the number of entanglements on the temperatures concerning gelation/crystallization and evaporation of solvent from the gel to form a film.     

Micellization and surface activity ofn-alkyldimethylaminopropanesulfonates in aqueous solutions

Surface tension experiments were performed on severaln-alkyldimethylaminopropanesulfonate aqueous solutions at 15°, 25°, and 35°C. The critical micellar concentrations have been obtained and the surface properties calculated. The enthalpic and entropic contributions to either micellization and adsorption processes have been discussed. The observed properties have been related to the zwitterionic character of these surfactants.     

Zero-point average structures of acetyl chloride and acetyl bromide

The zero-point average structures of acetyl chloride and acetyl bromide have been determined by the combined use of their moments of inertia and average distances, obtained by means of microwave spectroscopy and electron diffraction. The r_z parameters determined are as follows: r_z(CO) = 1.185 ± 0.003 Å, r_z(C-Cl) = 1.796 ± 0.002 Å, r_z(C-C) = 1.505 ± 0.003 Å, r_z(C-H) = 1.092 ± 0.005 Å, φ_z(OCCl) = 121.2 ± 0.6°, φ_z(CCCl) = 111.6 ± 0.6°, φ_z(HCH) = 108.8 ± 0.8° and tilt(CH3) = 1.3 ± 1.0°, for chloride; r_z(CO) = 1.181 ± 0.003 Å, r_z(C-Br) = 1.974 ± 0.003 Å, r_z(C-C) = 1.516 ± 0.003 Å, φ_z(OCBr) = 122.3 ± 1.5°, φ_z(CCBr) = 111.0 ± 1.5°, φ_z(HCH) = 109.9 ± 1.1°, tilt(CH₃) = 1.9 ± 1.0°, for bromide. The barriers V₃ to internal rotation have been revised to 1260 and 1256 cal mol⁻¹ for the chloride and bromide, respectively.     

The complete closed coexistence curves for 2H,3H,6H,7H,8H-5,8-(Dimethylmethano)-5(R)-methylquinoxaline with water and with deuterium oxide

The complete closed solubility curves for 2H, 3H, 6H, 7H, 8H-5,8-(dimethylmethano)-5(R)-methylquinoxaline with water and with deuterium oxide have been determined. With water the lower critical solution temperature (LCST) was found to be 51.4°C and the critical solution temperature (CST) was found to be 215.0°C. With deuterium oxide the values were 40.4°C for the LSCT and 221.7°C for the CST. The deuterium oxide curve completely encompassed the water curve. Solution compositions at the critical temperatures were also determined.     

Enthalpies of Dilution of Aqueous Solutions of HCl, MgCl2}, CaCl2, and BaCl2 at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of BaCl₂ at 300°C and 11.0 MPa, MgCl₂, CaCl₂, and BaCl₂ at 325°C and 14.8 MPa, and at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of MgCl₂ and CaCl₂ at 300°C and 10.3 MPa and for aqueous solutions of HCl at 250, 275, and 300°C at 10.3 MPa and 320°C at 12.8 MPa were included with the new data at 300°C and 11.0 MPa and at 350°C and 17.6 MPa when fitting the Pitzer parameters. The concentration range of the chloride solutions was 0.5 to 0.02 molal. Parameters for the Pitzer excess Gibbs ion–interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat-capacity changes for the association of alkaline earth metal ions and H⁺ with chloride ion were estimated from the heat data. For all systems, the enthalpy and entropy changes are positive and show accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

Quantum mechanical calculations on barriers to internal rotation

The barrier to internal rotation in hydrazine has been studied by the non empirical SCF-LCAO method, in the gaussian approximation. Calculations have been performed for values 0°, 60°, 120°, 180° and 94° (equilibrium conformation) of the dihedral angle, with all other bond angles and bond lengths fixed. The gaussian basis set used consisted of 9s + 3p for nitrogen and 3s for hydrogen. The calculated total molecular energy for the equilibrium conformation, –111.030 a.u., is 0.865 a.u. higher than the experimental value. The theoretical dihedral angle 94° is in good agreement with experimental indications of 90–95°. The computed rotation barriers are 11.5 kcal/mole for the cis position and 4.7 kcal/mole for the trans.

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Zusammenfassung Die Rotationsbarriere von Hydrazin wurde mit Gaußfunktionen nach einer nicht-empirischen SCF-LCAO-Methode studiert. Rechnungen wurden für die Werte 0°, 60°, 120°, 180°, 94° (Gleichgewichtslage) des Diederwinkels durchgeführt, wobei alle übrigen Bindungswinkel und -längen festgehalten wurden. Der Basissatz von Gaußfunktionen bestand aus 9s- und 3p Funktionen für Stickstoff und 3s-Funktionen für Wasserstoff. Die berechnete Gesamtenergie der Gleichgewichtskonformation, –111,030 at. E. liegt um 0,865 at. E. höher als der experimentelle Wert. Der theoretische Diederwinkel von 94° stimmt gut mit den experimentellen Daten von 90–95° überein. Die berechneten Rotationsbarrieren sind 11,5 kcal/mol für die cis- und 4,7 kcal/mol für die trans-Lage.

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Résumé La barrière de rotation interne de l'hydrazine a été étudiée par la méthode LCAO-SCF dans l'approximation des orbitales gaussiennes. Les calculs ont été effectués pour des valeurs de l'angle dièdre de 0°, 60°, 120°, 180° et 94° (valeur correspondant à l'équilibre), tout en gardant constants les autres angles et les longueurs des liaisons. On obtient pour la position d'équilibre une énergie moléculaire totale de –111.030 u.a., l'écart avec l'énergie expérimentale étant de 0.865 u.a. La valeur obtenue pour l'angle dièdre, 94°, est en bon accord avec les indications expérimentales de 90–95°. Les barrières de rotation théoriques sont de 11.5 kcal/mole pour la position cis et de 4.7 kcal/mole pour la position trans.