bluuebunny/crossref_metadata_2025_split huggingface dataset:
Madelung Constants
Authors: Hoppe R. 
Published: December 2003

AbstractMadelung constants are simple numbers which depend on the type of structure investigated. They are needed for the calculation (using the Born‐Haber cycle) of lattice energies and enthalpies of formation of ionic compounds. Each Madelung constant is the sum of partial Madelung constants which represent the contributions of the individual ions to the total lattice energy. The partial Madelung constants depend on the ionic charge and, clearly though not stringently, on the coordination number. On the other hand, each Madelung constant can be represented by a sum of Madelung constants for related simple primitive AB structures. Surprisingly, these Madelung constants are numerically interrelated in a simple manner, and are related to the partial Madelung constants of interstitial sites. – Madelung constants of parameter‐dependent structures (e.g. of the rutile or anatase type) and their variations with the structure‐determining quantities are of particular interest. Madelung constants also yield information in the case of complex compounds and – surprisingly – of non‐metal compounds (e.g. XeF2, XeF4, XeF2·XeF4).
Allyl‐Transition Metal Systems
Authors: Wilke G. , Bogdanović B. , Hardt P. , Heimbach P. , Keim W. , Kröner M. , Oberkirch W. , Tanaka K. , Steinrücke E. , Walter D. , Zimmermann H. 
Published: December 2003

AbstractAs a continuation of a report published in 1963, recent results in the field of allyl‐transition metal complexes are describedThe term “allyl compounds” in the present paper refers not only to compounds containing the simple allyl group (CH2CHCH2), but also to those that contain substituted allyl groups or allyl groups forming part of a ring system.
. Syntheses and reactions of these compounds, as well as the bonding between metal and allyl group, are discussed. Allyl‐transition metal complexes form the basis of extremely selective catalysts for homogeneous reactions of 1, 3‐diolefins and of olefins; the metal atoms in these “matrix” catalysts are either “bare”The description “bare” is applied to complexed metal atoms from which the ligands can be quantitatively displaced by the substances taking part in catalytic reactions.
or are bound to only a few ligands.
Diels‐Alder‐Reactions Part I: New Preparative Aspects
Authors: Sauer J. 
Published: December 2003

AbstractCycloadditions of conjugated dienes, named after their discoverers, have claimed preparative and mechanistic interest for nearly 40 years. The almost inexhaustible variability of the components of these one‐stage reactions offers entry to important classes of compounds. The systematization of the preparative uses of these reactions which is offered in this paper relates predominantly to recent results. The mechanistic aspects of the Diels‐Alder reactions will be discussed later in the second part of this contribution.
Specification of Molecular Chirality
Authors: Cahn R. S. , Ingold Christopher , Prelog V. 
Published: December 2003

AbstractThe topological analysis of chiral molecular models has provided the framework of a general system for the specification of their chirality. The application, made in and before 1956, of this system to organic‐chemical configurations is generally retained, but is redefined with respect to certain types of structure, largely in the light of experience gained since 1956 in the Beilstein Institute and elsewhere. The system is now extended to deal, on the one hand, with organic‐chemical conformations, and, on the other, with inorganic‐chemical configurations to ligancy six. Matters arising in connexion with the transference of chiral specifications from model to name are considered, notably that of the symbiosis in nomenclature of expressions of the general system and of systems of confined scope.For corrigendum see DOI:10.1002/anie.196605111
Spectroscopy with Polarized Light
Authors: Dörr F. 
Published: December 2003

AbstractPolarized light is used in electronic spectroscopy not only to obtain information about the positions. Intensities, and fine structures of absorption and luminescence bands, which can be obtained by normal electronic spectroscopy of solutions, but also to determine the orientation of the transition moments in relation to the molecular framework. The theoretical and experimental principles of molecular optical anisotropy are briefly described, and the three most successful methods (spectroscopy after mechanical alignment of the molecules on films and in crystals, or after electrical alignment in solution, and luminescence polarization of solid solutions) are discussed in detail and illustrated by typical examples. In connection with luminescence polarization, special emphasis is placed on triplet‐singlet phosphorescence. Reference is made to the importantce of polarization measurements on liquid solutions in biochemistry (study of intermolecular interactions of macromolecules by measurement of the rotational relaxation times).
Technology of the Microbiological Preparation of Organic Substances
Authors: Müller R. , Kieslich K. 
Published: December 2003

