bluuebunny/crossref_metadata_2025 huggingface dataset:
Conjugated Additions in Hydrogen Fluoride
Authors: German L. S. , Knunyantz I. L.
Published: December 2003

Fluorine and another substituent can be added in a single step to compounds having CC double bonds in anhydrous hydrogen fluoride. It is possible in this way to obtain e.g. α‐fluorinated β‐halogeno, β‐alkyl, β‐nitro, and β‐amino compounds, and also (in some cases by secondary reactions) fluorinated ethers, alcohols, esters, and carboxylic acids, β‐fluoro alcohols can be obtained by conjugated “hypofluorination” in the presence of oxenium ions.
Preparation of Cyclic Amidines by Reduction of Dinitriles with LiAIH4
Authors: Sieveking H. U. , Lüttke W.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196906171
Divalent Silicon Intermediates
Authors: Atwell W. H. , Weyenberg D. R.
Published: December 2003

Like carbenes, silylenes are assumed to occur as intermediates in many reactions. A detailed account of the reactivity of the silylenes is given and the reductive and thermolytic methods used for their preparation are discussed. Insertion and interception reactions emphasize the formal relationship between these species and the carbenes. Silacyclopropenes and silacyclopropanes have not, as yet, been isolated.
Topochemical Investigations on Peptide Systems
Authors: Shemyakin M. M. , Ovchinnikov Yu. A. , Ivanov V. T.
Published: December 2003

The basic principles of the topochemical approach to the investigation of the structure‐function relation in peptide systems are formulated. This approach makes use of the new possibility of transforming natural peptides, consisting in the modification of the molecule as a whole and utilization of the resultant analogs to elucidate the boundaries of the stereoelectronic complementarity of the biologically active peptide to the corresponding receptor. In particular, on the example of depsipeptide antibiotics and their topochemical analogs the fruitfulness of using such compounds as tools in elucidating the physicochemical basis of functioning of biological membranes is shown. The topochemical principle has also been applied in preparing specific competitive inhibitors of proteolytic enzymes, whose study may shed light on the nature of the forces binding the substrate to the contact site of the corresponding enzyme.
Non‐Enzymatic Activation of Molecular Nitrogen
Authors: Henrici‐Olivé G. , Olivé S.
Published: December 2003

Several transition metal complexes that can absorb nitrogen from the gas phase are now known. Some of the N2‐metal complexes are stable enough to be isolated and their structure elucidated, the N2molecule remaining chemically inert. In other cases reduction to N3−is possible, but the structure of the reactive intermediate N2‐metal complex can be approached only by mechanistic studies. In the stable complexes the nitrogen is bound via a lone pair of electrons in the direction of the molecular axis (“end‐on”), in the reducible complexes possibly “edge‐on”.
Cyclization of Acetylenic Compounds
Authors: Reppe W. , v. Kutepow N. , Magin A.
Published: December 2003

Cheap acetylene produced by a new process can compete with ethylene as a starting material for the large‐scale production of a number of organic products. Hydroquinone and methylated hydroquinones, which are valuable industrial starting materials or intermediates, are obtained by catalytic cyclizations.
Acid‐Catalyzed Cyclodimerizations via Vinyl Cations as Intermediates
Authors: Griesbaum K.
Published: December 2003

The electrophilic addition of hydrogen chloride and bromide to allene and of hydrogen bromide to methylacetylene at −70 °C leads not only to the simple Markownikoff adducts but also to cis‐ and trans‐1,3‐dihalo‐1,3‐dimethylcyclobutanes. These cyclodimerizations, which evidently proceed via vinyl cations, have opened up new short routes for the synthesis of cyclobutane‐, cyclobutene‐, and bicyclobutane derivatives starting from substrates that are industrially readily accessible.
Distortions of the π‐Electron System in Substituted Benzenes
Authors: Katritzky A. R. , Topsom R. D.
Published: December 2003

The factors leading to substituent effects on the electron distribution in aromatic molecules are discussed, particular attention being paid to the π‐electron system. IR spectroscopy has proved an extremely useful probe in this field of study. Substituent d‐orbital participation and the relevance of the π‐inductive effects are also considered.
The Chemical Behavior of Active Nitrogen
Authors: Brown R. , Winkler C. A.
Published: December 2003

Active nitrogen, which is formed on passage of an electric discharge through a stream of nitrogen, is detected by a characteristic yellow afterglow. It can be determined quantitatively, e.g. by gas phase “titration” with nitric oxide. Active nitrogen reacts with many chemical elements, as well as with organic and inorganic compounds. Although nitrogen atoms are responsible for many of the reactions of active nitrogen, electronically excited molecules also play a role.
Modern Steroid Problems
Authors: Wiechert Rudolf
Published: December 2003

The present article is concerned primarily with the latest developments in the fields of steroids exhibiting contraceptive, antiandrogenic, or cardiac activity and of steroid metamorphosis hormones. Both the biological action and the current sources of raw materials are considered.
Interferons
Authors: Murthy Y. K. S. , Anders Hans‐Peter
Published: December 2003

