bluuebunny/crossref_metadata_2025 huggingface dataset:
Basis and Limitations of the Reactivity‐Selectivity Principle
Authors: Giese Bernd
Published: December 2003

The 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

Studies 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

Fully 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

Communications 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.
Selective Monofunctionalization of Non‐Conjugated Dienes by Nitrogen Dioxide/Iodine Monoaddition
Authors: Jäger Volker , Günther Hans Jürgen
Published: December 2003

Unsymmetrical monoadducts (2) of symmetrical 1,5‐, 1,6‐, or 1,7‐dienes (1) have been obtained by reaction with stoichiometric amounts of N2O4 in the presence of I2. The bisadducts (3) are formed in <5% yield.
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Bis(trimethylsilyl)magnesium—The First Organosilyl‐magnesium Compound Isolated
Authors: Rösch Lutz
Published: December 2003

Transfer of silyl groups in the presence of magnesium has been postulated to involve organosilymagnesium compounds as intermediates. The first representative of this class (1), has now been isolated.
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Crystal Structure of As2O5
Authors: Jansen Martin
Published: December 2003

The first single crystals of As2O5 have now been obtained by annealing amorphous As2O5 under oxygen excess pressure and with careful exclusion of moisture. They were suitable for X‐ray structure analysis.
Trifluoromethanol, CF3OH
Authors: Seppelt Konrad
Published: December 2003

The simplest perfluoro alcohol, CF3OH, has now been prepared at −120°C in CF3Cl. CF3OH melts at −82°C and slowly decomposes at −20°C into F2CO and HF.
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The Wittig Reaction in Industrial Practice
Authors: Pommer Horst
Published: December 2003

The 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.
Dichloronitronium Hexachloroantimonate, ONClSbCl
Authors: Dehnicke Kurt , Aeissen Henning , Kölmel Marianne , Strähle Joachim
Published: December 2003

The first NCl2 species containing pentavalent nitrogen, i.e. the dichloronitronium ion isoelectronic with phosgene, has now been prepared in the form of the salt (1) and characterized by crystal structure analysis.
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Investigations of Mitochondrial Adenine Nucleotide Translocation by Means of Nucleotide Analogs
Authors: Schlimme Eckhard , Boos Karl Siegfried , Bojanovski Dubo , Lüstorff Joachim
Published: December 2003

ATP 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.
A Cobalt‐Catalyzed One‐Step Synthesis of Annelated Pyridines
Authors: Naiman Alaric , Vollhardt K. Peter C.
Published: December 2003

5,6,7,8‐Tetrahydroisoquinolines and other relatively inaccessible annelated pyridines (3) are now available by the reaction sequence (1) + (2) → (3). This synthesis is much simpler and otherwise superior to previous methods.
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Versatile Principle for the Synthesis of Functionalized Hydrocarbons via Organoarsenic Compounds
Authors: Kauffmann Thomas , Joussen Rolf , Woltermann Annegret
Published: December 2003

Compounds of the type HalCH(Alk)E cannot be synthesized directly from HalCH2Alk. A substitute reaction utilized the Ph2As(O) group as halogen equivalent: after reduction, (1) can be halogenated to HalCH(Alk)E.
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Binding of Urease to Anodized Sheet Aluminum
Authors: Grunwald Peter , Gunsser Walter , Scheer Siegfried
Published: December 2003

A novel support for adsorbed proteins is anodized sheet aluminum. It is shown for urease that the enzyme possesses residual activity, can be reused, and is thermally stable.
Dichloro(porphyrinato)molybdenum(IV)—Synthesis and Structure
Authors: Diebold Tharcis , Chevrier Bernard , Weiss Raymond
Published: December 2003

Two porphyrinato‐molybdenum(IV)compounds without and MoO bond have now been synthesized and thoroughly characterized. The paramagnetic compounds should prove useful starting materials for the synthesis of other porphyrin complexes of low‐valent Mo.
The Selectivity of Chemical Reactions Disguised by Diffusion. Part I: Chemical Selectivity Disguised by Mixing
Authors: Rys Paul
Published: December 2003

A 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

This 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

The 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

Organomercurials 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.
Selenium Dioxide Insertion into the Iron‐Methyl Bond of η5‐C5H5Fe(CO)2CH3
Authors: Lorenz Ingo‐Peter
Published: December 2003

The first seleninato complex to be obtained by SeO2 insertion is a brown solid that is stable for several days on exposure to air. It was characterized by its mass, 1H‐NMR, and IR spectra (seleninato‐Se type). SO2 insertions into transition metal‐carbon bonds are known.
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Synthesis of cyclo‐Heptasulfur, S7, from S8
Authors: Steudel Ralf , Mäusle Hans‐Joachim
Published: December 2003

