bluuebunny/crossref_metadata_2025 huggingface dataset:
Further Contributions to the Knowledge of Semimetals
Authors: Klemm W. , Niermann H.
Published: December 2003

Measurements on semimetals have been continued. Studies of the dependence on temperature of various properties have provided details regarding the transition from the nonmetallic to the more metallic structure. A second‐order transition has been found for tin at 170 °C, in which the c‐axis remains unchanged, while the a‐axis undergoes a small, discontinuous elongation.
Preparation of Carbon Tetrachloride from Phosgene
Authors: Glemser O. , Schröder J. , Kleine‐Weischede K. , Meyer Boris , Peuschel G. , Flügel R. , Velde D.
Published: December 2003

Carbon tetrachloride can be prepared from phosgene at 300–450°C. The catalysts for the reaction are transition metals of Groups V to VIII deposited on activated charcoal as carrier. Carbon monoxide and chlorine may be used as starting materials instead of phosgene.
A Secret of Chinese Porcelain Manufacture
Authors: Weiss Armin
Published: December 2003

The secret of old Chinese porcelain is the technique by which a material, capable of forming extremely thin‐walled articles, was obtained from a slightly plastic kaolin. Intercalation compounds, which form by treating kaolinite with decaying urine, give the key to the preparation of this material.
Theories of the Glass Electrode
Authors: Schwabe K. , Suschke H. D.
Published: December 2003

A review of the various theories of potential formation on the glass‐electrode is followed by a discussion of the deviations from the ideal hydrogen (H) electrode function in the acidic and alkaline ranges from the viewpoint of the phase‐boundary‐potential theory. The effect of the composition and solubility of the glasses on the electromotive behavior is interpreted as a “medium effect” in the gel layer.
The Biochemistry of Yeast Threonine Deaminase
Authors: Holzer H. , Boll M. , Cennamo C.
Published: December 2003

An optical assay, according to Warburg, for measuring the activity of the enzyme threonine deaminase (threonine → α‐ketobutyrate + NH) is described. Some of the properties of the enzyme from yeast have been studied using this assay. Pyridoxal phosphate and pyridoxamine phosphate stabilize the enzyme in the crude extract. Valine, leucine, and isoleucine, and to a lesser extent threonine, NH, and K+ protect the enzyme from inactivation when diluted with buffer. The enzyme is inhibited by isoleucine. The extend of the inhibition is dependent on the pH. Thus, in yeast, just as described for Escherichia coli by Umbarger, isoleucine exerts a control on its biosynthesis from threonine by means of a feed‐back mechanism, the extend of the control being related to the consumption of isoleucine in protein synthesis. NH represses the biosynthesis of threonine deaminase. This mechanism regulates the threonine deaminase‐catalysed formation of NH from threonine in accordance with the NH‐requirements of the growing cell.
Protonic States in Chemistry
Authors: Zimmermann H.
Published: December 2003

Protons are subject to the wave/particle dualism of matter. Hitherto, only the copruscular picture has been generally used in chemistry for describing protons. In contrast, the wave picture is considered in the present article. Protonic states, proton delocalization, and the tunnel effect in chemistry are discussed and illustrated by examples.
Coordination Chemistry and Catalysis. Investigations on the Synthesis of Cyclooctatetraene by the Method of W. Reppe
Authors: Schrauzer G. N. , Glockner P. , Eichler S.
Published: December 2003

The relationship between the structure and the catalytic activity of nickel(II) complexes in the synthesis of cyclooctatetraene by the method of W. Reppe is discussed. The cyclotetramerization of acetylene takes place within labile Ni(II)‐acetylene π‐complexes. Inhibition tests have made it probable that four molecules of acetylene are grouped around the nickel ion in the transition state, in a configuration which favors the formation of the eight‐membered ring.
Polar Addition of Hydrogen Halides onto Olefins
Authors: Dewar J. S. , Fahey R. C.
Published: December 2003

Various structures have been proposed for the intermediates of electrophilic additions onto olefins; these include halonium ions, classical carbonium ions, π‐complexes (i.e. nonclassical carbonium ions), and π‐complexes with back‐coordination. It is shown here that it is impossible to use any one of these entities alone to explain all such electrophilic additions; the electrophile itself determines the nature of the transition state formed. Polar addition of hydrogen halides onto olefins appears to proceed via a classical carbonium ion which does not occur as the free ion but as an undissociated ion pair. Various other mechanisms have been excluded by studies reported here of the stereochemical course of such additions.
The Peroxyester Reaction
Authors: Sosnovsky G. , Lawesson S.‐O.
Published: December 2003

The reactions of t‐butyl peroxyesters with various classes of compounds in the presence of a catalytic amount of copper ions produce well‐defined acyloxy derivatives. This peroxyester reaction, discovered by Kharasch and Sosnovsky, can be used to effect one‐step oxidation of saturated and unsaturated hydrocarbons, alcohols, aldehydes, esters, ethers, sulfides, organosilicon compounds, etc. The reaction can be highly selective: in most cases only one specific carbon atom is attacked. However, with some ethers and, sulfides the reaction can take a more complex course, other products being formed in addition to the acyloxy derivatives. The mechanism of the reaction has been extensively investigated, and several concerted and chain mechanisms have been proposed.
Structure and Specificity of Organic Chelating Agents
Authors: Bayer Ernst , Fiedler H. , Hock K. L. , Otterbach D. , Schenk G. , Voelter W.
Published: December 2003