Interferons are proteins which bring about a nonspecific and nonimmunological defence reaction against virus infections in vertebrates. Interferon formation is induced in vivo and in vitro by viruses and other agents, e.g. endotoxins, nucleic acids, synthetic anionic copolymers, and phytohemagglutinins. All attempts to produce pure interferons have so far been unsuccessful. Interferons can only exert an antiviral action when the cellular RNA and protein synthesis is intact.
Gas‐Liquid Chromatography and Mass Spectrometry in Methylation Analysis of Polysaccharides
Authors: Björndal Håkan , Hellerqvist Carl Gustaf , Lindberg Bengt , Svensson Sigfrid
Published: December 2003

New methylation procedures and the combined application of gas‐liquid chromatography and mass spectrometry for the qualitative and quantitative analysis of mixtures of methylated sugars permit methylation analysis of polysaccharides to be performed more accurately, faster, and with less material than previously.
Developments in Inorganic Arc Plasma Chemistry
Authors: Landt U.
Published: December 2003

For some 10 to 15 years, plasma chemistry has been in a state of rapid development on the research side, whereas only a few reactions are at present carried out industrially in a plasma jet. After a short description of the properties of thermal plasmas, the technique of production and stabilization of arc plasmas and the various types of arc plasma generators are discussed. The course of chemical reactions at plasma temperatures is then considered, with particular reference to kinetic and thermodynamic aspects. A special part of the review is devoted to a detailed description of the inorganic reactions that have been carried out in the plasma jet (preparation e.g. of compounds containing nitrogen, CN and CF compounds, ozone, nitrides, cyanides, carbides, metal oxides, and metals from metal oxides and from halides).
Volatile Flavoring Substances in Foodstuffs
Authors: Maier Hans Gerhard
Published: December 2003

The odor of most foods is produced by mixtures of many volatile flavoring substances. Over the past century, numerous food flavors have been analyzed in sufficient detail to allow a survey of the classes of substances responsible, the formation of individual flavoring substances, and their fixation in the foods. In addition to special biosynthetic pathways, the breakdown of fats and the Maillard reaction have been found to be particularly important to the formation of flavoring substances.
Progress in the Hetaryne Field
Authors: Kauffmann Thomas , Wirthwein Rolf
Published: December 2003

During recent years, instead of concentrating on the detection of the intermediacy of new hetarynes, as they did between 1958 and 1964, workers in this field have been more concerned with the critical sifting and checking of the earlier work. Special interest has been shown in the relation between structure and reactivity in the hetarynes. It has been shown that in addition to the elimination‐addition mechanism (EA; hetaryne intermediate), other reaction paths (anomalous addition‐elimination mechanism [AEa] and “Reinecke mechanism”) are possible for nucleophilic cine‐substitutions on hetaryl halides. The use of deuterated hetaryl halides has proved very valuable for the elucidation of the mechanism of nucleophilic substitutions. Even where substitution mechanisms are superimposed on one another the occurrence of a hetaryne intermediate can be detected by a technique known as the “base competition method”. A five‐membered hetaryne (4,5‐didehydro‐1‐methylimidazole) has been detected for the first time by this method with a probability that borders on certainty. Selectivity determinations have shown that the replacement of a CH group in 1,2‐didehydrobenzene and in 1,2‐didehydronaphthalene by an N atom distinctly increases the reactivity to bases. According to EHT (Extended Hückel Theory) calculations, the as yet hypothetical 2,3‐didehydropyridine is richer in energy than 3,4‐didehydropyridine, this agrees more closely with the experimental findings than the opposite result obtained from simple MO calculations. Besides cine‐substitution (1,2 shift), tele‐substitution (1,3‐shift) has also been observed on reaction of hetaryl halides (pyridine, quinoline, and pyrimidine systems) with bases. An EA mechanism (via m‐didehydrohetarenes) and an AEa mechanism are considered as alternatives for the tele‐substitution.
Biochemistry and Function of Biogenic Amines in the Central Nervous System
Authors: Seiler Nikolaus , Demisch Lothar , Schneider Herbert
Published: December 2003

A number of amines are of the utmost importance to the normal function of the nervous system; numerous relationships also exist between certain diseases of the nervous system and the metabolism of these amines. Noradrenaline, serotonin, and histamine are taken as examples to offer some idea of the possibilities and methods of biochemical research that help to elucidate the physiological and pathological processes in the nervous system. The article shows that our knowledge of the functioning of the nervous system, even in a field that has been studied as thoroughly as the transmission of nerve stimuli at synapses, is still in its infancy.
New Methods for the Synthesis of Vinyl Azides
Authors: L'abbé Gerrit , Hassner Alfred
Published: December 2003

A critical survey of synthetic approaches to vinyl azides is presented, focusing especially on stereo‐ and regiochemical problems. The com bined procedure of azidohalogenation of olefins followed by dehydrohalogenation, leads to regiospecific and, in the case of ionic additions, also to stereospecific formation of vinyl azides. Nucleophilic substitutions by azide ions on activated olefinic halides result in β‐azidovinyl ketones, esters, nitriles, etc., and proceed predominantly with retention of configuration about the CC bond. The known synthetic methods leading to α‐azidovinyl ketones and esters give rise to the thermodynamically more stable trans‐vinyl azides.
50 Years of Hydrogen Bond Theory
Authors: Huggins Maurice L.
Published: December 2003

