bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclization of Acetylenic Compounds
Authors: Reppe W. , v. Kutepow N. , Magin A. 
Published: December 2003

AbstractCheap 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

AbstractThe 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

AbstractThe 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

AbstractActive 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.
Interferons
Authors: Murthy Y. K. S. , Anders Hans‐Peter 
Published: December 2003

AbstractInterferons 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

AbstractNew 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

AbstractFor 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

AbstractThe 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

AbstractDuring 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

AbstractA 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

AbstractA 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

AbstractThe “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

AbstractIn 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

AbstractThe 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

AbstractMulticomponent 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

AbstractSeveral 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

AbstractSystems 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

AbstractPericyclic 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

AbstractThe 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

AbstractA 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).
Metal Ion Function in Carbonic Anhydrase
Authors: Prince R. H. , Woolley P. R. 
Published: December 2003

AbstractThe 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

AbstractCooperative 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

AbstractThe 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

AbstractVarious 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.
Shift Reagents in NMR Spectroscopy
Authors: von Ammon Reinhard , Fischer R. Dieter 
Published: December 2003

AbstractThe 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

AbstractIn 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

AbstractFor 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

AbstractThe 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

AbstractThe 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.
Aromatic Keto Compounds as Initiators in Photopolymerizations
Authors: Heine H.‐G. , Rosenkranz H.‐J. , Rudolph H. 
Published: December 2003

AbstractThe 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

AbstractFive‐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.