bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chiral Derivatives of Achiral Molecules: Standard Classes and the Problem of a Right‐Left Classification
Authors: Ruch Ernst 
Published: December 2003

AbstractChemistry judging by its applications, physics according to its methods, and heavily reliant upon the tools of mathematics—that is what makes theoretical chemistry. And yet that is where its strength lies—in the variety of these sciences. It is quite natural that, in answer to specific problems, results and methods can sometimes be developed whose scope extends far beyond the original application. Rather it is a mark of quality if consequences can be found in chemistry and physics and the pathway leads via new mathematical procedures and concepts. Regrettably, any publication aiming to present such aspects will usually encounter little resonance since the linguistic confusion in science, its disciplines, and subdisciplines, lies like a veil over our understanding. The author nevertheless wishes to attempt to present, in a series of articles, results of research into chemical themes in a manner designed to appeal to the interest of chemists, without neglecting interdisciplinary aspects. All that is required to understand the argumentation is a lively interest.The first two articles are concerned with the chirality of molecules, and in particular with questions relating to the chirality phenomenon of molecules in the framework of molecular classes. In view of the algebraic nature of the mathematical methods adopted, it is not surprising that precise statements result. It appears of primary interest to establish the degree to which such statements can be considered valid for molecular models or molecules themselves.
Basis and Limitations of the Reactivity‐Selectivity Principle
Authors: Giese Bernd 
Published: December 2003

AbstractThe reactivity‐selectivity principle (RSP), which describes a linear relationship between the decrease in selectivity and increase in reactivity of molecules Xm in their reactions with Y1 and Y2, has been much criticized during the last few years. The present paper shows the kind of reactions where the RSP does not hold and reveals how the individual types of reaction can be distinguished by varying the solvent. The dependence of molecule selectivity on temperature produces a further effect. An isoselective relationship (ISR) can be deduced when this dependence is taken into account. This relationship is not concerned with the connection between the temperature‐dependent rate and competition constants, but with the connection existing between activation enthalpies and activation entropies, which are temperature‐independent over wide ranges. The application of the ISR to different types of reactions makes it possible to characterize and distinguish between short‐lived intermediates and underlines the significance of the isoselective temperature (Tis) in interpreting the reaction parameters of linear free energy relationships and in planning syntheses.
Organic Fluorescence Reagents in the Study of Enzymes and Proteins
Authors: Kanaoka Yuichi 
Published: December 2003

AbstractStudies designed to elucidate life processes require close cooperation between various scientific disciplines. A pertinent example is seen in the application of fluorescence spectroscopy to biological studies, where biological sciences, physical and organic chemistry, and technical innovations complement one another. This report reviews the application of fluorescence probes which bind covalently to certain sites of proteins. The major organic fluorescence reagents used in this field are tabulated.
Fully Automatic Potentiometric Titrations [New analytical methods (9)]
Authors: Ebel Siegfried , Seuring Angelika 
Published: December 2003

AbstractFully automatic titration systems consist of at least two units: the sample‐changing system and the measuring system, the latter including addition of the reagent. These systems are preferably coupled to a computer. The possibilities of fully automatic titration can be best utilized if the sources of error are taken into account and the evaluation procedure optimal for the specific analysis is selected.
Synthesis of Thiol and Selenol Esters from Carboxylic Acids and Thiols or Selenols, Respectively
Authors: Gais Hans‐Joachim 
Published: December 2003

AbstractCommunications are brief preliminary reports of research work in all areas of chemistry which, on account of its fundamental significance, novelty, or general applicability, should be of interest to a broad spectrum of chemists. Authors of communications are requested to state reasons of this kind justifying publication on submission of their manuscript. The same reasons should be clearly apparent from the manuscript. In cases where the editorial staff decide, after due consultation with independent referees, that these conditions are not met, manuscripts will be returned to the authors with the request to submit them for publication in a specialist journal catering for scientists working in the field concerned.
The Wittig Reaction in Industrial Practice
Authors: Pommer Horst 
Published: December 2003

