Chemiluminescence Determination of Cyanide Ions

It was found that alkaline solutions of luminol exhibit chemiluminescence in the presence of p-nitrobenzaldehyde (p-NBA), hemin, and cyanide ions. Air oxygen dissolved in the solutions is an essential component of the process. The kinetics of luminol chemiluminescence in the presence of p-NBA, hemin, and cyanide ions indicates the catalytic nature of the process. A scheme was proposed for the series of reactions resulting in chemiluminescence and generated by superoxide radicals formed in the p-NBA-catalyzed reaction between hemin-activated air oxygen and hydrated p-NBA species. A procedure was developed with a determination limit of (1.0 ± 0.3) × 10^?7 mg/mL (n = 5, P = 0.95) for cyanide ions.     

Kinetic and thermodynamic parameters of hydrogen release during the heterogeneous catalytic dehydrogenation of <Emphasis Type="Italic">cis</Emphasis>- and <Emphasis Type="Italic">trans</Emphasis>-isomers of perhydro-m-terphenyl

Comparative studies on the temperature dependence of the dehydrogenation of cis- and trans-isomers of perhydro-m-terphenyl are performed in a flow catalytic reactor. Rate constants and equilibrium constants of all elementary acts of this reaction are calculated on basis of experimental data using the KINET 0.8 program for the mathematical modeling of the kinetics of complex reactions. The resulting data indicate that perhydro-m-terphenyl cis- and trans-isomers structural differences have no appreciable effect on dehydrogenation.     

About selective methods of synthesis of 6-<Emphasis Type="Italic">tert</Emphasis>-butyl-2-methylphenol and 6-<Emphasis Type="Italic">tert</Emphasis>-butyl-2,4-dimethylphenol

Vapor phase catalytic methylation with methanol of 2-tert-butylphenol at the temperature 280–300°C proceeds selectively with formation of 6-tert-butyl-2-methylphenol. Elevating reaction temperature above 300°C leads to formation of 2,6-dimethylphenol. Reaction of 2-tert-butylphenol with methanol in alkaline medium in the presence of zinc oxide is shown to lead initially to formation of a mixture of calixarenes and methylenebisphenols that at elevated temperature exert splitting leading in future to 6-tert-butyl-2,4-dimethylphenol. Obtaining it in this reaction from 2,2′-methylenebis-(6-tert-butyl-4-methylphenol) proceeds selectively. Pathways of the reductive methylation of methylenebisphenols with methanol in alkaline medium is considered.     

Use of the bond-projected superposition principle in determining the conditional probabilities of orbital events in molecular fragments

The problem of defining and determining the multi-conditional probabilities of many-orbital events in the chemical bond system of a molecule is addressed anew within theoretical framework of the one-determinantal orbital representation of molecular electronic structure. Its solution is vital for determining the information-theoretic indices of bond couplings between molecular fragments or the reactant/product subsystems in chemical reactions. The superposition principle of quantum mechanics, appropriately projected into the occupied subspace of molecular orbitals, is used to condition the atomic orbitals or general basis functions of the self-consistent-field calculations. The conditional probabilities between the subspaces of basis functions (atomic orbitals) are derived from an appropriate generalization of the bond-projected superposition principle. They are then used to define the triply-conditional probabilities, relating one conditional event to another. The resulting expression is shown to satisfy the relevant non-negativity and symmetry requirements. It is applied to probe the π-bond coupling in butadiene and benzene.     

Enantioselective catalysis of Suzuki reaction with planar-chiral <Emphasis Type="Italic">CN</Emphasis>-palladacycles: competition of two catalytic cycles

The investigations of the catalysis of atroposelective Suzuki reaction with chiral CN-palladacycles showed that two competing catalytic cycles operate in this process, the relative contributions of each of them depend on the structure of the catalyst and reaction conditions. The reactions in aprotic medium at reduced temperature predominantly follow the pathway, in which the structure of palladacycle was retained, thus providing enantioselectivity up to 53% ee, when a nonmetallocene planar-chiral iminate CN-dimer was used as the catalyst. The structure of the μ-iodide cyclopalladated CN-dimer recovered upon reaction completion was confirmed by X-ray diffraction and spectroscopic studies of its triphenylphosphine derivative.     

How does the extent of substitution of methane with chlorine influence the mechanism and kinetics of the reactions between chloromethanes and atomic chlorine

A theoretical investigation of the reaction mechanism and kinetics of the reaction between chloromethanes CH_4–xCl_x (x = 1–3) and chlorine atoms was performed. The height of the reaction barrier was found to decrease with the degree of substitution of chloromethanes with atomic chlorine. A direct dynamics method was employed to study the kinetic nature of these hydrogen-abstraction reactions. The sequence of calculated reaction rate coefficients is: k(CH₃Cl + Cl) < k(CH₂Cl₂ + Cl) < k(CHCl₃ + Cl).     

Zur Strukturaufklärung der Isomeren von α-Oximinocarbonsäureestern

The theoretical and experimental dipole moments for a number ofsyn- andanti-α-oximino esters are determined.NMR- andIR-spectra are reported. On the basis of these and previous chemical investigations the preferred steric structures of thesyn- andanti-forms are ascertained. Two rotational isomers exist in the same degree with thesyn-forms. Due to resonance effects and hydrogen bonds they are relatively stable.     

