bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on Warburganal, Muzigadial and Related Compounds
Authors: Nakanishi Koji , Kubo Isao 
Published: November 2013

AbstractWarburganal and muzigadial are two new sesquiterpenes isolated from a medicinal plant. They are two of the strongest antifeedants against the monophagous African army worm; in addition they possess potent molluscicidal activity and other antibiotic properties. A general account is given on these aspects as well as the spectral data leading to determination of their structures.
V. One‐Electron Density Functions and Many‐Centered Finite Multipole Expansions
Authors: Stewart Robert F. 
Published: November 2013

AbstractThe one‐electron density function, ρ(r), (in principle deduced from elastically scattered X‐ray intensities) is the probability distribution function of an electron, averaged over the positions of all other electrons. A partitioning of ρ(r) into constituent parts is an intellectual exercise that does not lend itself to unique measurement from elastic X‐ray scattering experiments. It is shown that in the limit of perfect data and an infinite Ewald sphere, a least‐squares fit with a many‐centered finite multipole expansion of the charge density about the N nuclei will necessarily satisfy the q‐centered multipoles of the molecule for q = 1, 2,…, N. This means that a large number of static‐charge physical properties (averages over ρ(r)) are correctly given. Several expressions for averages of ρ(r) or over FH are given. It is shown that outer moments, such as atomic charges, dipole moments and quadrupole moments, always depend on a shape function. On the other hand, inner moments such as potentials, electric forces, and electric field gradients, may be represented by direct Fourier analysis of FH (obs) (suitably phased, of course). Nuclear vibrations have been neglected throughout the discussion.
VI. Charge Deformation Models
Authors: Kurki‐Suonio Kaarle 
Published: November 2013

AbstractBasic construction principles of charge‐density models based on independent deformed atoms are presented. The asymptotic validity of the rigid free‐atom model in reciprocal space; mathematical properties of possible radial bases of multipole expansions; requirements put by symmetry, by regularity, by approximate free‐atom nature, by approximate harmonicity of motion and by N‐representability on the deformation models; and the connection between orthogonality and independence of model parameters are discussed together with consequent conclusions about the analysis of diffraction data in terms of deformation models.
VII. Vibrational Averaging of X‐Ray Scattering Intensities
Authors: Stewart Robert F. 
Published: November 2013

AbstractThe adiabatic potential for vibrational wavefunctions is given in a Preface. The vibrational average of ℐXRel(K;Q) is studied by taking a canonical‐ensemble average of the states of motion for the nuclei. A simple example for an oriented diatomic molecule (one vibration) is used to illustrate the sin θ/Λ dependence of ℐBragg and ℐTDS. The averaged X‐ray intensity, ℐav, is then fully developed (as done by Born) within the harmonic‐oscillator and rigid‐pseudoatom approximations for molecules and a crystal lattice. It is shown that generalized X‐ray scattering factors, characteristic of static charge properties, cannot in general be extracted from FOBSBragg. With the rigid‐pseudoatom model, relationships betweeen the dynamical matrix and electric‐field gradients and charge densities are given. In this way self‐consistency between Born's scattering matrix and pseudoatoms can be imposed on charge‐density models.
XII. The Combination of Aspherical‐Atom Least‐Squares Refinements with Fourier Methods in the Study of Electron Distributions
Authors: Coppens Philip , Hansen Niels K. 
Published: November 2013

AbstractSince electron density fitting in real and reciprocal space are equivalent, the convergence of aspherical‐atom least‐squares refinements may be judged from Fourier density maps. Residual densities, least‐squares model densities and X–N or X–X difference densities are defined and used in the analysis. A further criterion is provided by comparison of atomic parameters from multipolar refinements with neutron or X‐ray high‐order results. Derived molecular properties such as dipole moments can be obtained from the least‐squares results and compared with quantities from direct‐space integration. Expressions for both methods of integration are presented.
XIX. Nuclear Quadrupole Resonance Spectroscopy in Solids
Authors: Vega Shimon 
Published: November 2013

