Showing papers in "Theoretical and Experimental Chemistry in 1989"
TL;DR: In this paper, an n-electron operator is associated with a 2nelectron molecular wave function, and conditions are formulated which guarantee that a state with a given spin corresponds to a state of interest.
Abstract: An n-electron operatorX
n
, called a wave operator, is associated with a 2n-electron molecular wave function. Electron densities and energy are written in terms ofX
n
. An equation defining an exact wave operator is found. Thus, a 2n-electron vector problem (for the wave function) is rigorously reduced to an n-electron operator problem. Conditions are formulated which guarantee thatX
n
corresponds to a state with a given spin. The configuration-interaction problem is considered and methods of approximate construction ofX
n
are discussed. In particular, a matrix algorithm is proposed for calculations in the two-body approximation. A generalizaton of the approach to the case of systems with an odd number of electrons is given. The waveoperator model developed forms a general basis for construction of covariant electron models of molecules.
13 citations
TL;DR: In this article, it was found that porphyrins add chain propagation radicals of vinylpyrrolidone and of certain other monomers during radical polymerization, and that the addition may proceed either with disruption of the π-conjugation ring system, or with its retention.
Abstract: It was found that porphyrins add chain propagation radicals of vinylpyrrolidone and of certain other monomers during radical polymerization. Depending on the structure of porphyrin, the addition may proceed either with disruption of the π-conjugation ring system, or with its retention. The latter is realized when meso-tetraaryl-derivatives of porphyrin are used and can have practical application as a method for grafting porphyrins onto a polymeric carrier. If the polymerization is carried out under long polymeric chain conditions, the porphyrins play the role of a crosslinking agent.
8 citations
TL;DR: In this article, the electron-donor properties of ordinary and modified activated carbons were compared on the basis of quantum-chemical calculations and electrochemical investigations, and the mechanisms of the effect of heteroatoms and functional groups on the aromatic system of the carbon matrix were shown on the electronic level.
Abstract: The electron-donor properties of ordinary and modified activated carbons were compared on the basis of quantum-chemical calculations and electrochemical investigations. The mechanisms of the effect of heteroatoms and functional groups on the aromatic system of the carbon matrix were shown on the electronic level.
7 citations
TL;DR: In this paper, a three-stage mechanism was proposed for ammonia synthesis based on simple Langmuir concepts, which leads to a kinetic equation which agrees with the data of Winter on the kinetics of NH3 decomposition and the data from Benton on the retardation of the NH3 synthesis reaction by the product.
Abstract: It is shown that the mechanism proposed by Temkin and Pyzhev for ammonia synthesis does not correspond to the experimental data on the properties of the catalyst surface and the stages of the process. A three-stage mechanism is discussed: 1) N2+ Z = ZN2; 2) 2ZN + 3H2 = 2NH3 + 2Z; 3) 2ZN2 + Z\(\vec \equiv \) 2ZN (2 and 3 are equilibria, 3 being displaced to the right, 1 is the limiting stage), based on simple Langmuir concepts, which leads to a kinetic equation which agrees with the data of Winter on the kinetics of NH3 decomposition and the data of Benton on the retardation of the NH3 synthesis reaction by the product. An equation is derived for dissociative adsorption on a uniform surface involving the adsorption of each adatom at two adsorption sites; the equation corresponds to the same dependence of θ on P as the logarithmic adsorption isotherm.
7 citations
TL;DR: In this paper, an MNDO calculation and an x-ray crystallographic investigation of tert-butyl hydroperoxide (I) were undertaken, and it was shown that the difference between the experimental value of the COOH dihedral angle (average 100°) and the calculated value (128.5°) is most likely due to the formation of intermolecular hydrogen bonds in the crystal, the energies of which (∿30 kJ/mole) are considerably larger than the calculated excess energy of the conformers observed in a crystal (3.
