bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic and Structural Consequences Derived from Ageing Effects on Electrochemically Formed Layers
Authors: Arvía A. J. 
Published: November 2013

AbstractThe influence of different ageing processes on electrochemical reactions is analysed. Three main types of ageing processes are described: open circuit ageing, potentiostatic ageing and potentiodynamic ageing. The data derived from different electrode processes show that the films are composite systems themselves. They involve various nonequilibrated species which accordingly react to attain either a single equilibrium configuration or a configuration involving equilibria among the various surface species. Surface restructuring and cluster‐type reactions are important contributions toward understanding the dynamic behaviour of electrochemical interfaces.
The Nature of the Anodic Films Formed on Platinum Electrodes in the Presence of 1‐Naphthol
Authors: Babai M. , Gottesfeld S. , Gileadi E. 
Published: November 2013

AbstractThe adsorption and electrochemical surface reactions of 1‐naphthol on platinum in 0.5 M sulfuric acid were investigated by optical and electrochemical methods. At low anodic potentials (up to 0.65 V vs. dhe) monolayer adsorption of the organic molecule was observed with a significant extent of charge transfer. At more anodic potentials electrochemical polymerization occurs with films reaching several hundred Angstroms in thickness. Film growth is halted if the potential is decreased below 0.65 V. A parabolic rate of growth is observed and is attributed to slow, rate determining migration of electrons from the film/solution interface to the metal via the π electron systems of the polymeric film. At higher anodic potentials (above ca. 1.00 V) the parabolic growth law is no longer followed due to the occurrence of side reactions. The polymeric film is microporous, allowing passage of water molecules and ions at a low rate (low diffusion coefficient in the film). As a result the rate of electrochemical reactions on the film‐covered surface is diffusion controlled and depends mainly on bulk concentration, resulting with an apparent selectivity with respect to oxidation or reduction of the solvent.
Comparison of Liquid Crystal Properties of Isoelectronic 4,4′‐Disubstituted O‐, S‐, Se‐ and Te‐Aryl Benzoates
Authors: Kohne B. , Praefcke K. , Heppke G. , Richter E. J. 
Published: November 2013

AbstractAll compounds examined in the two series of isoelectronic O‐, S‐, Se‐ and Te‐4′‐pentylphenyl 4‐heptyloxy‐ and 4‐octyloxy‐benzoates \documentclass{article}\pagestyle{empty}\begin{document}$ (\bar 7 \cdot {\rm X} \cdot {\rm 5;}\,{\rm \bar 8} \cdot {\rm X} \cdot {\rm 5;}\,{\rm X = O, S, Se, Te)} $\end{document} display nematic and smectic phases. The corresponding phase transition temperatures and enthalpies are listed and discussed. The DSC‐measurements indicate that the selenol ester \documentclass{article}\pagestyle{empty}\begin{document}$ \bar 8 \cdot {\rm Se} \cdot 5 $\end{document} shows N‐SA as well as SA‐SC second order phase transitions as has been observed with the thiol ester \documentclass{article}\pagestyle{empty}\begin{document}$ \bar 8 \cdot {\rm S} \cdot 5 $\end{document}. No liquid‐crystal behaviour was detected in the similarly substituted phenylbenzamides \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {\bar 7 \cdot {\rm NH} \cdot {\rm 5; \bar 8} \cdot {\rm NH} \cdot {\rm 5}} \right) $\end{document}, which had been synthesized for the first time.
Reactive Crystals. II. Participation of Hydrocarbons in the Solid‐State Photodimerization of 3,4‐Dichlorocinnamic Acid
Authors: Nakanishi Fusae , Hirakawa Masayuki , Nakanishi Hachiro 
Published: November 2013

AbstractSolid‐state photodimerization of 3,4‐dichlorocinnamic acid (3,4‐DCCA) in the presence of hydrocarbons has been investigated. Irradiation of 3,4‐DCCA crystals dispersed in hydrocarbons leads to formation of t – 3, t – 4‐bis‐(3,4‐dichlorophenyl)‐cyclobutane‐r – 1, c – 2‐dicarboxylic acid (β‐truxinic acid type dimer) incorporating certain amounts of the dispersant. Various kinds of hydrocarbons, such as linear ones from pentane to nonane, cyclohexane, and benzene, are incorporated in this way. It was found that these hydrocarbons influence the reaction rate and the crystallinity of the dimer. Some possible mechanisms of incorporation are discussed.
Organized Monolayers by Adsorption. II. Molecular Orientation in Mixed Dye Monolayers Built on Anisotropic Polymeric Surfaces
Authors: Sagiv Jacob 
Published: November 2013

