bluuebunny/crossref_metadata_2025 huggingface dataset:
Acrolein Polymers
Authors: Schulz R. C.
Published: December 2003

The unsaturated aldehyde acrolein is a suitable source for different types of high polymers. If it is regarded as a 1,3‐diene analogous to butadiene, then all the known modes of its polymerization can be systematically described and further possibilities predicted. A survey is given on this basis of the results obtained during the past decade. It is shown that acrolein is one of the few monomers which contain two polymerizable groups of differing reactivities. This fact allows the formation from acrolein of new homopolymers, copolymers, and graft copolymers, a scope which is not encountered with many other monomers.
A New Method for the Determination of Fluorine
Authors: Seel F. , Steigner Elli , Burger Inge
Published: December 2003

A new, particularly simple and reliable method of quantitative fluorine analysis is described; it is based on the conversion of insoluble silver oxide into soluble silver fluoride by fluorosilicic acid released from the sample by Willard‐Winter‐Tananaev steam distillation, the silver fluoride then being determined volumetrically according to Volhard.
A Synthetic Route to the Corrin System
Authors: Bertele E. , Boos H. , Dunitz J. D. , Elsinger F. , Eschenmoser A. , Felner I. , Gribi H. P. , Gschwend H. , Meyer E. F. , Pesaro M. , Scheffold R.
Published: December 2003

The synthesis of the nickel(II) complex of (±)‐1,8,8,13,13‐pentamethyl‐trans‐corrin illustrates a synthetic route to the corrin system. Repeated use of triethyloxonium tetrafluoroborate in this synthesis demonstrates the preparative value of the trialkyloxonium salts discovered by Meerwein et al.
The Modes of Reaction of Ambident Catioins
Authors: Hünig S.
Published: December 2003

The effect of the nature of the coreactants and the reaction conditions on the ability of certain mesomeric cations to react with nucleophilic reagents to form isomeric products has been studied. The structures of the products isolated are determined by competition between a kinetically controlled but reversible reaction and a thermodynamically controlled reaction.
Chromatographic Separations on Porous Gels
Authors: Determann H.
Published: December 2003

Over the past few years, fractionation of mixtures of substances on the basis of differences in their molecular weights has become an important method in chemistry and biochemistry. A survey is given of the theory and practice of separations applying porous gels, and the multifarious uses of such gels are indicated.
Metallo‐Complexes
Authors: Bergerhoff G.
Published: December 2003

Ternary and quasiternary compounds consist of either one cationic and two anionic,or one anionic and two cationic components. The size of the ions and the bonding forces between them determine the structure of the compounds. A compound is regarded as a complex when its lattice contains structural groups in which the interaction between the constituent atoms is substantially greater than or different from that between these structural groups and the other components of the compound. Metallo‐complexes are built up of one cationic and two anionic components; in contrast to the complexes with cationic central atoms which have been thoroughly investigated, they contain an anionic central atom surrounded by cationic ligands. A list is given of many compounds which can be formulated as metallo‐complexes after discussion of methods for their preparation and their chemical properties; the reason that only few metals can function as ligands of an anionic central atom is deduced from the pertinent crystal structures.
Protonic States and the Mechanism of Acid‐Catalysed Esterification
Authors: Zimmermann H. , Rudolph J.
Published: December 2003

Protons can be very mobile in condensed phases; the length of time they are present in any one place is minute. The significance of proton mobility in the course of chemical reactions is considered in the case of acid‐catalysed esterification by the normal carbonyl addition mechanism. – The properties of the protons in the carboxylic acid/alcohol system can be discussed on the basis of a semiconductor term diagram. The high mobility of the catalysing protons in the semiconductor system suggests that formation of the esterification intermediates occurs in two reaction steps which proceed at different rates. In the first rapid step the transition state is reached by proton transfers via hydrogen bridges. The proton rearrangement involved proceeds so rapidly that the heavy molecular skeletons retain their mutual spatial positions (Franck‐Condon principle for proton‐catalysed reactions). In the second slower step, the intermediate is formed by rearrangement of the groups of atoms. – Decomposition of the intermediate, with formation of either the starting materials or the end products, proceeds via a mechanism similar to that for the formation.
Recent Results of Configurational Research
Authors: Schlenk W.
Published: December 2003

The problems involved in configurational research differ from those of many of the currently important fields of general chemistry. Consequently, many chemists are less familiar with recent developements in this field than, for example, with those of the generally important modern ideas on valence and reaction mechanisms. A survey of new methods and recent results of configurational studies is attempted in this review, some unpublished experimental findings by the author being included. However, no attempt has been made to present an exhaustive review, nor to give a detailed treatment of individual problems which may interest the specialist.
The Use of Silylation in Organic Syntheses
Authors: Birkofer L. , Ritter A.
Published: December 2003

