bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diterpenoid Irritants and Cocarcinogens in Euphorbiaceae and Thymelaeaceae: Structural Relationships in View of their Biogenesis
Authors: Adolf W. , Hecker E. 
Published: November 2013

AbstractDiterpene esters exhibiting toxic, irritant, cocarcinogenic as well as antileukemic activities have been isolated from many Euphorbiaceae and Thymelaeaceae species. They contain the structurally closely related polycyclic skeletons of tigliane, daphnane and ingenane. They are being used in all facets of cancer research as both tumor promoters and inhibitors. They are also considered as second‐order carcinogenic risk factors in the etiology of human cancer. The authors review possible biosynthetic pathways for the plant diterpenes and discuss structural relationships in view of their biogenesis.
X. Data Processing and Structure‐Factor Determination
Authors: Rees Bernard 
Published: November 2013

AbstractThe different steps in the determination of precise X‐ray or neutron structure factors are reviewed. Items discussed are: absorption, extinction, X‐ray polarization, scale factor, Λ/2 contamination, long‐range intensity variations, anomalous dispersion, averaging of equivalent reflections, magnitude and phase of the structure factor.
Azulene Revisited: Picosecond Decay of the S1 State in the Gas Phase and in Solution
Authors: Huppert Dan , Jortner Joshua , Rentzepis P. M. 
Published: November 2013

AbstractIn this paper we report the results of an experimental study of picosecond time‐resolved relaxation dynamics of the S1 state of the azulene molecule in solution and in the low pressure gas phase, utilizing consecutive two‐photon excitation S0 → S1(v) → S2 (or S3), with the exciting and the monitoring picosecond pulses chosen at the same wavelength. The nonradiative electronic relaxation times for azulene in solution were τnr = 4 ± 3 ps for S(v = 5), excited at 530 nm, and τnr = 3 ± 2 ps for S(v = 2), excited at 625 nm, while for the “isolated” molecule case τnr = 4 ± 3 ps for S(v = 2), excited at 625 nm. The electronic relaxation rate of the S1 manifold exhibits only a weak dependence on the excess vibrational energy Ev up to Ev = 4800 cm−1. The electronic relaxation rate is practically unaffected by solvent perturbations, as appropriate for the statistical limit of intramolecular radiationless transitions.
Gas and Solution Phase Reactivities of Triplet Aromatic Carbonyls
Authors: Berger Michael , Camp R. Nicholas , Demetrescu Ioanna , Giering Linda , Steel Colin 
Published: November 2013

AbstractAbsolute rate studies pertinent to the gas and solution phase photochemistry of triplet benzaldehyde, acetophenone and benzophenone have been carried out, and it has been confirmed that, in the gas phase, attack on a hydrocarbon by the carbonyl results in the expected hydrogen abstraction. Also absolute rates in both the gas phase and solution (acetonitrile) are quite comparable. For a given carbonyl the differences in the rates of abstraction are largely accounted for by activation energy changes. The activation energies vary from a high of 4.8 kcal mol−1 for abstraction of a primary hydrogen by acetophenone to a low of 1.4 kcal mol−1 for abstraction of tertiary hydrogen by benzaldehyde. At room temperature the relative reactivities of primary, secondary and tertiary C—H bonds for all the carbonyls are 1:23:190. In solution benzophenone is two times more reactive than acetophenone, while benzaldehyde is ten times more reactive. In the gas phase benzaldehyde is about 18 times more reactive than acetophenone. Molecular orbital calculations indicate that the greater reactivity of benzaldehyde as compared to acetophenone stems from steric hindrance in the latter. The quenching of acetophenone triplets by various other substrates including naphthalene, benzene, isopropanol and triethylamine is also discussed.
Pentafluorosulfur Peroxides: Synthesis, Properties and Vibrational Spectra of SF5OOH, SF5OOF, SF5OOCl and Evidence for the Trioxide, SF5OOOSF5
Authors: Desmarteau Darryl D. , Hammaker Robert M. 
Published: November 2013