Abstract: An MNDO calculation and an x-ray crystallographic investigation of tert-butyl hydroperoxide (I) were undertaken. The two symmetrically independent molecules of (I), which in fact have identical geometric parameters, form infinite chains along the y axis through staggered hydrogen bonds. The chains have local symmetry, described by a noncrystallographic slip plane. The difference between the experimental value of the COOH dihedral angle (average 100°) and the calculated value (128.5°) is most likely due to the formation of intermolecular hydrogen bonds in the crystal, the energies of which (∿30 kJ/mole) are considerably larger than the calculated excess energy of the conformers observed in the crystal (3.4 and 1.9 kJ/ mole).
6 citations
TL;DR: In this article, a wave-operator method was used to calculate the electron polarizabilities of conjugated hydrocarbons, based on complete configuration interaction, for singlet and triplet states in π systems.
Abstract: Electron polarizabilities α have been calculated for the π shells in certain conjugated hydrocarbons on the basis of complete configuration interaction. The calculations have been based on the wave-operator method (Teor. Eksp. Khim., 25, No. 1, 1 (1989)). In a polyene series, α increases nonadditively with the chain length, but not as sharply as MO calculations predict. Results are compared for singlet and triplet states in π systems with various types of topology.
5 citations
TL;DR: It has been shown that the red chemiluminescence in the Belousov-Zhabotinskii system with Mn(II, III) cannot be attributed to the formation of excited oxygen or its dimers during the process as discussed by the authors.
Abstract: It has been shown that the red chemiluminescence (CL) in the Belousov-Zhabotinskii system with Mn(II, III) cannot be attributed to the formation of excited oxygen or its dimers during the process. Chemiluminescence has been discovered upon the reduction of Mn(III) by malonic acid, and its spectrum coincides with the spectrum of the CL in the oscillatory system (with a maximum at λ ≅ 680–720 nm) and is found in the same region as the photoluminescence of Mn(II),- which is known from the literature data. It has been concluded that the principal emitter of the oscillatory CL is Mn(II), which is formed in an excited state upon the reduction of Mn(III).
5 citations
TL;DR: In this paper, the catalytic properties of macrocyclic and polychelate complexes of cobalt in the reaction of methyl methacrylate polymerization are compared with their donor-acceptor and redox properties.
Abstract: Information is presented on the catalytic properties of macrocyclic and polychelate complexes of cobalt in the reaction of methyl methacrylate polymerization. The catalytic activities of these compounds are compared with their donor-acceptor and redox properties.
5 citations
TL;DR: In this paper, a single-center method is proposed for solving the one-particle Schrodinger equation for molecules other than hydrides and for clusters, based on the method of associated differential and integral equations.
Abstract: A new single-center method is proposed for solving the one-particle Schrodinger equation for molecules other than hydrides and for clusters, based on the method of associated differential and integral equations. The higher terms of the expansion of the wave function of the electron are replaced by linear combinations of analytical functions. This reduces the system of integro-differential equations to a system of differential and algebraic equations, for which stable numerical solutions have been worked out. Calculations are given of the energy and functions of the 2s state of an oxygen atom with a displaced center.
4 citations
TL;DR: In this article, it was shown that the inner-sphere transfer of an electron from the copper ion to thiuram disulfide (tds) in a complex of the type [CuI(tds)]+ leads to the formation of copper(II) dithiocarbamate which is recorded in the absorption spectra and by EPR.
Abstract: The kinetics of the oxidation of copper(I) perchlorate with thiuram disulfide (tds) in acetonitrile and its mixtures with benzene or ethyl bromide have been investigated. It has been shown that the rate of the reaction is limited by the inner-sphere transfer of an electron from the copper(I) ion to tds in a complex of the type [CuI(tds)]+. The subsequent dissociation of the anionradical tds —proceeds rapidly and leads to the formation of copper(II) dithiocarbamate which is recorded in the absorption spectra and by EPR. The rate constant of electron transfer has been determined (3·10−4sec−1) and it was found that it is practically independent of the polarity of the medium. The absence of such a correlation is attributed to the negligible energies of reorganization of the solvent in the inner-sphere electron transfer.
