Half-century history of clathrate chemistry

This paper is devoted to the history of a new field of knowledge — clathrate chemistry, whose 50th anniversary is being celebrated. The Historical Dates section contains data on clathrates from the first observations of these compounds (late 18th century) to the pioneering works (1947–1948) of the English crystallographer Herbert Marcus Powell explaining their nature. Major trends of research into clathrate chemistry since Powell’s works are discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 40, No. 5, pp. 797–808, September–October, 1999     

Synthesis of amino-acid derivatives of chrysin

Various conjugates of amino acids with chrysin in which the amino acid was bonded through the C- or N-terminus to the flavone were prepared using peptide chemistry methods (symmetric anhydrides and activated esters). Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 569–574, November–December, 2008.     

电负性均衡

电负性是分子中一个原子把电子拉向它自身的能力,是化学理论的基本概念之一。继Pauling建立第一个电负性标度后,提出了众多的电负性标度。只是在密度泛函理论的基础上,电负性概念和电负性均衡原理,才被精密地论证。近二十多年来,电负性理论的重要发展是:应用电负性均衡模型或方法,可以快速地计算分子体系的电荷分布,从而确定分子的其他性质,甚至包括分子的结构和反应性指标。通常的电负性均衡方法只把分子划分到原子区域,虽然简单直观,但其精度和应用范围受到限制。原子与键电负性均衡方法,把分子划分到包括原子区域、化学键区域和孤对电子区域,能够较快速精密地计算分子的电荷分布和其他性质,并被应用到构建新一代可极化或浮动电荷力场的探索中,有广阔的应用前景。     

Dichroism of absorption and polarization of phosphorescence of molecules of the closed form of nitrobenzospirothiopyran

The spectral-polarization characteristics of absorption and phosphorescence of molecules of the initial form of nitro-substituted indolinospirobenzothiopyran were studied in oriented polyethylene films and in solutions with different polarity. An oscillator model of the electron transitions responsible for the formation of absorption and luminescence spectra was suggested. It was established that the principal differences in the spectral and photophysical properties of the compound studied and its oxygen-containing analog are associated with the fact that the electronegativity of the S atom is lower than that of the O atom. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1143–1146, June, 1997.     

The notion of structure in modern chemistry. II. Structural variety of condensed phases. Generalized crystal chemistry

The structural variety of condensed phases with crystalline (c) or quasicrystalline (q) order or complete/partial disorder (d) is represented as a triangular diagram. The c, q, or d characteristic refers to one of the three dimensions so that the type of condensed phase is denoted by three symbols (ccc is the ideal crystal; cqd is a phase where disorder is combined with crystalline and quasicrystalline orders). Comparative studies of various condensed phases with data extrapolation to other states is termed generalized crystal chemistry. M. V. Lomonosov Moscow State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 99–102, May–June, 1994. Translated by L. Smolina     

The reactivity of silanes in free-radical reactions: Analysis in terms of the parabolic model of the transition state

Rate constants and activation energies of free-radical reactions of silanes and silyl radicals were analyzed in terms of the parabolic model of the transition state. The kinetic parameters were estimated for 16 groups of reactions of silanes and silyl radicals. These parameters were used to calculate the activation energies for 112 free-radical reactions and to estimate the dissociation energies of the Si−H bond for 21 compounds and those of the C−Cl bond for 12 substituted benzyl chlorides. Triplet repulsion, electronegativity, and radii of atoms of the reaction center of the transition state were shown to play an important role in the formation of the activation barrier. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1311–1316, July, 1998.     