AbstractThe effects of a scientific discovery on industrial practice are illustrated with reference to the Wittig reaction. The aim of utilizing the Wittig reaction of linking terpenoid building blocks to give vitamin A and carotenoids on an industrial scale prompted extensive research and development work of a synthetic and chemical engineering nature. The importance of the Wittig reaction and its variants in the synthesis of active compounds and fine chemicals in industrial research is demonstrated in the present article.
Investigations of Mitochondrial Adenine Nucleotide Translocation by Means of Nucleotide Analogs
Authors: Schlimme Eckhard , Boos Karl Siegfried , Bojanovski Dubo , Lüstorff Joachim 
Published: December 2003

AbstractATP and ADP are transferred across the inner mitochondrial membrane by means of a carrier (translocator), an inner membrane integral lipoprotein. Translocation of the adenine nucleotides occurs in two steps: specific binding and transport. By using substrate analogs with modified adenine, phosphate, or ribose moieties it is possible to check which structural properties of the substrate are essential for binding and transport.
The Selectivity of Chemical Reactions Disguised by Diffusion. Part I: Chemical Selectivity Disguised by Mixing
Authors: Rys Paul 
Published: December 2003

AbstractA mixing‐reaction model (MIRE) is used to develop criteria, readily accessible by experiment, which permit the chemist to decide whether and when mixing effects influence the product distribution in competitive consecutive or parallel reactions. The validity of these criteria is demonstrated by comparison of prediction and experiment in the examples used.
Spontaneous Alternating Copolymerization via Zwitterion Intermediates
Authors: Saegusa Takeo 
Published: December 2003

AbstractThis article describes a new concept of copolymerization which occurs spontaneously without any added catalyst. A nucleophilic monomer (MN) combines with an electrophilic one (ME) to generate a zwitterion [+]MN—M, which is responsible for the initiation and propagation of copolymerization. Twenty‐three novel copolymerizations have been explored on the basis of the new concept. MN monomers which have been investigated are five‐ and six‐membered cyclic imino ethers, dihydro‐2(3H)‐furanimine, an azetidine, a cyclic phosphinic acid ester and a Schiff base; the ME monomers include β‐propiolactone, a cyclic dicarboxylic acid anhydride, a sultone, acrylic acid, acrylamide, a β‐hydroxyalkyl acrylate and ethylenesulfonamide. In most combinations, alternating 1 : 1 copolymers were produced. In addition to the above‐mentioned combinations, the alternating 1 : 1 copolymerization of cyclic phosphite with α‐keto acid was discovered.
Industrial Applications of Photochemical Syntheses
Authors: Fischer Martin 
Published: December 2003

AbstractThe principal industrial applications of photochemistry have so far been in the fields of free‐radical chlorination, sulfochlorination, sulfoxidation, and nitrosation. In addition, however, photochemical reactions are being utilized on an increasing scale for the synthesis of vitamins, drugs, and fragrances. The present article surveys the various kinds of light‐induced reactions exploited industrially, the equipment developed, and uses of the photochemical products. Furthermore, the problems encountered in designing a photochemical production plant are discussed for the example of photonitrosation of cyclohexane.
Organomercury Compounds in Organic Synthesis
Authors: Larock Richard C. 
Published: December 2003

AbstractOrganomercurials have been known since 1850 and many synthetic routes to these compounds presently exist. The ability of these compounds to accommodate a wide variety of functional groups and to tolerate quite diverse reaction conditions makes them attractive as synthetic intermediates. While the solvomercuration‐demercuration and divalent carbon transfer reactions remain the most widely used of the organomercurial reactions, a number of new synthetic procedures employing organomercurials have been developed in recent years. Many of these involve transmetallation reactions with palladium salts.
The Realities of Extended Homoaromaticity
Authors: Paquette Leo A. 
Published: December 2003