4 citations
TL;DR: In this article, an additive generative function method was used to derive analytic expressions for the charge and bond-order distributions in polymethine chains for binuclear polymETHine compounds.
Abstract: An additive generative function method previously proposed has been used to derive analytic expressions for the charge and bond-order distributions in polymethine chains for binuclear polymethine compounds. The π-electron wave amplitude is determined primarily by the electron-donor capacity in the terminal groups at the edges and in the difference of those capacities at the center. The electron-donor capacity governs the charge exchange between a terminal group and the chain in the ground state. That approximation gives a rigorous basis for the terms used in the literature: polymethine and polyene types of compound, as well as for the smooth transition between them.
TL;DR: A 31P NMR method has been used to study sorbents based on titanium and zirconium phosphates synthesized by bulk mixing the reagents and treatment of x-ray amorphous TiO2, rutile and ZrO2 by phosphoric acid as discussed by the authors.
Abstract: A 31P NMR method has been used to study sorbents based on titanium and zirconium phosphates synthesized by bulk mixing the reagents and treatment of x-ray amorphous TiO2, rutile and ZrO2 by phosphoric acid. In the bulk titanium and zirconium phosphates the phosphorus occurs in four different states, phosphate groups bonded through cross-linking oxygen atoms with one, two, and three atoms of the metal and molecules of phosphoric acid trapped in the matrix of the sorbent in the synthesis process. It is established that the method of grafting the phosphate groups to the surfaces of the hydrated TiO2 and ZrO2 is determined by the crystalline and chemical properties of the surfaces.
TL;DR: In this article, pulse-gradient NMR has been used to determine self-diffusion coefficients for acetone, acetonitrile, benzene, hexane, methanol, and trimethylchlorosilane on aerosil.
Abstract: Pulse-gradient NMR has been used to determine self-diffusion coefficients for acetone, acetonitrile, benzene, hexane, methanol., and trimethylchlorosilane on aerosil. A comparison is made with the corresponding values for silica gel.
TL;DR: The photo-initiated oxidation of alcohols by carbon tetrachloride was studied in this paper, where the main reaction products formed during the irradiation of CCl4 solutions in ethanol with light of λ = 254 nm are chloroform, acetaldehyde, and hexachloroethane.
Abstract: The photo-initiated oxidation of alcohols by carbon tetrachloride was studied. The main reaction products formed during the irradiation of CCl4 solutions in ethanol with light of λ = 254 nm are chloroform, acetaldehyde, and hexachloroethane. With increase in concentration of CCl4 in the mixture with ethanol from 0.5 to 5 mole/liter, the quantum yields of the formation of CHCl3 and CH3CHO decrease from 9.2 to 4.4 and from 4.3 to 1.4, respectively, while the quantum yield of formation of C2Cl6 increases from 0.38 to 0.68. By using semiconductor photocatalysts (TiO2, TiO2/Pd, CdS), the oxidation of alcohols can be carried by the action of light of the near-UV and visible regions of the spectrum (320 < λ < 520 nm). When the reaction is carried out photocatalytically, the maximum quantum yields of the formation of CHCl3 and CH3CHO were attained with a palladized TiO2 (0.77 and 0.36, respectively). The initial stage of the mechanism of the photochemical process involves the cleavage of the C-Cl bond with absorption of a quantum of light by the CCl4 molecule, and this is followed by reactions of free radicals. When semiconductor photocatalysts are used, the cleavage of the C-Cl bond occurs either by the action of hydroxyethyl radicals, formed by the reaction of ethanol molecules with valence zone “holes” of the semiconductor (in the case of TiO2), or electrons of the semiconductor conductivity zone (in the case of CdS).