AbstractThe synthesis and properties of the novel pentafluorosulfur peroxides, SF5OOH, SF5OOF and SF5OOCl are described. The hydroperoxide obtained by the hydrolysis of SF5OOC(O)F is the parent compound of this series and the halogen derivatives are obtained by reactions with fluorine and chlorine monofluoride. The preparation of SF5OOF results in the formation of another unstable compound, believed to be SF5OOOSF5.The vibrational spectra of SF5OOX and the related SF5OX (X = H,Cl,F) are analyzed in a consistent manner by assigning the most intense Raman band to the symmetric SF4 square stretching mode. Previous assignments for pentafluorosulfur peroxides had assigned the most intense band to the O‐O stretch.
The Reaction of Thiazylfluoride with Hexafluoropropene
Authors: Bludssus W. , Mews R. , Glemser O. , Alange G. G. 
Published: November 2013

AbstractNSF (1) reacts with CF3CF=CF2 in the presence of CsF to give the known sulfides (CF3)3CF‐S‐S‐CF(CF3)2 (3) and (CF3)2CF‐S‐CF(CF3)2 (4) and the linear thiazenes (CF3)2C=N‐S‐CF(CF3)2 (5), (CF3)2CF‐S‐N=S=N‐CF(CF3)2 (6), [(CF3)2CF‐S‐N=]2S (7), and (CF3)2CF‐S‐NSF2 (8); (CF3)2CF‐S‐NSO (9) results from the decomposition of (8) with glass. Yields of (3)‐(9) depend on the reaction conditons; an attempt is made to explain the formation of the products.
Fluorine‐Containing Dithioethers
Authors: Sharp David W. A. , Miguel Hugo Torrens 
Published: November 2013

AbstractThe dithioethers CH3SCF2CH2SCH3, CH3SCH(CF3)CH2SCH3, CH3SCH(CF3)CH(CF3)SCH3, CH3SCH(CH3)CH2SCH3, CH3SCH(CH3)CH(CH3), C6F5SCH2‐CH2SC6F5, CF3SCH2CH2SCH3, and C6F5SCH2CH2SCH3 have been prepared by photochemical addition to olefines or by metathetical reactions. Physical and some chemical properties are described.
Synthetic Methods and Reactions.43. Preparation of Fluorohydrins from Epoxides with Pyridinium Poly‐hydrogen Fluoride
Authors: Olah George A. , Meidar David 
Published: November 2013

AbstractThe use of pyridinium poly‐hydrogen fluoride for the convenient production of fluorohydrins is described. Pyridinium poly‐hydrogen fluoride as the hydrofiuorinating agent for epoxides allows the reaction to be carried out under mild conditions without heating the reaction mixture. The method is applicable to both aliphatic and aromatic epoxides.
Mass Spectrometric Identification of New Derivatives of PGA's and 19‐hydroxy‐PGA's Specific for Multiple Ion Detection
Authors: Roselló J. , Sunol C. , Gelpi E. 
Published: November 2013

AbstractThe mass spectra of the new piperidyl‐PGA (TMS), derivatives, formed by reaction of prostaglandin A1 or A2 with BSTFA/piperidine, are characterized by a dominant M − 173 ion, remarkably specific for MID applications. Similar derivatives have also been obtained with mixtures of BSTFA and other heterocyclic amines (hexamethylenimine, pyrrolidine, morpholine and propylenimine), which give the respective heterocycle‐PGA (TMS), derivatives. Likewise, the corresponding 11‐piperidyl‐19‐OH‐PGA (TMS)4 seem specially suited for the selected ion detection of PGA “artifacts” in extracts of human semen. The postulated structure of fragments at M − 173 and M − 423 (series I) and M − 425 (series II) is in favour of a pushpull type of reaction mechanism leading to these derivatives by nucleophilic addition of the amine on the C‐11 atom of the PGA's and concurrent formation of an enolate ion from the 9‐keto group with silanization of all reactive groups by BSTFA. An example of an application to the determination of PGA's and 19‐OH‐PGA's in a biological extract is given.
Luminescent Excited States of Phthalideisoquinolines: Studies on Low Temperature Spectra with some Observations on the Photochemistry and Mass Spectrometry of these Compounds
Authors: Turnbull James H. , Bowd Alexander 
Published: November 2013

AbstractThe phthalideisoquinolines narcotine and hydrastine show anomalous blue fluorescence emissions in glassy media at 77 K, whereas the closely related compound bicuculline, in which the configuration of the C–1 proton is reversed, shows no such effect. We propose that this blue emission arises from a phthalidestilbene system formed by a reversible excited‐state isomerisation.
On Some New Oxidation—Reduction Polymers
Authors: Manecke Georg , Ehrenthal Einhart , Finck Wilhelm , Wunsch Friedrich 
Published: November 2013