Macromolecular chelating agents possessing high selectivity for rare metal ions have been synthetized. One of these, with the complexing group of glyoxal bis‐2‐mercaptoanil, is suitable for selective enrichment of gold from sea‐water, while another is suitable for copper and uranium. – The enrichment of metallic ions in nature is discussed, taking hemocyanin as an example. – Both stereochemistry and isomerism, as well as cyclic conjugation during chelate formation, may influence the selectivity of complexing agents. The quasi‐aromatic properties of chelates are discussed.
Organosodium and Organopotassium Compounds. Part II: Preparation and Synthetic Applications
Authors: Schlosser M.
Published: December 2003

A selection of well established procedures for the preparation of the most common organosodium and organopotassium compounds is given. The wide synthetic applicability of organoalkali‐metal compounds is shown by means of examples. Unlike Part I, Part II deals not only with “true”organoalkali compounds, but also with salt‐like compounds such as sodium acetylides and sodiocarboxylic esters, since these posses considerable preparative value.
The Chemical Composition of the Stars
Authors: Unsöld A.
Published: December 2003

The abundances of the elements in the atmospheres, i.e. the directly observable layers, of the stars are related to the energy production by nuclear processes in the interior of the stars and to their evolutionary states. For purposes of quantitative analysis of a given stellar spectrum, several “model atmospheres” are first calculated, assuming tentative numerical values for the effective temperature Te, for the gravitational acceleration g at the surface of the star, and for the relative abundances of the more important elements. The appropriate temperature distribution is obtained from the theory of radiative equilibrium in conjunction with the quantum theory of the continuous absorption coefficient; the pressure stratification is obtained from the hydrostatic equation. Evaluation of the Fraunhofer lines requires a theory of line absorption coefficients and line widths. In conclusion, the final numerical values for Te, g, and the abundances of the elements in the stellar atmosphere are determined by comparison of the calculated spectra with the measured spectrum of the star. The main sequence stars and the hot supergiants, i.e. the star population I of the spiral arms and the disk population of the Milky Way, all have the same chemical composition, which coincides with that of the interstellar medium. In the old population II stars of the galactic halo (high velocity stars, subdwarfs), on the other hand, the abundance of all the heavy elements relative to that of hydrogen is reduced by a factor of as high as 200, possibly even 500; hydrogen seems to be the original material of our Milky way. In helium stars, almost all the hydrogen has been transformed into helium even in the atmosphere; it is likely that these are well mixed stars.
Free Radicals and Free‐Radical Reactions of Monovalent and Divalent Sulfur
Authors: Schmidt Ulrich
Published: December 2003

Organic free radicals of monovalent sulfur have not been hitherto observed in solution or in melts. Steric hindrance and resonance stabilization, which are responsible for the stability of the triarylmethyl, diphenylnitrogen, and phenoxyl radicals, are apparently insufficient to stabilize the organic free radicals of monovalent sulfur in such concentrations that they can be detected by current physical methods. – It was only in 1963 that aminopolysulfur radicals (R2NSnS·) were detected in solution, and arylsulfur radicals (Ar–S·) and phenylselenium radicals were isolated at ca. −180°C. – Organically bound sulfur can be stabilized in the free‐radical state if association of the radicals is prevented by fixing in a crystal lattice (“cystine radical”), by repulsion between radical ions (sulfinium salts), or by freezing‐in (arylsulfur radicals).
Structure and Acidity of Organic Compounds
Authors: Simon W.
Published: December 2003

Elucidation of the structures of organic acids and bases with the aid of their acidity constants is greatly hindered by their low solubilities in water and by the small quantities of material normally available. Apparent acidity constants K* can be determined potentiometrically on small samples (about 0.5 mg) for many classes of compounds of medium acidity. The apparent acidity constants K determined in the solvent system methyl cellosolvel water can be correlated, in a similar manner to thermodynamic quantities, with structural parameters (e.g. Hammett's σ* and Taft's σ* values). K values can yield information on the axial or equatorial position of carboxyl groups in cyclohexanecarboxylic acids.
Gradient and Low‐Temperature Thin‐Layer Chromatography
Authors: Stahl E.
Published: December 2003

The preparation and the use of gradient layers for thin‐layer chromatography are described. On a gradient layer there are three flow surfaces, all differing in their separation behavior. It is therefore possible to determine, for example, the basicity and/or activity which gives the optimum separation for a mixture of substances. Gradient thin‐layer chromatography was also carried out at low temperatures, after the effect of temperature on the separation of various mixtures had been studied.
Intermediates of α‐Eliminations
Authors: Kirmse W.
Published: December 2003

α‐Elimination denotes the removal of two substituents from the same carbon atom. Present‐day knowledge of these reactions, their intermediates, and end‐products is reviewed, with particular emphasis on the question of the occurrence of carbenes and the role of organometallic (carbanion) intermediates.
Syntheses of Oxide Halides
Authors: Dehnicke K.
Published: December 2003

Knowledge of the oxide halides has made significant advances in recent years as a result of new methods of preparation. Moreover, the systematic study of older methods has led to versatile syntheses which permit the preparation of many new oxide halides. A brief outline of the scope, limitations, and difficulties of the various processes is given together with a number of examples.
Strained Polycyclic Systems Consisting of Three‐ and Four‐Membered Rings
Authors: Seebach D.
Published: December 2003