2 Million tonnes of cyclo‐S7 exist in equilibrium in the 30 million tonnes of liquid sulfur produced annually throughout the world. It is now possible to extract cyclo‐S7 from quenched melts on a preparative scale, thus making the species readily accessible.
A New Synthetic Entry to Mono‐, Bis‐, and Tris‐(amino)sulfonium Salts
Authors: Kresze Günter , Rössert Michael
Published: December 2003

N‐Sulfinylimmonium tetrafluoroborates (3) are valuable reagents and certainly not mere inorganic curiosities; they are readily accessible by alkylation of N‐sulfinylamines (1). Former syntheses of similar salts were much more involved. The salts (3) are very good cycloaddition partners, and also provide a new entry to aminosulfonium salts of type (4).
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The Realities of Extended Homoaromaticity
Authors: Paquette Leo A.
Published: December 2003

Homoaromaticity 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

This 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

Photoacoustic 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.
Mineralization of Chlorofluorocarbons in the Sunlight of the Troposphere
Authors: Gäb Siegmar , Schmitzer Johannes , Thamm Hans‐Willi , Korte Friedhelm
Published: December 2003

The extent to which the ozone layer is being destroyed by chlorofluorocarbons is a subject of intensive research and controversy. It has now been found that chlorofluorocarbons adsorbed on SiO2 are “mineralized” to CO2, CO, and HCl on exposure to UV light or to sunlight at ground level. Whether this effect contributes significantly to conservation of the ozone layer in the troposphere cannot yet be decided.
Chemical Ionization—A Mass‐Spectrometric Analytical Procedure of Rapidly Increasing Importance
Authors: Richter Wilhelm J. , Schwarz Helmut
Published: December 2003

The 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.
Reflections on an Anniversary of Chemical Synthesis
Authors: Quinkert Gerhard
Published: December 2003

The significance of chemistry as a science and as a branch of industry, as well as its role in the evolution of scientific thought during the past 150 years, are thoughts which come to mind while contemplating the development of organic synthesis.
Intramolecular Ene Reactions in Organic Synthesis
Authors: Oppolzer Wolfgang , Snieckus Victor
Published: December 2003

Thermal 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

Recent 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

Ion 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.
Methylenesulfur Tetrafluoride H2CSF4
Authors: Kleemann Gert , Seppelt Konrad
Published: December 2003

The new pentacoordinated species H2CSF4, a gas stable up to at least 100°C, is not an ylide, but instead shows carbene‐type reactions. The 19F‐ and 1H‐NMR spectra are compatible with a Berry pseudorotation.
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Simple Method for the Esterification of Carboxylic Acids
Authors: Neises Bernhard , Steglich Wolfgang
Published: December 2003

Addition of 4‐dimethylaminopyridine (DMAP) accelerates the dicyclohexylcarbo‐diimide (DCC)‐activated esterification of carboxylic acids to such an extent that side reactions are eliminated and even sensitive acids such 2,5‐cyclohexadiene‐1‐carboxylic acid readily form the tert‐butyl ester. DMAP has so far been used mainly as acylation catalyst.
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4‐Dialkylaminopyridines as Highly Active Acylation Catalysts. [New synthetic method (25)]
Authors: Höfle Gerhard , Steglich Wolfgang , Vorbrüggen Helmut
Published: December 2003

The 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

The 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

Phytoalexins 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.
The Responsibility of the Scientist
Authors: Mohr Hans
Published: December 2003

The tradition of mutual trust between science and the public appears to have been broken in recent years. It is necessary to define the boundaries of science and to reflect upon the responsibility of the scientist.
Separation with Supercritical Gases: Practical Applications
Authors: Zosel K.
Published: December 2003

Extraction 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

This 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

Mixtures 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.
Thermal Degradation of Cellulose and Chitin in Supercritical Acetone
Authors: Köll Peter , Metzger Jürgen
Published: December 2003

Degradation of natural or man‐made polymers in supercritical acetone offers considerable advantages because sensitive products can be detected and secondary reactions largely suppressed. Cellulose and chitin serve as examples to demonstrate the conveint nature of this procedure.
Carbonylation of Transition‐Metal Carbyne Complexes, a New Method for the Synthesis of Metal‐Substituted Ketenes
Authors: Reissl Fritz R. , Uedelhoven Wolfgang , Eberl Karl
Published: December 2003

Surprising reactions of carbon monoxide with transition metal complexes have been observed with compounds (1) and (2). The carbyne complex (1) takes up CO at normal pressure and −30°C to form the metalated ketene (2) which itself is deoxygenated by CO at +60°C and under 60atm pressure to form the metalated acetylene (3) (L = P(CH3)3).
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Oxygen Evolution from Water via Redox Catalysis
Authors: Kiwi John , Grätzel Michael
Published: December 2003