AbstractRedox polymers are among the most well‐documented polymer reagents, and tailored redox polymers are obtainable. The synthesis and the redox properties of some new silica‐anchored quinones are described. A high redox reaction velocity was found with a modified pore‐controlled glass. Polymer reagents with N‐chlorobenzotriazole units were obtained from suitable benzotriazole derivatives or by polymer‐analogous reactions starting from p‐aminostyrene polymers. With these products chlorinations as well as mild oxidation reactions were performed with good yields. Reusability and mechanical properties were good.
Matrix Effects on Size‐Selectivity of Polymeric Reagents and Catalysts
Authors: Regen Steven L. , Lee Dan P. 
Published: November 2013

AbstractSelectivity has been investigated for the catalytic hydrogenation of alkenes using a polymeric catalyst derived from a polystyryldiphenylphosphine resin and tris(triphenylphosphine)chlororhodium (I). These data together with the selectivity observed for a closely related polymeric phosphine reagent capable of converting alcohols to alkyl chlorides provide compelling evidence that a polymer support can impose a modest degree of size‐selectivity to an attached reagent and catalyst.
The Properties of Oxide Layers Formed on Iridium, Rhodium and Ruthenium Electrodes During Potential Cycling
Authors: Woods R. 
Published: November 2013

AbstractCycling the potential of iridium, rhodium or ruthenium can result in the growth of a metal oxide on the electrode surface. The formation of the oxide layer depends on both the upper and lower potential limits of the cycle and on the composition of the electrolyte solution. Reversible changes in valency of the metal atoms in the oxide, accompanied by proton transfer, occurs during a potential cycle and give rise to voltammetric peaks which are symmetrical about the potential axis. The nature and composition of the oxides and their electrocatalytic activity for oxygen evolution are discussed.
Influence of Electrosorption on Kinetics and Selectivity of Electroorganic Synthetic Reactions
Authors: Köster K. , Riemenschneider P. , Wendt H. 
Published: November 2013

AbstractNecessary conditions for the use of the influence of electrosorption on electrode kinetics, consecutive chemical kinetics and selectivity of electroorganic synthetic reactions are discussed. The role of electrosorption for the performance of four selected examples of electroorganic reactions is demonstrated. Three of these reactions are anodic and the fourth is cathodic. In the two cases of anodic formation of disaryliodonium cations and anodic oxidation of olefins, it is shown that the adsorptive character of the anode material is decisive for the success of the respective synthesis. For the first reaction, high current yields with only little loss of the precious iodoarene by formation of polymers, as well as avoidance of self coupling can only be obtained at Pt‐anodes in acetonitrile. Anodic dimer formation by olefin oxidation only gives high yields at graphitic carbon anodes in methanol. Here semiquantitative data for electrosorption of olefins and supporting electrolyte anions have been obtained by electrode‐kinetic measurements. They explain the influence of the supporting electrolyte anion on the dimer yield by the different spacial demands of the adsorbed anions of the supporting electrolyte. Due to very poor adsorption of radicals at Pt‐anodes and strong radical adsorption at carbon‐anodes, the anodic radical addition to olefins yields quite different product mixtures at these two anode materials. The optical inductive effect of electrosorbed strychninium cations on the cathodic reduction of acetylpyridine are shown to be caused by the enormous concentration enhancement of the alkaloid due to adsorption at the interphase. This is the precondition for complex formation between the negatively charged carbonation formed by disproportionation of the 1‐e reduction product and the positively charged inductor cation. The preference of one of the two possible steroisomers is obtained only by this complex formation.
Preparation and Catalytic Behaviour of Polymers with Pendant Oligoethyleneoxy‐groups (Polymers of Non‐cyclic Crown Ethers)
Authors: Hiratani Kazuhisa , Reuter Peter , Manecke Georg 
Published: November 2013