AbstractHomoaromaticity has been the subject of many investigations and continues to remain an extraordinarily rich area of chemistry. Quantitative experimental evaluation of the level of long range delocalization and assessment of interactions in molecules having two or more insulating atoms, together with various theoretical estimates of energies and geometries, are areas currently being examined. The primary intention of this review is to provide a critical up‐to‐date survey of relevant spectral and structural data, as well as an analysis of the many reactions believed to involve generation of homoaromatic ions. Extensively discussed are mono‐,bis‐, and trishomoaromatic systems arranged on the basis of their cationic, anionic, or uncharged nature. Presentation of these individualized segments is preceded by a brief analysis of homoaromatic overlap.
Photochemical Rearrangements and Fragmentations of Alkenes and Polyenes
Authors: Kaupp Gerd 
Published: December 2003

AbstractThis article presents a systematic analysis of the numerous intramolecular reactions of electronically excited alkenes categorized according to substance class and reaction type. The rearrangements and fragmentations observed in simple alkenes are usually rediscovered in non‐conjugated and conjugated dienes and polyenes, where they are accompanied by reaction types such as rearrangements involving several double bonds, cyclizations, and intramolecular cycloadditions. Geometrical factors largely determine which reaction of a series of energetically feasible competing processes actually takes place. The industrial syntheses of vitamin D utilize many of the reaction types to be discussed.
Photoacoustic Spectroscopy of Condensed Matter
Authors: Somoano R. B. 
Published: December 2003

AbstractPhotoacoustic spectroscopy is a new analytical tool that provides a simple nondestructive technique for obtaining information about the electronic absorption sprctrum of samples such as powders, semisolids, gels, and liquids. It can also be applied to samples which cannot be examined by conventional optical methods. Numerous applications of this technique in the field of inorganic and organic semiconductors, biology, and catalysis have been described. Among the advantages of photoacoustic spectroscopy, the signal is almost insensitive to light scattering by the sample and information can be obtained about nonradiative deactivation processes. Signal saturation, which can modify the intensity of individual absorption bands in special cases, is a drawback of the method.
Chemical Ionization—A Mass‐Spectrometric Analytical Procedure of Rapidly Increasing Importance
Authors: Richter Wilhelm J. , Schwarz Helmut 
Published: December 2003

AbstractThe mode of ionization of a molecule has a strong influence on its behavior in the mass spectrometer and thus on the information that can be obtained from its mass spectrum. In chemical ionization a reagent gas, e.g. methane, is first ionized by electron impact. The ions formed in ion‐molecule reactions, in particular [CH5]+, [C2H5]+, and [C3H5]+, then react “chemically” with the substrate M in fast acid/base type reactions to form ions of the type [MH]+, [M(C2H5)]+, etc., which subsequently fragment to various extents. Alternatively, chemical ionization can be effected by charge exchange, in that ions of a reagent gas, e.g. [He]+•, react with the substrate M to form molecular ions [M]+·. Chemical ionization can thus be conducted in a more or less mild fashion and the extent of the fragmentation can be controlled over a very wide range.
Intramolecular Ene Reactions in Organic Synthesis
Authors: Oppolzer Wolfgang , Snieckus Victor 
Published: December 2003

AbstractThermal cyclizations of appropriate dienes, enynes and related unsaturated systems, some of them carried out on an industrial scale, demonstrate increasingly the preparative power of the intramolecular ene reaction. A variety of substituted, fused and bridged ring systems, including natural products, are thus easily accessible in a regio‐ and stereo‐selective manner. Numerous examples are discussed systematically illustrating the possibilities, limitations, and common features of this cyclization reaction and its reverse ring‐opening process.
Organic Reactions at Alumina Surfaces
Authors: Posner Gary H. 
Published: December 2003

AbstractRecent examples are given to emphasize that alumina can cause many different and often unexpected chemical reactions of adsorbed organic molecules. Recent developments are summarized to publicize that reagent‐doped alumina can be used deliberately to achieve some very mild and highly selective organic transformations. The scope and limitations of organic reactions at alumina surfaces are discussed, and the advantages of these heterogeneous reactions over the corresponding homogeneous ones are pointed out. The role of the alumina and future problems are discussed briefly.
Ion Implantation into Semiconductors
Authors: Fritzsche Christian 
Published: December 2003