Electron density distribution in crystals of the antimony(V) spiroendoperoxide complexes

The experimental and theoretical electron densities in complexes [6-(2,6-di-iso-propylphenyl)imino-2,4-di-tert-butylcyclohexa-2,4-diene-1-peroxo-1-olato-N,O,O′]tris(p-chlorophenyl)antimony(V), (p-Cl–C₆H₄)₃Sb(2,6-iso-Pr–Ph–AP) · O₂ (I), and [6-(2,6-dimethylphenyl)imino-2,4-di-tert-butylcyclohexa-2,4-diene-1-peroxo-1-olato-N,O,O′]tris(p-chlorophenyl)antimony(V), (p-Cl–C₆H₄)₃Sb(2,6-Me–Ph–AP) · O₂ (II), where AP is 4,6-di-tert-butyl-N-o-iminobenzoquinone dianion, are studied on the basis of high-resolution X-ray diffraction data and theoretical calculations using the density functional theory (B3LYP/DGDZVP). The nature of chemical bonds and the charge distribution on atoms are studied, and the energy of molecular oxygen addition to the Sb(V) o-aminophenolate complexes is estimated. The structures are deposited with the Cambridge Crystallographic Data Centre (CIF files CCDC nos. 1560600 (spherical refinement) and 1560601 (multipole refinement) for complex I; 1560602 (spherical) and 1560603 (multipole) for complex II).     

Study of the chemical mechanism of color reactions of selenium(IV) with <Emphasis Type="Italic">o</Emphasis>-arylenediamines

o-Arylenediamines are promising for the photometric determination of selenium. The search for new reagents of this group is desirable. To obtain information necessary for this purpose, the chemical mechanism of color reactions of selenium(IV) with o-arylenediamines was studied. The optimum conditions of these reactions and the spectrophotometric characteristics of reagents and complexes were found. The ratio of components in the reaction products (piazoselenols) of 1: 1 was determined by elemental analysis, NMR spectroscopy, and the isomolar series method. The formation of the selenium-nitrogen bond was confirmed and the quasiaromatic character of piazoselenols was revealed by IR and NMR spectroscopy. Binding energies of valence orbitals, electron density distribution, and charges of nitrogen and selenium atoms were estimated by x-ray photoelectron spectroscopy. In the case of piazoselenol from 1,2-phenylenediamine, the existence of two tautomeric forms with the oxidation numbers of selenium close to +2 and +4 were found. Piazoselenol based on N-phenyl-1,2-phenylenediamine predominantly occurs as a single compound with the oxidation number of selenium close to +2. The most probable structures of the resulting piazoselenols were proposed, and the probable schemes of the reactions of selenium(IV) with 1,2-phenylenediamine and N-phenyl-1,2-phenylenediamine were justified.     

Reactivity of fluoroalkanes in reactions of coordinated molecular decomposition

Experimental results on the coordinated molecular decomposition of RF fluoroalkanes to olefin and HF are analyzed using the model of intersecting parabolas (IPM). The kinetic parameters are calculated to allow estimates of the activation energy (E) and rate constant (k) of these reactions, based on enthalpy and IPM algorithms. Parameters E and k are found for the first time for eight RF decomposition reactions. The factors that affect activation energy E of RF decomposition (the enthalpy of the reaction, the electronegativity of the atoms of reaction centers, and the dipole–dipole interaction of polar groups) are determined. The values of E and k for reverse reactions of addition are estimated.     

Kinetics of mechanochemical dissolution of chromium in iron

The kinetics of solid Fe–Cr solution formation has been studied during mechanical alloying of Fe and Cr powders taken in an atomic ratio of 80: 20. X-ray diffraction and Mössbauer spectroscopy data have been analyzed within the framework of the energetic approach. It has been established that, in this system, reaction product yield N is related to mechanical energy dose D and specific surface area S of Fe nanograin boundaries in an ideal manner: N ~ D² at S ~ D and N ~ D at S = const.     

Concerted cycloaddition reactions: a study using the parabolic model and quantum chemical modeling

Concerted cycloaddition reactions were studied by the method of intersecting parabolas (M3IP) and quantum chemical calculations. Experimental data were processed within the framework of the M3IP method and an algorithm for calculating the activation energies (E) and rate constants (k) for reactions from the enthalpies of reactions was developed. The parameters E and k for twelve cycloaddition reactions not studied previously were calculated. Factors affecting the activation energies were established and evaluated; these include the enthalpy of reaction, substituents, and the molecular structure of reactants. Quantum chemical modeling and topological analysis of transition states (TS) of six concerted cycloaddition reactions were performed. Depending on structure of the starting olefins, the TS of reactions can have either a symmetric or asymmetric geometry. This influences their electronic structures, the energies of chemical bonds, and the activation energies of reactions. A comparison of the activation energy values obtained from the M3IP and DFT(B3lyp/6-311++G** ) calculations revealed good agreement between them.     

