bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structures and Syntheses of Carboranes
Authors: Köster R. , Grassberger M. A. 
Published: December 2003

AbstractFollowing a discussion of bonding, the structures of the known carboranes of the clovo type and of the incompletely condensed types are described; the recently discovered carboranes with high carbon contents, such as tetracarbahexaborane (“boracarbane”) are also discussed. The preparation of carboranes from polyboranes and the possibility of obtaining organo carboranes from organoboranes are then described. Some rearrangements which take place within the carborane skeleton are also mentioned.
Reactions with Molecular Oxygen
Authors: Fallab S. 
Published: December 2003

AbstractMolecular oxygen is an important oxidizing agent both in industrial and in biological processes. In many of these processe, the O2 molecule reacts preferentially with free radicals, which are frequently paramagnetic metal ions. Homogeneous systems of this type that are described in the literature are discussed, and an attempt is made to establish the factors that determine the course and mechanism of the reaction.
Hexamethyl(Dewar Benzene) (Hexamethylbicyclo[2.2.0]hexa‐2,5‐diene)
Authors: Schäfer W. , Hellmann H. 
Published: December 2003

AbstractHexamethyl(Dewar benzene) was first obtained by bicyclotrimerization of 2‐butyne in the presence of aluminum chloride. This preparation provided a basis for a comprehensive study of the chemical reactivity of Dewar benzene derivatives. Interesting information concerning the reactivity of the permethylated Dewar benzene system can be deduced from its behavior on hydrogenation and oxidation, and, in particular, from the addition of H‐acidic compounds and from the substitution and elimination reactions of the resulting adducts.
Polymerization of Trioxane
Authors: Weissermel K. , Fischer E. , Gutweiler K. , Hermann H. D. , Cherdron H. 
Published: December 2003

AbstractA survey of the possible modes of polymerization of trioxane is followed by a discussion of current ideas concerning the course of the polymerization. The polymerization, which involves ring cleavage, is characterized by a number of side reactions of the growing polyoxymethylene cations, such as chain transfer, transacetalization, and hydride shift. These reactions not only determine the nature of the end groups and the molecular weight of the resulting polyoxymethylenes, but are also responsible for their chemical and molecular uniformity. Special emphasis is placed on the role of the monomeric formaldehyde formed during the polymerization of trioxane.
Electrophilic Substitution of Heteroaromatic Compounds with Six‐Membered Rings
Authors: Katritzky A. R. , Johnson C. D. 
Published: December 2003

AbstractThe limited amount of quantitative data available on the electrophilic substitution of heterocycles is surveyed. Initial objectives are first to determine the species undergoing substitution and then to find out the amount by which the heterocyclic atom or group activates or deactivates the ring by comparison with the corresponding benzenoid compound. When sufficient data are available it is hoped to correlate this by means of a Hammett‐type treatment or by MO methods.
Formation and Properties of Carbosilanes
Authors: Fritz G. 
Published: December 2003

AbstractThe present paper describes the formation of silicon‐carbon compounds (carbosilanes), the molecular skeletons of which consist of alternate Si and C atoms, and which can be obtained by thermal decomposition of Si(CH3)4, CH3SiCl3, (CH3)2SiCl2, and (CH3)3SiCl. The description of the formation of carbosilanes is followed by a discussion of the reactions of polychlorinated carbosilanes with organometallic compounds.
Chemical Gamma‐Resonance Spectroscopy
Authors: Goldanskii V. I. 
Published: December 2003

AbstractTwo of the most important contributions that nuclear physics has made to modern science and technology have been in the fields of nuclear energy and isotope labeling. In recent years nuclear physics has stimulated the appearance and extremely rapid development of yet another new and equally important scientific discipline, namely gamma‐resonance spectroscopy. This new branch of spectroscopy, which is based on the Mössbauer effect[1–3] is playing an increasingly important role in physics, chemistry, biology, geology, and in the elucidation of various technical problems. – This paper deals briefly with the basic physics of the Mössbauer effect and the characteristics of Mössbauer (gamma‐resonance) spectra, and then considers various applications of this new type of spectroscopy. Particular attention is paid to the fundamentals and development of chemical gamma‐resonance spectroscopy [4–9] as a technique for the resolution of problems in various fields of chemistry and biology and to the range of problems tackled in recent years in our laboratory of nuclear and radiation chemistry at the Institute of Chemical Physics of the Academy of Sciences of the USSR. A number of reviews and monographs dealing with the application of the Mössbauer effect in chemistry have already been written [4–12]. The following work is based mainly on experimental results obtained by research workers in the Soviet Union.
Physical Causes of Aging in Plastics
Authors: Stuart H. A. 
Published: December 2003