AbstractMethods for producing close‐packed monolayers with controllable molecular organization in the layer plane are investigated. Adsorption of oleophobic monolayers containing dyes on smooth surfaces of stretched polyvinyl‐alcohol films is shown to yield a preferred orientation of the dye chromophores resembling the uniaxial distribution pattern of the polymeric chains forming the surface of the support. Attempts to induce a similar molecular organization in Langmuir monolayers deposited from the water‐air interface failed. As a by‐product of this study, the surface composition and structure of two types of oxidized polyethylene were investigated. It is shown that information regarding the structure of a polar solid surface may be obtained by studying the molecular organization induced in a mixed dye monolayer adsorbed on that surface. The orientational effects were estimated from linear dichroism measurements.
Model Studies on the Binding of Lithium and Beryllium in Biological Systems
Authors: Blomberg M. R. A. , Fischer‐Hjalmars I. , Henriksson‐Enflo A. 
Published: November 2013

AbstractComplexes [(C2H2X2)2M]n with ligating atoms X = O, S and central atoms M = Li (n = 0, ± 1) and Be (n = 0, ± 2) have been studied by quantum chemical ab initio calculations. Total energies, relative binding energies and orbital energies of mainly planar complexes of standard geometry have been studied. The effect of variation of geometry including non‐planarity has also been considered. The primary binding region is found to contain appreciable interactions not only within pairs MX but for the sulfur case also of the type XX'. The chelate form of the ligands is shown to be essential to the properties of the complexes.
Studies on Charge‐Transfer Theory Mulliken Population and Measure of Charge Transfer
Authors: Re G. Del , Otto P. , Ladik J. 
Published: November 2013

AbstractThe gross occupations of molecular orbitals in charge‐transfer complexes are defined in terms of a multiconfigurational scheme over nonorthogonal orbitals. Their physical significance is illustrated by reference to Mulliken's gross atomic populations, of which they are the molecular analogs: under well specified approximations the corresponding net atomic charges provide a uniquely defined set of point charges representing a molecule in an electric field. Alternatives and limitations to the use of gross occupations as measures of charge transfer (and to methods for obtaining them) are illustrated byab initiocomputations of Li+‐H2O, HCN‐CO, formamide‐glyoxal, TCNE‐Benzene: in particular, geometrical criteria for partitioning the total charge density are briefly presented.
Ab Initio MRD‐CI Calculations for HAB Molecules I. Isomerization Energies for HOS, HNP and HCSi and Their Positive Ions
Authors: Buenker Robert J. , Bruna Pablo J. , Peyerimhoff Sigrid D. 
Published: November 2013

AbstractA series of ab initio calculations is reported which employs the MRD‐CI method in a standard AO basis of double‐zeta plus polarization quality for the HSO‐HOS, HPN‐HNP and HSiC‐HCSi isomers and their corresponding positive ions. The equilibrium geometries of each of these twelve systems has been carefully optimized (in some cases in a variety of low‐lying electronic states) and the structural results are found to be in substantial agreement with the qualitative predictions of the Mulliken‐Walsh MO model, although some significant deviations from this general pattern are indicated for certain of the more relatively unstable isomeric species. Unusually large isomerization energies are calculated in a number of instances and a strong preference for structures with the second‐row atom at the terminal position of the molecule is noted generally. The largest and smallest distinctions in the relative stabilities of the isomers studied to date are found to occur for systems with 10 and 12 valence electrons respectively (110 kcal/mole for HCS+‐HSC+ and 2 kcal/mole for ‘A’ HOS+‐HSO+, for example) and from a survey of such findings it is concluded that each type of molecular orbital exhibits a characteristic effect on the magnitude of these energy differences. Finally it is pointed out that in isovalent series isomerization energies tend to increase with the electronegativity of the second‐row atom in HAB systems of mixed first‐ and second‐row composition.
Structural Considerations in Chemical Kinetics: Gas Phase H‐Atom Transfer Reaction Series
Authors: Agmon N. , Levine R. D. 
Published: November 2013

AbstractStructure–reactivity correlations are discussed and applied to the X + H2→ XH + H and Cl + HX → ClH + X series of gas phase reactions where X is a halogen atom. In particular, potential energy surfaces for the (collinear) XH2system are obtained in terms of the diatomic, H2and XH, potentials and two parameters which are common to all members of the series. These surfaces are in quantitative accord with the Evans–Polanyi, Leffler and Hammond postulates. The rate constants satisfy the reactivity‐selectivity principle.
Semiclassical Study of the Quenching of Excited‐State Fluorine Atom by Hydrogen Molecule: Comparison between Reactive and Nonreactive Processes
Authors: Yuan Jian‐Min , George Thomas F. , Skuse Brian M. , Jaffe Richard L. , Komornicki Andrew , Morokuma Keiji 
Published: November 2013

