Theoretical Investigation of the C2H2B2 Potential Energy Surface

Fifteen unique energy minima and thirteen transition states on the C ₂H₂B₂ potential surface have been located and optimized at the MP2 level of theory with the 6-311G(d,p) basis set. The planar four-membered ring isomer , 1, an analog of cyclobutadiene, is a transition state lying 37 kcal/mol above the nonplanar four-membered ring , 3. The planar , 10, is the second most stable species found, lying 72.2 kcal/mol below 3. The nonplanar, butterfly-shaped ring, 4, is a local minimum 33.7 kcal/mol more stable than 3. A four-membered ring isomer with alternating boron–carbon locations, , 5, lies 67.0 kcal/mol below 3 and 33.3 kcal/mol below 4. The ring of 5 is planar with one hydrogen above and one below the plane (C _2h symmetry). The borylene-substituted boracyclopropene, , 8, is a planar local minimum lying 36.0 kcal/mol above 5. The most stable C₂H₂B₂ isomer found was the planar, four-membered ring system 22 (D _2h symmetry) composed of two BCC three-membered rings fused across the C-C bond. Structure 22 lies 22.2 kcal/mole below 10, 105.4 kcal/mol below 3, 71.7 kcal/mol below 4, and 38.2 kcal/mol below 5. Isomer 22 is the structural analog of the trialene form of C₄H₂. The most stable linear isomer, HB BH, 26, was surprisingly 50.5 kcal/mol less stable than 22. The stabilities of the two most stable cyclic isomers 10 and 22 may be explained by aromaticity.     

Molecular Structure and Conformation of p-Bis(trimethylsilyl)benzene: A Study by Gas-Phase Electron Diffraction and Theoretical Calculations

The molecular structure and conformation of p-bis(trimethylsilyl)benzene have been investigated by gas-phase electron diffraction, ab initio MO calculations at the HF/6-31G*, MP2(f.c.)/6-31G*, and B3LYP/6-31G* levels, and MM3 molecular mechanics calculations. The calculations indicate the syn- and anti-coplanar conformations, with two bonds in the plane of the benzene ring, to be energy minima. The perpendicular conformations, with two bonds in a plane orthogonal to the ring plane, are transition states. The two coplanar conformers have nearly the same energy with a low interconversion barrier, 0.3–0.5 kJ mol^–1. The calculated lengths of the and bonds differ by only a few thousandths of an angstrom, in agreement with electron diffraction results from molecules containing either or bonds. The geometrical distortion of the benzene ring in p-bis(trimethylsilyl)-benzene may be described by superimposing independent distortions from each of the two SiMe₃ groups. The electron diffraction intensities from a previous study (Rozsondai, B.; Zelei, B.; Hargittai, I. J. Mol. Struct. 1982, 95, 187) have been reanalyzed, imposing constraints from the theoretical calculations, and using a model based on a 1:1 mixture of the two coplanar conformers. The effective torsion angles of the SiMe₃ groups may indicate nearly free rotation. Important geometrical parameters from the present electron diffraction analysis are , and . While the mean bond lengths are virtually the same from the previous and present analyses, the new ipso angle is in better agreement with the MO calculations [HF, 116.9° MP2(f.c.), 117.1° B3LYP, 116.9°].     

Configuration and conformation of substituted 1,3,2-dioxaarsenanes

The configuration and conformations often 2-, 4-, and 5-substituted 1,3,2-dioxaarsenanes were studied from their PMR spectra. Inversion of the shielding constants of protons in the 4, 6, and 5 positions and of methyl groups in the 5 position was established, and the axial orientation of the As-Cl and As-OR bonds, the equatorial orientation of the 4-CH₃ group, and the chair conformation of the six-membered heteroring were proved. The anisotropies of the diamagnetic susceptibility were estimated for the first time: and (dipole approximation); and (nondipole approximation). The cyclic torsion angle (= 58°) as found for 2-chloro-1,3,2-dioxaarsenane by the R-factor method. Conclusions regardiwng the conformation of the ring and substituents were confirmed by a study of the specific effect of an aromatic solvent on the position of the resonance lines.Communication I from the series Investigation of the Stereochemistry of Organic Arsenic Compounds by NMR Spectroscopy.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 457–463, April, 1973.     