AbstractA number of physical changes that take place in a polymer below the glass transition temperature without the action of a medium are first described, and are then explained on the basis of changes in supramolecular order. Pure stress crazing with the characteristic self‐limitation of craze growth is then considered. Models are developed to explain stress crazing under the influence of a wetting medium. Attempts to reduce stress crazing are then treated and the article closes with a discussion of the influence of morphological structure on crazing and cracking.
Nitrenes and the Decomposition of Carbonylazides
Authors: Lwowski W. 
Published: December 2003

AbstractThe decomposition of organic carbonylazides can lead to the formation of nitrenes. Ethoxycarbonylnitrene is formed in the photolytic and thermal decomposition of ethyl azidoformate and by α‐elimination from N‐(p‐nitrobenzenesulfonyloxy)urethan. Both of the possible electronic states of this nitrene take part in intermolecular reactions. Pure singlet nitrene is formed by α‐elimination from the urethan and on thermal decomposition of ethyl azidoformate, but changes so rapidly into the triplet form that the reactions of both forms are observed. Singlet ethoxycarbonylnitrene undergoes selective and stereospecific insertion into CH bonds and adds stereospecifically to olefins. Triplet ethoxycarbonylnitrene, however, does not undergo insertion into CH bonds, and adds to olefins with complete loss of the geometric configuration. By following quantitatively the stereospecificity of the addition reaction and by selective interception of the triplet and singlet forms of the nitrene, it can be shown that the photolysis of ethyl azidoformate leads directly to nitrene of which one third is in the triplet state. In the decomposition of aryl‐ and alkylcarbonylazides (acid azides), the removal of nitrogen is accompanied by a synchronous rearrangement to isocyanates (Curtius rearrangement). In this system, nitrenes are obtained only by photolysis. They add to double bonds and undergo very selective insertion into CH bonds, but do not rearrange at a measurable rate to isocyanates. The photolytic Curtius rearrangement is also a concerted reaction.
Hydration of cn bonds in heteroaromatic substances
Authors: Albert A. 
Published: December 2003

AbstractMany aromatic N‐heterocycles add water across the CN double bond. Methods are described for recognizing this phenomenon and for diagnosis of the site of attack. These methods are extended to the determination of (a) the ionization constants of unstable states (whether hydrated or anhydrous), (b) the ratio of hydrated to anhydrous forms at equilibrium, and (c) the rate constants of hydration. The features that stabilize hydration in a molecule are discussed. The literature through 1965 and 1966 is reviewed with special reference to the emergence of new principles, such as di‐hydration and the shifting of hydration within a molecule.
Formation and Properties of Medium and High Molecular Weight Compounds of Elements of Groups 3, 4, and 5
Authors: Fritz G. 
Published: December 2003

AbstractThe differences between compounds of carbon and of silicon are discussed, and the role of silicon as a fundamental structural component in inanimate nature is described. Starting with silicic acid and silicates, the structure and properties of the silicones and of compounds having SiCSi skeletons are described. The possibilities for the formation of high molecular‐weight compounds between elements of Groups 3 and 5 of the periodic system are considered, with particular reference to boron nitride and to aluminum‐phosphorus compounds.
Directed Aldol Condensations
Authors: Wittig G. , Reiff H. 
Published: December 2003

AbstractThe present article describes the discovery of a new procedure for aldol condensations for the preparation of α,β‐unsaturated carbonyl compoundsG. Wittig, H. Pommer, and W. Stilz, German Patent 1199252 (April 5, 1963), BASF; Chem. Abstr. 63, P 1739c (1965).
. The scope of this process is demonstrated by many examples, including some from the natural products sector; at the same time, however, these examples also mark its limitations. The metalated Schiff's bases may be classified as ambident anions; this also explains acylations on the nitrogen. A comparison of the new directed aldol condensation with the formation of unsaturated carbonyl compounds through olefination via phosphorylids shows that the latter method fails when a ketone is used as the substrate. This is where the described procedure using metalated Schiff's bases proves its value.
The Mechanism of the Wolff‐Kishner Reduction, Elimination, and Isomerization Reactions
Authors: Szmant H. H. 
Published: December 2003