The “hydrogen bond” or “hydrogen bridge” concept has proved to be one of the most useful structural concepts in modern science. The properties of substances containing hydrogen bonds depend on the strength, symmetry, and polarity of these bonds. These characteristics, in turn, are related to the effective electronegativities of the bridgehead atoms, the distance between these atoms, and the degree of coupling with other hydrogen bonds. Symmetrical hydrogen bonds exist in the FHF− and H5O ions and in some acidic compounds. Coupled hydrogen bond systems exist, for example, in ice, liquid water, hydroquinone clathrates, starch, cellulose, polypeptides, nucleic acids, KH2PO4, and silicate hydrates. It is suggested that systems of coupled, nearly symmetrical, hydrogen bonds should be interesting subjects of further research.
The Synthesis of Physiologically Active Peptides
Authors: Geiger Rolf
Published: December 2003

In addition to the classical protective groups and linkage.methods for the synthesis of peptides, there are now a number of new techniques that allow the synthesis of fairly long peptide chains without racemization. In the present progress report, the diagnostic and therapeutic importance of the analogs obtainable by chemical synthesis is illustrated by some examples, particularly from the field of the peptide hormones secreted by the neurohypophysis, oxytocin and vasopressin, as well as corticotropins and releasing hormones. With the advance of synthesis technique, it will become possible to include fairly complicated molecules, such as insulin and even enzymes in such considerations.
The Mechanism of Contact Elimination, A Contribution to Understanding the Function of Polar Catalysts
Authors: Noller Heinrich , Andréu Paulino , Hunger Manfred
Published: December 2003

The current ideas of organic chemists based on the work of Ingold and his school are applied to heterogeneous catalytic eliminations (mostly from haloalkanes and aliphatic alcohols). It is deduced from the activity of the catalysts, the reactivity of the substrates (reactants), and the primary product distribution that these eliminations proceed by a heterolytic mechanism similar to that involved in the liquid phase. The activity of the catalysts (salts and oxides) increases with increasing charge and decreasing radius of the cations and with increasing basicity of the anions. The reactivity of the substrates behaves in much the same manner as in the liquid phase. In contrast with the liquid‐phase reaction, the cis‐olefins are frequently favored as primary products. The stereospecificity of the reaction is determined from the relative strengths of the interactions between the catalyst cation and the leaving group X−, and between the catalyst anion and the leaving proton. Only trans elimination has so far been found in the concerted mechanism.
New Routes to Multicomponent Oxide Glasses
Authors: Dislich Helmut
Published: December 2003

Multicomponent oxide glasses can be produced not only by melting methods but also by hydrolysis and condensation of alkoxide complexes with several metals. This requires temperatures only up to the transformation range of the glass in question, usually 500–600 °C. The process does not pass through the molten phase. It is possible to obtain glasses or polycrystalline substances, depending on the composition. The method is particularly suitable for the production of thin, transparent multicomponent oxide layers of almost any composition on substrates. Some of these layers provide protection against climatic attack or against oxidation.
Reactions of Atoms
Authors: Wagner Heinz Georg , Wolfrum Jürgen
Published: December 2003

Several methods for the quantitative investigation of reactions of free atoms in the gas phase have been developed in recent years. The present article deals with reactions of hydrogen, carbon, oxygen, and halogen atoms with simple molecules. The results of such investigations are of fundamental importance for the understanding of chemical reactions and for many technical applications, such as explosion and combustion processes, halogenations, and chemical lasers.
Systems of Monomolecular Layers—Assembling and Physico‐Chemical Behavior
Authors: Kuhn Hans , Möbius Dietmar
Published: December 2003

Systems of monomolecular layers can form functional units having properties not exhibited by the individual layers. On UV irradiation, for example, an energy transfer takes place from a sensitizer (S) layer to an acceptor (A) layer and results in fluorescence of A. S and A may be cyanine dyes. Monomolecular layers can be manipulated in many ways and combined to construct novel systems; the energy transfer method can be used to establish whether the desired structure has in fact been produced. The monolayer assembling technique can also be used for the investigation of the deactivation of excited molecules; an interesting example is the spectral sensitization of the photographic process.
Aromaticity and Pericyclic Reactions
Authors: Dewar Michael J. S.
Published: December 2003

Pericyclic reactions formally resemble the conversion of one Kekulé structure into another; the transition state may be “aromatic”, “nonaromatic”, or “antiaromatic”. Thermally induced pericyclic reactions proceed preferentially via aromatic transition states whereas their photochemical counterparts lead to products that are formed via antiaromatic transition states.
Macrocyclic Polyethers and Their Complexes
Authors: Pedersen C. J. , Frensdorff H. K.
Published: December 2003

The most important, and almost unique, property of the macrocyclic polyethers (“crown compounds”) is their tendency to form complexes with alkali metal salts and salts with similar cations. Such complexes are held together by electrostatic attraction between the cation and the negative end of the CO dipoles. The stability of the polyether complexes depends primarily upon how well the cation fits into the polyether ring; other factors are the charge density of the cation and—in solution—the solvating power of the medium. Cyclic polyethers have been successfully employed, inter alia, in experiments with ionic compounds in organic solvents and in studies of ion transport in biological systems.
ESCA: Electron Spectroscopy for Chemical Analysis
Authors: Nordling Carl
Published: December 2003