AbstractIon implantation is a method of introducing foreign atoms into solids that guarantees a high accuracy even with very small amounts and very short penetrations. It is basically a way of doping solids by bombarding them with accelerated ions, and its main application lies in the manufacture of semiconductor components. The action of implantation is closely connected with the accompanying radiation damage and its repair by annealing.
4‐Dialkylaminopyridines as Highly Active Acylation Catalysts. [New synthetic method (25)]
Authors: Höfle Gerhard , Steglich Wolfgang , Vorbrüggen Helmut 
Published: December 2003

AbstractThe synthesis of 4‐dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately 104 times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever‐increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4‐dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into α‐acyl aminoketones and polymerization of isocyanates. In addition, N‐substituted 4‐dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non‐polar solvents, is due, in part, to the formation of high concentrations of N‐acylpyridinium salts which are present in solution as loosely‐bound, highly reactive ion pairs.
Histidine in Enzyme Active Centers
Authors: Schneider Friedhelm 
Published: December 2003

AbstractThe presence of histidine in the active center of an enzyme can be demonstrated by kinetic measurements, chemical modification, NMR spectroscopy or X‐ray structure analysis. Histidine is the only naturally occurring amino acid to contain an imidazole residue as a side chain. The role of histidine in enzyme catalysis depends, inter alia, upon the special features of the imidazole residue: it thus tends to form hydrogen bonds, combines donor and acceptor properties and can take part in either nucleophilic or base catalysis. In some of these enzymes the position of each atom is known; however, the theories as to how the catalysis proceeds at a molecular level are controversial.
Phytoalexins, Chemical Defense Substances of Higher Plants?
Authors: Grisebach Hans , Ebel Jürgen 
Published: December 2003

AbstractPhytoalexins are defense substances with antimicrobial properties which are produced by plants after infection. They include various groups of natural substances (e.g. isoflavonoids, terpenoids, polyacetylenes and dihydrophenanthrenes). Induction of phytoalexin formation can be caused not only by living microorganisms but also by products of microbial origin (elicitors) or by stress treatment (cold, UV light). The elicitor from the mycelial walls of the fungus Phytophthora megasperma var. sojae (Pms) is a β‐1,3‐glucan with branches at C‐6. In some cases the basic features of the biosynthesis of the phytoalexins are known. The activity of the enzymes involved in phytoalexin biosynthesis is increased by the action of the elicitor on plant tissues. The ability of some microorganisms to chemically modify the phytoalexins may be related to their pathogenicity. The role of phytoalexins as defense substances is not yet fully clear.
Separation with Supercritical Gases: Practical Applications
Authors: Zosel K. 
Published: December 2003

AbstractExtraction with supercritical gases combines, to a certain extent, the characteristics of both distillation and extraction; the term “destraction” is therefore proposed for this method of separation. The principles of the method are illustrated in this article by a series of color photographs comparing extraction and destraction. Of the practical uses of this new method may be mentioned the separation of cod‐liver oil into 50 fractions, each differing in saponification value and iodine number, by means of supercritical ethane and, in particular, the decaffeination of raw coffee with supercritical carbon dioxide.
Fluid Extraction of Hops, Spices, and Tobacco with Supercritical Gases
Authors: Hubert Peter , Vitzthum Otto G. 
Published: December 2003

AbstractThis report provides an introduction to the principal methods of extraction with supercritical gases, illustrated by the processing of some natural products with carbon dioxide. The combination of pressure and temperature as process parameters makes it possible to vary the solvent power of the medium within certain ranges as desired without having to change the composition of the solvent, as would be necessary in conventional solvent extraction. The problem‐free handling of carbon dioxide and also of the products obtained open up possibilities whose development has only just started.
The Separation of Nonvolatile Substances by Means of Compressed Gases in Countercurrent Processes
Authors: Peter Siegfried , Brunner Gerd 
Published: December 2003