Polyclic compounds consisting of small rings have been known for several years. Their chemical and physical properties, which are of both theortical and practical interest, are discussed, and methods of preparation of a few examples are illustrated. The carbon skeletons of tetrahedrane, Dewar benzene, prismane, and cubane are discussed in greater detail, since the preparation of these compounds has now been achieved, or has at least been made possible.
Recent Advances in the Total Synthesis of Steroids
Authors: Velluz L. , Valls J. , Nominé G.
Published: December 2003

In the total synthesis of steroids on the industrial scale, three factors are important: stereoselectivity of the reactions used, resolution of racemic intermediates at the earliest possible stage, and convergence of the synthesis. Theoretical advances and wider practical experience in the chemistry of polycyclic compounds have recently led to the development of the first syntheses which are suitable for the industrial production of steroid hormones.
Light‐Induced Formation of Acids from Cyclic Ketones
Authors: Quinkert G.
Published: December 2003

Ultraviolet irradiation of aqueous solutions of cyclic ketones having a tetrahedral carbon atom in at least one of the two positions adjacent to the light‐absorbing carbonyl group results in ring opening accompanied by the formation of a carboxylic acid. Cyclohexadienones which are blocked in the ortho‐position are converted to hexadienoc acids. Cycloalkanones give saturated carboxylic acids and, in the presence of oxygen, also some unsaturated ones. The scope of the reactions is illustrated, and favorable conditions are described. The structure of the products and the route by which they are presumably formed are discussed.
Fused Salts and Their Use as Reaction Media
Authors: Sundermeyer W.
Published: December 2003

Apart from being of interest for physicochemical investigations, ionic liquids are a very important supplement to the non‐aqueous and water‐like solvents. The present discussion of the physical properties and current ideas on the structure of fused salts is followed by a report on the solubilities of gases, salts and metals. Our knowledge of fused salt baths and their use in electrochemical and electrometallurgical processes has recently been considerably expanded. Special attention is drawn to chemical reactions in fused electrolytes. Fused salts can also act as catalysts, so that they may often be advantageous reaction media for synthesis, if not the only media which can be used.
Formation and Reactivity of Phosphonium Salts in the Vitamin A Series
Authors: Freyschlag H. , Grassner H. , Nürrenbach A. , Pommer H. , Reif W. , Sarnecki W.
Published: December 2003

For syntheses in the carotenoid field using the Wittig reaction, particularly on the technical scale, it was necessary to carry out extensive studies on the preparation and properties of the intermediates. Hear the part of this work is discussed which dealt with quaternary phosphonium compounds of trimethylcyclohexene derivatives.
Metal Chelates as Polymerization Initiators
Authors: Kastning E.‐G. , Naarmann H. , Reis H. , Berding C.
Published: December 2003

Metal chelates can be used as initiators in the polymerization of vinyl compounds. Their action, as shown here for the polymerization of styrene, is determined by both the central atom and the ligand. Chelates of manganese (III) and cobalt (III) with 1,3‐dicarbonyl compounds are most effective. The metal chelate initiators can be activated by γ‐ or ultraviolet irradiation, or else by combination with cocatalysts such as organic halogen compounds or unsaturated hydrocarbons which are typical π‐complex formers. There is some evidence indicating that the polymerization takes place via a free‐radical mechanism. The central metal atom affects the steric configuration of the polymer chain.
New Reactions of Alkylidenephosphoranes and their Preparative Uses. Part I: The Acid‐Base Character of Phosphonium Salts and Alkylidenephosphoranes
Authors: Bestmann H. J.
Published: December 2003

Phosphonium salts may be regarded as Bronsted acids, and alkylidenephosphoranes as the conjugate bases. Compounds of the two classes exist in equilibrium with each other. Phosphonium salts and alkylidenephosphoranes can be obtained by this “transylidation”. Other methods are also given for the preparation of members of both classes.
The Chemistry of Nitrous Acid and of its Derivatives in Liquid Hydrogen Fluoride
Authors: Seel F.
Published: December 2003

The reaction of liquid hydrogen fluoride with nitrous acid, dinitrogen trioxide, dinitrogen tetroxide, and nitrosyl compounds leads to unexpectedly high‐boiling liquids which contain nitrosyl fluoride in the form of remarkably stable, electrolytically dissociated hydrogen fluoride solvates. Nitrosyl fluoride solvated by pure hydrogen fluoride is a new reagent, valuable in fluorine chemistry since it reacts with many elements and compounds to form fluorine derivatives of preparative importance.
Modern Theoretical Views on the Chemical Bond
Authors: Preuss H.
Published: December 2003

Starting from classical concepts, semi‐empirical approaches to an understanding of the chemical bond are critically discussed, particularly with respect to their limitations. Rules such as the additivity of the bond constants and the octet rule are reviewed in relation to new chemical compounds. It is shown that these rules are not sufficient to explain chemical bonding; this is also true of the simple concept of hybridization, the basis of which is discussed. Some generally valid statements regarding the chemical bond can be propounded on the bais of wave‐mechanical considerations. It is shown that the hybridization concept and a number of other rules are too primitive to provide generally valid information or a basis for predictions about the chemical bond, and even that they are partly based on false premises. A better foundation for an understanding of the chemical bond can only be laid with the aid of wave mechanics.
Molecules Undergoing Fast, Reversible Valence‐Bond Isomerization. (Molecules with Fluctuating Bonds)
Authors: Schröder G. , Oth J. F. M. , Merényi R.
Published: December 2003

