bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dwell Time Distribution Behind Reflected Shocks in a Single Pulse Shock Tube
Authors: Lifshitz Assa , Schechner Pinchas 
Published: November 2013

AbstractThe variations of the dwell time along the sampling zone of a single pulse shock tube, the expansion of the reaction mixture, and the change in its position during the cooling process are discussed. A method to evaluate a correct space average dwell time is described. The method requires the reading of the final equilibrium pressure in the system. Approximately 10% error in the reaction time is introduced when the change in the position of the gas during the cooling process is neglected. The question of the space average dwell time vs. a concentration average is also discussed and results are shown for first‐ and second‐order rate equations.
The Effect of Hydrogen Donors on the Catalase‐Hydrogen Peroxide System in the Steady State
Authors: Kremer Mordechai L. 
Published: November 2013

AbstractAn analytical derivation is presented showing that in catalase‐containing systems in which peroxide is generated continuously, the addition of hydrogen donors (alcohol) always causes a reduction of the steady state concentration of the catalase‐H2O2 intermediate complex.
Preparation and Crystal Structure of KFeCl3 and KFeBr3
Authors: Amit M. , Horowitz A. , Makovsky J. 
Published: November 2013

AbstractThe preparation and crystal structures of anhydrous KFeCl3 and KFeBr3 are described. X‐ray diffraction data obtained at room temperature indicate that the two compounds belong to the orthorhombic system, space group Pnma and z = 4. Unit cell parameters are a = 8.712 Å, b = 3.845 Å, c = 14.15 Å for KFeCl3 and a = 9.220 Å, b = 4.026 Å, c = 14.899 Å for KFeBr3. Atomic positions were determined.
Fluidity and Order in the Hydrocarbon‐Water Interface of Synthetic and Biological Micelles as Determined by Fluorescence Polarization
Authors: Shinitzky M. 
Published: November 2013

AbstractA fluorescence polarization technique which was previously described was Utilized for the evaluation of microviscosities, \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar \eta $$\end{document}, transition temperatures and degrees of order in the hydrocarbon‐water interface of a series of micellar systems. The systems studied were micelles of compounds with a hexadecyl chain attached to different polar heads, and liposomes of lecithin and lecithin‐cholesterol (∼ 2:1). 1‐Dimethylamino naphthalene 5‐sulfoamide (DNSA) was found to dissolve in a well‐defined region of the micelles studied and was employed as the fluorescence probe. The DNSA inclusion region possesses an apparent dielectric constant in the range of 28–40, inferred from the emission maximum of the embedded DNSA, and was therefore interpreted to be the hydrocarbon‐water interface. In all systems studied the value of \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar \eta $$\end{document} falls in the narrow range of 17–40 centipoises at 27°C. From the change of \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar \eta $$\end{document} with temperature in the range of 0–60°C, phase transitions at 37, 33, 29 and 19°C were detected for micelles of cetyltrimethylammonium bromide, tetramethylammonium palmitate, cetylbetaine and egg lecithin, respectively. No phase transition was observed for lecithin‐cholesterol liposomes. Fluorescence polarization spectra of DNSA dissolved in the micelles indicated that a certain degree of order prevails in their hydrocarbon‐water interface.
The Determination of Total Cholesterol in Blood Serum with Antimony Pentachloride Reagent
Authors: Jungreis Ervin , Rapp Hedva 
Published: November 2013

AbstractA quick method for the determination of total cholesterol in blood serum is described. The method uses antimony pentachloride solution as reagent, a chemical not used in quantitative determination of total cholesterol hitherto. A very fast extraction of the cholesterol from the blood serum is assisted by the selective permeability of vyon discs of different solvents. A correlation study between this method and the Kinn‐Goldberg method, and an interference study, are included.
Synthesis of ω‐Halogenohydroxamic Acids and Their Characterization by Appropriate Condensations
Authors: Bittner S. 
Published: November 2013