AbstractIn these lecture notes some basic aspects of Nuclear Quadrupole Resonance (NQR) spectroscopy are presented. The parameters of the Electric Field Gradient (EFG) tensor which are obtained from NQR experiments are discussed. The theory of Townes and Dailey is used for the derivation of the expressions for the occupation numbers of electronic wave function of spn hybridized atoms in terms of the asymmetry parameter η and the nuclear quadrupole coupling constant eq. The point‐charge model is applied in order to obtain the possible sp2 and sp3 configurations for which η = 1.
Appendix 2. A Deformation Density Refinement Program
Authors: Hirshfeld F. L. 
Published: November 2013

AbstractA computer program is described that permits the refinement of the static charge deformation in a flexible atom‐centered multipole expansion, together with positional and vibrational parameters, against X‐ray and neutron data. Other options allow for rigid‐body constraints on some or all of the atomic vibration tensors and the imposition of local symmetry on a set of atoms such as a methyl group.
Exciplex Formation between Indole Derivatives and Polar Solutes
Authors: Lasser N. , Feitelson J. , Lumry R. 
Published: November 2013

AbstractThe interaction between 3‐methylindole (3‐MeI) in cyclohexane with the polar molecules ethyl acetate (EA) and dimethylacetamide (DMA) was studied. The kinetic analysis of the fluorescence data shows that 3‐MeI forms an excited state complex with EA in a diffusion controlled process. The temperature dependence of the exciplex formation indicates that its dissociation rate constant too is of appreciable magnitude. UV, IR and fluorescence measurements all indicate that DMA forms complexes with 3‐MeI both in the ground and in the excited states. The latter complex is rather strong i.e. its dissociation rate is negligibly small. The findings imply that the fluorescence properties of tryptophan residues within a protein often must be determined by their interaction with neighboring polar groups rather than by the degree to which they are exposed to the ambient solution.
Photochemical Studies. XV. Photochemistry of 1,2‐Dihydrophthalic Anhydride and Related Compounds
Authors: Fuchs Benzion , Scharf Gad 
Published: November 2013

AbstractIrradiation induced fragmentation of 1,2‐dihydrophthalic anhydride (2) as well as of its precursor, 7‐oxonorbornen‐2,3‐dicarboxylic anhydride (1) yields benzene as the major product, accompanied by bicyclo[2.2.0]hex‐5‐ene‐2,3‐dicarboxylic anhydride (3) and tropone (5), in wave‐length dependent chemical‐ and quantum‐yields. It is shown that (2) is the key compound in the sequence, reacting from a singlet excited state and a biradical intermediate.
Reactions of Electropositive Chlorine Compounds with Fluorocarbons
Authors: Schack Carl J. , Christe Karl O. 
Published: November 2013

AbstractThe reactions of simple chlorine containing compounds of the general composition XCl are reviewed and discussed. The compounds included for review are ClF, RfOCl, SF5OCl, CF3OOCl, SF5OOCl, ClOSO2F, ClOClO3 and ClONO2. It is concluded that most of the known reaction chemistry of electropositive chlorine compounds can be rationalized in terms of either addition of Cl‐X across multiple bonds or oxidative addition to atoms, such as iodine or sulfur in their lower oxidation states. The observed variety of final reaction products can be explained by a multitude of secondary reactions which can involve either eliminations, further additions or degradations. The observed reactions are easily moderated and controlled and only seldom is no reaction encountered.
On High Pressure Synthesis in Inorganic Solid State Fluorine Chemistry
Authors: Hoppe Rudolf 
Published: November 2013