Compounds which undergo fast and reversible valence‐bond isomerization (i.e. which have fluctuating cyclopropyl and/or double bonds) are taken to be those in which the average life‐time of the valence‐bond isomers at 0 °C is of the order of 100 seconds at most, and for which the maximum activation energy of the bond migration is 20 kcal/mole. The fast, reversible bond shift can scarcely be detected by chemical means, but can be recognized by NMR spectroscopy, since the time for which a proton occupies a position with a given magnetic environment has a pronounced influence on the NMR spectrum. Some examples of molecules with fluctuating bonds are cyclooctatetraene and its derivatives, unsaturated seven‐ membered ring systems, homotropilidene, bridged homotropilidene systems, bullvalene, and substituted bullvalenes. The last class is particularly interesting, since here the carbon atoms are continually changing their relative positions and neighbors.
Recent Advances in the Theory of Liquids
Authors: Ree Teresa S. , Ree T. , Eyring H.
Published: December 2003

In this paper, the methods of calculation of liquid properties using cluster integrals or the radial distribution function are not discussed. Rather, the theories using a model approach are presented. The basic principles involved in the cell theory, tunnel theory, and significant structure theory are reviewed, and the merits of the three theories are examined by comparing theoretical and experimental values of the pressures, molar volumes, compressibility factors, and excess entropies of real liquids. ‐ The thermodynamic properties of two‐and three‐ dimensional arrays of hard discsand spheres are also calculated, and compared with the machine calculation.–One finds that the significant structure theory gives the best results in every case.
Thermal Fragmentation and the Determination of the Structure of Organic Compounds
Authors: Simon W. , Giacobbo H.
Published: December 2003

A pyrolysis apparatus with high‐frequency induction heating has been developed, which, owing to the small dead volume in the pyrolysis zone (≥ 5 μl), can be used for pyrolysis gas chromatography utilizing capillary columns without a sample split system. Thin films of the samples are deposited on ferromagnetic conductors, and can be reproducibly heated in routine operation to an accurately defined temperature (the Curie point) in from 20 to 40 msec. Microgram quantities of natural amino acids can be identified by this method with the aid of standard pyrolysis gas chromatograms. When a thin film of the sample is used on the ferromagnetic conductor, the gragments are closely related to the structure of the original compound.
Heterocycles Containing Phosphorus
Authors: Märkl G.
Published: December 2003

The preparation of heterocycles containing phosphorus is described. The chemical behavior of ring systems containing trivalent phosphorus is mainly determined by their phosphine character; heterocyclic behavior in the ordinary sense is shown by rings containing functional groups. Syntheses and reactions of cyclic compounds of pentavalent and hexavalent phosphorus are particularly interesting.
Sequence Distribution in Copolymers
Authors: Harwood H. James
Published: December 2003

The physical properties of copolymers are determined by their compostions and by the distribution of monomeric sequences in their chains. In some cases, sequence distributions can be determined from or correlated with physical properties observed for copolymers. Such determinations or correlations are relatively simple when calculations are based on run numbers.
The Structural Chemistry of Condensed Inorganic Phosphates
Authors: Thilo E.
Published: December 2003

After it had become known that three types of condensed inorganic phosphates, i.e. metaphosphates, polyphosphates, and ultraphosphates, exist, attempts were made to elucidate their formation, properties, and mutual relationships. Metaphosphates and polyphosphates containing up to eight or ten monomer units can be separated chromatographically. In the melts, equilibria exist between the various types of phosphate anions. Annealing of the glasses leads to crystalline products, sometimes containing only one type of anion. The glass‐crystal transition proceeds via monomeric XO anions. This has been shown in the case of polyarsenatophosphates, in which the As atoms are randomly distributed over the chains in the vitreous state, but are located at preferred positions in the crystalline state. The maximum degree of dissociation of polyphosphates and polyphosphoric acids in water is 30%, which accounts for the ion exchange and the chelating effects. The cation‐catalysed decomposition of polyphosphates can take place either by hydrolytic degradation from the chain ends, or by rearrangement within the chains to form metaphosphates.
Novel Approaches to the Synthesis of Some Heterocycles Containing Nitrogen
Authors: de Stevens G. , Blatter H. M. , Carney R. W. J.
Published: December 2003

Some syntheses of heretofore unknown pyrimidines, tetrahydroquinazolines, and quinazolines are described. These methods are uniquely simple one‐ or two‐step reactions, general and versatile in scope, and give high yields. Some interesting chemistry associated with these heterocyclic systems is discussed.
Contributions to the Chemistry of the Binary Compounds of the Transition Elements
Authors: Haraldsen Haakon
Published: December 2003

Phase and structural relationships of the sulfur, selenium, and tellurium compounds of the 4d and 5d transition elements of groups IV to VII of the periodic system are discussed. Homologous elements behave very similarly with respect to the chalcogens, and this is particularly the case for niobium and tantalum, and for molybdenum and tungsten. However, zirconium, niobium, and molybdenum have a greater tendency towards formation of chalcogen‐poor phases than their homologues hafnium, tantalum, and tungsten. Subchalcogenides are known only for zirconium and niobium. The number of phases and the tendency towards formation of solid solutions are considerably smaller among the tellurides than among the sulfides and selenides. The crystal structures of the telluride phases also differ from those of the sulfide and selenide phases of analogous composition. In addition, a review of the phase and structural relationships of the arsenic and antimony compounds of the 4d and 5d transition elements of groups V to VII is given.
Color Centers in Alkali Borate Glasses Containing Cobalt, Nickel, or Copper
Authors: Juza R. , Seidel H. , Tiedemann J.
Published: December 2003