AbstractSemiclassical calculations are carried out for the quenching of excited‐state fluorine atom by collinear collisions with hydrogen molecule. The overall quenching probability is the sum of two contributions: the reactive quenching probability associated with the formation of hydrogen fluoride and the nonreactive quenching probability leading to ground‐state fluorine atom and hydrogen molecule. The reactive probability is greater in the threshold region of the collision energy, whereas the nonreactive probability dominates for energies above the threshold region.
A Group Theoretical Analysis of Conformational Flexibility
Authors: Dugundji James , Showell John , Kopp Rosemarie , Marquarding Dieter , Ugi Ivar 
Published: November 2013

AbstractThe chemical identity group of a conformationally flexible molecule has very special properties. An analysis of its group structure leads to a detailed interpretation of the properties of the conformationally flexible molecules and their permutation isomers. In contrast to conventional conformational analysis our treatment of conformationally flexible molecules on the basis of chemical identity groups emphasizes ensembles of interconverting conformers. This leads to an interpretation of the observed increase in “symmetry” through conformational flexibility.
Updating the Molecular–Mechanical Force Field for Organic Halides
Authors: Meyer A. Y. , Allinger N. L. , Yuh Y. 
Published: November 2013

AbstractIn extension of previous molecular mechanical studies of organic halides, we examine three pathways to enlarge the scope of the force field. These are: adaptation of the constants to a new formulation of the basic force field; substitution of the monopole for the dipole approximation, in evaluating the electrostatic strain; estimation of solvation energies and conformational equilibria in solution. The structures studied are mono‐ and non‐geminal dihaloalkanes, and monohaloketones (fluorides, chlorides, bromides). We discuss the quantitative separation of steric and electrostatic effects in halocyclohexanones, and identity the minimum‐energy rotamers in haloacetones.
Structural Requirements in Chiral Diphosphine–Rhodium Complexes. XIV. Heptagonal Chelating Ring Flexibility in Rhodium(I) Complexes of Trans‐1,2‐bis(Diphenylphosphinomethyl)cycloalkanes
Authors: Glaser Robert , Geresh Shimona , Twaik Menachem 
Published: November 2013

AbstractZ‐N‐acyldehydroamino acids and esters were hydrogenated with in‐situ prepared rhodium(I) complexes, containing trans‐4,5‐bis(diphenylphosphinomethyl)‐2,2‐dimethyl‐1,3‐dioxolan (DIOP) or its carbocyclic analogues — trans‐1,2‐bis(diphenylphosphinomethyl)cycloalkanes. The optical purities of the N‐acylamino acid and ester products do not reflect a simple correlation with the PCH2–C–C–CH2P torsional angle within the diphosphine moiety of the catalytic complex, but are related to the flexibility of the heptagonal chelating ring. The relationship between the chiral sense of the major reduction product and the structure of the diastereomeric enamide adduct complexes is also discussed.
Structures of 8α‐ and 8β‐t‐Butyl‐trans‐decahydroquinoline Picrates and 8α,Nβ‐Dimethyl‐trans‐decahydroquinoline p‐Toluenesulfonate
Authors: Hargrave Karl D. , Eliel Ernest L. 
Published: November 2013

AbstractThe structures of the title compounds I, II and III have been determined by X‐ray crystallography. All three compounds, including the 8β‐t‐butyl isomer II(axial t‐butyl), exist in double chair forms. Compound II is deformed by an outward tilt as well as a substantial twist (16.2°) of the t‐butyl group away from the staggered conformation. A slightly lesser twist of 13.7° is found in the equatorial t‐butyl isomer I. Outward bending of the axial N‐methyl group also occurs in compound III.
The Molecular and Crystal Structure of 3,3‐Diphenyl‐1,2‐oxathiolane‐2,2‐dioxide, The Reaction Product of 1,1‐Diphenylpropane‐1,3‐diol with Thionylchloride
Authors: Petit G. H. , Lenstra A. T. H. , Geise H. J. , Hellier Desmond G. , Phillips A. M. 
Published: November 2013