The term silylation is used to denote the introduction of a triorganosilyl moiety, especially the trimethylsilyl species, into organic compounds. ‐ Silylated amino acids and sugars are particularly suitable for the syntheses of peptides and saccharides, respectively, since the silyl group can be cleaved off readily under mild conditions. Many diamines undergo ring closure, e.g. with phosgene, only after silylation. ‐ O‐silylated lactim ethers (i.e. cyclic imino ethers) are converted into N‐alkyl derivatives by alkyl halides. Compounds with a strongly polarized SiC bond may be used for chain extension. Silyl esters of halogeno fatty acids yield lactones with silver cyanate. ‐ Trimethylsilyl azide is thermally very stable and behaves like organic azides. It reacts with acetylenic compounds, trialkylphosphines, and triarylphosphines to yield silylated triazole derivatives, trialkylphosphines N‐silylimines, and triarylphosphines to yield silylated triazole dervatives, trialkylphosphine N‐silylimines, and triarylphosphine N‐silylimines, respectively, from which the silyl groups can be removed under mild conditions.
Equilibrium and Transport Properties of Concentrated Electrolyte Solutions
Authors: Haase R.
Published: December 2003

A historical survey is followed by a discussion of a number of problems associated with concentrated solutions of electrolytes containing two ion constituents: general thermodynamic properties, dissociation equilibria, phase separation, analytical representation of the thermodynamic functions over the entire range of concentrations, and general relationships in electrical conductivity, diffusion, and sedimentation. A number of relationships valid at all concentrations is formulated, and known relationships pertaining to dilute solutions are derived from these as special cases. The discussion of concentrated solutions is illustrated by numerical examples, most of which are based on recent results.
Chemiluminescence in Organic Compounds
Authors: Gundermann K.‐D.
Published: December 2003

As a result of the development of very sensitive equipment, it is now possible to show that the chemiluminescence of organic compounds in solution is quite a common phenomenon. Notable advances have been made during recent years in the investigation of the chemiluminescence of substituted phthalic acid hydrazides and related compounds. A new and probably generally applicable method of producing chemiluminescence has recently been discovered in the reaction of aromatic free‐radical anions with appropriate free‐radical cations.
Organic Dyes as Photoelectric Semiconductors
Authors: Meier Hans
Published: December 2003

Photoconduction in organic dyes is caused by the formation and migration of electronic charge carriers, and is not due to impurities or photochemical decomposition. The phenomena of dark and light‐induced conduction in dyes can therefore be interpreted in the same way as in inorganic semiconductors.
Formation of Nucleophilic Carbenes from Heterocyclic N‐Methyl Betaines
Authors: Quast H. , Frankenfeld E.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196508792
Conformational Analysis in Mobile Cyclohexane Systems
Authors: Eliel E. L.
Published: December 2003

By “Conformational Analysis” is meant the analysis of the physical and chemical properties of a compound in terms of its preferred “conformations”, i.e. rotational arrangements about single bonds. This particular review deals with cyclohexanoid compounds capable of existing in two or more stable conformations.
Conformational Analysis of Cyclohexane Derivatives by Nuclear Magnetic Resonance Spectroscopy
Authors: Franklin N. C. , Feltkamp H.
Published: December 2003

Nuclear Magnetic Resonance is today one of the best methods available for the conformational analysis of cyclohexane derivatives. It is possible with this technique to investigate the spatial orientation of the substituents in fixed molecules, as well as the equilibrium position in mobile systems. For these determinations the areas under the signals, the chemical shifts, the coupling constants, and the band widths of particular signals can be used.
Applications and Limitations of Magnetic Methods in Free‐Radical Chemistry
Authors: Müller E. , Rieker A. , Scheffler K. , Moosmayer A.
Published: December 2003

The paper describes the application and limitations of magnetic methods to the problems of free‐radical chemistry (detection and quantitative investigation of the free‐radical state, relationships between structure and free‐radical formation, “distribution” of the unpaired electron, detection of mesomeric C, O, N, P, As, and Sn radicals, g‐factors, triplet states, and hyperfine structure). The problem of the diradical is described, and the paper closes with a discussion of the “Selwood effect”.
Compounds of Phosphorus with Silicon and Aluminum
Authors: Fritz G. , Becker G. , Poppenburg G. , Rocholl M. , Trenczeck G.
Published: December 2003

The formation and properties of silicon‐phosphorus and aluminum‐phosphorus compounds are described. Silylphosphines are decomposed solvolytically by H2O, C2H5OH, NH3, hydrogen halides, C2H5I, and boron halides at the SiP bond; decomposition may be preceded by formation of an addition compound. Extensive side reactions during the reaction of halogenosilanes with LiPEt2

The following abbreviations are used in this paper: Et = C2H5; Me = CH3; M = alkali metal

(formation of Et2PPEt2, HPEt2, Si‐rich residues) are due to an excess of LiPEt2 in the reaction mixture. The reaction of LiPEt2 with AlCl3, AlHCl2, and AlH2Cl leads to definite aluminum‐phosphorus compounds if only one PEt2 group is present per Al atom, e.g. in (Cl2Al–PEt2)3, or if salts such as Li[Al(PEt2)4] and Li[AlH2(PEt2)2] can be formed with an excess of LiPEt2.
The Significance of Enterobacterial Mutants for the Chemical Investigation of their Cell‐Wall Polysaccharides
Authors: Lüderitz O. , Westphal O.
Published: December 2003