AbstractThe preparation of organic substances with the aid of the enzyme systems of micoorganisms has become competitive as a result of recent progress in the technology of fermentation. The relatively high cost of apparatus and the lower production capacity of microbiological plants in relation to the plants used in purely chemical processes are offset in many cases by the advantages of biological methods (reactions at conventionally inactive positions in the molecule, stereospecific substitutions, coupling of several reactions, mild reaction conditions, possible use of waste products).
Synthesis of Isocyanates and Carbodiimides
Authors: Ulrich H. , Sayigh A. A. R. 
Published: December 2003

AbstractThe reaction of 1,3‐disubstituted ureas and 1‐arylsulfonyl‐3‐alkylureas with phosgene permits the preparation of a number of isocyanates and sulfonyl isocyanates that had not previously been described, or that were difficult to prepare. 1,3‐Disubstituted thioureas and 1‐aryl‐(or alkyl)sulfonyl‐3‐alkylthioureas give carbodiimides. Thionyl chloride and phosphorus pentachloride react with the urea derivatives in the same way as phosgene. Oxalyl chloride reacts with ureas to form parabanic acid derivatives, whereas with thiourea it gives 2‐imino‐1,3‐thiazolidine‐4,5‐diones, which can isomerize to parabanic acid derivatives.
The Chemistry and Biochemistry of Insulin
Authors: Klostermeyer H. , Humbel R. E. 
Published: December 2003

AbstractThe protein hormone insulin occurs widely in the animal kingdom. Although its biological function is always the same, its amino‐acid composition varies widely. Insulin consists of two polypeptide chains, which are linked by three cystine residues to form a bicyclic system with a 20‐membered and an 85‐membered ring. The protein crystallizes in various forms with foreign ions. In solution, insulin normally forms aggregates of 2n molecules. The hormone can be regenerated from the separated polypeptide chains, and its total synthesis has been achieved in a similar manner from synthesized peptide chains. In the biosynthesis of insulin, the two chains are evidently built up separately and subsequently linked together. Insulin promotes the synthesis of glycogen, fat, and protein in the organism; insulin deficiency leads to an increase in the blood‐sugar level. At the molecular level, the mechanism of action of the hormone is still unknown. Current hypotheses are discussed. No specific active center has so far been detected in the insulin molecule, which contains several antigenic regions.
Relation of Microbes to Blood‐Group Active Substances
Authors: Springer G. F. 
Published: December 2003

AbstractSubstances with blood‐group ABH(0) specificity are not confined to human red blood cells. Rather, such substances are ubiquitous antigenic surface structures which Nature has preserved throughout the phylogenetic development from microbes to man. — It could be shown experimentally that so‐called “pre‐existing natural” antibodies can result from inapparent immunization by these widely distributed antigens. — The blood‐group specific structures of bacteria are chemically closely related to the determinant structures of the human blood‐group ABH(0) glycoproteins. The situation is more complicated for the blood‐group active substances from higher plants; these give extraordinary immunochemical reactions and two of their blood‐group specific monosaccharides precipitate antibodies. — Recently the nature of the M and N blood‐group antigens of erythrocyte surfaces has been elucidated. They are the main antigens of the second of at least 14 human blood‐group systems. These substances, which are glycoproteins, are also excellent myxovirus receptors and inhibitors. The NN antigen is the first reported physically homogeneous, chemically defined and highly blood‐group active cell surface structure of human origin. As surface structures, blood‐group active substances appear to be frequently endowed with receptor properties in addition to those for blood‐group antibodies.
Heterolytic Fragmentation. A Class of Organic Reactions
Authors: Grob C. A. , Schiess P. W. 
Published: December 2003

AbstractHeterolytic fragmentation is a widespread but neglected class of organic reactions. It involves the regulated cleavage of molecules containing certain combinations of atoms such as carbon, oxygen, nitrogen, sulfur, phosphorus, silicon, boron and halogens. Fragmentation reactions are useful in degradation and structure elucidation, some are also of preparative value. A knowledge of the structural and electronic requirements makes it possible to predict and influence the course of reactions. From a theoretical viewpoint the recognition of heterolytic fragmentation has lead to the classification and correlation of a large number of apparently diverse reactions. Selected cases are reviewed in this article.
Trifluorophosphine Complexes of Transition Metals
Authors: Kruck Th. 
Published: December 2003