A substance on which X‐rays fall emits photoelectrons and Auger electrons. The energy spectra of the electrons emitted provide information about the electronic structure in the specimen, ranging from the innermost atomic levels and their dependence on the chemical environment to the molecular orbitals of the valence electrons and the band structure in solids. Electron spectra of this nature can now be recorded with high‐resolution instruments; their analysis offers new aspects for investigation of chemical composition. The method of electron spectroscopy developed for this purpose, which has now been developed to a high degree of perfection, will be referred to in the following discussion as ESCA (Electron Spectroscopy for Chemical Analysis).
Mechanisms of Reactions in the Solid State
Authors: Hardel Kurt
Published: December 2003

The reaction of two solid phases X and Y to give a solid compound XYv is taken as an example for the discussion of transport mechanisms and reaction steps. The following methods of investigation are discussed: determination of the rate law, marker experiments, and calculation of the reaction rate. It is pointed out that the investigation of powder reactions leads to problematic conclusions.
Metal Ion Function in Carbonic Anhydrase
Authors: Prince R. H. , Woolley P. R.
Published: December 2003

The purpose of this review is to present an up‐to‐date account of the chemistry of the metal ion in the enzyme carbonic anhydrase. The interest lies in how the study of the metal may lead to deductions concerning the chemistry of the enzyme's action and in the way that metalloenzyme chemistry seems to demand a new appraisal of some aspects of the established chemistry of metal complexes.
Kinetics of Cooperative Conformational Transitions of Linear Biopolymers
Authors: Schwarz Gerhard , Engel Jürgen
Published: December 2003

Cooperative conformational transitions of proteins and nucleic acids are of decisive importance to many processes of molecular biology, and particularly to their regulation. They proceedvianumerous interdependent elementary processes, and their kinetics are therefore often complicated. They are frequently also very fast. However, kinetic analyses can be carried out by chemical relaxation methods. The theoretical interpretation is comparatively simple in the case of linear biopolymers. When the linear Ising model extended for kinetics was applied to model peptides and polynucleotides, it provided an insight into the fundamental principles of cooperative transformations.
Metal‐Olefin and ‐Acetylene Bonding in Complexes
Authors: Hartley Frank R.
Published: December 2003

The molecular orbital (MO) and valence bond (VB) descriptions of the bonding in metalolefin and ‐acetylene complexes are examined in relation to their ability to explain the known properties of these complexes. It is concluded that whereas there are difficulties with the valence bond description, the molecular orbital description can satisfactorily explain all the known properties of these complexes and has the necessary versatility to enable it to be readily applied to any series of metal‐olefin or ‐acetylene complexes. It is further shown that olefin and acetylene complexes can be usefully divided into two main classes: those that resemble the platinum(II)‐complexes (class S), and are either square‐planar or octahedral with essentially free rotation about the metal‐olefin bond; and those that resemble platinum(0)‐complexes (class T) and are either trigonal planar or trigonal bipyramidal and in which there is no rotation about the metal‐olefin or ‐acetylene bond.
Nuclear Magnetic Resonance in Solid‐State Chemistry
Authors: Weiss Alarich
Published: December 2003

Various problems of solid‐state chemistry can be solved by spectroscopic investigation of the nuclear magnetic resonance (NMR and NQR methods). This progress report presents a survey of the nature of the interactions in the crystal that underlie such measurements, of the observations in the spectrum, and of the information obtainable from it. The field of application of the methods covers both static and dynamic properties of solids.
Metal Isotope Effect on Metal‐Ligand Vibrations
Authors: Nakamoto Kazuo
Published: December 2003

Exploitation of the isotope effect using heavy metal isotopes now makes it possible to give clear‐cut assignments of the metal‐ligand vibrations in the IR and Raman spectra of complex compounds. The results previously obtained with this new method and their current limitations form the subject of this progress report.
Shift Reagents in NMR Spectroscopy
Authors: von Ammon Reinhard , Fischer R. Dieter
Published: December 2003

The number of possible applications of NMR spectroscopy has rapidly increased during the past few years. New fields of applications have been opened by the development of supraconducting solenoids and various spin‐decoupling techniques and by the method of “pulsed Fourier transform NMR‐spectroscopy”. These methods originate mainly from progress in instrumentation. Recently, another “technique” has been introduced into NMR spectroscopy, which—principally on the basis of chemical and spectroscopic experience—is much less expensive but nevertheless useful. The basic principles, background, and most important applications of this method, known as the “NMR‐shift‐reagent technique”, form the subject of this paper.
Organic Syntheses via Free‐Radical Displacement Reactions of Organoboranes
Authors: Brown Herbert C. , Midland M. Mark
Published: December 2003

In the few short years since the discovery that organoboranes undergo facile free‐radical substitution, application of these reactions has become a major new area of synthetic utility. Organoboranes undergo a wide variety of free‐radical reactions such as autoxidation to the alcohol or hydroperoxide, 1, 4 addition to α,β‐unsaturated derivatives, addition to disulfides, and oxygen‐induced radical coupling. It is evident that organoboranes constitute a versatile new source of free radicals and that these reactions can be readily controlled to give very clean syntheses. The application of these reactions will be discussed.
Enzymatic Hydroxylations with Molecular Oxygen
Authors: Ullrich Volker
Published: December 2003

For thermodynamic reasons, biological hydroxylations cannot usually proceed according to the β‐oxidation scheme, but are possible only with the aid of molecular oxygen by a route requiring a large amount of energy. The corresponding enzymes, known as “mixed function oxygenases” or more appropriately “monooxygenases”, require two reduction equivalents for the activation of oxygen. The cytochrome P‐450‐dependent monooxygenases are taken as examples for the discussion of the chemistry of the enzymatic catalysis. The central problem of the activation of oxygen has not yet been solved, but an “oxenoid” mechanism can be deduced from model investigations.
Cathodic Dimerization
Authors: Beck Fritz
Published: December 2003