AbstractReaction of 1,1‐diphenyl‐propane‐1,3‐diol with thionyl‐chloride gave a product, which was identified by X‐ray analysis as 3,3‐diphenyl‐1,2‐oxathiolane‐2,2‐dioxide. The compound crystallizes at room temperature in the monoclinic space group Pt/n with a = 8.888, b = 11.460, c = 12.895 Å, β = 96.51° and Z = 4. The structure was solved using direct methods and difference Fourier techniques and refined by block‐diagonal least‐squares to a final R‐value of 4.8%. Spectral data (IR, NMR) and a possible reaction mechanism are discussed.
Configurational Stability of Unsubstituted Cyclohexyllithium
Authors: Lambert Joseph B. , Majchrzak Michal W. , Rosen Bruce I. , Steele Kent P. , Oliver Sarah Ann , Urdaneta‐Pérez Migdalia 
Published: November 2013

AbstractThe configurational stability of cyclohexyllithium was examined by the proton label method without the influence of perturbing substituents. According to this method, configurational changes are followed by the steric arrangement of protons and deuterons. The desired labeling pattern was obtained by conversion of cyclohexanol‐2,2,6‐d3 (1H and 6H either cis or trans) to bromocyclohexane‐2,2,6‐d3. Good yield and high stereoselectivity was achieved by formation of the tosylate and treatment of the tosylate with magnesium bromide. The two stereoisomers of bromocyclohexane‐2,2,6‐d3 were allowed to react separately with lithium in pentane. The separate reactions give the same racemized mixture of cyclohexanecarboxylic‐2,2,6‐d3 acids after treatment with CO2. The racemization probably occurs during formation of the organolithium reagent on the surface of the metal or during the lifetime of a short‐lived radical intermediate. It is not likely that the aggregated organolithium reagent itself undergoes racemization.
On the Energy Additivity of the Acyclic Polyene Reference Structure for Aromaticity
Authors: Schaad L. J. , Hess B. A. Jr. 
Published: November 2013

AbstractBecause of their energy additivity, acyclic conjugated hydrocarbons are used as reference structures in the computation of the aromatic character of cyclic compounds. The origin of this additivity is investigated by treating conjugated acyclics as collections of perturbed ethylene molecules. Odd order perturbations affect individual orbital energies, but, at least for most acyclics, do not change total π energies. Additivity is shown to persist through sixth order for the even terms.
Diaminocyclopropenethiones: Synthesis and Reaction Feature
Authors: Yoshida Zen‐Ichi , Konishi Hisatoshi , Ogoshi Hsanobu 
Published: November 2013

AbstractSeveral diaminocyclopropenethiones (1) are prepared by the reaction of diaminochlorocyclopropenium or triaminocyclopropenium salts with NaSH, and physical properties are characterized by IR, UV, PMR and CMR spectra. Reactions of 1 with electrophiles afford various diaminothiocyclopropenium salts. Diaminocyclopropenium salts (10) are prepared via reaction of 1 with oxidizing agents and characterized. The effect of amino‐substituents on cyclopropenium ion is discussed.
Hydrogenolysis of Small Cycloalkanes, VIII Hydrogenation of Vinyl Cyclopropanes
Authors: Büchle‐Kallfass Doris , Gagel Martin , Hauschild Christa , Musso Hans , Rossnagel Ingrid , Schreiber Cornelia 
Published: November 2013

AbstractIn 1‐vinyl substituted cyclopropanes hydrogenation with Pd/C leads mainly to simultaneous saturation of the side chain and specific ring opening at the adjacent C(1)‐C(2) bond. 1,4‐Addition of hydrogen is indicated by the detection of olefinic intermediates.
Cyclopropanes. XLI. Electron Transfer from Lithium Metal Surfaces to (±) and (−)‐(S)‐1‐Fluoro‐1‐methyl‐2,2‐diphenylcyclopropane
Authors: Walborsky H. M. , Powers E. J. 
Published: November 2013

AbstractThe reaction of (I)‐1‐fluoro‐1‐methyl‐2,2‐diphenylcyclopropane (1) with lithium metal produced a variety of ring‐opened, as well as cyclopropane, products. Initial electron transfer from the lithium metal surface to 1 is to the phenyl ring of 1 rather than to the carbon‐fluorine bond. Using chiral 1, the 1‐lithio‐1‐methyl‐2,2‐diphenylcyclopropane produced yielded, upon carbonation, the corresponding acid which was largely racemized. The mechanism of the electron transfer reaction is discussed.
Mechanisms of Energy Transduction in Plant Photosynthesis: ESR, ENDOR and MOs of the Primary Acceptors
Authors: Forman A. , Davis M. S. , Fujita I. , Hanson L. K. , Smith K. M. , Fajer J. 
Published: November 2013