AbstractA number of ω‐halogenohydroxamic acids were prepared by condensation of the appropriate carboxylic acids with hydroxylamine by means of dicyclohexylcarbodiimide. Characterization of the hydroxamic acids is based on their inter‐ or intramolecular condensation under basic conditions.
The Thermal Decomposition of Ammonium Perchlorate Doped with Cu+2 and Mn+2
Authors: Pelly I. 
Published: November 2013

AbstractThe thermal decomposition of ammonium perchlorate doped with Cu+2 and Mn+2 was studied, using DTA and TGA. Small concentrations (0.1 − 0.01%) of these ions inhibit the decomposition by eliminating the first exotherm. At higher concentrations a catalyzed decomposition is observed. Either the influence of doping ions on the mechanism of the thermal decomposition is different from that of added oxides or a modification of the electron transfer mechanism is needed.
The Isothermal Compressibility of Organic Liquids Over an Extensive Temperature Range
Authors: Shraiber L.S. 
Published: November 2013

AbstractA description is given of a new method and apparatus for precise measurements of the isothermal compressibility of liquids over an extensive temperature range using a small excess of pressure. Data are presented of an experimental study of the isothermal compressibility of six organic compounds (some of them for the first time) over a large temperature range (10–90° C).
Correlation between the Activity of Water in the System H2O + 2‐Butanol and its Solubility in the Organic Phase at 25°C
Authors: Sahar A. , Apelblat A. , Michaeli I. 
Published: November 2013

AbstractThe solubility of water in the organic phase of the system water + 2‐butanol, is very sensitive to the activity of the water in the vicinity of aw = 1. This property permits an accurate calculation of the activity of water in very dilute aqueous solutions of some mineral electrolytes.
The Reaction of Acid Chlorides with Magnesium Enolates Resulting from the Reaction of Vinylmagnesium Chloride and Carboxylic Acid
Authors: Watanabe Shoji , Suga Kyoichi , Fujita Tsutomu , Koiso Hideyuki 
Published: November 2013

AbstractThis note describes a new preparative method of vinyl esters and diketones. Vinyl‐magnesium chloride was added to benzoic acid in tetrahydrofuran to give a magnesium enolate. Without decomposition of the reaction mixture, propionyl chloride was added to give a mixture of 1‐phenyl‐1,4‐pentadienyl propionate and 2‐allyl‐1‐phenyl‐pentane‐1,3‐dione.
Prebiotic Polynucleotides and Polypeptides
Authors: Orgel Leslie E. 
Published: November 2013

AbstractWork on the non‐enzymatic replication of polynucleotides is discussed emphasizing sequence dependence and showing that alternating polynucleotides should replicate more easily than any others. Experimental work is described showing that polypeptides in which hydrophobic and hydrophilic residues alternate, adopt a β‐structure in aqueous solution. The possible relevance of these observations for the evolution of the genetic code is given.
Some Novel Methods of Structure Determination by Mass Spectrometry
Authors: Williams Dudley H. 
Published: November 2013

AbstractStructural studies in mass spectrometry divide into two distinct areas (i) studies of the structure of ions and (ii) attempts to elucidate the structures of the neutral molecules from which the mass spectrum is derived. Novel approaches in both areas will be described. In the first area it will be demonstrated that reaction energetics (including measurement of the kinetic energy released in a reaction) may be used to infer reactant and product configurations. In the second area, it will be demonstrated that new ionisation techniques (including a modified probe technique, field desorption, and chemical ionisation) can complement the structural information obtained by conventional electron impact mass spectrometry.
Photodissociation Spectroscopy: Symmetry and Lifetime of the Excited State
Authors: Bersohn R. 
Published: November 2013