Double exchange in polynuclear mixed-valence clusters

A method for calculating the energies of the tunnel states of mixed-valence, clusters is proposed. It is based on the secondary quantization technique and allows one to obtain analytical expressions for all matrix elements that appear in double exchange theory as well as to determine the microstructures of the parameters of this theory. The energy spectra of trimeric systems are calculated with allowance made for the three-center transfer integrals, and the magnetic properties of these systems are investigated. Moldova State University. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 4, pp. 644–653, July–August, 1995. Translated by I. Izvekova     

Virtual geometrical symmetry group of a nonrigid molecule with energetically nonequivalent equilibrium configurations

The notion of a virtual geometrical symmetry group of a nonrigid molecule with energetically nonequivalent equilibrium configurations is introduced. Due to this, methods of qualitative analysis of intramolecular effects for such molecules using the concept of symmetry group chains are significantly generalized. Insitute of Applied Physics, Novgorod. Translated fromZhumal Struckturmoi Khimii, Vol. 37, No. 3, pp. 432–439, May–June, 1996.     

Stereochemical analysis by simplex representation of molecules

Stereoanalysis of molecules by partitioning a spatial structure into a system of simplices is described in detail. Potentialities of simplex representation of molecules in defining stereochemistry are demonstrated for chiral structures of various complexity and planar unsaturated molecules (“two-dimensional stereochemistry”). A concept of “stereochemical charge” is introduced. A. V. Bogatskii Physicochemical Institute, Ukrainian Academy of Sciences. Odessa State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 553–558, May–June, 1998.     

Vitrification and structural differences between metal glass,quasicrystal, and Frank-Kasper phases

The concept of icosahedral short-range order is extended to metallic glass, quasicrystal, and Frank-Kasper phases. The cluster model, together with the theory of local structural fluctuations, explains the static elasticity of glass, which distinguishes glass from liquid. An elastic peak of the dynamic structural factor indicates the possibility of transverse mode propagation in glass. As opposed to dislocations and disclinations in crystals, those in glass are artificially introduced defects, which serve as easily perceptible structural models. Thermodynamic relaxation theory may only be used for limited groups of vitrifying compounds the same applies to representation of vitrification as the second-order phase transition. The structure of real quasicrystals may not be adequately represented by Penrose tiling even after its decoration. This is associated with packing defects, inclusions of other phases, and chemical inhomogeneities. Quasicrystals have specific defects in an icosahedrally coordinated network of bonds, which distinguish them from Frank-Kasper phases. Criteria for isolating physically realizable Penrose tiling from all possible mosaics of this type are suggested. Structural distortions that transfer the diffraction rings of quasicrystalline samples into ellipses are explicable even in a linear approximation for the stress field created by a phason. The term “long-range order” seems to be wrong even for ordinary crystals. For quasicrystals, the notion of “rotational” order is more pertinent. Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 1, pp. 138–158, January–February, 1996. Translated by L. Smolina     

再论电负性标度的发展

电负性是化学中的一个重要概念,在基础化学课程中起着关键作用。本文将电负性研究过程分为三个阶段,简述了关于电负性标度的认识不断深入、逐步发展的过程,在讨论不同电负性标度的基础上,着重讨论了绝对电负性标度和Pauling类型电负性标度的差别性、Allen电负性标度及其修正的Rahm标度等,对深刻理解电负性标度这一基本概念及促进无机化学教学内容的改革均有重要意义。     

Compact method for calculating intermolecular interactions

The development of efficient methods for calculating intermolecular interactions (which are responsible for the existence of stable molecular associates, solvation shells, etc.) is a pressing problem of quantum chemistry. We propose a new method for correct calculations of intermolecular interactions, which is based on the solution of SCF equations with fractional occupation numbers. Calculating intermolecular interactions by this method does not require the use of exchange potentials in an explicit form. The method is intended primarily to describe the charge transfer between interacting subsystems. The calculations by this method are compact since the dimensions of matrix problems remain unchanged in the course of the numerical procedure. V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 3, pp. 401–405, May–June, 1995. Translated by I. Izvekova     