1H and 13C NMR spectra,isomers, and imine-enamine tautomers of N-(1,2,5-trimethyl-4-piperidylidene)aniline

The product of condensing 1,2,5-trimethylpiperidin-4-one with aniline has been investigated by NMR spectroscopy. Three isomers of N-(1,2,5-trimethyl-4-piperidylidene)aniline have been identified differing in the configuration of the methyl groups at C₂ and C₅ of the piperidine ring and the Z,E isomerism about the C=N bond. Traces of the enamine tautomeric form of the imine were also detected. , , and spin-spin couplings were used to determine the structural configuration of the isomers.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1405–1408, October, 1989.     

Electrical and electro-chemical characterisation of La0.99Fe1−x Ni x O3−δ perovskites

(LFN, 0<x<0.6) perovskites were synthesised by a solid-state route and were characterised by powder XRD, dilatometry, four-point DC conductivity measurements and electro-chemical impedance spectroscopy (EIS) on cone-shaped electrodes using a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte. All the compounds were of single phase, and they belong to either the cubic or the hexagonal crystal system. The thermal expansion coefficient (TEC) was in the range 10.7*10⁻⁶ K⁻¹ to 13.4*10⁻⁶ K⁻¹, which continued to increase with increasing nickel content. The highest electronic conductivity was measured for the composition giving a value of 670 S/cm at 380 °C. The highest electro-chemical performance was measured for the composition giving an area specific resistance as low as 5.5 Ωcm² at 600 °C based on EIS measurements on a cone-shaped electrode. Composite cathodes made from and CGO10 revealed a rather low performance due to an un-optimised micro-structure.

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Kinetics and mechanism of the reaction of a quasi-aromatic copper(II) complex, [Cu(PnAO)-6H]0, with formaldehyde

The kinetics of the reaction of CH₂O with a quasi-aromatic metal complex (1,1,2,8,9,9-hexamethyl-4,6-dioxa-5-hydro-3,7,10,14-tetraazacyclotetradecane-2,7,10,12-tetraene)copper(II), [Cu(PnAO)-6H]⁰ (AH), have been studied spectrophotometrically under neutral conditions in 1/3(v/v) MeOH–H₂O. The Cu, 2N, 3C quasi-aromatic heterocyclic ring in AH is highly reactive towards CH₂O at the central-aromatic-carbon atom, C(12) and the following reaction mechanism is proposed. The compounds AH, A—CH₂OH and A—CH₂—A were isolated and identified by i.r spectroscopy and by elemental analysis. The kinetic data supported the proposed reaction sequence. All reactions were second order overall. The rate constants and corresponding activation parameters for every step were obtained and are discussed.     

Molecular Structure of tert-Butylazide: A Gas-Phase Electron Diffraction and Quantum Chemical Study

The molecular structure of tert-butylazide has been determined by gas-phase electron diffraction and quantum chemical calculations. The HF/6-31G* and B3LYP/6-31G** calculations yielded near C _s symmetry for the tert-butyl group, anti conformation of the (C)N—N bond with respect to one of the bonds, and an essentially free rotation around the bond with a 0.34 kcal/mol energy difference between syn and anti conformations of the CNNN moiety, the anti being the more stable form. The electron diffraction analysis was carried out by modeling a mixture of conformational isomers, generated by rotating the terminal nitrogen of the azide group, using a computed rotational potential. The data are consistent with C _s symmetry for the tert-butyl group. The bond, however, was found to be rotated out of the anti position, with respect to one of the bonds, by 12.5(12)°. The electron diffraction analysis yielded the following bond lengths (r _g), bond angles, and torsional angles: , .     

Triterpene glycosides ofHerniaria glabra. I

Conclusions FromHerniaria glabra L. two triterpene glycosides, glabrosides B and C, have been isolated. We have shown that the first is the -D-glucopyranosyl-(16)--D-glucopyranoside, and the second is the Khimiya Prirodnykh Soedinenii, Vol. 6, No. 3, pp. 307–311, 1970     

Luminescence Behavior of Polynuclear Alkynylcopper(I) Phosphines

A series of soluble trinuclear and tetranuclear copper(I) complexes containing ₃-^l acetylides , and have been synthesized and shown to exhibit rich photoluminescent behavior at room temperature. The electrochemistry of the trinuclear Cu(I) acetylide complexes and the excited-state redox properties of have been investigated. The X-ray crystal structures of and have been determined.     