The technical, electrochemical, and preparative aspects of cathodic dimerization, which leads to bifunctional compounds, are reviewed. With the hydrodimerization of acrylonitrile as an example, the effects of the reaction parameters and the mechanism are discussed in detail. In addition to the hydrodimerization of activated compounds, the coupling can also proceed via elimination of halide orviathe discharge of cations. Processes of special preparative interest are those in which two different molecules are coupled, which can yielde.g.esters, alcohols, or ketones with cyano groups, as well as asymmetric diols. The reductive dimerizations of acrylonitrile, β‐chloropropionitrile, acetone, acetylpyridine, nitrobenzene (→ benzidine), and pyridinium salts have already found industrial use.
Self‐Organization of Molecular Systems and Evolution of the Genetic Apparatus
Authors: Kuhn Hans
Published: December 2003

The aim of the work described in this report is to find pathways leading to self‐organization of molecular systems. The idea is not to trace the historical pathway of evolution but to describe a model whose experimental verification should help to clarify the important principles of evolution. The difficulty of accepting the origin of living organisms as a physico‐chemical phenomenon and the deeply rooted notion that a system of such complexity as the genetic apparatus could never be the outcome of processes based solely on the known laws of physics have influenced philosophical thinking very strongly. This study is also intended as an attempt to overcome this psychological problem by systematic pursuit of a model pathway composed of many, readily comprehensible steps. A process thus becomes understandable which cannot be grasped as a whole, and is therefore alien to our conceptual habits.
Computer Model of the Formation of Self‐Organizing Systems
Authors: Försterling Horst‐Dieter , Kuhn Hans , Tews Karl‐Heinz
Published: December 2003

A model of a simple self‐organizing system is investigated. Mechanisms that are important to a molecular‐biological understanding of evolution are studied with the aid of the model.
Aromatic Keto Compounds as Initiators in Photopolymerizations
Authors: Heine H.‐G. , Rosenkranz H.‐J. , Rudolph H.
Published: December 2003

The present article deals with the primary photochemical reactions of carbonyl compounds commonly used as photoinitiators. It is shown that radical formation results mainly from three processes, i.e. hydrogen abstraction, β‐cleavage, and α‐cleavage. The difference in the suitability of the radicals for chain initiation is discussed.
Syntheses of Heterocycles by Intramolecular Acylation of Nitrile‐Hydrogen Halide Adducts
Authors: Simchen Gerhard , Entenmann Günther
Published: December 2003

Five‐membered, six‐membered, and seven‐membered aza‐, diaza‐, and thiazaheterocycles can be prepared by cyclization of. ω‐cyano carboxylic acid halides in the presence of hydrogen halides in aprotic solvents. Nitrile‐hydrogen halide adducts occur as intermediates in this novel heterocycle synthesis of wide application. The acylating cyclizations of nitriles in protonic media, which proceed via imidic esters or amides, are not discussed.
Chemistry and Biology of the Acylneuraminic Acids
Authors: Schauer Roland
Published: December 2003

Acylneuraminic acids occupy an outstanding position both sterically and with respect to biological functions in gangliosides and in many glycoprotein molecules. Acylneuraminic acids are N‐acylated and partly O‐acylated derivatives of neuraminic acid, a polyhydroxyamino keto acid that has the properties of a carbohydrate and is therefore capable of forming a glycoside linkage. The present report provides a survey of our knowledge of the chemistry and biology of the acylneuraminic acids, which occur widely in particular in the animal kingdom.
Quartz Crystals and Their Colors
Authors: Lehmann Gerhard , Bambauer Hans Ulrich
Published: December 2003

The many colors found in quartz crystals are always due to the presence of impurity atoms, whose concentrations rarely exceed 0.1 wt.%. The impurity atoms occupy either silicon sites in the lattice or interstitial sites in the channels parallel to the c axis of the quartz structure; very fine precipitations of foreign phases are sometimes also observed, though this is less common. In addition to intrinsic colors of transition metal ions, one also finds color centers produced by ionizing radiation. Regular distributions of impurity atoms and colors may develop in the crystals as a result of some factor connected with its growth. Most of the natural quartz colors, as well as others that do not occur in nature, have been produced in synthetic quartzes.
Bredt Compounds and the Bredt Rule
Authors: Köbrich Gert
Published: December 2003

The Bredt rule, which proved useful in earlier decades mainly as an exclusion criterion in the assignment of structures, has in recent years become the stimulus for efforts to synthesize strained bicyclic systems with a bridgehead double bond. On the basis of the ring‐strain forces operating in such systems, an extended Bredt rule is discussed. The “Bredt comgounds” to which this rule applies, which include bicyclic systems not prevoously consodered from this point of view (e.g. bridged methylenecyclopropanes), form a clearly circumscribed, interesting field within the chemistry of highly‐strained hydrocarbons with ring unsaturation.
Chemical Analysis of Synthetic Fibers
Authors: Nissen Dietmar , Rossbach Volker , Zahn Helmut
Published: December 2003