AbstractVinyl monomers with oligoethyleneglycolether moieties as pendant groups, having different lengths of the oligoether chain and different end groups such as the ethyl‐ and quinolinyl‐group, have been prepared. Homopolymers, a copolymer with styrene and crosslinked copolymers with p‐divinylbenzene were obtained by radical polymerization of the vinyl monomers. The catalytic activity of these polymers in comparison with that of the low molecular weight model compounds was investigated in the nucleophilic substitution of benzylchloride with the acetate ion. The influence of the counter cation of the acetate ion, the lengths of the oligoethyleneglycol chain, the nature of its end group and the effect of different solvents on the catalysis were studied.
Asymmetric Reactions in Chiral Hydrophobic Binding Sites
Authors: Sugimoto Toyonari , Baba Naomichi 
Published: November 2013

AbstractWith a number of illustrations from the asymmetric reactions conducted in chiral hydrophobic binding sites provided by chiral micelles, cyclodextrins and non‐enzyme globular proteins, this research account presents a cross section of recent biomimetic research related to stereospecificity in enzyme reactions.
The Photochemistry of the Polymerization of Diacetylenes in Multilayers
Authors: Fouassier J. P. , Tieke B. , Wegner G. 
Published: November 2013

AbstractThe quantum yield Φ of the photopolymerization of the amphiphilic diacetylene derivate pentacosa‐10,12‐diynoic acid (1) in form of multilayers was investigated. The multilayers were obtained by the Langmuir–Blodgett technique. The quantum yield for monochromatic irradiation at Λ = 254 nm depends strongly on conversion and slightly on temperature. It is independent of light intensity and number of multilayers. The quantum yield Φ extrapolated to zero‐conversion was found to be 10.3 ± 0.2 at 25°C. It increases linearly with increasing temperature. The activation energy of the photopolymerization was determined as EA = 4 ± 1 kcal mol−1. Φ seems to decrease nearly linearly with increasing conversion and reaches about half its initial value at 65 percent conversion. 3,3′‐Distearyl thiacarbocyanine iodide (2) was found to act as a sensitizer of the photopolymerization, if it was included into the multilayers by cospreading with 1. Photopolymerization occurs upon irradiation into the absorption band of the dyestuff‐monomer up to 600 nm. At higher concentration of 2, when dimers or multimers are formed, the photopolymerization is quenched.
Micellar Catalyzed Dephosphorylation The Role of Hydrophobicity of the Nucleophile
Authors: Bunton Clifford A. , Sepulveda Luis 
Published: November 2013

AbstractCationic micelles of hexadecyltrimethyl ammonium bromide (CTABr) increase the rate of dephosphorylation of p‐nitrophenyldiphenyl phosphate (PNPDPP) by aryloxide ions by factors of almost 104. The rate‐surfactant profiles for reactions of p‐ethyl‐, p‐propyl‐, p‐t‐butyl‐ and p‐t‐amyl‐phenoxide ion and of 2‐naphtholate ion can be interpreted quantitatively in terms of the distributions of the two reactants between aqueous and micellar pseudophases. The second order rate constants in the micellar pseudophase are slightly smaller than in water, showing that the rate enhancements are due largely to concentration of reactants at the water–micelle interface. Similar conclusions can be drawn from analysis of the micellar catalysis of the dephosphorylation by oximate ions of p‐nitrobenzaldehyde and 2‐quinoline carbaldehyde.
Organized Monolayers by Adsorption. III. Irreversible Adsorption and Memory Effects in Skeletonized Silane Monolayers
Authors: Sagiv Jacob 
Published: November 2013

AbstractOleophobic mixed monolayers of n‐octadecyltrichlorosilane (OTS) and surfactant dyes are adsorbed on polar solid surfaces. The dye molecules are then removed by solvent treatment leaving holes entrapped within a stable network of chemisorbed and polymerized silane molecules. Surfaces coated with such skeletonized OTS monolayers are shown to exhibit adsorption properties related to specific geometrical features of the displaced molecules. This provides a new artificial means for directing molecular organization taking place at a solid‐liquid interface. Practical applications to the study of liquid crystals, chemical reactions of oriented molecules and chromatography are suggested.
Light Induced Redox Reactions in Simple and Functional Surfactant Systems and Their Relevance to Energy Conversion Problems
Authors: Grätzel Michael 
Published: November 2013

AbstractSelf‐assembly of surfactant molecules in aqueous solution yields micellar aggregates. These, through local polarity and electrostatic potential effects, can be used kinetically to control light‐initiated electron transfer reactions. Cooperative effects assisting charge separation are observed with functional micelles where the redox relays are linked to the surfactant molecule. The implications for energy conversion systems are discussed.
Quantum Mechanical Aspects of the Molecular Structure Hypothesis
Authors: Woolley R. G. 
Published: November 2013