TL;DR: In this paper, the electronic wave functions and binding energy of two electrons in an ionic crystal were investigated in terms of a model resembling the helium atom or hydrogen molecule, where the role of the attractive Coulomb potentials of the nuclei is played by polarization potential wells calculated in the macroscopic approximation.
Abstract: We consider the electronic wave functions and binding energy of the bipolaron, which is a bound state of two electrons in an ionic crystal. The system is considered in terms of a model resembling the helium atom or hydrogen molecule, where the role of the attractive Coulomb potentials of the nuclei is played by polarization potential wells calculated in the macroscopic approximation. The importance of correlations in the motion of the electrons in the bipolaron is demonstrated. An existence criterion for the bipolaron is established and its binding energy and characteristic size is determined. We also consider quasimolecules formed in a polarizable medium from like-charged particles of different masses (such as an electron plus aμ− meson).
TL;DR: It was established by IR spectroscopy and chemical analysis that bis(trimethylsilyl) sulfate reacts chemically with isolated silanol groups of silica even at room temperature, and is quantitatively chemisorbed at 373 K as discussed by the authors.
Abstract: It was established by IR spectroscopy and chemical analysis that bis(trimethylsilyl) sulfate reacts chemically with isolated silanol groups of silica even at room temperature, and is quantitatively chemisorbed at 373 K. Sulfidation of the silica does not occur. Chemisorption of [(CH3)3Si]2SO4 on the surface of silicon(IV) oxide is not complicated by side processes.
TL;DR: In this paper, the electronic structure of a series of alkyl- and alkenyltetrazoles is discussed on the basis of an analysis of the data from 13C and 1H NMR and IR spectroscopy in conjunction with the results from quantum-chemical calculations by the LCAO-MO SCF method in the MNDO approximation.
Abstract: The electronic structure of a series of alkyl- and alkenyltetrazoles is discussed on the basis of an analysis of the data from13C and1H NMR and IR spectroscopy in conjunction with the results from quantum-chemical calculations by the LCAO-MO SCF method in the MNDO approximation. Good agreement was obtained between the calculated and existing experimental data with respect to certain properties of the investigated compounds.
TL;DR: In this article, the authors have carried out the calculations for inelastic neutron scattering spectra for thermal neutrons scattering on amixed-valence trimer d1-d 1-d2 cluster, and investigated the selection rules.
Abstract: We have carried out the calculations for inelastic neutron scattering spectra for thermal neutrons scattering on amixed-valence trimer d1-d1-d2 cluster, and we have investigated the selection rules. The forbidden transitions include the A1 ↔ A2 transitions, independently of spin, as well as the1A2 ↔1E transition. The rest of the transitions with ΔS = 0, 1 are allowed, and in turn are subdivided according to intensity into “strong” and “weak” transitions. The scattering cross sections of the latter include the differences in the form factors of the mixedvalence ions (the indicated form factors are close) and are small in magnitude. The scattering cross sections and the line positions in the spectrum depend considerably on the tunneling and exchange parameters of the cluster.
TL;DR: In this paper, the activation energies for the immobilization of the trimethylsilyl and isothiocyanate (or isocyanates) groups and the loss of the free silanol groups as a result of the chemisorption of the silanes have been calculated.
Abstract: The kinetics of the chemisorption of trimethylisothiocyanatosilane and trimethylisocyanatosilane on surfaces of dehydrated silica have been studied with the aid of infrared spectroscopy. The activation energies for the immobilization of the trimethylsilyl and isothiocyanate (or isocyanate) groups and the loss of the free silanol groups as a result of the chemisorption of the silanes have been calculated. The reactivity of the immobilized groups in their interactions with water and methanol has been studied.
TL;DR: In this paper, the preferred form of the bonds of acetone and acetonitrile with transition metals is by dative action, in which the d-electrons of the metal are localized on the antibonding π*-orbitals of the functional groups of these molecules.