The outer cell surface of Enterobacteriaceae, i.e. the cell wall, consist of a rigid structure (murein) on which additional proteins, lipids, and polysaccharides are deposited. In the bacterial wild types (S forms) the polysaccharide is species‐specific and carries the serologically determinant groups of the respective O antigen. These specific polysaccharides often consist of a large number of monosaccharides; up to eight different monosaccharides may be involved. Bound to lipid A, the cell‐wall lipopolysaccharides represent the endotoxins of the bacteria. During the past few years the structures of the enterobacterial cell‐wall polysaccharides have been elucidated by chemical, immunochemical, biochemical, and genetic investigations, particularly in the Salmonella. Here the polysaccharides consists of a basal polysaccharide common to all species, to which (in the S form) are bound longer species‐specific side chains, consisting of repeating oligosachharide units. Spontaneous S → R mutation leads to R forms which are deficient mutants of the wild types in regard to the biosynthesis of the complete cell‐wall polysaccharide. In contrast to the multiplicity of the serological specificities of the somatic antigens of the S forms, only a few serological types were found among the R forms (R I, R II, etc.). These R polysaccharides correspond to intermediates in the biosynthesis of the wile‐type polysaccharides. The S → R mutation leads to the loss (or block) of an enzymes (transferase, synthetase) participating in the synthesis of the S polysaccharides. Recently many deficient mutants have been isolated and analysed, and in this way numerous stages in the biosynthesis of the cell‐wall polysaccharides, for example, of Salmonella minnesota, have been made accessible to direct analysis. According to these investigations, the cell‐wall polysaccharides of Salmonella consist of a basic polyheptose phosphate core which is bound to lipid A via ketodeoxyoctonic acid. To the basic core are linked pentasaccharide units of

equation image

(R II structure). All other R forms are structurally deficient mutants of R II. In the complete polysaccharides of Salmonella S forms (wild types), the repeating oligosaccharide units of the specific side, chain are bound to the terminal N‐acetylglucosamine of the R II structure.
The Surface Tension of Solids
Authors: Sell P.‐J. , Neumann A. W.
Published: December 2003

The surface tension of a solid, unlike that of a liquid, cannot be measured directly. After a discussion of the most important methods used so far, all of which are subject to uncertainty the determination of the surface tension of solids from the wetting equilibrium is described.
Scrambling Equilibria and Analysis of Labile Mixtures
Authors: Van Wazer J. R. , Moedritzer K.
Published: December 2003

In this brief review, it is attempted to point up the importance of chemical equilibria in structural inorganic chemistry and to show how the kind and yield of various molecules may be treated quantitatively. Because of the importance of kinetic control in organic chemistry and because the chemistry of carbon compounds is by far the most advanced branch of general and descriptive chemistry, preparative inorganic chemists have often overemphasized the value of reaction‐mechanism theory to their studies and have thereby neglected the powerful quantitative approach of thermodynamics which may be used in equilibrated systems. The general theorems for treating in terms of small molecular segments the multitude of equilibria present in families of compounds are surveyed superficially with the hope that the interested reader will turn to the original papers for details. Not only physical‐inorganic chemists, but also those interested solely in preparative work can advantageously employ the theoretical ideas discussed.
Classification and Analysis of NMR Spectra
Authors: Dischler B.
Published: December 2003

The use of nuclear magnetic resonance as the basis of a spectroscopic method in organic analysis is steadily growing.

K. H. Hauser, Angew. Chem. 68, 729 (1956). J. D. Roberts, Angew. Chem. 75, 20 (1963); Angew. Chem. internat. Edit. 2, 53 (1963).

. The object of the present article is to present a general picture of the classification and interpretation of the NMR spectra obtained at high resolutions. In simple cases complete interpretation is possible with the aid of only a few equations; otherwise it is often necessary to use a laborious mathematical procedure, which is discussed here. For a more profound study, the reader is referred to more detailed publications.

J. A. Pople, W. G. Schneider, and H. J. Bernstein: High–resolution Nuclear Magnetic Resonance, McGraw Hill, New York 1959.

L. M. Jackmann: Appplications of Nuclear Magnetic Resonance Spectroscopiy in Organic Chemistry. Pergamon Press, London 1959.

P. L. Corio, Chem. Reviews 60, 363 (1960).

J. D. Roberts: An Introduction to the Analysis of of Spin‐Spin Splitting in High‐Resolution Nuclear Magnetic Resonance Spectra. Benjamin, New York 1961.

J. Ranft, Fortschr. Physik 9, 149 (1961). H. Strehlow: Magnetische Kernresonanz und chemische Struktur. Steinkopff, Darmstadt 1962.
Alcohols as Petrochemicals
Authors: Kropf H.
Published: December 2003

Efficient processes have been developed in recent years for the large‐scale manufacture of alcohols from petrochemicals. These allow production of aliphatic alcohols both with short and with long alkyl groups more economically than was previously possible by fermentation. In this paper the most important principles and the technical execution of the hydration of olefins, the air oxidation of paraffins, and especially the synthesis reactions (e.g. the catalytic hydroformylation of olefins with carbon monoxide and hydrogen according to Roelen, the Reppe synthesis, and the Ziegler growth reaction with ethylene and triethylaluminum) are described.
Coupling Principles in Organic Dyes
Authors: Dähne S. , Leupold D.
Published: December 2003