AbstractThe mechanism of the Wolff‐Kishner reaction is discussed in the light of accumulated information about the kinetics, thermodynamics, and solvent effects of the process. Wolff‐Kishner reduction under normal conditions is thought to involve the trans hydrazone anion, which, in the rate‐determining step, exhibits a more or less concerted proton capture at the carbanion terminal and undergoes a solvent‐induced proton loss at the nitrogen terminal. The stereochemistry of the Wolff‐Kishner reduction is believed to be affected by the presence of “ortho” substituents and by a change to a nonpolar, aprotic reaction medium. The mechanism elaborated for the Wolff‐Kishner reduction is extended to the Wolff‐Kishner elimination and isomerization reactions. Conformational analysis of the intermediates permits correlation of the competitive reduction and elimination processes with the structures of acyclic systems.
Ternary Nitrides, Phosphides, and Arsenides of Lithium
Authors: Juza R. , Langer K. , Von Benda K. 
Published: December 2003

AbstractTernary phases have been prepared from lithium, another metal, and nitrogen, phosphorus, or arsenic. The ternary compounds, in particular the nitrides, are thermally more stable than the binary compounds. The lithium gives rise to a relatively high polar bonding component. At high temperatures, lithium and the second metal are often randomly distributed among the interstices of the metalloid lattice. The ordering processes that take place with decreasing temperature are investigated by X‐ray and magnetic methods and by differential thermal analysis. The phases are classified on a structural basis into seven groups.
Luciferins, Bioluminescent Substances
Authors: Goto T. , Kishi Y. 
Published: December 2003

AbstractThe bioluminescence of the American firefly Photinus is due to the reaction of 2‐(6‐hydroxybenzothiazol‐2‐yl)‐Δ2‐1,3‐thiazoline‐4‐carboxylic acid (“firefly luciferin”) with the enzyme luciferase in the presence of ATP and magnesium ion. In the crustacean Cypridina, on the other hand, the bioluminescence is due to the reaction of a luciferase with 8‐(3‐guanidinopropyl)‐6‐indol‐3‐yl‐2‐(1‐methylpropyl)‐3,7‐dihydroimidazo[1,2‐a]‐pyrazin‐3‐one (“Cypridina luciferin”). The luciferin in Latia is 1,3,3‐trimethyl‐2‐(4‐formyloxy‐3‐methyl‐3‐butenyl)‐1‐cyclohexene and that in Renilla is a tryptamine derivative that has not yet been accurately identified; the luciferins of other luminescent organisms are not yet known. A review is given of the investigations which have been carried out on the above luciferins and the course of the luciferin‐luciferase reaction is examined. Numerous spectral data obtained during the examination of these compounds are included in the text.
Dodecacarbonyltriruthenium
Authors: Bruce M. I. , Stone F. G. A. 
Published: December 2003

AbstractSince the pioneering work of Mond and his coworkers the metal carbonyls and their derivatives have been under active study, and, as in other areas of inorganic chemistry, research activity has greatly increased in the last twenty years. Whereas hitherto our knowledge of the carbonyls of the heavier transition metals has been seriously hampered by a lack of good methods of synthesis, new preparative methods have recently been developed for Ru3(CO)12, and many new ruthenium carbonyl complexes are being discovered as its chemistry is explored.
The Oxidizing Properties of the Third Transition Series Hexafluorides and Related Compounds
Authors: Bartlett Neil 
Published: December 2003