Abstract: IR-spectroscopic and quantum chemical methods have been used to establish that the preferred form of the bonds of acetone and acetonitrile with transition metals are by dative action, in which the d-electrons of the metal are localized on the antibonding π*-orbitals of the functional groups of these molecules. During adsorption of (CH3)2CO it is also possible to form a donor-acceptor complex, when there is a transfer of π-electrons from the ketone molecule to the free dorbital of the metal.
TL;DR: In this article, the parameters of the IR bands for the Ν(AH) stretching vibration (the frequencies, the widths, and partly the intensities) were measured in a series of AH... B H complexes between one base B (ethylene oxide) and 17 various OH, NH, and CH acids in carbon tetrachloride solutions.
Abstract: The parameters of the IR bands for the Ν(AH) stretching vibration (the frequencies, the widths, and partly the intensities) were measured in a series of AH ... B H complexes between one base B (ethylene oxide) and 17 various OH, NH, and CH acids in carbon tetrachloride solutions. The width Ν1/2 and shift δΝ=Ν0 0−Ν (from the frequency Ν0 0 of the gaseous AH) of the investigated bands amount to 530 and 740 cm−1. A relationship close to direct proportionality between the broadening and the shift of the band for the H bond was found for all the H complexes. The relationship was insensitive to the medium and was preserved for the gaseous complex and in the undiluted ethylene oxide; it did not change greatly when δΝ was calculated from the “free” AH in carbon tetrachloride. This “partial” (with constant B) proportionality is not observed in the traditional series of acids (phenol, alcohol) with various bases, where agreement is only observed for Ν1/2 and δΝ. cThe electric-donating power of ethylene oxide (0.79±0.03) on the E scale (with reference to diethyl ether, E=1) was determined from the increase and shift of Ν(AH).
TL;DR: In this article, a study of the UV spectra of chalcones of the chroman and 1,4-benzodioxane series at 293 and 183 K has been carried out, and the bands have been assigned on the basis of quantum-mechanical calculations.
Abstract: A study of the UV spectra of chalcones of the chroman and 1,4-benzodioxane series at 293 and 183 K has been carried out, and the bands have been assigned on the basis of quantum-mechanical calculations. It has been shown that the localization of the transitions in most of the molecules on one of their cross-conjugated fragments is stipulated by the localization of several of their highest occupied MO's, which is attributed to specific features of the electronic structure of the CO group. In cases in which the energies of the MO's of fragments which are conjugated by means of a CO group are degenerate delocalization of the transitions takes place. As a result, a discontinuous dependence of the degree of localization of the transitions on the number and positioning of the substituents is observed. This results in partial violation of the rule of the selective displacement of bands upon substitution.
TL;DR: In this paper, the structure of the surface chemical compounds on modified pyrogenic silica has been studied by 31P magic-angle-spinning NMR spectroscopy and it has been established that the surface silyl dichlorophospite groups obtained as a result of the reaction of PCl3 with dehydrated silica are hydrolyzed upon the adsorption of water vapor with the formation of phosphorus acid.
Abstract: The structure of the surface chemical compounds on modified pyrogenic silica has been studied in this work by 31P magic-angle-spinning NMR spectroscopy. It has been established that the surface silyl dichlorophospite groups (186 ppm) obtained as a result of the reaction of PCl3 with dehydrated silica are hydrolyzed upon the adsorption of water vapor with the formation of phosphorus acid. The thermal treatment of such samples in a vacuum is accompanied by the formation of condensed polyhydrophosphoryl structures.
TL;DR: In this article, the organic conductor (BEDT-TTF)AgXIY (X ≅ 1.8 and Y≅ 2.9) was synthesized and the activation energy for diffusion of Ag ions was equal to 0.2 eV.
Abstract: We have synthesized the organic conductor (BEDT-TTF)AgXIY (X ≅ 1.8 and Y≅ 2.9). This compound has, in addition to high electronic conductivity (σ300 k ≅ 5–10 Ω−1 · cm−1), significant ionic conductivity connected with the motion of silver ions. The value of this ionic conductivity at room temperature is 10−3 Ω−1 · cm−1. The activation energy for diffusion of Ag ions is equal to 0.2 eV.