Dye molecules containing two or more polymethine structural units, or at least one polymethine and one polyene structural unit, generally exhibit coupling effects that determine the spectroscopic behavior and other physicochemical properties of the substance. The coupling concept can be used inter alia to fit the quinone dyestuffs, the indigoids, and the indanthrenes into a general poymethine color system and to perdict new dye structures.
Diels‐Alder reactions II: The Reaction Mechanism
Authors: Sauer J.
Published: December 2003

The possible mechanisms of the preparatively so productive Diels‐Alder reactions are discussed critically on the basis of experimental data. Although most of the facts can be explained readily by a synchronous mechanism, a number of problems remains.
Reactions of Halogen Azides
Authors: Dehnicke K.
Published: December 2003

Until recently, the explosive nature of halogen azides made these compounds unsuitable for preparative uses and greatly impeded investigation of their physical properties. Reactions of ClN3 and BrN3 with metal halides, metal carbonyls, and organometallic compounds to from metal azide halides, nitride halides, carbonyl azide halides, and alkylmetal azides were reported only very recently. The stability relationships of the halogen azides are discussed.
Additions to the Activated CC Triple Bond
Authors: Winterfeldt E.
Published: December 2003

The possibilities of additions to the activated CC triple bond are discussed with the aid of a number of examples. The additions of donors that contain no active hydrogen are generally initiated via a dipolar primary complex, which can undergo stabilization by rearrangement, cyclization, or addition reactions. Preparative aspects of these reactions are also discussed. They offer routes for the preparation of heterocycles, particularly pyrrole and thiophene derivatives.
Sigma‐Bonded Organochromium Compounds. Hydrogen Transfer Reactions
Authors: Zeiss H. H. , Sneeden R. P. A.
Published: December 2003

The preparation and properties of two classes of organochromium compounds and their interconversion have been studied actively in recent years. These are the σ‐bonded organochromium compounds in which alkyl, aryl, or aralkyl groups are covalently bonded to chromium (II or III) and the π‐arenechromium complexes in which “aromatic” nuclei are covalently bonded to chromium (0 or I). From certain reactions of the σ‐bonded organochromium compounds, evidence has accumulated which shows that the chromium atom acts not only as a coordination center, but also as a hub for hydrogen transfer and H/D exchange[1,2]. σ‐Organochromium compounds may act as sources of radicals and carbanions. The present paper deals with the preparation and properties of σ‐bonded organochromium compounds; particular attention is given to hydrogen transfer reactions and rearrangements to bis(π‐arene)chromium complexes.
Spatial Arrangement and Preparative Organic Synthesis
Authors: Velluz L. , Valls J. , Mathieu J.
Published: December 2003

This review deals with the stereoselective formation of organic compounds. A number of examples of such syntheses, especially those of alkaloids and steroids, are described. An asymmetric synthesis, which avoids the intricacies and wastefulness of optical resolution, has been successful in a few cases only. The procedures of configurational change and of optical resolution, as well as the planning of multi‐step stereoselective syntheses, are discussed.
Isomerizations in Cyclobutenes
Authors: Criegee R.
Published: December 2003

The present article deals with acid‐catalyzed rearrangements and thermal valence isomerizations in cyclobutenes. The characteristic features of small rings, i.e. their practically planar structure and the ring strain, are in fact the causes of the rearrangements discussed.
Recent Developments in the Stereochemistry of Cyclopropane Ring Opening
Authors: Sarel S. , Yovell J. , Sarel‐Imber M.
Published: December 2003

This review article deals with the stereochemistry of the following ring opening reactions: 1. Homoallylic rearrangement of secondary and tertiary cyclopropyl alcohols in the presence of electrophilic reagents, 2. The addition of carboxylic acids to vinylcyclopropanes, 3. The thermal rearrangement of vinylcyclopropanes into cyclopentenes. An account is also given of the NMR spectroscopic determination of the conformations of substituted vinylcyclopropanes.
Studies on the Adsorption of Gases on Clean Metal Surfaces with the Aid of Field‐Emission and Field‐Ion Microscope Techniques
Authors: Sachtler W. M. H.
Published: December 2003

Studies on the adsorption of gases such as xenon, hydrogen, nitrogen, and carbon monoxide on the surface of a single crystal of tungsten with the aid of field‐emission and field‐ion microscopy have, in the past few years, led to new, fundamental insights into chemisorption and heterogeneous catalysis. Important phenomena which were discoverd and elucidated by these techniques include the pronounced face specificity of the adsorption, the fact that several different adsorption complexes of a gas are found on one and the same crystal face, and the rearrangement of the surface atoms through chemisorption. Many of the interpretations thus gained for the systems studied can also be generalized for other chemisorption complexes.
Tetraaminoethylenes as Strong Electron Donors
Authors: Wiberg N.
Published: December 2003

Depending on the nature of the electron acceptor and of the tetraaminoethylene (TAE), the electron pairs of the ethylenic double bond (A), of the nitrogen (B), or of the entire electronic system (C) of TAE react with the acceptor. Thus oxidizing agents convert TAE into the mono‐and dications TAE+ and TAE2+ by path (A); acids add on to the ethylenic carbon (A) or the amine nitrogen (B) (the addition of acid is often followed by cleavage of the CC or CN bond); organic π‐electron acceptors from deeply colored donor‐acceptor complexes with TAE (C).
Oligophenyls, Oligophenylenes, and Polyphenyls, a Class of Thermally Very Stable Compounds
Authors: Ried W. , Freitag D.
Published: December 2003