AbstractResults of high pressure fluorination (300–3000 bar F2) are given and discussed, e.g. fluorides of CrIV, MnIV, NiIV, CuIV, PtIV, PrIV, NdIV(?), DyIV(?) and RhV, AuV. Newly prepared were BaNiF6 (monoclinic, a = 9.465 Å, b = 4.950 Å, c = 6.655 Å, β = 103.3O), Cs2‐xRbxNiF6, Rb2‐xKxNiF6 (K2PtCl6‐type) all carmine‐red; BaPrF6 (RbPaF6‐type, a = 8.027 Å, b = 11.593 Å, c = 5.617 Å), SrPrF6 (LaF6‐type, a = 7.090 Å, c = 7.290 Å), both colourless powders; Cs2KNdF7 (a = 9.605 Å), Cs2KDyF7 (a = 9.479 Å), both cubic, orange‐yellow powders, (NH4)3, ZrF7‐type; MnF4 (trig., a = 19.53 Å, c = 12.59 Å), ultramarine‐blue single crystals, O+2[MnF5]− (monoclinic, a = 17.55 Å, b = 8.43 Å, c = 9.10 Å, β = 101.8°), bright‐red single crystals, and yellow single crystals, O+2[AuF6]−, which decomposed even under F2 during X‐ray radiation.
Intramolecular Nucleophilic Displacement of Fluorine
Authors: Hudlicky M. 
Published: November 2013

AbstractIntramolecular nucleophilic displacement in organic fluorine compounds takes place if a fluorine atom is located in the molecule at such a distance from a nucleophilic functional group as to allow cyclization to three‐membered rings (in aliphatic compounds only), five‐membered rings, six‐membered rings, and, exceptionally, seven‐ and polymembered rings (in aromatic series only). The nucleophilic functions can be hydroxyl groups of alcohols, enols, phenols and carboxylic acids, sulfhydryl groups, primary or secondary amino groups, and carbanionic carbon atoms. The reaction is common with aliphatic monofluorides and aromatic polyfluorides, and rare with geminal and trigeminal fluorides. Whereas in the aliphatic series it is usually an undesirable side‐reaction, in the aromatic series it is useful as a means of synthesizing carbocyclic and heterocyclic polynuclear compounds.
Reactions Involving Fluoride Ion. Part XV. Oligomers From Chlorotrifluoroethylene
Authors: Chambers Richard D. , Lindley Andrew A. , Philpot Paul D. , Fielding Harold C. , Hutchinson John 
Published: November 2013

AbstractReaction of chlorotrifluoroethylene with caesium fluoride in tetraglyme gives CF3CFCl2 and higher molecular weight compounds which do not contain chlorine, C8F16, C10F18, C12F22, etc. The mechanism of this process, including the production of additional unsaturated sites, is discussed. Chlorotrifluoroethylene also reacts with perfluorobut‐2‐ene, giving mainly C6F12, C8F16 and C10F18, and with C8F16, giving mainly C10F18, C12F22 and C14F24. It is now established that reaction of perfluorobut‐2‐ene with caesium fluoride gives C8F16 and C12F22 and it is proposed that this fluoride‐ion induced defluorination is promoted by the formation of caesium polyfluorides.
Field Desorption of Oligosaccharides and Glycolipids by the Cationization Method
Authors: Prome Jean‐Claude , Puzo Germain 
Published: November 2013

AbstractIn the FD–MS of oligosaccharide derivatives by the cationization method, the influence of the nature of the cation was studied so as to observe either monomeric doubly or singly charged ions. Trehalose was used as a model for this study. The use of alkaline‐earth salts does not allow the desorption of doubly charged monomeric ions. These ions are formed during the desorption of mixtures of trehalose and NaI, but the narrowness of their desorption temperature range limits the applicability of the method. Monomeric cationized ions are formed with alkaline cations: cesium iodide seems to be a suitable cationizing reagent as regards the appearance‐emitter temperature, the width of the desorption temperature range, and the sensitivity. The FD/Cs spectra of several diacyl trehaloses are presented. The desorption of a synthetic “cord factor” (dimycoloyl trehalose) containing 100 carbon atoms produces an intense peak at the expected m/e value for the (M + Cs) ions. The spectrum of the natural “cord factor” from Corynebacterium diphtheriae is presented.
Mass Spectrometry of Steroid Systems. XXVII. Mass Spectrometry and Stereochemisty of Vitamin D3 and its Analogs
Authors: Zaretskii Ze'ev V. I. 
Published: November 2013