Wilhelm Ostwald’s energetics 2: energetic theory and applications,part I

This is the second of a series of essays on the development and reception of Wilhelm Ostwald’s energetics. The first essay described the chemical origins of Ostwald’s interest in the energy concept and his motivations for seeking a comprehensive science of energy. The present essay and the next discuss his various attempts, beginning in 1891 and extending over almost 3 years, to develop a consistent and coherent energetic theory. A final essay will consider reactions to this work and Ostwald’s replies, and will also seek to evaluate his program of research. Ostwald’s project – to reconstruct physics and chemistry “as a pure energetics” – is worth attending to for several reasons: first, because Ostwald did ground-breaking work in chemistry (he was awarded a Nobel Prize in 1909 for his studies in catalysis and rates of reaction); second, because an important school of physical chemistry formed around him at Leipzig, a school that promoted his ideas; and, finally, because he was a prominent and vigorous participant in debates at the end of the nineteenth century concerning the proper course of physical theory.     

Tautomeric transformations of arylidenebarbiturates in solutions

IR and UV spectroscopy and quantum chemistry were employed to investigate the structure of arylidenebarbiturates able to undergo tautomeric transformations. The composition of tautomeric mixtures depends on the properties of the solvent and on the concentrations of the solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 769–775, April, 1997.     

On the non-existence of parallel universes in chemistry

This treatise presents thoughts on the divide that exists in chemistry between those who seek their understanding within a universe wherein the laws of physics apply and those who prefer alternative universes wherein the laws are suspended or ‘bent’ to suit preconceived ideas. The former approach is embodied in the quantum theory of atoms in molecules (QTAIM), a theory based upon the properties of a system’s observable distribution of charge. Science is experimental observation followed by appeal to theory that, upon occasion, leads to new experiments. This is the path that led to the development of the molecular structure hypothesis—that a molecule is a collection atoms with characteristic properties linked by a network of bonds that impart a structure—a concept forged in the crucible of nineteenth century experimental chemistry. One hundred and fifty years of experimental chemistry underlie the realization that the properties of some total system are the sum of its atomic contributions. The concept of a functional group, consisting of a single atom or a linked set of atoms, with characteristic additive properties forms the cornerstone of chemical thinking of both molecules and crystals and Dalton’s atomic hypothesis has emerged as the operational theory of chemistry. We recognize the presence of a functional group in a given system and predict its effect upon the static, reactive and spectroscopic properties of the system in terms of the characteristic properties assigned to that group. QTAM gives physical substance to the concept of a functional group.     

To the theory of electron scattering by polyatomic molecules

Within the Born-Oppenheimer adiabatic perturbation theory, an equation was obtained for the intensity of fast electron scattering by polyatomic molecules. All of its parameters are explicitly defined by vibronic interaction in a molecule; due to this, quantum chemical calculations are fully applicable to electron diffraction studies of molecular geometries. Engels Anti-Aircraft Missile Higher Military School. Translated fromZhurmal Strukturnoi Khimii, Vol. 35, No. 2, pp. 40–45, March–April, 1994. Translated by L. Smolina     

Configurational degeneracy of exchange type in the vibration-rotation spectrum of a nonrigid molecule

In the vibration-rotation spectrum of a nonrigid molecule, the degeneracy that is due to several independent energetically equivalent equilibrium configurations related by exchange transitions is described using the concept of configurational spin. For the CH₃OH molecule with three independent configurations related by exchange transitions occurring by internal rotation, the algebraic and symmetric properties of this spin are analyzed, and effective operators of physical quantities are qualitatively constructed based on exchange degeneracy. Institute of Applied Physics, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 1, pp. 9–15, January–February, 1995. Translated by O. Kharlamova     

The shape of vibronic absorption bands and the structure of dye dimers

The shape of absorption bands of rhodamine 6G (R6G) and methylene blue (MB) dimers is compared with calculations by the Hemenger theory based on the model of the degenerate ground state (DGS). An interpretation of the origin of long-wave maxima in the spectra of the dimers is proposed from which it follows that their structure belongs to the “sandwich” type with a parallel position of axes of the monomers forming a dimer. Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 1, pp. 49–52, January–February, 1994. Translated by L. Chernomorskaya