The classical and modern syntheses of oligophenyls and polyphenyls are compared to illustrate the value and the range of applications of the preparation methods described. The investigations showed a relationship between the number, arrangement, and substitution of the aromatic rings and the physical properties of the products. The melting point of the p‐polyphenyls rises with increasing degree of condensation. Methylation, and linkage in the m‐positions lowers the melting point and at the same time improves the solubility. o‐Oligophenyls melt at lower temperatures than the p‐isomers. The highest‐melting substance in this class in p‐septiphenyl, which melts at 545 °C.
Chalcogenocarbonic Acids and Their Anions
Authors: Dräger M. , Gattow G.
Published: December 2003

Carbonic acids in which the oxygen has been wholly or partly replaced by sulfur, selenium, and/or tellurium are known as “chalcogenocarbonic acids”. The aim of the present article is to review existing knowledge of these acids and so establish a basis for further systematic syntheses. The anions required for the synthesis of chalcogenocarbonic acids will also be briefly characterized.
Transport Phenomena in Membranes
Authors: Läuger P.
Published: December 2003

The realization that many elementary biological processes occur at membrane‐like structures has led to renewed interest in the theory of molecular transport through membranes. Coupling phenomena in membranes, some of which are very complex, can now be rationally described with the aid of the thermodynamics of irreversible processes. The investigation of theoretical membrane models has proved a valuable complement to the thermodynamic method.
Metal Complexes of Thiophosphinic and Selenophosphinic Acids
Authors: Kuchen W. , Hertel H.
Published: December 2003

The anions of thiophosphinic and selenophosphinic acids R2P(X) YH (X = S, Se; Y = O, S, Se) can act as bidentate ligands. They combine with many metals to form complexes containing a four‐membered chelate ring, or to give coordination polymers in which they form ligand bridges. The preparation, properties, and reactions of these compounds, as well as the dielectric properties and analytical use of dithiophosphinato complexes, which are also of industrial interest, are described. Some thiophosphinato and selenophosphinato complexes exhibit concentration‐dependent association via ligand bridges. Evidence of the chelate nature of the ligands R2P(X)Y⊖ was obtained from IR spectroscopic studies. The ligand field parameters of the anion (C2H5)2P(S)S⊖ were deduced from the electronic spectra of octahedral diethyldithiophosphinato complexes, and the position of the ligand in the spectrochemical and nephelauxetic series were determined from these parameters.
Structure and Biosynthesis of the Ergot Pigments
Authors: Franck B.
Published: December 2003

In addition to the well known alkaloids, ergot contains two groups of yellow to red pigments, between which there is a close and novel biogenetic relation. The pigments are anthraquinonecarboxylic acids and dimeric hydroxanthone derivatives (ergochromes), the structures of which, including the absolute configurations at 80 centers of chirality, have been completely determined. The intermediates involved in the biosynthesis have been largely established by feeding with labeled precursors, and its course by model experiments.
A New Type of Corrin Synthesis
Authors: Yamada Yasuji , Miljkovic D. , Wehrli P. , Golding B. , Löliger P. , Keese R. , Müller K. , Eschenmoser A.
Published: December 2003

Work towards a synthesis of vitamin B12 has inspired a new type of corrin synthesis. The key step is a light‐induced 1,16‐hydrogen transfer leading to an antarafacial (π→σ)‐cycloisomerization of a seco‐corrinoid metal complex. The construction of the seco‐corrinoid ligand system is achieved by coupling monocyclic ring precursors in their enamide or enamine form through the methods of sulfide‐contraction via oxidative coupling and of iminoester‐enamine condensation.
Methods and Possibilities of Nucleophilic Acylation
Authors: Seebach D.
Published: December 2003

Nucleophilic acylation is the attachment of anmagnified imagegroup to an electrophilic center. A brief discussion of the advantages offered by acylations of this type in syntheses is followed by a description of the direct methods (reactions with acylmetal compounds) and the methods proceeding via “masked” acyl anions. The latter methods are based on the use of either metalated vinyl ether derivatives or carbanions derived from acetals. Organyllithiums of sulfur‐stabilized carbanions are important reagents of this type.
Elemento‐Organic Amines and Imines
Authors: Scherer O. J.
Published: December 2003

Amines with mixed substituents containing two or three ElN bonds

El = a higher IVa, Va, or VIa element; by IVa, Va, and VIa elements are meant elements of the IV, V, and VI main groups of the periodic system

. are relatively stable if one or two of these bonds are (CH3)3 SiN bonds. IR and 1HNMR studies indicate that the (p → d)π bond components of the element‐nitrogen bonds steadily decrease from silicon, phosphorus, and sulfur toward their higher homologs. Because of the differences in the polarities of the element‐nitrogen bonds, these substances can be used for selective insertion and cleavage reactions. The reaction of metalated N‐silylaminoarsines with methyl chloride as well as the reaction of metalated N‐trimethyl(IVa)‐element‐substituted amino‐tert‐butylphosphines with halogenotrimethyl(IVa) element compounds open new, simple routes for the conversion of elemento‐organic amine systems into imine systems. The problem of reversible and irreversible (CH3)3 El ligand migration (1,3 shift) is discussed for trimethyl(IVa)element‐substitued benzamidines, diaminophosphines, aminoiminophosphoranes, sulfinamides, and aminosulfimines.
The Coordination Number – an “Inorganic Chameleon”
Authors: Hoppe R.
Published: December 2003

