bluuebunny/crossref_metadata_2025 huggingface dataset:
Dinitrophenylation and Thiolysis as a Tool in Protein Chemistry
Authors: Shaltiel Shmuel
Published: November 2013

The thiolytic cleavage of 2,4 dinitrophenyl derivatives of sulfhydryls, imidazole imino‐nitrogens, and phenolic hydroxyls converts dinitrophenylation into a reversible method for masking or labeling these functional groups. The merits of this method are illustrated in the synthesis of peptides and polyamino acids (including a potent synthetic immunogen), in sharpening the specificity of dinitrophenylation, in masking “super reactive” nucleophiles in proteins while labeling “buried” functional groups, and in the probing and three‐dimensional mapping of enzyme active sites. Analytical techniques for monitoring the rate and extent of the thiolysis step are described.
Some Stereochemical Implications of the Molecular Conformation of Collagen
Authors: Traub Wolfie
Published: November 2013

A space‐filling model of collagen has been constructed in accordance with the conformation found for (Gly.Pro.Pro)n. The model shows that leucyl and phenylalanyl residues can be easily accommodated at position X of the collagen tripeptide sequence Gly.X.Y, but are severely constrained by steric hindrance at position Y. Examination of the model has also led to the suggestion that hydrogen bonding of hydroxyproline OH through a water molecule to glycyl CO on the same polypeptide chain might account for the stabilisation of the triple helix conformation by hydroxyproline.
Chemistry of Parathyroid Hormone
Authors: Potts John T.
Published: November 2013

Advances in newer techniques for high sensitivity sequence analysis of polypeptides coupled with improvements in solid phase synthesis procedures have led to systematic analyses of structure‐activity relations in parathyroid hormone. Twenty‐five amino acids at the amino terminus of the 84 amino acid peptide suffice for biological expression of hormonal actions on kidney and bone in vivo and in vitro.
Uranyl Halide Species Sorbed on Ion Exchangers
Authors: Heitner‐Wirguin C. , Gantz M.
Published: November 2013

Uranyl ions were sorbed on a cation and anion exchanger from fluoride, chloride, and bromide solutions. The visible and IR spectra of the sorbed species were recorded. The species identified were UO2F−3, UO2Cl+, UO2Cl−3 and UO2Cl2−4, UO2Br+ and UO2Br2−4. Analysis of the spectra obtained made possible the determination of the coordination number and the symmetry of the species, i.e., the cationic species have the coordination number six, while the anionic species have the coordination number four.
Dwell Time Distribution Behind Reflected Shocks in a Single Pulse Shock Tube
Authors: Lifshitz Assa , Schechner Pinchas
Published: November 2013

The 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

An 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

The 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

A 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

A 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.
Solid‐Gas Reactions. Part IV the Effect of Light on the Bromination of Some Solid Cinnamic Acids
Authors: Hadjoudis E.
Published: November 2013

Light slows down the rate of reaction of gaseous bromine with some solid cinnamic acids. An explanation of the effect is given.
Synthesis of ω‐Halogenohydroxamic Acids and Their Characterization by Appropriate Condensations
Authors: Bittner S.
Published: November 2013

A 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

The 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

A 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

The 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

This 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

Work 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

Structural 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

Photodissociation 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

The 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

The 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

Z‐(−)‐(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

A 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

Chirality 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

The 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

Sulfenamides 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

It 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

The 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

Starting 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.
XV. Assessment of Accuracy
Authors: Rees Bernard
Published: November 2013

The uncertainty of X‐ray structure factors is discussed. Formulae are given for the estimation of variances and covariances in experimental electronic charge and deformation densities, and in related quantities, e.g. atomic charges.
Appendix 1. Use of the Gaussian‐70 Molecular Orbital and Electron Density Programs
Authors: Engel Y. M. , Hagler A. T.
Published: November 2013

We 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

A 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

The 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

Excited 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

Recent 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

The 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

Relatively 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

Carbonyl 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

In 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

The 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.
The Alternating Current Electrode Processes
Authors: Venkatesh S. , Chin Der‐Tau
Published: November 2013

This paper reviews the fundamentals of the alternating current (AC) electrochemical processes. The topics include: the faradaic impedance, the faradaic rectification, AC polarography, AC corrosion and the AC electrolytic methods currently being used in the industry.
Kinetic and Structural Consequences Derived from Ageing Effects on Electrochemically Formed Layers
Authors: Arvía A. J.
Published: November 2013

The 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

The 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

All 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

Solid‐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

Methods 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

Complexes [(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.
A Transformation Approach to the Eckart Hamiltonian
Authors: Sutcliffe B. T.
Published: November 2013

An alternative transformational approach to the Eckart Hamiltonian is proposed, the aim being to show that much of the structure of the Hamiltonian does not depend on precise co‐ordinate choices but reflects the underlying symmetry invariances.
Studies on Charge‐Transfer Theory Mulliken Population and Measure of Charge Transfer
Authors: Re G. Del , Otto P. , Ladik J.
Published: November 2013

The 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.
The Number of Independent Internal Coordinates in Symmetrical Molecules
Authors: Pople John A. , Sataty Y. Aviva , Halevi E. Amitai
Published: November 2013

A simple algorithm is presented for determining the number of internal degrees of freedom of a symmetrically constrained molecule.
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

A 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

Structure–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

Semiclassical 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

The 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

In 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

Z‐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

The 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

Reaction 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

The 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

Because 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.
Chemistry of the Oxocarbons
Authors: West Robert
Published: November 2013

The chemistry of the oxocarbons is reviewed, with emphasis on findings published within the last ten years.
Diaminocyclopropenethiones: Synthesis and Reaction Feature
Authors: Yoshida Zen‐Ichi , Konishi Hisatoshi , Ogoshi Hsanobu
Published: November 2013

Several 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

In 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

The 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

Comparison 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.