AbstractComparison of the optical, paramagnetic and redox properties of the reduced primary acceptors of Photosystems (PS) I and II with those of chlorophyll and pheophytin anions suggests that chlorophyll is the primary reduced product in PS I and pheophytin in PS II. Molecular orbital calculations provide a description of the electronic profiles of the radicals, and indicate that the protein environment of the chromophores in the reaction center may impose specific orientations and induce hydrogen bonding to some of the chlorophyll substituent groups. Examination of all the primary acceptors postulated for green plants and purple bacteria suggests that (bacterio)chlorophyll‐like acceptors may be obligatory to effect the rapid primary charge separation, because they allow favorable orbital overlap between donor and acceptor. Extrapolation of these results to green bacteria suggests that bacteriochlorophyll a and bacteriopheophytin c may act as transient electron acceptors in these organisms.
Control of Photosynthetic Electron Transfer from the Reaction Center to Electron Carriers of Photosystem II Studied by Fluorescence Induction
Authors: Malkin Shmuel 
Published: November 2013

AbstractThe relationships between the primary electron acceptor (Q) and the secondary pool (A1) are examined from fluorescence induction curves, at various illumination times and relaxation dark times. The fast‐phase in the fluorescence rise curve, obtained after insufficient relaxation time, indicates the occurrence of “unconnected” Q, i.e. the reaction between Q− and A1 is blocked. Various treatments bring about similar disconnection: high pH, ethylene glycol, low temperature (all reversible), trypsin and reduction of A1 by dithionite. All these treatments are similar to DCMU treatment. A scheme is suggested in which Q is mostly unconnected in the dark and becomes immediately connected as it is reduced by light. The above treatments inhibit the reconnection reaction in the light. The thermodynamic equilibrium between the Q populations that can or cannot be reconnected was analyzed from the fluorescence curves at various temperatures. The connection‐disconnection switching reaction is probably controlled by conformational changes of an associated protein. This scheme explains the difference of apparent redox equilibria of Q and A in the light or in the dark, as well as the IDP wave in the fluorescence induction of intact cells.
Energy and Electron Transfer in Photosynthetic Units
Authors: Mauzerall David 
Published: November 2013

AbstractIt is proposed that energy transfer by electron exchange is a likely alternative to that by electric‐dipole coupling for the case of chlorophyll and carotenoid proteins of the antennaes of photosynthetic systems. Biliproteins fit the criteria expected for the traditional Förster transfer. The criteria are fluorescence yield and lifetime of the pigments and structure and polarizability of their environment.
The Effect of Ring Strain on Ortho‐Annelated Aromatic Molecules
Authors: Thummel Randolph P. 
Published: November 2013

AbstractThis paper examines the effect of fusing a small carbocyclic ring onto the ortho positions of an aromatic nucleus. Benzene derivatives are considered to which have been fused one, two or three small rings. The effect of varying the size and orientation of the rings is discussed with respect to changes in the σ‐ and π‐bonding networks, the geometry of these molecules and their chemical reactivity. Other aromatic nuclei, such as pyridine, thiophene, naphthalene and the tropylium ion, are also described. Variations in physical properties appear to be best explained by a rehybridization theory which functions in the plane of the system. Perturbations of the π‐bonding framework are better manifested by changes in chemical reactivity.
cis‐ and trans‐Tris‐[2.2.2]‐σ‐Homobenzenes
Authors: McMullen Gabrielle , Lutterbeck Monika , Fritz Hans , Prinzbach Horst , Krüger Carl 
Published: November 2013

AbstractThe cis‐ and trans‐dicyano‐tris[2.2.2]‐σ‐homobenzenes 9/10 have been synthesized and characterized by spectroscopic methods and X‐ray structural analyses. From the relative ease of their transformations and from the products of their vapour phase pyrolyses, it is concluded that a pericyclic mechanism is no longer operative.
1,2‐Bridged Quadricyclanes
Authors: Hart Harold , Peng Cheng‐Tai 
Published: November 2013

AbstractThe readily available benzodihydropentalene 6 and dimethyl acetylene‐dicarboxylate react to give norbornadiene diester 8, with a three‐carbon bridge from C1 to C2. Inrradiation of 8 gives the corresponding C1‐C2 bridged quadricyclane diester 9, a new ring system. Diester 9 is quite stable, reverting to 8 with a t1/2 of 30 min at 170°C. The corresponding diacid 11, also prepared, reverts to its norbornadiene precursor at a considerably lower temperature, possibly as a consequence of acid catalysis.