The purpose of the present article is to describe the changing ambiguous character of the term “coordination number” and its present‐day definition in structural chemistry, particularly of typical solids (assemblies of particles with short‐range and long‐range order). An effort is made at the same time to describe the crystal structure of solids as simply as possible while also taking long‐range order into account, i.e. by determining “effective” coordination numbers by the geometrical “polyhedron method” or from MAPLE (Madelung Part of Lattice Energy) values.
Polyurethane Ionomers, a New Class of Block Polymers
Authors: Dieterich D. , Keberle W. , Witt H.
Published: December 2003

Linear polyurethanes containing ionic centers at wide intervals are heteropolymers having a pronounced segment structure, i.e. ionomers. As a result of interactions between chains (Coulomb forces and hydrogen bonds), their properties are similar to those of crosslinked elastomers. They are strongly associated both in organic and in aqueous solutions. Polyurethane ionomers in polar organic solvents spontaneously form stable aqueous dispersions on addition of water, with the ionomer as the disperse phase. The particle size can be varied between 20 nm and 1 mm.
Organogold Chemistry
Authors: Armer Brunhilde , Schmidbaur Hubert
Published: December 2003

Organogold compounds having at least one Au–C δ or π bond and gold‐carborane complexes have recently received rapidly increasing attention, from the point of view of valence theory and structure as well as on practical grounds. Interesting possibilities are offered particularly in connection with the use of gold and its derivatives as heterogeneous or homogeneous catalysts for organic reactions, and new problems also arise.
The Behavior of Acid Halides Toward Lewis Acids and Lewis Bases
Authors: Lindner Ekkehard
Published: December 2003

Reactions of some typical acid halides of carbonic and trithiocarbonic acids and of orthophosphoric and sulfuric acids with Lewis acids and Lewis bases are compared. Acylium, perfluoroacylium, thioacylium, and even sulfonylium ions are obtainable with Lewis acids. It is possible by conductivity measurements and by electronic and above all IR spectroscopic investigations to determine whether the 1:1 adducts of acid halides and Lewis compounds are acylium or sulfonylium salts or donor‐acceptor complexes. In the reaction with Lewis bases, the halogen atom in the acid halide is replaced by the electron donor, generally with formation of nonpolar molecular compounds or complexes.
Inelastic Interactions of Slow Electrons with Adsorbed Particles
Authors: Menzel Dietrich
Published: December 2003

When slow electrons impinge on metal surfaces which are covered with an adsorbed layer, desorption of neutral particles as well as of positive ions, partly accompanied by fragmentation of the adparticles, is observed. The mechanism of these processes is of interest in connection with existing concepts of the surface bond. The effect can also be used as a probe for the investigation of complex adsorption layers.

Transfer of much smaller energies to the adsorbate can lead to vibrational excitation. This process may find application in the vibrational spectroscopic study of adsorbates. If the energy transferred in the inelastic collision is high enough to ionize low‐lying levels of the surface atoms, radiationless re‐ordering of the electron configuration (Auger‐effect) can occur subsequently. The secondary electrons of characteristic energy emitted in these processes can be used for qualitative analysis of the surface.
The Differential Calorimetric Study of the Reactivity of Unstable Compounds
Authors: Koch Erhard
Published: December 2003

The detection of unstable intermediates in chemical, photochemical, and radiation‐chemical reactions can be greatly facilitated by the use of thermoanalytical methods. Special advantages are offered by differential thermal analysis (DTA), since it permits fast, easy investigation, from about −150°C upward in some cases, over a wide temperature range. In this way processes that under normal conditions follow one another with immeasurable rapidity can be separated on the basis of their different temperature dependences. The great sensitivity of the method also allows the use of very dilute solutions, so that the studies can be confined to unimolecular processes.

The value of the method for the determination of energetic and kinetic data is illustrated by its application to the photochemically obtanable, unstable, ozonide‐like epidioxydihydrofurans.
Electroplating of Plastics in Theory and Practice
Authors: Heymann Kurt , Riedel Wolfgang , Woldt Günter
Published: December 2003

Electroplated plastics combine many advantages of plastics and of metals; they have the low weight and ease of shaping of plastics, together with the luster, hardness, and electrical conductivity of metals. An important part of any process for the electroplating of plastics is a pretreatment to ensure good adhesion of the metal film. Etch activation in the straight‐through method requires only six steps for pretreatment.
Recent Chemistry and Biochemistry of Bile Pigments
Authors: Rüdiger Wolfhart
Published: December 2003

Bile pigments are not merely waste products of the degradation of hemoglobin, but have specific functions in plants and lower animals, in which they occur in the form of chromoproteins (biliproteins). Chromic acid degradation under controlled conditions is particularly suitable for structural investigations. In the case of the phycobilins (bile pigments of red and blue algae), not only have the structures been established, but the linkages with the proteins have also been located.
Disorder in Solids (Ionic Crystals and Metals)
Authors: Nölting Jens
Published: December 2003

Important properties of crystalline solids are due to deviations from the ideal crystal structure. Lattice defects can be divided into structural defects (grain boundaries, dislocations, impurities) and intrinsic defects. The present article deals mainly with the problems and possibilities for the determination of intrinsic disorder. This disorder, which varies reversibly with temperature, plays an important role in many solid‐state processes, such as diffusion, ionic conduction, and chemical reactions in the solid phase.