AbstractThe relative stabilities of stereoisomers in the vitamin D3 series were established using the appearance — ionization energies differences obtained for the main fragmentation processes characteristic of these compounds. The influence of (Z)‐and (E)‐configurations of the 5,6‐double bonds in vitamin D3 stereoisomers on the previtamin D ‐ vitamin D equilibrium in gas phase, have been also studied.
Sex Pheromones of the American Cockroach, Periplaneta americana
Authors: Talman E. , Verwiel P. E. J. , Ritter F. J. , Persoons C. J. 
Published: November 2013

AbstractTwo sex pheromones, periplanone A and periplanone B were isolated from the American cockroach Periplaneta americana. The technique is described for collecting periplanone B from the alimentary tracts of virgin females. Periplanone A was extracted from the excreta of the insects. Mass spectral analysis of the pheromones and related compounds were performed and the results are reported here. Evidence is presented suggesting that periplanone A is in fact a degradation product of periplanone B. A reaction scheme is considered for the pathway: periplanone B → periplanone A → (stable, but inactive) PA 22–VII.
Preparation and Properties of tert‐Butyloxycarbonylaminoacyl‐4‐(oxymethyl) phenylacetamidomethyl‐(Kel F‐g‐styrene) Resin, an Insoluble, Noncrosslinked Support for Solid Phase Peptide Synthesis
Authors: Kent Stephen B. H. , Merrifield R. B. 
Published: November 2013

AbstractThe Boc‐aminoacyl‐OCH2‐Pam‐ derivative of Kel F‐g‐styrene resin has been synthesized by a chemically unambiguous route. Direct amidoalkylation of the unsubstituted resin followed by hydrazinolysis gave the aminomethyl‐resin. The loaded resin was obtained by reaction with a Boc‐aminoacyl‐OCH2‐phenylacetic acid and DCC. The stability of this resin derivative towards acidolysis in trifluoroacetic acid was determined. Only 0.01–0.02 mol% loss of chains will occur in a single deprotection cycle in solid phase peptide synthesis. The peptidyl‐ and aminoacyl‐OCH2‐Pam‐(Kel F‐g‐styrene) resins were cleaved with anhydrous HF‐anisole at 0°C in near‐quantitative yield. Simultaneous syntheses of the model peptide Leu‐Ala‐Gly‐Val on this resin and on Val‐OCH2‐Pam‐poly(styrene‐co‐1% divinylbenzene) resin gave the same low levels of byproducts. No (<0.1%) intersite aminolysis was observed on treatment of Leu‐Ala‐Gly‐Val‐OCH<2‐Pam‐(Kel F‐g‐styrene) resin with 5% diisopropylethylamine in dichloromethane for 22 h.
The Use of Polymer Supports in Organic Synthesis. 17. The Synthesis of Unsymmetrical Diamides and Monoamide Monotosylamides from Symmetrical Diamines
Authors: Dixit Dilip M. , Leznoff Clifford C. 
Published: November 2013

AbstractA 1 or 2% crosslinked divinylbenzene‐styrene copolymer, incorporating benzyl alcohol groups (1) was treated with p‐nitrophenyl chloroformate to give a polymer‐bound benzyl p‐nitrophenyl carbonate (2). The reaction of (2) with an excess of the symmetrical diamines 1,4‐diaminobutane (3a), 1,6‐diaminohexane (3b), 1,8‐diaminooctane (3c), 1,10‐diaminodecane (3d) and 1,12‐diaminododecane (3e) gave the respective monoprotected polymer‐bound aminocarbamates (4a‐e). Benzoylation or tosylation of (4a‐e) gave the polymer‐bound N‐benzoyl or N‐tosyl carbamates (7a‐e) or (8a‐e) respectively. Cleavage of (7a‐e) with trifluoroacetic acid liberated the N‐benzoyl‐N'‐trifluoroacetyl‐1, ω‐diaminoalkanes (9a‐e) in 80% yield. Cleavage of (8a‐e) with HCl in benzene, followed by acetylation yielded N‐acetyl‐N'‐tosyl‐1, ω‐diaminoalkanes (11a‐e) in 80% yield. From both cleavage reactions about 20% of the symmetrical diamines were recovered as their N,N'‐ditrifluoroacetyl or N,N'‐diacetyl derivatives (10a‐e) or (12a‐e) respectively.
Synthesis of Polymers Containing Lipoic Acid Structure and Study of the Acyl Transfer Reaction
Authors: Okawara Makoto , Fujimoto Atsuko , Endo Takeshi 
Published: November 2013