AbstractSome of the transition metal hexafluorides demonstrate an astonishing oxidizing power. In particular may be mentioned PtF6, which is capable of oxidizing molecular oxygen or xenon, a process requiring an electron affinity, E(PtF6), > −156 kcal·mole−1. From a comparative study of all of the hexafluorides of the third transition series the electron affinity is seen to increase regularly in the sequence WF6 < ReF6 < OsF6 < IrF6 < PtF6. The increase in E with unit increase in atomic number of M appears to be ≈ −20 kcal·mole−1. On the other hand the ability of the hexafluorides to accept F− decreases along this series. This effect enables IrF6 to be more effective than PtF6 in the generation of nitrogen oxide trifluoride, ONF3, by the oxidative fluorination of nitrosyl fluoride, ONF. Both PtF6 and IrF6 interact spontaneously with ONF or O2NF to generate fluorine, at or below room temperature. The decrease in F− ‐acceptor ability along the series, which stands in sharp contrast to the increase in electron affinity, suggests that ligand crowding increases sharply across the series from WF6 to PtF6. This accords with the observed decrease in molecular volume along the series, both in the hexafluorides and in the MF6− salts. It is clear from this comparison that the species IrF6 and PtF6 are close to a minimum volume for this series. The oxide pentafluorides ReOF5 and OsOF5 are similar in oxidizing ability to their respective hexafluorides but are poorer F− acceptors. Evidently the ligand crowding in MOF5 molecules is greater than in MF6.
Cyclobutenediylium Dyes
Authors: Sprenger H.‐E. , Ziegenbein W. 
Published: December 2003

AbstractIn agreement with the aromaticity and electrophilic behavior of squaric acid, a cyclobutenediyliumtetroxide ion is formulated as a limiting form of the squarate dianion. These views are confirmed by the structure of a series of new compounds that are readily obtainable from squaric acid or its derivatives, and most of which are deeply colored. The compounds contain the cyclobutenediyliumdioxide grouping as the chromophore, and form a new class of dyes, for which the name cyclobutenediylium dyes is proposed.
Small Antiaromatic Rings
Authors: Breslow R. 
Published: December 2003

AbstractAccording to quantum mechanical calculations, systems with 4n π electrons ought to have anti‐aromatic character, i.e. be destabilized by resonance. This prediction is examined for the case of cyclopropenyl anion, the simplest system having 4n π electrons (n = 1). Isolation of compounds containing the cyclopropenyl anion has not, as yet, been achieved; however, kinetic measurements indicate the existence of the ion and confirm the unusual properties predicted.
Synthesis of Cyclopropyl Ethers and Cyclopropanols by Carbene Transfer – Acetolysis of Cyclopropyl p‐Toluenesulfonates
Authors: Schöllkopf U. 
Published: December 2003

AbstractThe reaction of chloromethyl phenyl ether with butyllithium in olefins yields phenoxy‐cyclopropanes. 1‐Chloro‐1‐phenoxycyclopropanes can be prepared in a similar manner, though the yields are poor. Alkoxycyclopropanes are formed when dichloromethyl alkyl ethers are treated with methyllithium/lithium iodide in the presence of olefins. Cyclopropanols can be obtained in good yields by reaction of (β‐chloroethoxy)cyclopropanes either with butyl‐ or ethyllithium or with bases. – As was shown by acetolysis experiments with cyclopropyl p‐toluenesulfonates having a known steric configuration, the rearrangement of a cyclopropyl derivative into an allyl cation proceeds in accordance with the Woodward‐Hoffmann‐DePuy rule. The solvolysis of exo‐bicyclo[n.1.0]alkyl p‐toluene‐sulfonates is assumed to proceed via “semi‐open” intermediates, which are somewhere between an allyl cation and a cyclopropyl cation.
Recent Developments in the Adhesives Field
Authors: Matting A. , Brockmann W. 
Published: December 2003

AbstractThe applications of adhesives have been greatly extended by the use of synthetic organic high polymers. It is possible nowadays to bond, not only wood, leather, and paper, but also glass, high‐strength plastics, and metals with adhesives of this type. They give satisfactory adhesion, flexibility, and mechanical properties even at high temperatures. A particularly important advance was the introduction of chemically or mechanically blocked polymer systems, which can reduce the cost of curing equipment when used as adhesives.
Nucleophilic Reactions of Metal Carbonyl Anions with Fluorocarbons
Authors: Bruce M. I. , Stone F. G. A. 
Published: December 2003

AbstractThis article describes the formation of carbon‐metal bonds by reacting carbonylmetalate ions with fluorocarbons. Complex formation depends on the nucleophilic behavior of the anions, and the susceptibility of fluorocarbons to this form of attack.
Trends in Radiation Polymerization
Authors: Potter R. C. , Schneider Christel , Ryska M. , Hummel D. O. 
Published: December 2003