After an introduction to the usual physical and chemical descriptions of the state of disorder, the principal methods of investigation are discussed. Special emphasis is placed on methods of determining disorder data from “anomalous” specific heats.
Chemical Information Services
Authors: Weiske Christian
Published: December 2003

The definition of information services derives from the demarcation between documentation and information. The main criteria for information services are up‐to‐dateness, clarity, manageability, relevance, and flexibility. In addition to the printed information media (tables of contents, lists of titles, abstract journals) services have been offered in recent years which are prepared with the aid of data processing machines and which operate on the basis of data tapes (SDI, profile searches).
Theoretical Aspects of Communication in Chemistry
Authors: Fugmann Robert
Published: December 2003

Successful searching for publications on the basis of subject obeys rules whose relations to thermodynamics are unmistakable. As a collection of literature grows, the degree of order required increases, since the patience, time, and memory used by man to compensate for lack of order cannot keep pace. The high degrees of order that are necessary nowadays in scientific literature cannot be attained by traditional documentation methods. If modern techniques are used to improve communication, the conceptual basis of such a documentation method must be revised and adapted to suit the new possibilities. The conditions in chemistry are relatively favorable for the effective use of modern technical and conceptual methods, since the terminology has been developed further than in most other sciences.
Versatile Computer Techniques for Searching by Structural Formulas, Partial Structures, and Classes of Compounds
Authors: Meyer Ernst
Published: December 2003

The principles of the topological encoding of formulas and machine searching are briefly described. These methods have been developed to the point where it is now possible to carry out a computer search for a given structural fragment without the risk of false drops. It is also possible to carry out searches whose requirements, while well‐defined and readily used by chemists, cannot be represented exclusively by element symbols and chemical bonds.
A System for the Documentation of Chemical Reactions
Authors: Schier Oswald , Nübling Wolfgang , Steidle Walter , Valls Jacques
Published: December 2003

The Documentation Ring of the chemical and pharmaceutical industries uses a punched card system to record chemical reactions. The starting materials and the end products are encoded with a fragmentation code, and the bonds that change during the reaction are recorded in the same way. Reaction modifiers and physical data can also be stored. In the case of multistage reactions, both the individual stages and various groups of stages are recorded.
Solvated and Stabilized Electrons in Radiation‐Chemical Processes
Authors: Eiben Klaus
Published: December 2003

The electrons solvated in metal‐ammonia solutions are relatively stable; by contrast, hydrated electrons are very unstable and have been discovered only recently during radiolysis of water. They can be regarded as the simplest radicals. Radiation chemical production of solvated electrons has proved to be a particularly elegant method for the qualitative and quantitative investigation of the reactions between these electrons and numerous compounds, whose rates are partly controlled by diffusion. It has been possible in some cases to identify optically and ESR‐spectroscopically the resulting short‐lived products (radical‐anions). The similarity between the physical and chemical properties of electrons solvated in solutions and those of electrons stabilized in the solid phase suggests that the two species are identical.
Preparative Solid State Chemistry: The Present Position
Authors: Schäfer Harald
Published: December 2003

Two types of reaction are distinguished in solid state chemistry: those in which high mobility of the reactants is aimed at (which can be achieved by the use of high temperatures, by the introduction of defects, by the promotion of surface diffusion, or by means of chemical transport phenomena), and those reactions in which the nature of the products is determined by existing structural elements or lattice defects of the reactants. The importance of paying more attention than hitherto to reaction pathways in preparative solid state chemistry is pointed out.
Blood Coagulation and Fibrinolysis
Authors: Heimburger Norbert , Trobisch Heiner
Published: December 2003

As a result of advances in protein chemistry it is now widely accepted that blood coagulation proceeds via a series of reaction steps of the nature of enzyme‐substrate reactions catalyzed by phospholipids. This also applies to the compensatory process of fibrinolysis. The factors taking part in both mechanisms as well as the inhibitors regulating the equilibrium have been shown to be proteins, some of them with a high carbohydrate content. Modern diagnostic methods and therapy are based on this knowledge.
Lac Repressor
Authors: Müller‐Hill Benno
Published: December 2003

Repressors are proteins that interact with inducers and operators to regulate the synthesis of enzymes in the cell. Lac repressor ensures that sufficient β‐galactosidase is available to the bacterium Escherichia coli, depending upon the amount of lactose present in the culture medium. It has proved possible to isolate lac repressor from E.coli. The present progress report describes how these discoveries were made, as well as the formation and mode of action of the repressor.
Optical Activity from Asymmetric Transition Metal Atoms
Authors: Brunner Henri
Published: December 2003

The preparation and resolution of asymmetric organometallic compounds of the transition series with four different ligands on the metal atom are described. Some of the optically active complexes retain their configuration, while others undergo racemization in solution. Their properties and reactions are discussed. Centers of asymmetry at transition metal atoms can also be detected on the basis of the magnetic nonequivalence of diastereotopic groups. Information about the configurational stability of such compounds can be obtained by investigation of the temperature dependence of the nuclear magnetic resonance spectra.
Synthesis of Heterocyclic Ring Systems for Heat‐Resistant Plastics from Polyisocyanates
Authors: Merten Rudolf
Published: December 2003