AbstractThe present paper deals with a new class of inorganic coordination compounds, the first member of which, tetrakis(trifluorophosphine)nickel(0), was discovered in 1951. Not only have the neutral metal(0) trifluorophosphines been prepared, but also a number of their derivatives (trifluorophosphinemetal hydrides and trifluorophosphinemetallates, as well as nitrosyl, carbonyl, halogeno, and aromatic trifluorophosphine complexes). These compounds have been characterized by their chemical behavior and by spectroscopic and magnetochemical studies. Trifluorophosphine has the strongest π‐acceptor properties of all neutral ligands, and is therefore particularly suitable for the stabilization of unusually low oxidation states (zero and negative) of transition metals.
Sulfines and Sulfenes – the S‐Oxides and S,S‐Dioxides of Thioaldehydes and Thioketones
Authors: Opitz G. 
Published: December 2003

AbstractFour sulfines have so far been prepared by elimination of HCl from sulfinyl chlorides with triethylamine and by oxidation of diaryl thioketones with peracid. They are colored, crystalline compounds, which slowly decompose at room temperature. Attempts to prepare sulfenes have not yet been successful, but mesylsulfene[1] has been isolated as the trimethylamine adduct. It can be shown by interception reactions that sulfenes are formed as intermediates by the action of trialkylamines on aliphatic sulfonyl chlorides and by the action of sulfur dioxide on diazoalkanes. They react with ROD to form monodeuterated sulfonates, with diazoalkanes to give three‐membered rings, with enamines, dienamines, ketene O,O,O,N‐, and N,N‐acetals, and chloral, and in some cases with vinyl ethers, to give four‐membered rings. They also react with nitrones to give five‐membered rings, and with β‐aminovinyl ketones and dienamines to give six‐membered rings.
Syntheses of Thiocarbamates
Authors: Walter W. , Bode K.‐D. 
Published: December 2003

AbstractThe methods suitable for the preparation of thiocarbamates are described and illustrated by examples and procedures. They are grouped under the following headings:
Addition of Alcohols and Thiols to Isothiocyanates
Thioacylation of Amines
with chlorothioformates
with O,S‐diesters of dithiocarbonic acid
with trithiocarbonates

Thioacylation of Alcohols, Phenols, and Thiols
with thiocarbamoyl chlorides
with N,N‐dialkylmercaptochloroformimidium chlorides
with N,N′‐thiocarbonyldiimidazole

Reaction of Thiocyanates and Cyanates with Hydrogen Sulfide
Alkylation of Metal Dithiocarbamates
Additions to Thiocyanic Acid
The Solvent Dimethyl Sulfoxide
Authors: Martin D. , Weise A. , Niclas H.‐J. 
Published: December 2003

AbstractThe dipolar aprotic solvent dimethyl sulfoxide is liquid over a wide range of temperatures, is a strong electron donor, and has a high polarity. It is therefore an excellent and selective solvent for many organic and even polymeric compounds, and can enter into H‐bonding and dipole‐dipole association. The structure of dimethyl sulfoxide, with a “hard” oxygen atom and a “soft” sulfur atom, leads to good solvation of cations and poor solvation of anions. Mixtures of alkoxides with dimethyl sulfoxide are therefore among the most strongly basic systems in organic chemistry, and are excellently suited for the deprotonation of weakly acidic OH, NH, and CH bonds, for eliminations, and for the initiation of polymerizations.
Benzene Oxide‐Oxepin Valence Tautomerism
Authors: Vogel E. , Günther H. 
Published: December 2003

AbstractBenzene oxide and the potential 8π‐electron system oxepin exist in valence‐tautomeric equilibrium with each other, to which both components contribute to approximately the same extent. NMR spectroscopic measurements show that the equilibrium is rapidly established (activation energies of the forward and reverse reactions 9.1 and 7.2 kcal mole−1, respectively). The present knowledge of the properties of oxepin justifies its classification as a “heterotropilidene”. Benzene oxide‐oxepin represents a system having fluctuating bonds, the equilibrium of which can be displaced from one extreme to the other by means of suitable substituents. The oxide component determines the reactions of the system with most agents.With 1,6‐oxido[10]annulene, which is formally a 2,7‐bridged oxepin, the oxepin character is completely suppressed by the formation of a delocalized 10π‐electron system extending over the C10 perimeter. The existence and aromatic character of 1,6‐oxido[10]‐annulene give rise to the conception of a homologous series of oxygen bridged annulenes (1,6; 8,13‐bisoxido[14]annulene, 1,6; 8,17; 10,15‐trisoxido[18]annulene etc.), which, like the parent acenes, possess a (4n + 2)π‐electron system. Molecular models demonstrate that a considerable flattening of the C4n+2 perimeter is achievable in the case of a syn or all‐syn arrangement of the oxygen bridges, and that the requirement for aromaticity is thus satisfied. This is confirmed in a striking manner by the synthesis and properties of syn‐1,6; 8,13‐bisoxido[14]annulene.
Recent Chemistry of Bullvalene
Authors: Schröder G. , Oth J. F. M. 
Published: December 2003