The analytical characterization of synthetic fibers has not kept pace with their development and production. Whereas the “second‐generation” fibers have already conquered the market, the chemical investigation methods used until now for the three classical fiber polymers of the polyester, polyamide, and polyacrylonitrile types are still frequently unsatisfactory. Though they satisfy the requirements of production supervision and quality control, they do not supply enough information to enable us to understand and to explain the degradation of and damage to the polymers under hydrolytic, thermal, or thermooxidative influences. This report presents methods of chemical analysis that open up new possibilities for investigations of this nature on synthetic fibers. The results reported for commercial products must not be taken as an assessment of quality. They are simply intended to show the diversity to be expected in the chemical properties and to emphasize the practical basis of the chemical analysis of synthetic fibers.
Reactive Monomeric Carbonic Acid Derivatives
Authors: Kühle Engelbert
Published: December 2003

Monomeric carbonic acid derivatives that can react by addition or substitution are systematically discussed according to the three tabular surveys A, B, and C, from which a principle for the classification of carbonic acid derivatives can be readily deduced. For each type of compound, a brief description is given first of the principal syntheses and then of the reactions, and the heterocycles obtainable by addition, disubstitution, or coupled addition‐substitution are also considered. The carbonic acid derivatives discussed can be synthesized from very simple and in most cases cheap base chemicals.
Chemistry and Significance of the Carbohydrate Moieties of Human Serum Glycoproteins
Authors: Heide Karl , Schwick Hans‐Gerhard
Published: December 2003

The glycoproteins exercise important biological functions as transport proteins, inhibitors, enzymes, hormones, complement factors, and immunoglobulins. Their chemistry is characterized by a number of rules. Thus only asparagine, threonine, or serine can carry the oligosaccharide groups; for the N‐acylglycosylamine linkage involving asparagine, the grouping Asn‐X‐Thr or Asn‐X‐Ser is always present in the peptide chain. However, practically no agreement is found in the molecular weights of the glycoproteins, their carbohydrate contents, and the relative contents of the‐various sugars. The biological significance of the carbohydrate fraction has not yet been explained, but some idea of the part played by the easily removable neuraminic acid is being formed.
The Chemistry of Dichloromethylenammonium Salts (“Phosgenimonium Salts”)
Authors: Viehe Heinz Günter , Janousek Zdenek
Published: December 2003

Dichloromethylenammonium salts, particularly dichloromethylenedimethylammonium chloride, occupy a unique place as stable but reactive building blocks for synthesis. They contain three mobile chlorine atoms activated by an amino group on the same carbon atom. These salts can be regarded as chlorinated Vilsmeier or Mannich reagents and are thus at a higher oxidation level. As in the Mannich or Vilsmeier reaction, the carbon condenses here as an electrophile with formation of CC or Chetero atom bonds in a variety that is still far from being exhausted.
Oxathiazinone Dioxides—A New Group of Sweetening Agents
Authors: Clauss Karl , Jensen Harald
Published: December 2003

1,2,3‐0xathiazin‐4(3H)‐one 2,2‐dioxides bearing lower alkyl substituents on C‐5 and C‐6 represent potential sweeteners. They are formed from chloro‐ or fluorosulfonyl isocyanate and acetylenes, ketones, β‐diketones, β‐oxo carboxylic esters, or benzyl vinyl ethers via N‐halosulfonyl β‐oxo carboxamides as common intermediates.
The “Nickel Effect”
Authors: Fischer Karl , Jonas Klaus , Misbach Peter , Stabba Reinhold , Wilke Günther
Published: December 2003

Whereas the reaction of ethylene and triethylaluminum under pressure at 100°C yields trialkylaluminum compounds having long alkyl chains, the presence of small amounts of nickel salts induces the formation of butene. The discovery of this “nickel effect” represents the starting point for the development of the Ziegler catalysts. Comparatively little was formerly known about the nature and the mode of action of the catalytically active nickel species. A basis for the elucidation of the effect was provided by studies on the reduction of nickel compounds by organoaluminum compounds, on the occurrence and existence of nickel hydrides, and on interactions between nickel(0) and Lewis acids as well as organic compounds of main group metals. The most significant result of these studies is the recognition that multicenter bonding systems involving trialkylaluminum compounds and nickel atoms are involved. These react further with complex bonded ethylene in what is probably a concerted manner.
Structure‐Property Relationships in a Polymer
Authors: Andrews E. H.
Published: December 2003

The way in which polymer molecular structure controls structure on higher levels of organization in a solid polymer is briefly reviewed, as is also the way in which structure, on all levels, controls physical properties. The “line of descent” from molecular structure to physical properties is then illustrated for cis‐polyisoprene (natural rubber). It is shown how the crystalline‐amorphous morphology in the solid is controlled both by the chemical microstructure of the polymer and by the physical conditions (temperature, time, strain) under which solidification occurs. By changing these “processing conditions” great changes can be effected in the morphology.
Recent Discoveries in the Evolution of Proteins
Authors: Acher Roger
Published: December 2003

Is it possible to reconcile the great diversity of present‐day proteins with a unitary theory of the evolution of these molecules? The mechanisms of diversification of proteins are undoubtedly not yet all known, but it is clear that the linear construction of polypeptide chains lends itself to operations such as addition, insertion, deletion, and fusion. Combinations of these modifications would explain the development of an infinite number of entirely different proteins from one ancestral molecule.
The Stable Isotopes of Oxygen in Research and Technical Applications
Authors: Staschewski Dieter
Published: December 2003