Dissociation Constants for Citric Acid in NaCl and KCl Solutions and their Mixtures at 25 °C

The constants for the dissociation of citric acid (H₃C) have been determined from potentiometric titrations in aqueous NaCl and KCl solutions and their mixtures as a function of ionic strength (0.05–4.5 mol-dm^–3) at 25 °C. The stoichiometric dissociation constants (K_i^*)

Effect of the mediator in feedback mode-based SECM interrogation of indium tin-oxide and boron-doped diamond electrodes

Indium tin-oxide (ITO) and polycrystalline boron-doped diamond (BDD) have been examined in detail using the scanning electrochemical microscopy technique in feedback mode. For the interrogation of electrodes made from these materials, the choice of mediator has been varied. Using ferrocene methanol (FcMeOH), and approach curve experiments have been performed, and for purposes of comparison, calculations of the apparent heterogeneous electron transfer rates (k _app) have been made using these data. In general, it would appear that values of k _app are affected mainly by the position of the mediator reversible potential relative to the relevant semiconductor band edge (associated with majority carriers). For both the ITO (n type) and BDD (p type) electrodes, charge transfer is impeded and values are very low when using FcMeOH and as mediators, and the use of results in the largest value of k _app. With ITO, the surface is chemically homogeneous and no variation is observed for any given mediator. Data is also presented where the potential of the ITO electrode is fixed using a ratio of the mediators and In stark contrast, the BDD electrode is quite the opposite and a range of k _app values are observed for all mediators depending on the position on the surface. Both electrode surfaces are very flat and very smooth, and hence, for BDD, variations in feedback current imply a variation in the electrochemical activity. A comparison of the feedback current where the substrate is biased and unbiased shows a surprising degree of proportionality.Dedicated to Alan, a good friend and colleague on his 60th birthday.     

Polarization Fourier transform infrared spectroscopy on ionic single crystal surfaces: Davydov splittings, adsorbated structures and 2D-phase transitions on NaCl(100) and MgO(100)

Polarized infrared spectra of adsorbates on NaCl(100) and MgO(100) single crystal cleavage planes reveal Davydov splittings, structures with adsorbate orientations and/or 2D-phase transitions, in concert with diffraction studies. CO₂ on NaCl shows the sharpest adsorbate spectra known ( ).     

First and second thermodynamic mixing functions of ethylbenzene+n-nonane, +n-decane,and+n-dodecane at 25 and 45°C

Isothermal compressibilities _T and isobaric thermal expansion coefficients _p have been determined for mixtures of ethylbenzene+n-nonane, +n-decane, and +n-dodecane at 25 and 45°C in the whole range of composition. The excess functions and have been obtained at each measured mole fraction. The first one is zero for ethylbenzene +n-nonane, positive for ethylbenzene +n-decane, and +n-dodecane and increases with chain length n of the n-alkane. The function is positive for the three studied systems and nearly constant with n. Both mixing functions increase slightly with temperature. From this measurement and supplementary literature data of molar heat capacities at constant pressure C _P , the isentropic compressibilities _S, the molar heat capacities at constant volume C _V and the corresponding mixing functions have been calculated at 25°C. Furthermore, the pressure dependence of excess enthalpy H ^B , at zero pressure and at 25°C has been obtained from our experimental results of and experimental literature values for excess volume V ^E .     

Synthesis and properties of azoles and their derivatives. 23. Electron impact mass spectrometry of regio- and stereoisomeric diarylnitro-Δ2-isoxazolines

It was shown that the general paths of dissociation of molecular ions of 3-phenyl-4(5)-aryl-5(4) nitro-²-isoxazolines involve the primary elimination of the NO ₂ ^. , HNO₂, and OCHNO₂ particles, and also the formation of the C₆H₅CN^+., C₆H₅ ⁺, ions and substituted tropylium cations. The 3,5- and 3,4-diaryl isomers differ most sharply in the probability of formation of ions, the peaks of which are maximal in the first case. The mass spectra of cis- and trans-isomers in the 3,5-diarylisoxazoline series differ little quantitatively.For Communication 22, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 88–94, January, 1990.     