The absorption spectra and the magnetic moments of Co2+, Ni2+, and Cu2+ in alkali borate glasses of various compositions and in halide‐containing glasses have been explained from the point of view of the ligand field theory. Spectra and magnetic moments are highly dependent on the composition of the base glass; this must be ascribed to the change in the coordination of the transition‐metal ions. There are far‐reaching analogies with corresponding complexes in solution or in the crystalline state.
The Quaternary Structure of Proteins
Authors: Sund H. , Weber K.
Published: December 2003

Many protein molecules, particularly those with high molecular weights, consist not of a single polypeptide chain, but form a complex made up from several polypeptide chains. This structure, which can be reversibly broken down, is known as the quaternary structure. A number of metabolic phenomena can be explained on a molecular basis by invoking the quaternary structure.
Some Advances in the Inorganic Chemistry of Bromine
Authors: Stenger V. A.
Published: December 2003

Recent advances in the chemistry of bromine and its inorganic compounds are covered under the headings of technology, properties and reactions, liquid bromine as an inorganic solvent, analysis, and new or newly studied compounds. Much of what is new is bromine chemistry is characteristic also of what is new in inorganic chemistry as a whole. That is, more detailed information about compounds and reactions is becoming available from the application of new instrumental and theoretical techniques.
Ring Closures with Carbon Monoxide
Authors: Falbe J.
Published: December 2003

Carbon monoxide undergoes catalytic reactions with unsaturated compounds to give heterocyclic carbonyl compounds. This cyclization has led to new syntheses of imides, lactams, lactones, phthalimidines, indazolones, and tetrahydroquinazolines.
Functional Groups on the Surfaces of Solids
Authors: Boehm H.‐P.
Published: December 2003

Atoms or groups foreign to the structure of a solid are often bonded to its surface. On diamond, graphite, and even silicon dioxide, the foreign atoms are bonded covalently, whereas the bonding of the structural groups to titanium oxide and alumina is predominantly ionic. Oxides are normally covered with a monomolecular hydroxide layer. Changes in the valence of the metal atoms lead to changes in the acidity of the surface; for example, reduction of surface Ti4+ions gives the surface of TiO2 an acidic nature.
New Methods and Results in the Study of Polyacids
Authors: Jahr K. F. , Fuchs J.
Published: December 2003

The present status of research on condensed vanadic, molybdic, and tungstic acids is reviewed. Information about the structure and formation of polyanions can be obtained by X‐ray analysis and from nuclear magnetic resonance, infrared, and Raman spectra, as well as from complex formation in aqueous solution. Salts of the polyacids can be prepared in organic solvents by hydrolysis of esters of the metal oxoacids.
Some Recent Developments in the Chemistry of Transition Metal Oxocations
Authors: Selbin J.
Published: December 2003

The range of stability of transition metal oxocations in aqueous solution is discussed. Species with a metal‐oxygen bond of order higher than unity are particularly interesting. Bond orders can sometimes be determined from bond lengths and angles, but generally only by infrared spectroscopy. – The frequency range of the metal‐oxygen stretching vibration, previously assumed as about 900–1100 cm−1, must according to these investigations be extended at least to 780 cm−1 if all multiple bonds, particularly those in trans‐dioxo complexes, are to be included. Broad bands down to 650 cm−1 are ascribed to metal‐oxygen bridges. — The existence of cations such as ZrO2+ and VO, or of the “well‐known” titanyl ion, TiO2+, has never been proved. In many cases polynuclear, oxygen‐bridged oxometal species must be assumed.
Silicon‐Nitrogen Heterocycles
Authors: Fink W.
Published: December 2003

Great progress has recently been made in the chemistry of the silicon‐nitrogen bond

C. Eaborn: Organosilicon Compounds. Butterworths, London 1960, p. 339.

R. Fessenden and J. S. Fessenden, Chem. Reviews 61, 361 (1961).

K. A. Andrianov, I. Haiduc, and L. M. Khananashvili, Uspekhi Khim. 32, 563 (1963); Chem. Abstr. 59, 8782 (1963).

U. Wannagat, Advances inorg. Chem. Radiochem. 6, 265 (1964).

I. Haiduc: Westep do Chemii Nieorganicznych Zwiazkow Pierscieniowyrh. WPN, Warsaw 1964, Chap. 10 (in Polish).

. Whereas attention was formerly concentrated on open‐chain silazanes and silylamines, growing interest is now being shown in the cyclic SiN compounds. A major factor which has contributed to the rapid development in this field is the need for better polymers and liquids for use above 350 °C

Cf. E. G. Rochow, Chim. et Ind. 85, 897 (1961).