The stable isotopes of oxygen have proved to be efficient research tools; however, only a small fraction of the possible applications of these isotopes have been examined so far. The present progress report deals with five basic types of isotopic effects whose investigation and evaluation offer information of a new kind about physical, chemical, and biological systems and processes.
The Chemistry of Hydroxamic Acids and N‐Hydroxyimides
Authors: Bauer Ludwig , Exner Otto
Published: December 2003

This progress report is concerned primarily with problems relating to the structure and reactions of hydroxamic acids and N‐hydroxyimides, and also surveys some of the biological activities of these compounds. Particular significance attaches to the Lossen rearrangement of O‐acylated hydroxamic acids, which leads to isocyanates or their reaction products.
Carbon Suboxide in Preparative Organic Chemistry. New synthetic methods (1)
Authors: Kappe Thomas , Ziegler Erich
Published: December 2003

Although it has been known for nearly 70 years, carbon suboxide was used almost exclusively for the preparation of simple malonic acid derivatives until about 1960. Since then, however, the significance of this unusual “bisketene” has steadily increased in synthetic chemistry (especially that of heterocyclic compounds). This progress report surveys the possible applications of C3O2 in preparative organic chemistry, including photochemical reactions.
Antimetabolites of Coenzyme Q. Their Potential Application as Antimalarials
Authors: Porter Thomas H. , Folkers Karl
Published: December 2003

Malaria is transmitted to man by the bite of the female Anopheles mosquito, man acting as the intermediate host, and the mosquito as the definitive host for the plasmodia. Plasmodia are found to have become resistant to certain chemotherapeutic agents. A new fundamental approach to malaria chemotherapy is based on the biochemical rationale of inhibition of the electron transfer mechanism in the metabolism of plasmodia by antimetabolites of coenzyme Q, which is essential for electron transfer. Coenzyme Q refers to 2,3‐dimethoxy‐5‐methyl‐1,4‐benzoquinones with isoprenoid chains of varying length on C‐6. In this progress report a series of synthetic antimetabolites are presented together with a discussion of their action in current pharmacological tests.
Enzymatic Reduction of Ribonucleotides: Biosynthesis Pathway of Deoxyribonucleotides
Authors: Follmann Hartmut
Published: December 2003

Ribonucleotide reductases are enzymes that synthesize the deoxyribonucleotides required for the replication of DNA in dividing cells. They thus have a key function for the growth of microorganisms and of all plant and animal tissues. The enzymes reduce all four purine and pyrimidine ribonucleotides (as the 5′‐diphosphates or triphosphates) with direct substitution of the 2′‐hydroxyl group by hydrogen. The physiological reducing agents are the mercapto groups of thioredoxins, a group of small proteins, which are regenerated from the oxidized form by NADPH‐dependent thioredoxin reductases. There are two known types of ribonucleotide reductases (I and II), which catalyze hydrogen transfer with the aid of protein‐bound iron ions or of 5′‐deoxyadenosylcobalamin (coenzyme B12); free radicals can be detected in both cases. The enzymes are regulated by effector nucleotides. There may exist a homeostatic mechanism, which guarantees the supply of DNA precursors to the cell.
What Do We Know about the Deeper Layers of the Earth?
Authors: Schwab Roland G.
Published: December 2003

In the last twenty years modern chemical and physical methods have done much to extend our knowledge of the Earth. Some new questions have been raised, e.g. the question of the bonding relationships in the Earth's interior, which make the Earth an interesting object of research to chemists as well. This progress report attempts to give a survey of the Earth's structure as seen at the present day. Naturally, special emphasis has been placed on those aspects which concern the chemist.
Umpolung of Amine Reactivity. Nucleophilic α‐(Secondary Amino)‐alkylation via Metalated Nitrosamines
Authors: Seebach Dieter , Enders Dieter
Published: December 2003

There are basically two kinds of hetero atoms in organic molecules: one kind confers electrophilic character upon the carbon atom to which it is bound, and the other kind turns it into a nucleophilic site. The development of methods permitting transitions between the two resulting categories of reagents has become an important task of modern organic synthesis. The scope of such umpolung of the reactivity of functional groups is discussed for the case of amines as an example. A method of preparing masked α‐secondary amino carbanions consists in nitrosation of the secondary amine, followed by metalation of the resulting nitrosamine α‐to the nitrogen, reaction with electrophiles, and subsequent denitrosation. Many examples are given for each of these steps which illustrate the wide scope of the overall synthetic operation (electrophilic substitution at the α‐C atom of the secondary amine). Preliminary applications and a method for avoiding the handling of nitrosamines are presented, and the report concludes with a brief account of the significance of nitrosamines in the study of carcinogenesis and mutagenesis.
Isomerization Polymerization of Lactams
Authors: Reimschuessel H. K.
Published: December 2003

Isomerization polymerization affords a macromolecule whose repeating unit is derived from an isomer of the original monomer. Thus hexa‐ and heptacyclic β‐carboxymethyllactams yield polymers containing glutarimide units, whereas penta‐ and hexacyclic β‐carboxylactams furnish polymers containing succinimide units. Some dimethyl derivatives of β‐carboxylactams isomerize or rearrange, and 5‐oxopyrrolidine‐3‐acetic acid does not react at all. These observations can be explained in terms of a bicyclic intermediate.
Geochemistry of Stable Isotopes
Authors: Hoefs Jochen
Published: December 2003