AbstractMixtures of nonvolatile and heat‐sensitive substances can be separated by means of compressed gases in countercurrent processes. Moreover, such separations can be carried out at lower temperatures than in vacuum distillation. Addition of an entrainer enables alteration of the relative volatilities of the components. That such a method of separation is feasible on a large scale is illustrated using as example the separation of monoglycerides from a mixture of oleic glycerides at e.g. 110°C/135 bar. Propane is used as compressed gas, and acetone as entrainer.
From the Principle of Areno‐Analogy to Heterocyclopolyaromatic Compounds
Authors: Kauffmann Thomas 
Published: December 2003

AbstractOrganometallic linkage of heteroaromatic compounds provided a means of synthesizing complicated combinations of heteroaromatic compounds; not only nucleophilic aromatic substitution, but also “ArCu/ArHal linkage”, “organometallic oxidative linkage”, and “metal amide linkage” have been employed. The heterocyclopolyaromatic compounds are made of one, two, or three kinds of heteroaromatic species as ring members. These syntheses illustrate the construction of heterocycles from large, performed structural units. Competition experiments showed that the reactivity typical of the individual species is enhanced in open‐chain combinations (ArNu)n and (ArE)n (ArNu, ArE: nucleo‐ and electrophilic heteroaromatic systems, respectively); the opposite situation is mostly encountered in the case of ArNuAE combinations.—Cycloocta[1,2‐b:4,3‐b′5,6‐b″:8,7‐b‴]tetrathiophene, the only heterocyclopolyaromatic system yet to have been studied in detail, proved surprisingly inclined to undergo monosubstitution reactions.
Empirical Parameters of Solvent Polarity as Linear Free‐Energy Relationships
Authors: Reichardt Christian 
Published: December 2003

AbstractAlthough the effect of solvent on the rate and the position of equilibrium of chemical reactions has been known since the last century, there are still no reliable and exact methods for a quantitative description and prediction of such solvent effects. Empirical parameters of solvent polarity are of great value in this respect and can be derived with the aid of the principle of “linear relationships between free energies” (LFE relationships). The present article deals with the possibilities of establishing reaction and absorption series using solvent‐dependent standard reactions or standard absorptions of organic compounds. Particular attention is merited by the summary of the 24 most important empirical parameters of solvent polarity and the table of ET(30) values for 151 solvents. In addition to examples of the application of these values, attempts to improve the LFE correlations of singular empirical parameters of solvent polarity with the aid of multiparametric equations are described.
Liquid Column Chromatography with Chemical Derivatizations after Separation. [New analytical methods (15)]
Authors: Schwedt Georg 
Published: December 2003

AbstractModern liquid column chromatography (high‐pressure liquid chromatography, HPLC) has evolved in the last few years into a highly efficient and versatile separation technique. The selectivity of an analytical process that depends upon a previous separation step can in many cases be increased considerably by chemical derivatizations after the separation. In addition, lower detection limits can be achieved in this way than in detection without derivatization. The physicochemical principles of these combined processes involving chromatographic separation and chemical derivatization prior to detection (coupling of HPLC and a reaction detector) are presented and discussed. The state of development is outlined, with a survey of the more important applications so far described in the literature.
Structural Chemistry of Fluorides and Oxide Fluorides of Nonmetals
Authors: Seppelt Konrad 
Published: December 2003

AbstractThe structural features of the nonmetal fluorides and oxide fluorides can now be explained and useful predictions can be made. The same applies in part to the chemistry of this class of compounds. Statements concerning structures can easily be made on the basis of the elctron pair repulsion model (VSEPR theory). Some rules for the number of ligands provide structural predictions for larger units than isolated molecules or ions. This is important for the fluorides and oxide fluorides of the heavier elements. This class of compounds has its limits in the lighter noble gases which, even with fluorine, form only weak bonds or no bonds at all.