AbstractPhotodissociation of a molecular beam with polarized light produces an angular distribution of photofragments of the form 1 + β (3/2 cos2 θ − 1/2) where θ is the angle between the electric vector of the light wave and the direction of dissociation. β is a product of a symmetry factor and a lifetime factor. The symmetry factor depends upon the orientation of the transition dipole with respect to the dissociation direction and the lifetime factor becomes small as the lifetime increases. Experiments show that alkyl iodides dissociate directly in a time comparable to a vibration period but that aryl iodides and bromides predissociate via an intermediate state. The lifetime of the intermediate state is of the order of a picosecond for aryl iodides but much longer for aryl bromides.
Large Scale Organisation of Flexible Polymers
Authors: De Gennes P. G. 
Published: November 2013

AbstractThe detailed shape and the correlations inside flexible coil polymers are discussed, with emphasis on (a) recent neutron scattering experiments and (b) theoretical developments based on a rigorous analogy between polymers and coupled spin systems (ferromagnets). For example, the size of a tagged (e.g. deuterated) molecule immersed in a semidilute solution of similar (hydrogenated) molecules has now been measured accurately, as a function of chain length, and polymer concentration. Remarkable laws have appeared – some of which go decidedly beyond the simple mean field analysis of Flory and Huggins. Extensions of these considerations to poor solvents (collapse or precipitation) will also be presented.
On the Concept of Isomerism
Authors: Eliel Ernest L. 
Published: November 2013

AbstractThe question as to whether two species of the same molecular composition are identical or isomeric in the conventional sense cannot be answered in the absence of stated experimental criteria of conditions and methods of observation. A new definition is proposed which minimizes such dependence on experimental criteria. “Residual isomerism” is defined as an auxiliary term to make the new definition practically useful.
Structural Requirements in Chiral Diphosphine‐Rhodium Complexes. V. Asymmetric Homogeneous Hydrogenation of Z‐α‐acetamidocinnamate Esters of Chiral Alcohols with DIOP‐Rhodium(I) Complexes and Symmetrical Diphosphine‐Rhodium(I) Complexes
Authors: Glaser Robert , Geresh Shimona , Blumenfeld Jeanine , Vainas Baruch , Twaik Menachem 
Published: November 2013

AbstractZ‐(−)‐(1R, 3R, 4S)‐menthyl‐α‐acetamidocinnamate was hydrogenated with neutral diphosphine‐rhodium(I) complexes containing (+)‐(2S, 3S) or (−)‐(2R, 3R)‐2,3‐isopropylidene‐2,3‐dihydroxy‐1,4‐bis(diphenylphosphino)butane(DIOP) to give a diastereomeric mixture of N‐acetylphenylalanine (1R, 3R, 4S)‐menthyl ester (76.8% diastereomeric excess [d.e.] (S, 3R) and 52.5% d.e. (R, 3R), respectively). The behavior of the unsaturated (−)‐menthyl ester substrate was also investigated with neutral diphosphine‐rhodium(I) complexes containing symmetrical α, ω‐bis(diphenylphosphino)alkanes {Ph2P(CH2)nPPh2} 6.6% d.e. (S, 3R) [n = 3]; 12.0% d.e. (R, 3R) [n = 4]; 7.2% d.e. (R, 3R) [n = 5]; and 7.4% d.e. (R, 3R) [n = 6]. Z‐(−)‐(1S, 2R, 4S)‐bornyl‐α‐acetamidocinnamate was similarly studied: 49.8% (S, 2R)[(+)‐(2S, 3S)‐DIOP]; 64.1% d.e. (R, 2R) [(−)‐(2R, 3R)‐DIOP]; 4.9% d.e. (S, 2R) [n = 3]; 9.1% d.e. (R, 2R) [n = 4]; 13.6% d.e. (R, 2R) [n = 5]; and 12.0% d.e. (R, 2R) [n = 6].
Helicenes: Chemically Induced Asymmetric Photosyntheses of Helicenes Skeletons
Authors: Cochez Y. , Martin R. H. , Jespers J. 
Published: November 2013