TL;DR: In this paper, a method for calculating adiabatic potentials of linear or quasi-linear threesite systems of mixed valence was proposed based on transformation of the potential energy matrix to two effective interacting modes.
Abstract: We propose a method for calculating adiabatic potentials of linear or quasi-linear threesite systems of mixed valence. The method is based on transformation of the potential energy matrix to two effective interacting modes. The adiabatic potential is calculated and its extrema are found. The electronic wave functions at the minima of the adiabatic potential correspond to complex charge distributions in a cluster. The barrier to transition of the “extra” electron between the terminal atoms is lower than for the transition from the terminal atom to the central atom.
TL;DR: In this paper, the reaction of human serum albumin (HSA) with dimethyl sulfoxide (DMSO) was studied by the PMR method according to the intensity of the proton signal of non-freezable water in the temperature range of 230-273°K.
Abstract: The reaction of human serum albumin (HSA) with dimethyl sulfoxide (DMSO) was studied by the PMR method according to the intensity of the proton signal of non-freezable water in the temperature range of 230–273°K. It was shown that the concentration of DMSO in the non-frozen liquid phase is much higher than should be expected for the simple eutectic. This is attributable to the binding of N molecules of DMSO with a molecule of HSA (at 270°K, N = 7–10). It was found that in the presence of DMSO, the amount of non-freezable water markedly increased, which is possibly due to a reaction between DMSO and proton-active centers of the protein through the intermediate water molecules.
TL;DR: In this paper, the color of cationic/anionic dyes in low-polarity solvents is governed by the properties of the ion pairs that are formed.
Abstract: The spectral properties of dyes containing colored organic cations and anions have been investigated in solvents differing in polarity. It has been established that the color of cationic/anionic dyes in low-polarity solvents is governed by the properties of the ion pairs that are formed. The chromophores in the ion pairs of cationic/anionic dyes interact, and this moves the absorption bands away from each other and redistributes their intensities.
TL;DR: The MO LCAO SCF method has been used in the MNDO approximation to examine the electronic structures and formation energies for adsorption complexes for water on SiO2 stabilized by hydrogen and coordination bonds as discussed by the authors.
Abstract: The MO LCAO SCF method has been used in the MNDO approximation to examine the electronic structures and formation energies for adsorption complexes for water on SiO2 stabilized by hydrogen and coordination bonds. Stabilization by several hydrogen bonds cannot explain the high initial heats of adsorption for dehydrated silica. H2O coordination complexes give higher energies, and hydroxylated silicon atoms on SiO2 are considered as primary water-adsorption centers.
TL;DR: In this paper, a study of the absorption spectra, circular dichroism in a magnetic field (MCD), and polarized fluorescence of individual NH-tautomers of free-base porphyrins with asymmetric substitution was made.
Abstract: A study has been made of the absorption spectra, circular dichroism in a magnetic field (MCD), and polarized fluorescence of individual NH-tautomers of free-base porphyrins with asymmetric substitution. The four-orbital model of Gouterman and the perimeter model of Michl have been used in demonstrating that, in spite of the basic differences in type of electronic spectra of the two NH-tautomers of each compound, their absorption spectra in the visible region are described by a system of two linear oscillators X and Y. The fluorescence polarization spectra of the tautomers in the region of band III are extremely sensitive to changes in the side substituents in the isocycle. From an analysis of the sign sequence of electronic bands in the MCD spectra, it has been established that these compounds may be classed as “hard” chromophores with identical type of orbital splitting for the HOMO (b1 and b2) and LUMO (c2 and c2) in the two tautomers of one and the same compound. A specific role has been found for the keto group in the isocycle, as manifested in inversion of the sign sequence of electronic bands in the MCD spectra of NH-tautomers with a cyclopentanone ring.