AbstractThe essential structural element of bullvalene is the homotropilidene system. Thus in any discussion of the chemistry of bullvalene, all bridged homotropilidenes must also be considered. The present article deals with new syntheses and with the thermal behavior of the homotropilidene system and of bullvalene. Emphasis is also placed on the syntheses and the NMR‐spectroscopic behavior of complexed bullvalene, of monosubstituted, disubstituted, and fused bullvalenes, and of some benzobullvalene derivatives.
Separation of the Isotopes of Uranium by the Separation Nozzle Process
Authors: Becker E. W. , Bier K. , Bier W. , Schütte R. , Seidel D. 
Published: December 2003

AbstractThe separation nozzle process is based on the partial spatial separation of components of different mass in an expanding supersonic jet stream. The process is of especial interest for the separation of uranium isotopes. Details of a systematic experimental determination of the most favorable operating conditions for such a separation are given and the construction and testing of a closed circulation system, the basic unit of a ten membered pilot cascade separator for uranium isotope separation, is described. The optimum values of the specific cost factors obtained experimentally for the separation nozzle process are compared with the corresponding values estimated for the gaseous diffusion process.
Siloxane Compounds of the Transition Metals
Authors: Schindler F. , Schmidbaur H. 
Published: December 2003

AbstractHeterosiloxanes of transition metals contain the characteristic grouping SiOX; in the compounds known so far, X may be Au, Zn, Cd, Hg, Ti, Zr, Hf, V, Nb, Ta, Cr, U, Re, Fe, Co, Ni, or Pt. Most of these compounds are obtained from silanols, metal silanolates, acyloxysilanes, disiloxanes, or alkoxysilanes, i.e. from compounds that already contain an SiO bond. The transition metal may be introduced e.g. as a halide, as an organometailic compound, as an alkoxy compound, or as an oxide. Heterosiloxanes are also formed on reaction of many silicon compounds that do not contain oxygen with transition metal compounds containing oxygen. Some of these compounds, e.g. some titanosiloxanes, are very stable, whereas others decompose explosively. Oligomeric and polymeric heterosiloxanes exist in addition to the monomeric compounds.
Mitochondrial Oxidative Phosphorylation
Authors: Schatz G. 
Published: December 2003

AbstractMitochondria can form ATP from ADP and inorganic phosphate, the required energy being supplied by respiration. This coupled process, which in sufficiently aerated normal animal cells furnishes the bulk of the cellular ATP, is termed oxidative phosphorylation. The overall reaction is intimately associated with the mitochondrial inner membrane and proceeds via a primary high‐energy intermediate. This intermediate, in a manner as yet unknown, energizes the anhydride formation between ADP and inorganic phosphate. The coupling between respiration and ATP synthesis is mediated by proteins of the mitochondrial inner membrane which are known as “coupling factors”. The mechanism of oxidative phosphorylation is at present being discussed in terms of three hypotheses which are generally referred to as “chemical”, “chemiosmotic”, and “conformational” hypotheses. None of these hypotheses has as yet been experimentally verified.
Circular Dichroism and Optical Rotatory Dispersion — Principles and Application to the Investigation of the Stereochemistry of Natural Products
Authors: Snatzke G. 
Published: December 2003

AbstractThe principles of circular dichroism and of optical rotatory dispersion are described. Examples are given to illustrate the use of these methods for the determination of the configurations and conformations of natural and synthetic products. Some limitations of the octant rule are mentioned.
α‐Lactams (Aziridinones)
Authors: Lengyel I. , Sheehan J. C. 
Published: December 2003