AbstractA systematic investigation of chemically induced asymmetric photosyntheses has been carried ou in the helicene series. The following points have been examined: the influence of the nature and of the position of the chiral inducing group in the precursor, the influence of the structure of the precursor and the effect of a double induction. The best asymmetric stereoselectivities were obtained: (a) when the photocyclisation gave rise to a helicene skeleton substituted at position 1‐; (b) at position 2‐, when an ester of optically pure 2‐hydroxymethyl[6]helicene was used as the chiral inducing group.
Experimentelle Prüfung von Näherungsansätzen für Chiralitätsfunktionen: Cyclopentan‐Derivate
Authors: Richter Wolf Jürgen , Richter Bernd 
Published: November 2013

AbstractChirality functions for cyclopentane‐derivatives with idealized D5h symmetry are developed and tested experimentally. The actual conformations of disubstituted cyclopentane‐derivatives are discussed, a series of compounds synthesized and their optical activity measured. A good correlation is obtained between experiment and theory for the 1, 2‐derivatives but not for the 1, 3‐disubstituted cyclopentane compounds. It could be shown that this method cannot be applied to higher substituted derivatives.
Polycyclic Molecules with Propeller Chirality—Optical Activity and Absolute Configuration of Some New Systems
Authors: Spielmann W. , Weitemeyer C. , Huang T.‐N. , De Meijere A. , Snatzke F. , Snatzke G. 
Published: November 2013

AbstractThe configurations of the trishomobarrelene and trishomobullvalene bridgehead derivatives 1b–1g, 2a–2e and 2g have been correlated with the absolute configuration of 1c as determined by X‐ray crystallography, on the basis of their circular dichroisms, especially those of the carboxylic acids 1b and 2b. All derivatives prepared from the dextrorotatory (+)‐1b and (+)‐2b resemble dextroverse propellers when looked upon from the substituted side. Attempts to prepare the new chiral trioxa‐[D3]‐trishomocubane 7 in optically active form, have failed so far. It is predicted, however, that (−)‐7 should have the same (all‐S)‐configuration as the levorotatory parent hydrocarbon (S)‐[D3]‐trishomocubane. In addition, a synthetic approach to two more C3‐symmetric propeller molecules, the hexahydrophenalene 13 and its trishomo derivative 14 is presented.
Equilibrium Asymmetric Induction in Sulfenamides—A Model for Asymmetric Synthesis
Authors: Raban Morton , Carlson Eric M. 
Published: November 2013

AbstractSulfenamides which contain an asymmetric carbon atom (stereostable chiral unit) in addition to the sulfenamide chiral axis (stereolabile chiral unit) exist as a mixture of diastereomers in equilibrium. The equilibrium constants, which can be measured by NMR spectroscopy, serve as a measure of the thermodynamic asymmetric induction of the stable chiral unit on the labile chiral unit. Two series of diastereomic sulfenamides (N‐alkyl‐N‐benzenesulfonyltrichloromethanesulfenamides and N‐alkyl‐N‐benzenesulfonyl‐2,4‐dinitrobenzenesulfenamides) were prepared and their equilibrium constants measured. The thermodynamic asymmetric induction in these systems is discussed and related to the asymmetric induction which occurs in asymmetric synthesis.
Observations on the Stereodynamic Behavior of Mono‐ and Polynuclear Iron Carbonyl Compounds Including a Survey of M(CO)3 Scrambling Processes
Authors: Cotton F. Albert , Hanson Brian E. 
Published: November 2013