During the past 25 years a new branch of research has developed under the name “stable isotope geochemistry”, and its importance within the earth sciences has steadily increased. The present progress report considers the scope, and also the limitations, of this discipline.
13C Spin‐Lattice Relaxation Times and the Mobility of Organic Molecules in Solution
Authors: Breitmaier Eberhard , Spohn Karl‐Heinz , Berger Stefan
Published: December 2003

While the chemical shifts and coupling constants of13C NMR belong to the most powerful tools available to the organic chemist for the solution of structural problems, increasing interest is being shown in13C spin‐lattice relaxation timesT1as structural parameters. Together with the nuclear Overhauser effects arising by proton decoupling of13C NMR spectra, theT1values of13C nuclei in a molecule permit conclusions to be drawn with regard to relaxation mechanisms. They reflect the inter‐ and intramolecular mobility of a molecule, and thus complement the results of temperature‐dependent NMR spectroscopy. TheT1differences within a molecule show, for instance, whether the molecular motion is anisotropic in solution, whether the internal motion of groups is subject to steric hindrance, the extent to which strong intermolecular or interionic interactions affect the flexibility of the molecule, and which parts of the molecule are rigid and which are flexible. Finally, differences between theT1values measured for the13C nuclei of a molecule frequently provide a reliable aid in the assignment of13C NMR spectra, particularly in cases of signal crowding and multiplet overlapping.
Investigation of Enzyme Mechanisms with Nucleoside Phosphorothioates
Authors: Eckstein Fritz
Published: December 2003

Nucleoside phosphorothioates are modified nucleotides in which an oxygen atom bound to a phosphorus atom has been replaced by a sulfur atom. These compounds are suitable for the investigation of enzyme mechanisms because, although they are bound by enzymes in many cases just as well as the natural substrate, the enzymatic reactions very often proceed considerably more slowly. Since nucleoside thiophosphate O‐esters exist as diastereomers these compounds can be used in suitable cases for information about the stereochemistry of enzymatic reactions.
New Element‐Carbon (p‐p)π Bonds
Authors: Jutzi Peter
Published: December 2003

Recent years have seen the preparation of π systems containing novel (p‐p)π bonds between carbon and elements from the third, fourth, and fifth Main Groups of the Periodic Table; most of these compounds are predicted to be incapable of existence according to the classical concepts of the double bond. (p‐p)π. Bonds between carbon and phosphorus, arsenic, and antimony have been successfully stabilized in resonance‐stabilized colored compounds of the cyanine and triphenylmethane type, and also in aromatic systems deriving from benzene, naphthalene, and anthracene. Bismuth‐carbon and boron‐carbon (p‐p)π bonds have likewise been confirmed in aromatic systems. Silicon‐carbon and germanium‐carbon (p‐p)π bonds have been detected in extremely reactive derivatives of silaethylene and germaethylene, respectively. The present report describes characteristic reactions of the new π systems. Their bonding follows from X‐ray structure analysis, from photoelectron, UV, and NMR spectra, and from calculations. Criteria for the existence of π systems which are not allowed by the classical double bond rule are discussed; these criteria remain valid on generalization.
Spectral Evidence for Lanthanoid and Actinoid Carbonyl Compounds
Authors: Sheline Raymond K. , Slater James L.
Published: December 2003

The co‐condensation of actinoid or lanthanoid atoms and a mixture of argon containing small amounts carbon monoxide on a surface cooled with liquid helium leads, after annealing of the argon matrix, to a series of new binary actinoid and lanthanoid carbonyl compounds. Evidence for these new carbonyls is obtained using infrared spectroscopy. Preliminary interpretation of the IR spectra suggests that at least six complexes, M(CO)1–6, have been observed for each metal. A distinct difference in the infrared spectra is observed for the ytterbium derivative, probably associated with the fact that ytterbium lacks one electron from having entirely filled 4f orbitals. A brief description of the possible bond hybridization and its effect on the MCO bonding, which may explain the difference between ytterbium and the other lanthanoids, is presented.
The Flipping of CO Ligand Groups in Metal Carbonyl Compounds and its Frequency in Fe(CO)5
Authors: Sheline Raymond K. , Mahnke Harald
Published: December 2003

It has been proven qualitatively by a number of authors using variable temperature NMR experiments that most metal carbonyl complexes are nonrigid. A quantitative determination of the ligand exchange frequency veis often achieved by a line shape analysis or by measurement of the transverse relaxation timeT2using the Carr‐Purcell method. In the case of a “very fast” exchange, however, both methods prove unsuccessful. It is shown in this study that a simultaneous fit of IR or Raman spectra on the one hand and NMR spectra on the other can make possible the determination of vefor the “very fast” exchange and can also facilitate the determination of vein “slow” and “medium” exchange cases considerably. The ligand exchange frequency thus found for Fe(CO)5, 1.1 × 1010s−1, is unexpectedly high; comparison with variable temperature measurements on solid Fe(CO)5, yields similar energy barriers. A mechanism of exchange closely related to the “Berry mechanism” is proposed. Finally the consequences of this surprisingly large ligand exchange rate are discussed with respect to IR band assignments for molecular “fragments” M(CO)x(wherex=coordination number, and M is a transition metal, typically lanthanoid or actinoid).