Abstractα‐Lactams have often been postulated as intermediates in numerous processes. The isolation of the first α‐lactam, N‐tert‐butyl‐3‐phenylaziridinone, was accomplished in 1962. Since then, further N‐ and C‐3‐substituted α‐lactams have been synthesized. Most of these very reactive compounds undergo easy thermal decomposition; remarkable is the relative stability of 1,3‐di‐tert‐butylaziridinone, which does not start to decompose below 140°C. The α‐lactam ring is opened by nucleophilic reagents. — The correlation of stability and substituents is discussed in the last section. An acyclic, planar or almost planar, charge‐delocalized intermediate is suggested to explain the observed effects.
The Cool Flames of Hydrocarbons
Authors: Fish A. 
Published: December 2003

AbstractThis review describes the properties of the cool‐flame and two‐stage ignition processes that characterize the gaseous oxidation of hydrocarbons and discusses the chemical reactions that are responsible for these phenomena. Cool flames result from a chainthermal acceleration of reaction rate. It is probable that the free‐radical chain involved is propagated by the reaction of an alkyl radical with oxygen to give an alkyperoxy radical which isomerizes to a hydroperoxyalkyl radical. The decomposition of this radical produces a hydroxyl radical, which attacks the hydrocarbon rapidly and unselectively to regenerate an alkyl radical. Branching probably results from the pyrolysis of mono‐ and dihydroperoxides, from the oxidation of aldehydes, and from radical‐molecule reactions. This reaction scheme explains the existence of a low‐temperature ignition peninsula and the relation of the extent and shape of this peninsula to the molecular structure of the hydrocarbon. The chemical relevance of cool flames to abnormal combustion phenomena, such as knock, in gasoline engines is discussed.
The Structure and the Function of Gangliosides
Authors: Wiegandt H. 
Published: December 2003

AbstractGangliosides are found in the brain and other organs, and are composed of sphingosine, fatty acids, hexoses, and sialic acid. Types of gangliosides differ in the fatty acids and the sugar residues. The carbohydrate residue in the quantitatively predominating brain gangliosides is ganglio‐N‐tetraose, a tetrasaccharide. In these gangliosides, this residue combines with one or more molecules of sialic acid. The oligosaccharide part is a carrier of serologic properties. Gangliosides are characteristic lipid components of some neuronal membranes in the central nervous system, and can be localized on the synaptic apparatus of nerve cells in the cerebral cortex. Their site of occurrence and physiological action point to their participation in the transmission of impulses. It was in the brains of the mentally ill that gangliosides were first discoverd, and indeed their pathologic accumulation can possibly be attributed to congenital defect of enzymes involved in their synthesis or metabolism. Gangliosides are produced from their components by acceptor‐specific transferases.
Recent Results in the Field of Liquid Crystals
Authors: Saupe A. 
Published: December 2003

AbstractThermotropic mesomorphous phases such as occur in the melts of many organic substances are considered. Though mesomorphous melts were first observed by Reinitzer in 1888, fundamental structural problems regarding such melts have not, as yet, been completely solved. Part I of this article deals mainly with such structural problems and with the theories of crystalline organic liquids. Part II describes the use of nematic solvents for magnetic resonance studies on oriented molecules. Examples are given to illustrate the possibilities offered by this procedure, and some of the results obtained so far are reviewed.
The Degradation of Poly(ethylene terephthalate)
Authors: Buxbaum L. H. 
Published: December 2003

AbstractThe penetration of new markets by polyester fibers has emphasized the need for increased stability of the polyester toward a variety of degradative reactions. Extensive studies of the nature of the thermal, hydrolytic, oxidative, and radiation‐induced degradation reactions have been reported. The interpretation of kinetic investigations and the identification of the reaction products have been facilitated by using suitable esters as model compounds in place of the polymeric species.
Formation and Properties of Solvated Electrons
Authors: Schindewolf U. 
Published: December 2003

AbstractIn the formulation of many chemical reactions, electrons are regarded as readily transferable particles, though their participation in these reactions cannot be directly observed. However, the discovery that electrons can be produced in various ways in suitable solutions and that they are stabilized by solvation and can thus be studied directly has recently led to a rapid growth of interest in these, the simplest and most reactive particles of chemistry. The solvated electron has physical properties that permit its detection by various methods even at very low concentrations, so that it is also possible to follow its many reactions, most of which are extremely fast.