AbstractIt has been shown conclusively by the observation of 57Fe–13C coupling (J = 8.3 Hz) that in Fe3(CO)12 the scrambling is intramolecular and that all of the CO groups have equal access to all three of the iron atoms. This result is fully in accord with the scrambling mechanism proposed in an earlier paper from this laboratory. We have found that for axially substituted amine derivatives of iron pentacarbonyl, AmFe(CO)4, the activation energy for CO scrambling is raised from the extremely low value (ca. 2 kcal mol−1) characteristic of Fe(CO)5 to a range (ca. 5.0–5.5 kcal mol−1) such that the coalescence temperatures are at, or very near, the threshold (ca. – 150°C) of experimental observation. The crystal and molecular structures of (1,2‐C4H4N2)Fe(CO)4 are also reported. The molecular structure is very similar to those of the (C5H5N)Fe(CO)4 and (1,4‐C4H4N2)Fe(CO)4 compounds. The space group is P21/n with unit cell dimensions a = 6.487(1)Å, b = 11.331(3)Å, c = 14.226(3)Å, β = 107.85(2)Å, V = 995.3(4)Å3. Finally, in the compound (C9H8O)Fe(CO)3, where C9H8O is derived from barbaralone, the scrambling of the three CO groups proceeds in a concerted manner with an activation energy of 16.5(3) kcal mol−1. The available data for CO scrambling in M(CO)3 moieties in general is summarized and discussed.
Synthesis and Biosynthesis of Spirobenzylisoquinoline Alkaloids
Authors: Maclean David B. 
Published: November 2013

AbstractThe synthesis and biosynthesis of the spirobenzylisoquinoline alkaloids is reviewed. The methods of synthesis are discussed under four headings: from indanones, from protoberberines, from phthalideisoquinolines, and miscellaneous methods.
II. Diffraction Physics
Authors: Feil Dirk 
Published: November 2013

AbstractStarting from the Schrödinger equation, the basic theory of scattering of X‐rays by electrons is given. The kinematic scattering, based on the first Born approximation, is treated in detail. The theory of phenomena, corresponding to a breakdown of this approximation, such as multiple and anomalous scattering, is given in outline. Kinematic scattering by a finite crystal is treated by using the convolution method. The consequences of finiteness of the crystal and of a series in a Fourier synthesis of the electron density are indicated.
Appendix 1. Use of the Gaussian‐70 Molecular Orbital and Electron Density Programs
Authors: Engel Y. M. , Hagler A. T. 
Published: November 2013

AbstractWe present here a short description of two programs used in the theoretical exercises: the Gaussian‐70 program, an ab‐initio molecular orbital program which solves the LCAO‐SCF (Linear Combination of Atomic Orbitals‐Self Consistent Field) equation and performs population analysis, and the electron‐density program which is used to calculate the electron density in molecular systems. Input data and output results are given for formaldehyde (H2CO) illustrating the use of both programs.
Statistical Aspects of Resonance Light Scattering in the Condensed Phase
Authors: Hochstrasser R. M. , Novak F. , Nyi C. A. 
Published: November 2013

AbstractA practical approach to understanding light scattering processes in the condensed phase is presented. First a theoretical discussion of the various parameters in resonance light scattering is given and there is a special emphasis on our simplified approach to this question. As with other approaches the two level density matrix in association with a quantum regression theorem leads to two types of emission from an ensemble of molecules at finite temperature (T2 ≠ 2T1). We have called one of these fluorescence and the other sharper emission Raman scattering because it results directly from the presence of a coherent polarization in the medium. A brief discussion of time dependent scattering is also given.An experiment that reproduces the main features of the theory is described for resonance scattering from azulene in naphthalene at 30 K. For all values of the laser frequency (near resonance) both a sharp (Raman) and diffuse (fluorescent) component occurs in the emission spectrum. These spectra when interpreted by the simplified theory yield a value of T2 = 0.7 ps from fluorescence linewidth, and T2 = 0.8 ps from the incoherent to coherent scattering ratio, for the 0–0 two level system of azulene in naphthalene. A discussion of practical aspects of the influence of inhomogeneous line broadening is also presented.
Polarized Absorption and Emission Spectra of 4,4′‐Dimethylstilbene
Authors: Yogev Amnon , Margulies Leon 
Published: November 2013

AbstractThe polarized absorption and emission spectra of 4,4′‐dimethylstilbene in frozen isotropic solutions and in an oriented matrix are described. A mathematical treatment for interpretation of the experimental data is given. The polarizations of the different electronic transitions were compared with theoretical predictions.
Electronic Overlap Population as Reactivity Measure. VII. Substituent Effects on the Photocyclization of Stilbenes
Authors: Muszkat K. A. , Kessel H. , Sharafi‐Ozeri S. 
Published: November 2013