Investigations on space flight and rockets carried out in particular in the United States have aroused great interest in plastics with enhanced thermal stability. It has become possible to pass far beyond the expected limits of thermal stability with organic plastics, and to synthesize plastics and polymers that can be used at temperatures between about 200 and about 500 °C, a range that formerly appeared to be the exclusive province of inorganic materials.
Generation of Carbenes by Thermal Cycloelimination
Authors: Hoffmann Reinhard W.
Published: December 2003

The growth of interest in carbenes has led to a need for methods that allow their generation in unimolecular decomposition processes, possible also in the gas phase, without troublesome by‐products. Besides the decomposition of diazo compounds, thermal cycloeliminations from carbocycles and heterocycles with odd numbers of ring atoms have been found to be suitable for this purpose. The problems, structural requirements, and scope of such cycloelimination reactions are discussed in the present progress report. The advantages of carbene generation by thermal cycloelimination are demonstrated with reference to dialkoxycarbenes, which are very dfficult to obtain in any other way.
Generation of Carbenes by Photochemical Cycloelimination
Authors: Griffin Gary W.
Published: December 2003

A wide variety of shelf stable substrates undergo photochemical cycloelimination under relatively mild conditions. Suitable substrates include cyclopropanes, oxiranes, aziridines, and diazirines, as well as 3 H‐pyrazoles and 1,3‐dioxolanes. Carbenes prepared from these substrates as well as certain cyclic carbonates, sulfites, and phosphoranes behave chemically in a manner similar to divalent carbon species produced from conventional diazo precursors, namely, they react with alkenes to give cyclopropanes and undergo insertion into CH bonds of alkanes. In many cases the carbenes formed may also be detected by EPR and optical spectroscopic methods.
The Anomalous Temperature Dependence of Enzyme‐Catalyzed Reactions
Authors: Talsky Gerhard
Published: December 2003

Breaks or curvatures in the plot of log vbr vs. 1/T have been described in the literature for a number of reactions. If sufficiently small temperature intervals are used in the investigation of the temperature dependence (STI method) a trend line is obtained instead. It is then possible to distinguish regions of linear behavior and regions of anomalous behavior. The effects of e. g. the pH, the ionic strength, and added salts as well as of the size of the enzyme and substrate molecules on the anomalies were examined. The anomalous temperature dependence of the reaction rate was found to be a particularly sensitive indicator of the reaction event on the enzyme. The course of the reaction is evidently affected even by relatively small changes in conformation, particularly in the region of the active center.
Translation of Genetic Information on the Ribosome
Authors: Schreiber Gerhard
Published: December 2003

The information for protein structure that is contained in the base sequence of the nucleic acids is translated on the ribosome into the amino acid sequence. This translation can be divided into chain initiation, chain growth, and chain termination. Several specific protein factors and nucleic acids are involved in each section.—For chain initiation, start complexes are formed from the initiating amino acyl‐tRNA, mRNA carrying the start signal, and the small and large subunits of a ribosome. GTP and the initiating factors are also involved in this process.—In chain elongation, one amino acid at a time is transferred, in a reaction cycle, from the linkage with tRNA into a linkage with the polypeptide chain. The amino acid to be incorporated is initially bound to the ribosome as amino acyl‐tRNA, a process for which GTP and protein factors are necessary. The subsequent formation of a peptide linkage is catalyzed by the peptidyl transferase of the large ribosomal subunit. The peptidyl‐tRNA with its newly added amino acid residue is then transferred from the amino acyl‐tRNA acceptor site A to the peptidyl donor site P of the ribosome. This requires another protein factor and cleavage of GTP into GDP and phosphate.–Ghain termination begins as soon as one of the three terminator triplets UAA, UAG, or UGA in the mRNA reaches the ribosome. The mRNA is moving in relation to the ribosome from the 5′ end to the 3′ end. Release of the completed polypeptide chain from the ribosome is dependent on release factors. Before initiation of a new polypeptide chain, the ribosomes dissociate into their subunits.
Applications of Mössbauer Spectroscopy to Problems in Solid‐State Chemistry
Authors: Greenwood Norman N.
Published: December 2003

The factors influencing the chemical isomer shift, quadrupole splitting and hyperfine magnetic interactions, are briefly summarized and applications to solid state systems reviewed. New results on the disordered rutile phases Fe2MgF6, FeMg2F6, and FeCoNiF2, and on the trirutile phase Li+ Fe2+ Fe3+ F6 are presented to illustrate the power of the Mössbauer technique in probing details of oxidation states, site symmetries and magnetic ordering. An extensive study on the nonstoichiometric wüstite phase Fe1−xO is also reported and analyzed in terms of diffusion broadening at high temperatures and defect clustering in quenched samples; the production of essentially stoichiometric FeO by annealing is also discussed. Recent results on the application of large external magnetic fields to diamagnetic compounds of tin are reviewed and results of a Mössbauer investigation of lunar samples returned by the Apollo 11 and 12 missions are discussed.