AbstractSeveral S‐acetyl and S,S‐diacetyl derivatives of dihydrolipoic acid and amide were prepared as model compounds to examine acyl transfer reactions similar to those in living systems. A macromolecule bearing the lipoic acid (1,2‐dithiolane) structure was synthesized by polymer reaction of polyacrylamide. The acyl transfer from these S‐acetates to nucleophiles such as amine, alcohol and thiol as well as the catalytic behavior of silver ion in these reactions was studied.
Insoluble Polymer‐Supported Conjugate Bases of Thiazolium Ions As Catalysts in Organic Chemistry
Authors: Castells J. , Dunach E. , Geijo F. , Pujol F. , Segura P. M. 
Published: November 2013

AbstractThe synthetic possibilities of the generalized benzoin condensation are examined: benzoin condensation in its strict sense and closely related reactions, Michael type additions of aldehydes to activated double bonds, and oxidative benzoin condensation. In solid phase chemistry, comments are made on cyanide resins and details are given on the preparation of insoluble 5‐(2‐hydroxyethyl)‐4‐methyl‐3‐(polystyrylmethyl)thiazolium chloride and of 4‐methyl‐3‐(polystyrylmethyl)thiazolium chloride. Examples of the use of polymer thiazolium salts in the three types of reactions mentioned are presented and information on the stability of these salts is presented.
Polymeric Carriers as Immobilizing Media — Fact and Fiction
Authors: Kraus Menahem A. , Patchornik A. 
Published: November 2013

AbstractThe use of crosslinked polymers as immobilizing media in chemical and biochemical processes is reviewed. Numerous successful immobilization experiments are described. A considerable number of unsuccessful attempts are also presented. In an attempt to settle the recent controversy as to the applicability of polymers as immobilizing matrices, a unified view is given of the subject, explaining both successful and unsuccessful results.
The Nature of Oxide Films on Ni(110) Electrodes
Authors: Macdougall B. , Mitchell D. F. , Graham M. J. 
Published: November 2013

AbstractElectropolished Ni(110) electrodes have a highly epitaxed 4 to 6 Å thick NiO surface film which is cathodically reduced in pH 2.8 Na2SO4 solution with a current efficiency of ∼ 60%. This oxide breaks down rapidly on open circuit in the same solution giving an arrest structure which, in conjunction with surface activity measurements, indicates localized removal of a very defective film. The open‐circuit breakdown characteristics of anodically formed passive oxide films indicate that these films contain a localized distribution of defects within the oxide. The number of defects and their stability is found to be highly dependent upon the condition of anodization. With increasing time of anodization at potentials in the passive region, the number of defect sites decreases and/or their stability increases, i.e. the film becomes more perfect The corresponding decrease in anodic current with increasing time of anodization indicates a correlation between this current and the electrochemical reactions at the defect sites. The anodic current is due mainly to nickel dissolution which occurs after breakdown and during inefficient repair of the defect oxide. Analysis of the passive oxide film indicates the presence of 9 to 12 Å of NiO. The time and potential of anodization has little effect on the average thickness or stoichiometry of the passive film, the condition of anodization only influencing the small (≦2%) coverage of defect sites on the surface. The passive film can be cathodically reduced but with only a very low current efficiency. The results obtained with the Ni(110) surface are in general agreement with those previously obtained for Ni(111) and Ni(100) electrodes.
Deposition of Palladium on Platinum in Hydrochloric Acid Media
Authors: Szabó S. , Nagy F. 
Published: November 2013