AbstractPreviously it was generally assumed that high energy radiation could only initiate radical polymerization in solutions of monomers. However, examples of radiation‐induced polymerization have recently become known that proceed via an ionic mechanism. Thus, solutions of a monomer can be polymerized ionically, preferably in the presence of a solid, at low temperatures. Suprisingly, this may also be accomplished with ultra‐pure, mainly anhydrous systems, even at room temperature. The nature of the ions has not yet been fully elucidated.
Kinetic Studies on Substitution Reactions of Carbonylmetal Complexes
Authors: Werner H. 
Published: December 2003

AbstractKinetic studies of substitution reactions of carbonylmetals and of carbonylmetal derivatives in which other ligands (n or π donors) besides CO are bound to the metal atom have recently attracted great interest, and the results of these investigations throw a new light on theoretical and preparative problems. The substitution mechanism is determined mainly by steric and electronic factors.
The Catalytic Activity of Transition Metal Compounds in the Liquid‐Phase Oxidation of Hydrocarbons
Authors: Emanuel N. M. , Maizus Z. K. , Skibida I. P. 
Published: December 2003

AbstractThe way in which dissolved transition metal compounds affect the liquid‐phase oxidation of hydrocarbons is demonstrated for compounds of cobalt, copper, and manganese. Kinetic investigations on model systems and comparisons with the non‐catalyzed reaction show that the catalysts participate in all the oxidation steps.
Crystal Structure Analysis by Neutron Diffraction I
Authors: Will Georg 
Published: December 2003

AbstractNeutron diffraction is a valuable complement to X‐ray diffraction methods for the determination of crystal structures. A description of the principles of the method is followed by specific examples of the additional information obtained from neutron diffraction experiments: in the structural analysis of benzene, oxalic acid dihydrate, vitamin B12, ferrites, metal cyanides and carbides; and in studies of hydrogen bonding, ferroelectric effects, and thermal vibrations in crystals. Anomalous dispersion in neutron diffraction is also discussed.
Thiiranium Ions as Reaction Intermediates
Authors: Mueller Wolfgang H. 
Published: December 2003

AbstractThe addition of sulfenvl chlorides or sulfur dichloride to unsaturated compounds proceeds via thiiranium ions. The present article reviews the electronic and steric factors influencing the nature of these ions and their effects on subsequent ring opening and product formation. For the purpose of this discussion results primarily from electrophilic ring opening have been chosen to illustrate these factors. Solvent and temperature effects have been disregarded.
Mechanisms and Stereochemistry of Heterolytic Fragmentation
Authors: Grob C. A. 
Published: December 2003

AbstractHeterolytic fragmentation can proceed by several mechanisms. A study of the solvolysis of γ‐aminoalcohol derivatives NCCCX, where X equals halogen or OSO2R, shows that fragmentation may occur by a one‐step mechanism or by several multi‐step mechanisms depending on structural, electronic, and steric factors. The one‐step synchronous mechanism has rigorous stereoelectronic requirements. It is associated with an increased reaction rate as evidenced by the “frangomeric” effect. Ketoxime derivatives RR′CNX may undergo Beckmann fragmentation by the synchronous mechanism or by prior rearrangement depending on their α‐substituents. Fragmentation is frequently accompanied by conventional substitution, elimination, and rearrangement reactions. Under such circumstances knowledge of all possible mechanisms of a given substrate is essential to bring about a desired transformation.
The Ene Reaction
Authors: Hoffmann H. M. R. 
Published: December 2003

AbstractThe ene reaction is defined as the indirect substituting addition of a compound with a double bond (enophile) to an olefin with an allylic hydrogen (ene). For a long time the reaction has been neglected and has remained overshadowed by the related Diels‐Alder addition. It is shown that the ene reaction possesses wide scope and applicability ranging from industrial to biosynthetic processes. Preparative aspects are summarized and current views on the mechanism are discussed.
Sorption Promotors in Biopharmaceutics
Authors: Ritschel W. A. 
Published: December 2003

AbstractThe absorption of drugs depends on the physico‐chemical properties of the constituent substances. Drugs that are absorbed only with difficulty or only slowly, or even not at all, can be made to penetrate into the skin and the mucous membrane (penetration) or to pass through them (permeation) with the aid of “sorption promotors”. The search for substances of this type and the elucidation of their principles of action form part of the field of biopharmaceutics.