AbstractA discussion of the quantum mechanics of molecules with the emphasis on quantum mechanical principles is presented in the expectation that a better understanding of the assumptions tacitly embodied in conventional quantum chemistry will follow. The discussion centres mainly on the position of the chemical structure hypothesis in a quantum mechanical theory based on quantum states. Various different kinds of molecular states are identified according to characteristic properties of their wavefunctions, ranging from the completely delocalized (fully symmetrized) eigenstates to the “molecular structure states” of rigid molecules. I suggest that the adiabatic separation of electrons and nuclei can be avoided by working with the generator coordinate method (GCM) which promises to be a powerful non‐adiabatic formalism for molecular quantum theory.
The Quantum Mechanical View of Molecular Structure and the Shapes of Molecules
Authors: Trindle Carl 
Published: November 2013

AbstractThe idea that a single molecule has a shape—that is, a longlived nearly fixed (relative) arrangement of nuclei in space—has been shown by Woolley to be a classical idea imposed on the quantum mechanical picture of matter. In this report the argument that the Born–Oppenheimer approximation is semi‐classical is reviewed, and some pioneering computations free of the Born–Oppenheimer approximation are discussed. The problem of reconciling the results of these computations with the powerful and successful molecular structure theory is described, and a mode of computation is proposed which strikes a compromise between the sometimes inadequate Born–Oppenheimer Hamiltonian and the complicated full molecular Hamiltonian.
The Concept of Molecular Structure in Quantum Theory: Interpretation Problems
Authors: Claverie Pierre , Diner Simon 
Published: November 2013

AbstractThe classical concept of molecular structure (namely, a set of atoms with a well‐defined geometrical arrangement in space) originated well before the advent of quantum theory, and, contrary to widespread views, these two conceptual schemes (classical molecular structure and quantum theory) are not easy to reconcile. We begin with a preliminary discussion of molecular structure in terms of space and time correlations in the framework of quantum theory. Then we summarize the salient features of some critical views raised‐during recent years (essentially by Woolley) concerning the concept of molecular structure. The essential claim of this viewpoint is that “molecular structure” is not an intrinsic attribute of an isolated molecule, and appears rather as an effect of the environment (other molecules? vacuum electromagnetic field, according to quantum electrodynamics?). Afterwards, we discuss these issues in detail: we show that it is necessary to distinguish between a “quantum” or “potential” structure (which may be deduced in a straightforward way from the quantum treatment of the molecule), and the “classical” molecular structure (according to which the molecule is considered as a set of rotating and vibrating material points, corresponding to the atoms); we briefly discuss some aspects of the Born–Oppenheimer approximation. From our discussion, we deduce that the “classical structure” concept is indeed non‐trivial from a purely quantum‐mechanical point of view; in actual fact, it is related to the problem of the “classical limit” of quantum mechanics, and it appears that, at the present time, none of these classical concepts and behaviours is convincingly derivable from a strict quantum mechanical basis. Finally, we consider these same problems from the point of view of stochastic electrodynamics (SED), which is one of the stochastic models for microphysics proposed so far as a possible alternative or extension of usual quantum theory. In the framework of such a theory, the “classical limit” and, in particular, the “classical molecular structure” no longer poses a problem, but aside from these satisfactory qualitative aspects, several quantitative failures of SED prevent us from accepting it, at least in its present state, as a genuine physical alternative to quantum theory. We therefore conclude that “classical molecular structure”, and classical concepts in general, remain an open problem in the framework of present‐day quantum physics.
Potential Energy Surface of BH4− and Molecular Deformations Induced by an External Cation
Authors: Eisenstein Odile , Dunitz Jack D. 
Published: November 2013

AbstractThe part of the potential energy surface of BH4− which describes molecular deformations preserving C3v symmetry is calculated using a 6–31 G basis set of atomic orbitals and fitted by analytical power functions up to cubic terms in symmetry coordinates and cartesians. Minimum‐energy paths drawn on this energy surface are compared with the path describing the deformation of BH4− induced by approach of a cation along a threefold axis and also with a path derived by assuming bond‐number conservation. The possible relevance of the conclusions for interpreting experimental deformation paths in crystal environments is discussed.