. The present article deals with monomeric cyclic compounds containing at least one silicon‐nitrogen bond in the ring, as well as the polycyclic compounds derived from these.
Methods and Applications of Quantum Chemistry. Part I: Physical and Mathematical Basis
Authors: Kutzelnigg W.
Published: December 2003

After an introduction to the fundamental concepts of quantum mechanics it is shown how to describe a chemical system in the language of theoretical physics. The equations which one obtains can not, in general, be solved in closed form. Approximate numerical methods that furnish sufficiently accurate solutions for many problems of interest are, however, available. The most important of these are presented briefly, and are given physically visualizable interpretations as far as this is possible. Special attention is devoted to more modern methods of quantum chemistry, to the basis assumptions underlying them, their scope, and their limitations. Treatment of the theory of the chemical bond is reserved for Part II.
Isotope Effects in Organic Chemistry and Biochemistry
Authors: Simon H. , Palm D.
Published: December 2003

The present article shows the extent to which isotope effects are likely to be encountered in the use of isotope techniques and what problems are studied with primary and secondary isotope effects. By way of example, the results of studies on E2 reactions, particularly in the Hofmann degradation, are discussed, followed by a discussion of some “analytical isotope effects”. Finally, the problems encountered and the information that can be obtained from isotope effects studies on enzyme reactions, and the advantages and disadvantages of competitive and non‐competitive techniques are described. In addition to a survey of isotope effects in dehydrogenase reactions, new isotope effects encountered in the dehydrogenation of T‐labeled alcohols are reported.
Polymers Containing Lactone Groups
Authors: Palm R. , Ohse H. , Cherdron H.
Published: December 2003

Polymers containing intact lactone groups are a new class of macromolecules with reactive groups, which are relatively easy to obtain by polymerization, polycondensation and polyaddition, as well as by reactions on existing macromolecules. Polymers with β‐lactone Groups in particular can enter into numerous addition reactions, which can be used, for example, to obtain macromolecules containing hydroxy acid or amino acid groupings. The reactions proceed under mild conditions, and can even be carried out in aqueous media, frequently giving water‐soluble polymers. The polymers can be cross‐linked at low temperatures, even from the aqueous phase, by the addition of bifunctional or oligofunctional reagents. Polymers containing β‐lactone groups can also be used as a basis for graft co‐polymers; polyester or polyether branches can be grafted on, depending on whether monomeric lactones or monomeric epoxides are used.
Inorganic, Organometallic, and Organic Analogues of Carbenes
Authors: Nefedov O. M. , Manakov M. N.
Published: December 2003

This review deals with inorganic, organometallic, and organic compounds, as well as with elements, that on the basis of their electronic structure and their reactions can be regarded formally as analogues of carbenes. These “carbene analogues” include in particular the compounds of monovalent boron, aluminum, nitrogen, and phosphorus; those of divalent silicon, germanium, tin, and lead; atomic oxygen; atomic sulfur; and atomic selenium. The preparation and chemical properties of the carbenes and their analogues are compared.
Nickel‐Catalysed Reactions of Allyl Halides and Related Compounds
Authors: Chiusoli G. P. , Cassar L.
Published: December 2003

Allyl compounds react with carbon monoxide, or with carbon monoxide and acetylene, in the presence of tetracarbonylnickel as catalyst. These catalysts are involved also in coupling reactions and addition reactions of activated olefins and ketones. Reactions of this type can be used for the preparation of unsaturated aliphatic acids, esters, nitriles, hydrocarbons, alicyclic ketones, keto acids, keto esters, diketones, lactones, phenols, and other compounds. The reactions proceed via π‐allylnickel complexes.
Synthesis of N‐(Fluorosulfonyl)iminosulfur Difluoride
Authors: Glamser O. , Roesky H. W. , Henize P. R.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196705711
The Bucherer Reaction and the Preparative Use of its Intermediate Products
Authors: Seeboth H.
Published: December 2003

The study of purified intermediate products of the Bucherer reaction has shown that this reaction proceeds, not via bisulfite addition compounds of the keto form of the naphthols and the ketimine form of the naphthylamines, but via tetralonesulfonic acids and tetraloniminesulfonic acids. The intermediates lead to compounds that are otherwise difficult or impossible to obtain, and some of which are new. The mechanism of the Bucherer reaction is discussed in detail.
The Norcaradiene Problem
Authors: Maier G.
Published: December 2003

Compounds having the norcaradiene structure are stable if one of the double bonds of the norcaradiene also belongs to a benzene ring or if C atoms 1 and 6 are fixed in position by a bridge. A similar effect that favors the norcaradiene form is produced by the incorporation of nitrogen atoms in positions 3 and 4. Cycloheptatriene and most of the simply substituted tropilidenes exist exclusively in the monocyclic triene form. It has been possible in some cases to detect a valence‐tautomeric equilibrium between the norcaradiene and the cycloheptatriene ring system. Non‐classical stabilization of compounds having norcaradiene or cycloheptatriene structure in the sence of a pseudoaromatic “homobenzene” is only very slight, if it occurs at all.
Eliminations in Cyclic cis‐trans‐Isomers
Authors: Hückel W. , Hanack M.
Published: December 2003

Solvolytic El eliminations from cis‐alkylated p‐toluenesulfonates of cycloalkanols (particularly menthols and decalols) lead almost exclusively to “Saytzeff hydrocarbons”; this fact is accounted for by the increase in the rate of solvolysis that results from the participation of the tertiary trans‐hydrogen. The corresponding trans‐alkylated compounds give mixtures. The solvolysis of these compounds is compared with the deamination of stereoisomeric primary amines and with the proton‐catalysed dehydration of tertiary alcohols. E2 reaction of vicinally alkylated cycloalkane derivatives involves attack on the secondary hydrogen, and in the case of the trans isomers leads to pure “Hofmann hydrocarbon”; with the cis‐isomers, competition occurs between the E1 and E2 reactions. The fact that the tertiary hydrogen is not attacked is explained by its anionic character. Reference is made to the competition of E1 and E2 reactions in exhaustive methylation.
Synthesis and Template Properties of Deoxyoligonucleotides with Repeating Triplet Sequences
Authors: Cramer F. , Frölke W. , Matzura H.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196706381
Aromatic Fluorine as a Chemical Label for Detecting Reaction Mechanism
Authors: Suschitzky H.
Published: December 2003

This article explains how nucleophilically activated fluorine can be used for the detection of ion‐pair formation during the decomposition of various aryl radical generators. Thus a concurrent dual mechanism for the breakdown of certain aryl radical sources can be experimentally demonstrated by fluorine labeling. The bearing of this information on the mechanism of diazo coupling is also discussed.