Quantum chemical studies of azoles 3. Thermodynamic stabilities of neutral molecules and intermediates formed in electrophilic substitution of azoles containing three or four heteroatoms

Density functional theory quantum chemical calculations of thermodynamic stabilities in the gas phase and in water were carried out for 1,3,4-oxadiazole and 1,3,4-thiadiazole, 1,2,4-1H-triazole and 1,2,4-4H-triazole, 1,2,3,4-1H-tetrazole and 1,2,3,4-2H-tetrazole molecules, and for cationic and bipolar (carbenoid) intermediates formed by these molecules in electrophilic substitution reactions (with proton as model electrophile) and the results obtained are compared. Differences in the chemical behavior of pairs of isomeric 1H- and 4H-1,2,4-triazoles and 1H- and 2H-tetrazoles are analyzed.     

<Emphasis Type="Italic">N</Emphasis>-Propylphthalimide-substituted bis-(NHC)PdX<Subscript>2</Subscript> complexes: synthesis,characterization and catalytic activity in direct arylation reactions

Palladium-catalyzed direct arylation of heteroaromatics has become a popular method for producing carbon–carbon bonds via C–H bond activation. A wide diversity of heteroaromatics such as furan, thiophenes and thiazoles can be used for this reaction. This paper reports the synthesis of N-propylphthalimide-substituted bis-(NHC)PdX₂ complexes (NHC = N-heterocyclic carbene), and their catalytic activity in direct arylation reactions. The complexes have been prepared from Ag(I)NHC precursors by transmetallation and characterized by spectroscopy and elemental analysis. The bis-(NHC)PdX₂ complexes show excellent activity as catalysts in the direct arylation reactions of 2-n-butylfuran, 2-n-butylthiophene and 2-isopropylthiazole.     

Structural and electronic properties of heptachlor

In this work, the molecular geometry of heptachlor is investigated using ab initio HF, DFT, LDA, and GGA methods. The natural bond orbital (NBO) analysis is performed at the B3LYP/6-311++G(d,p) level of theory. The first order hyperpolarizability β_total, the mean polarizability Δα, the anisotropy of the polarizability Δα, and the dipole moment μ, are calculated by B3LYP/6-311++G(d,p) and HF/6- 311++G(d,p) methods. The first order hyperpolarizability (β_total) is calculated based on the finite field approach. UV spectral parameters along with HOMO, LUMO energies for heptachlor are determined in vacuum and the solvent phase using HF, DFT, and TD-DFT/B3LYP methods implemented with the 6-311++G(d,p) basis set. Atomic charges and electron density of heptachlor in vacuum and ethanol are calculated using DFT/B3LYP and TD-DFT/B3LYP methods and the 6-311++G(d,p) basis set. In addition, after the frontier molecular orbitals (FMOs), the molecular electrostatic potential (MEP), the electrostatic potential (ESP), the electron density (ED), and the solvent accessible surface of heptachlor are visualized as a results of the B3LYP/6-311++G(d,p) calculation. Densities of states (DOS), the external electric field (EF) effect on the HOMO-LUMO gap, and the dipole moment are investigated by LDA and GGA methods.     

Rhodium(I) bisaldimine complexes in transfer hydrogenation

The reactions of hydrogen transfer from 2-propanol on acetophenone in the presence of the system [Rh(cod)Cl]₂–L] (L is bisaldimine ligands based on (R,R)-1,2-cyclohexanediimine and pyridine-, quinoline-, and thiophenecarboxaldehyde) were studied. Rhodium(I) complexes with optically active ligand showed a high catalytic activity (up to 345 h^–1) and moderate enantioselectivity [up to 55% ee of (R)-1-phenyethanol]. The structure of rhodium complex with N,N'-(1R,2R)-cyclohexane-1,2-diyl-bis[1-(pyridine-2-yl)methanimine] was determined on the basis of the data of ¹H and ¹³C NMR spectroscopy and quantum chemical calculations.     

Chemical oscillation in electrochemical oxidation of methanol on Pt surface

Based on dual path reaction mechanism, a nonlinear dynamics model reflecting the potential oscilla- tion in electrooxidation of methanol on Pt surface was established. The model involves three variables, the electrode potential (e), the surface coverage of carbon monoxide (x), and adsorbed water (y). The chemical reactions and electrode potential were coupled together through the rate constant ki = exp(ai(e ? ei)). The analysis to the established model discloses the following: there are different kinetics be- haviors in different ranges of current densities. The chemical oscillation in methanol electrooxidation is assigned to two aspects, one from poison mediate CO of methanol electrooxidation, which is the in- duced factor of the chemical oscillation, and the other from the oxygen-containing species, such as H2Oa. The formation and disappearance of H2Oa deeply depend on the electrode potential, and directly cause the chemical oscillation. The established model makes clear that the potential oscillation in methanol electrooxidation is the result of the feedback of electrode potential e on the reactions in- volving poison mediates CO and oxygen-containing species H2Oa. The numerical analysis of the estab- lished model successfully explains why the potential oscillation in methanol galvanostatic oxidation on a Pt electrode only happens in a certain range of current densities but not at any current density.