Kinetics and mechanism of oxidation of hydroxylamine by tetrachloroaurate(III) ion

The oxidation of H₂NOH is first-order both in [NH₃OH⁺] and [AuCl₄ ^–]. The rate is increased by the increase in [Cl^–] and decreased with increase in [H⁺]. The stoichiometry ratio, [NH₃OH⁺]/[AuCl₄ ^–], is 1. The mechanism consists of the following reactions.

The thermal decomposition of zirconium oxyhydroxide

The thermal decomposition of zirconium oxyhydroxides prepared by the mixture of aqueous zirconium oxychloride solutions and aqueous solutions of sodium hydroxide or ammonium hydroxide under various conditions has been examined by thermogravimetry, differential thermal analysis, X-ray diffraction study and infrared spectrophotometry. As a result, it is seen that the thermal decomposition of zirconium oxyhydroxide, in which the composition is ZrO_2-x(OH)_2xyH₂O where x2 and 1y<2, proceeds according to the following process:

Thermodynamics of Solutions of Trimethyl Aluminum and Trimethyl Gallium with Tetramethyl Tin

The enthalpies and entropies of evaporation of Al(CH₃)₃–Sn(CH₃)₄and Ga(CH₃)₃–Sn(CH₃)₄solutions were determined. It was established that solvates are formed in these systems and that the dissociation energies of specific interactions in them change in the following order: (10.3) > > > (4.08 kJ mol^–1), (6.52) > (5.14) > > (4.08 kJ mol^–1).     

Atranes

A method of synthesizing hitherto unknown 1-aroxysilatranes (R=aryl) is worked out. It is based on transesterification of lower tetraalkoxysilanes with an equimolecular mixture of triethanolamine and the appropriate phenol (naphthol). Using the method, 12 compounds of the indicated type have been prepared and characterized, the yields in the main exceeding 90%.For Part VII see [1].     

Ester Elimination: A General Solvent Dependent Non-Hydrolytic Route to Metal and Mixed-Metal Oxides

Molecular routes to metal oxides has become an area of intensescientific interest due to the technological relevance of thesematerials. Molecular routes are proving important as a result ofthe possibility to control the physical and chemical propertiesof the final materials.We have chosen to study non-hydrolytic methods, namely esterelimination reactions between two prototypical molecularprecursors metal alkoxides, M(OR)_n, and metal carboxylates, M(O₂CR)_n, to synthesize metal oxides: This method allows for the synthesis of pure metal oxides bycomplete elimination of the organic supporting ligands withconcomitant formation of M-O-M bridges.Furthermore, incomplete esterelimination can lead to isolation of molecular clusters asintermediates which can also be used as building blocks for theformation of metal oxides with controlled microstructure.Here we report a series of reactions between Sn and Si alkoxidesand carboxylates designed to gain further insight into thefactors governing ester elimination reactions. By choosingcompounds with varying coordination environments and stericaccessibility we have devised a set of criteria which shouldallow for successful ester elimination between metal alkoxide andcarboxylate compounds. Furthermore we have also shown theability of ester elimination derived molecular clusters withspecific microstructure to be used in the synthesis of bulkmaterials retaining the structural attributes of the precursor cluster.     

Octahedral ruthenium(II) alkenyl complexes containing {\text{N}}{\text{S}} coordinated heterocyclic ligands

Summary Hexacoordinated ruthenium(II) alkenyl complexes of the type Ru(CO)(CR=CHPh)( )(PPh₃)₂ have been prepared from coordinately unsaturated -vinyl complexes [Ru(CO)Cl(CR=CHPh)(PPh₃)₂] (R = H or Ph) and the sodio-derivative of the containing heterocyclic ligands [ = 3,4-substituted 1,2,4-triazole-5-thione and 5-alkylthio-1,3,4-thiadiazole-2-thione] in a CH₂Cl₂/MeOH mixture at ambient temperature. The complexes were characterized by their elemental analysis, i.r., ¹H and ³¹P n.m.r. spectra. An octahedral structure with transphosphorus ligands has been assigned on the basis of the spectral data.