In addition, labeling with aromatic fluorine is applied to the thermolysis of aryl azides, the aminolysis of 3‐aryl‐4‐bromosydnones, and the hydrolysis of 3‐arylsydnone imines. Finally some mechanistic problems are posed which may possibly be solved by this labeling technique.
Syntheses of Isocyanide Dihalides
Authors: Kühle E. , Anders B. , Zumach G.
Published: December 2003

The methods for the preparation of isocyanide dihalides, and particularly of isocyanide dichlorides, are described. The scopes and courses of the various processes are critically discussed.
Neighboring‐Group Effects and Rearrangements in Reactions of Cyclopropylmethyl, Cyclobutyl, and Homoallyl Systems
Authors: Hanack M. , Schneider H.‐J.
Published: December 2003

The neighboring‐group effect produced by a double bond in the homoallyl position or by a cyclopropane or cyclobutane ring leads to interesting rearrangements, which are discussed in this paper mainly from the point of view of mechanism, but also from that of preparative work. The question of the postulated non‐classical carbonium ions acquires a special significance in this connection.
New Methods of Preparative Organic Chemistry. Transfer of Diazo Groups
Authors: Regitz M.
Published: December 2003

When an arenesulfonyl azide, particularly p‐toluenesulfonyl azide, reacts, in the presence of a base, with a compound containing an active methylene group, the two hydrogen atoms of the active methylene group are replaced by a diazo group to form a diazo compound and an arenesulfonamide. The method may be used for the synthesis of the diazo derivatives of cyclopentadienes, cyclohexadienes, 1,3‐dicarbonyl, 1,3‐disulfonyl, and 1,3‐ketosulfonyl compounds, ketones, carbonic acid esters, and β‐iminoketones. Secondary reactions can lead to azo compounds and heterocycles such as 1,2,3‐triazoles, 1,2,3‐thiadiazoles, and pyrazolin‐4‐ones. Azidinium salts react in the same way, but in this case an acidic reaction medium is necessary, a fact that is sometimes advantageous.
Higher Coordination Numbers of the Typical Elements
Authors: Hudson R. F.
Published: December 2003

The bonding in electron‐deficient molecules, e.g. the boron hydrides and certain metal alkyls, and in molecules which appear to violate the rare gas rule, e.g. hydrogen bonded complexes, interhalogen compounds and compounds of the typical elements with high coordination numbers such as PCI5 and SF6 can be described by a simple molecular orbital treatment involving delocalized α‐bonds. The contribution of d‐orbitals to the bonding in the interhalogen compounds and rare gas fluorides is very small. The stereochemistry and physical properties of the PX5 system are explained readily by the delocalization treatment and it is likely that here also the importance of spd hybridization has been overemphasized in the past.
Direct Synthesis of Organohalogenosilanes
Authors: Baźnt V. , Joklík J. , Rathouský J.
Published: December 2003

The direct synthesis of organohalogenosilanes, particularly methyl‐ and phenylchlorosilanes, is the main process for the production of the monomers required for silicone polymers. This complex heterogeneous catalytic reaction involves the interaction of a gaseous component (the organic halide) with two solid components (silicon and copper), the relative quantities of which change as the reaction proceeds. The mechanism of the direct synthesis has not yet been conclusively established. The free‐radical mechanism originally proposed supposes the formation of organic free radicals. On the other hand, the chemisorption mechanism suggested later postulates the dissociative adsorption of the organic halide on the silicon‐copper double center (the silicon and the copper being joined by a chemical bond). The results obtained so far indicate that the chemisorption mechanism is of decisive importance, but it is not impossible that both mechanisms operate simultaneously.
The Reduction of Organic Compounds with Chromium(II) Salts
Authors: Hanson J. R. , Premuzic E.
Published: December 2003

Chromium(II) salts can be used for a variety of reductions in organic chemistry; for example, alkyl halides and suitably substituted olefins may both be reduced to alkanes, and alkynes may be converted into trans‐olefins. Several epoxyketones are reduced to α,β‐unsaturated ketones or β‐hydroxyketones, and a nitro steroid was found to give a hydroxy(hydroxyimino) compound. The reduction of alkyl halides is reported to proceed by a free‐radical mechanism; the halogen atom that is set free forms a bridge between two chromium atoms.
Poly‐β‐amides
Authors: Bestian H.
Published: December 2003