AbstractPalladium adsorbed on platinum has been shown to decrease the amount of adsorbed hydrogen because the site requirement of Pdads is about 1.5 times higher than that of adsorbed hydrogen. Metal adsorption via the ionization of adsorbed hydrogen occurs in two steps: the first leading to bulk deposition. This is followed by bulk ionization and repeated reduction, producing the adsorbed metal layer. The electrosorption valency of the adsorbed Pd layer thus formed is about 1.8. The Pdads does not desorb in Cl−‐free media.
Di‐(trans‐4‐Alkylcyclohexyl)‐α‐Diketones A New Class of Liquid Crystal Compounds
Authors: Praefcke Klaus , Schmidt Dietmar , Heppke Gerd 
Published: November 2013

AbstractUp to the present time it was assumed that the properties of liquid crystal compounds arise not only from the presence of long chain molecules, but that these molecules must further contain at least two phenyl rings. However recent work has shown that complete hydrogenation of derivatives of alkylbenzoic acids,2,3 as well as of alkylcyanobiphenyls,4 leads to compounds with liquid crystal properties. Continuing our work on liquid crystals,1 we report here on di‐(trans‐4‐alkylcyclohexyl)‐1,2‐ethanediones 6a–c, which are the first representatives of a further class of saturated liquid crystal compounds.
Liquid Crystalline 4′‐Pentylphenyl 4‐Alkyloxydithiobenzoates
Authors: Kohne B. , Praefcke K. , Heppke G. 
Published: November 2013

AbstractThe 4′‐pentylphenyl‐4‐alkyloxydithiobenzoates (1a–e), prepared for the first time, form enantiotropic nomatic phases. Thus, the –CS.S– linking unit qualifies as a central group in the construction of new classes of liquid crystals. The compounds investigated are red in colour and exhibit only a slight tendency to form smectic phases.
Copolymerization in Liquid Crystalline Media
Authors: Hardy G. , Cser F. , Nyitrai K. 
Published: November 2013

AbstractThe data at our disposal on the copolymerization of potentially mesogenic monomers either in mesomorphic or in isotropic phases are reviewed. There are only very few convincing data concerning the effect of the mesophase on the ratio of kinetic constants of the monomer (ri = kij/kij). The p‐ethoxy‐p'‐acryloyloxy‐azobenzene (EOA) and cholesteryl acrylate (CA) gave different r values in cholesteric and in isotropic state copolymerizations (rCA,i = 0.28, rEOA,i = 0.57, rCA,m = 0.16, rEOA,m = 1.10). r values were determined in other systems consisting of p‐methyl‐p'‐acryloyloxyazoxybenzene (MAAB), phenyl‐p‐acryloyloxybenzoate (PAB), N‐acryloylpiperidine (AP), cholesterylvinylsuccinate (CUS) and cholesterylsuccinyl‐diglycoylacrylate (CSDA) as well as CA. (rCA = 0.58, rPAB = 0.62, rCA = 0.16; rAP = 1.14; rPAB = 0.16; rAP = 0.81; rCVS = 0.01, rPAB = 2.36, rCSDA = 0.20, rPAB = 1.26, rMAAB = 2.40; rCVS = 0.02). These data were obtained in isotropic phase reactions and they do not satisfy the generally accepted concepts of reactivity. The structure of the copolymers were invesitgated by X‐ray diffraction and by thermal treatment. The copolymer/comonomer state diagram for the MAAB/CVS system were also used to determine the structural features of this system.Copolymers consisting of potentially mesogenic vinyl‐monomers are macromolecules with anisotropic properties. Their transition temperatures (Tg, Tf, Ta→i) have minimal values at a given composition. The copolymers show different X‐ray Bragg periods before and after this composition. They can be regarded as anisotropic two phase systems, although they are not block copolymers.The data published in recent literature together with those obtained in our current work suggest that both the chemical and the physical structures of the copolymers built up from potentially mesogenic vinyl‐monomers are more dependent on topochemical than on pure chemical conditions.