AbstractExcited state electronic overlap populations for atom pairs forming the new bond were found to correlated satisfactorily with the photocyclization reactivity of a series of para and meta substituted stilbenes.
Tri‐ and Tetracoordinate Fluorosulfur(IV) and Pentacoordinate Fluorosulfur(VI) Compounds
Authors: Shreeve Jean'Ne M. 
Published: November 2013

AbstractRecent advances in the synthesis and reaction chemistry of fluorine‐containing tri‐ and tetracoordinate sulfur(IV) magnified image and pentacoordinate sulfur(VI) magnified image compounds are presented. Each molecule included contains sulfur bonded to fluorine or to a fluorinated group.
Electric Deflection and Molecular Structure: Determination of Polarities of Binary Fluorides and Oxyfluorides
Authors: Falconer W. E. 
Published: November 2013

AbstractThe principles of electric deflection spectroscopy and its relevance to molecular structure are reviewed. Application of this technique to gain insights into the structures of binary fluorides and oxide fluorides are described in detail. In particular, knowledge gained about nonrigid fluoride structures is described and some thoughts concerning future applications of electric deflection spectroscopy are presented.
Ferromagnetism in Fluorides
Authors: Tressaud Alain , Dance Jean‐Michel , Hagenmuller Paul 
Published: November 2013

AbstractRelatively few non‐metallic ferromagnetic materials are available. The authors give a survey of the ferromagnetic fluorides. Three main groups are considered: rare earth fluorides, layer‐type Cu2+ fluorides and LiSbF4‐type compounds.
Addition of Carbonyl Fluoride to Aromatic Nitriles: Formation of Aryldifluoromethyl Isocyanates and Aryltrifluoromethanes
Authors: Thompson James Wood , Howell Jon L. , Clifford Alan F. 
Published: November 2013

AbstractCarbonyl fluoride adds to arylmethanonitriles in the presence of anhydrous hydrogen fluoride and alkali metal fluorides to produce the corresponding aryldifluoromethyl isocyanates. The aryldifluoromethyl isocyanates react with two additional moles of arylmethanonitrile to yield aryltrifluoromethanes and 2‐hydroxy‐4, 6‐diaryl‐s‐triazines. Alkali metal fluorides also enhance this reaction and suppress the formation of 2, 4, 6‐triaryl‐s‐triazines. With electron‐withdrawing substituents on the aromatic ring, the reactions do not yield any significant quantity of the aryltrifluoromethanes, but stop at the aryldifluoromethyl isocyanate stage.
Detection of Fragment Genesis in the Mass Spectrometer. IV. Peptide Sequencing by DADI‐MS
Authors: Schlunegger Urs Peter , Hirter Peter 
Published: November 2013

AbstractIn oligomers, a structure element is repeated periodically. If a fragmentation pathway in the mass spectrometer is detectable arising from such a periodicity of structure, an analysis of the sequence of monomers is possible. This is the case in oligopeptides. Tracing the generation of consecutive ions stepwise by DADI‐MS leads successfully to the sequence of amino acids in tripeptides. This is demonstrated by different examples containing simple and more complex amino acids.
Electron Impact Induced Fragmentation and Rotational Isomers of Alicyclic Amines
Authors: Longevialle Pierre , Astier Alain 
Published: November 2013

AbstractThe electron impact mass spectra of the epimers 3β‐dimethylamino‐3α‐methyl cholestane and 3α‐dimethylamino‐3β‐methyl cholestane are different. The favoured loss of a methyl radical from the latter (further enhanced at low ionization voltage) is attributed to the predominance in the molecular ions of this compound, of one rotational isomer in which the nitrogen n orbital is antiparallel with the C3‐methyl bond. The mass spectra of the corresponding primary and secondary amines confirm this interpretation. These results show the role of the configuration of the amino‐group in the fragmentation and the existence of rotational isomers in the molecular ion.