High molecular weight poly‐β‐amides with fiber‐forming properties (repeating unitNHCR2CR2CO) differ from the polyamides of the nylon series in that the amide groups are much more closely spaced. These polymers are thus the nearest of the synthetic polyamides to natural silk. The production of poly‐β‐amides was made possible by a recent synthesis of β‐lactams from olefins and chlorosulfonyl isocyanate. The anionic polymerization of the β‐lactams gives poly‐β‐amides containing up to 10 000 monomer units in the chain. The molecular weight can be controlled as desired by means of initiators and chain terminators, and the properties can be varied within wide limits by the choice of the β‐lactam or by copolymerization of several β‐lactams. Remarkable differences are observed between polymers containing structural units in the threo form and those containing erythro structural units. The poly‐β‐amides can be spun into fibers having valuable textile properties.
Sulfonyl Hydrazones of Cyclic Amides and Quaternary Azo Sulfones of Heterocycles as Reagents in Azo Chemistry
Authors: Hünig S.
Published: December 2003

Sulfonyl hydrazones of cyclic amides undergo oxidative coupling with phenols and reactive methylene components. The reaction proceeds via the azo sulfones, which may be used as such, and which, as ambident cations, enter into many reactions with nucleophiles and extend the scope of oxidative coupling. The reaction with phenols is a two‐step process, in which the limiting cases k1 ≪ k2, k1 ≈ k2, and k1 ≫ k2 can be realized by slight variation of the reactants.
Reactions of Electron‐Rich Olefins
Authors: Hoffmann R. W.
Published: December 2003

Olefins are normally preferentially attacked by electrophiles. This trend is strengthened in enol ethers and enamines, and is particularly pronounced in tetramethoxyethylene and in tetraaminoethylenes. These electron‐rich olefins are accordingly also excellent reducing agents. In their reactivity, therefore, they behave as counterparts of tetracyanoethylene. This compound shares with the electron‐rich olefins a strong tendency to undergo cycloadditions, the electron‐rich olefins adding particularly readily to electrophiles.
Hereditary DNA Alterations
Authors: Freese Ernst
Published: December 2003

Mutations and recombinations are hereditary alterations of DNA, which is found mainly in the chromosomes of cells. They can occur spontaneously and they can be induced by high energy radiation or by chemicals. This article considers the developments following the discovery of the DNA structure that have led to a molecular explanation of point mutations, of large chromosome alterations, and of recombination. In conclusion, consequences for human society are drawn from the knowledge gained.
Electrocrystallization of Metals under Ideal and Real Conditions
Authors: Fischer Hellmuth
Published: December 2003

Ideal conditions during electrocrystallization, which are only approximately attainable, would lead to a perfect single crystal, whereas real conditions yield a monocrystalline or polycrystalline product containing many structural defects. The electrolytic production of quasi‐ideal single crystals requires an overpotential that supplies at least the activation energy necessary for the formation of two‐dimensional nuclei, since growth otherwise proceeds via screw dislocations with formation of a “real” crystal. The potential deviation in electrocrystallization under real conditions is due to electrochemical and/or crystallization overpotential, which can be determined separately. The investigation of electrocrystallization also offers possibilities for a systematic study of the formation of imperfections in real crystals.
Lysozymes: A Chapter of Molecular Biology
Authors: Jollès P.
Published: December 2003

Hen egg‐white lysozyme was the first enzyme whose tertiary structure could be elucidated. The peptide chain of this enzyme is arranged in two sections, of approximately equal size, that are separated by a deep cleft. Substrates (and inhibitors) are bound in this cleft via hydrogen bonds and are hydrolyzed under the action of Glu 35 and Asp 52, which form the active site of the enzyme. Although the lysozymes, which occur in many species of animals and plants, exhibit differences in their chemical behavior, they have the same qualitative biological activity; quantitatively important differences have been noted which also concern the specificity. Infection of E. coli with bacteriophages gives rise to a lysozyme whose formation is controlled by the phage DNA. The fact that mutated lysozymes are produced when the phages are treated with mutagens opens new fields of research in molecular biology.
Deactivation of Excited States
Authors: Stephenson L. M. , Hammond G. S.
Published: December 2003

Nature abhors an electronically excited state and strives to convert this energy to other forms. This article is concerned with the various pathways involved in the degradation of electronic excitation to ordinary “thermal” forms, but will primarily discuss the quenching of excited states by other molecules. The authors include as examples only those phototransformations and interactions encountered in solution.
Spectroscopic Investigation of Various Phosphorus‐Sulfur Bonds
Authors: Goubeau J.
Published: December 2003

The results of spectroscopic investigations on phosphorus‐sulfur compounds, and particularly the force constants, reveal several factors that decisively influence the bonding. The effects of hybridization, the other bonding partners and their electronegativities, the π‐bonding components, and the ionic charge are discussed. It is shown that the PS bond, unlike the PO bond, never attains full double bond character, despite its great variability.
Excimers
Authors: Förster Th.
Published: December 2003

Excimers are molecular associates that exist only in excited electronic states. They are therefore detectable only in emission spectra, and particularly in fluorescence spectra. Despite their short lifetimes, they are responsible for many photophysical and photochemical effects.
Phosphorus Isocyanates
Authors: Derkatsch G. I.
Published: December 2003

Compounds containing the PNCO grouping can be obtained e.g. from phosphorus halides and silver cyanate or esters of N‐chloroiminocarbonic acid and by thermal decomposition of alkoxycarbonylimino‐phosphoranes. The phosphorus (V) isocyanates resemble the “carbon” isocyanates in their chemical properties, whereas the phosphorus (III) isocyanates resemble the phosphorus (III) chlorides. Some of the compounds discussed have insecticidal or cytostatic actions.