The decomposition of water by sunlight is a fascinating concept in view of today's energy debate. Evolution of O2 according to the equation (1) or (2) could be a first step in this direction. Suitable redox catalysts are PtO2 and IrO2. Ce3+ and Ru(bpy) can be photochemically reoxidized with evolution of H2.
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Diorganodichlorophosphonium Hydrogen Dichlorides, a Novel Class of Compounds Containing [ClHCl]− Ions
Authors: Kuchen Wilhelm , Mootz Dietrich , Somberg Helnrich , Wunderlich Hartmut , Wussow Hans‐Georg
Published: December 2003

Stable salts of the dichlorohydrogenate ion are formed in the reaction shown below if R and/or R′ are p‐methoxyphenyl groups. X‐Ray structure analysis of (1), R′ = CH3, showed the two ClH bonds in the anion to be of different lengths. The only other known example, [Me4N]+[ClHCl]−, exhibits a similar asymmetry.
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From the Principle of Areno‐Analogy to Heterocyclopolyaromatic Compounds
Authors: Kauffmann Thomas
Published: December 2003

Organometallic 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

Although 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

Modern 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

The 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.
Methods of Reactivity Umpolung
Authors: Seebach Dieter
Published: December 2003

The past decade of organic chemistry may be charcterized as a period of violent development of new synthetic methods. This was accompained by a systematization of the analysis of synthetic problems (synthetic strategy). The planning of the synthesis of an organic target molecule is greatly facilitated by distinguishing between reagents X(C)n… with normal reactivity (acceptor properties at C1,3,5…, donor properties at X, C2,4…) and with reactivity umpolung (acceptor properties at X, C2,4…, donor properties at C1,3,5…). In this context, reactivity umpolung turned out to be useful as a heuristic principle, as a classification scheme, and as an aid for locating so‐called strategic bonds (synthon, transform, and antithesis according toE. J. Corey). There are six principal methods of umpolung: 1 2n‐oxidation, heteroatom exchange and modification, homologation and its reversal, the cyclopropane “trick”, use of acetylenes, and redox reactions; under certain circumstances none of these techniques is necessary in cases where direct umpolung is possible. Throughout the article, normal reactivity is indicated by green print; reactivity umpolung by red print.
Kinetics of Sorption, Desorption, and Diffusion in Zeolites
Authors: Doelle Hans‐Joachim , Riekert Lothar
Published: December 2003

Sorption and desorption in zeolites (molecular sieves) have to be considered as complex processes, involving simultaneous diffusion in zeolite crystals, mass transfer in the intercrystalline void of a pellet, and heat transfer between the zeolitic sorbent and its surroundings. The kinetics of sorption and desorption, respectively, of n‐C4H10 in zeolite X and of CO2 in zeolite A have been investigated: only the initial rates of uptake or release of the sorbet are controlled by mass transfer alone whereas ultimately they also depend on the rate of heat transfer from the sorbent to its surroundings or vice versa. Diffusivities of the sorbate in the zeolite crystals can be obtained from the kinetics of mass transfer, provided the resistance due to viscous or Knudsen flow between the crystals of the zeolitic sorbent can be eliminated. A sample consisting of a monolayer of single crystals had to be used for this purpose in the n‐butane/zeolite X system; the intracrystalline diffusivity obtained in this way is not in conflict with data obtained by NMR spectroscopy. The intracrystalline diffusivities obtained in this way—taking into account the coupling of several processes during sorption — are higher than values reported in the literature.
Circular Dichroism and Absolute Conformation: Application of Qualitative MO Theory to Chiroptical Phenomena
Authors: Snatzke Günther
Published: December 2003

Although chiroptical methods have been used in chemistry for some 150 years, and the basic theory was developed byRosenfeld50 years ago, their success in determining absolute conformation rests mainly on empirical rules. Some of these can be proved theoretically; however, in the case of more complex molecules this is not yet always possible. In what follows, an attempt is made to bridge the wide gap between theory and empiricism: “qualitative MO‐theory”, which has already been successfully used to explain reaction mechanisms, the shape of molecules, or photoelectron spectra, can also be applied to circular dichroism (CD). In general we shall have to be content with a reasonable interpretation of the experimentally determined sign correlation, but even this will be of great value since it can yield general relations between the geometry of molecules and the sign of CD. Such relations become particularly important when only a few examples of a given chromophore are known. If first and second sphere of a molecule are achiral then sector rules can be put forward, and in other cases helicity or chirality rules.
Mesityl(diphenylmethylene)arsane
Authors: Klebach Theo C. , van Dongen Hans , Bickelhaupt Friedrich
Published: December 2003

A localized AsC double bond bearing three aryl groups is found in the new compound (1). This compound adds even traces of water to give (2), the reaction occurring faster than air oxidation.
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Cyanohalophosphates(III)—Hypervalent Anions Containing λ5‐Phosphorus(III)
Authors: Schmidpeter Alfred , Zwaschka Franz
Published: December 2003

Hypervalent phosphorus(III) compounds (having four ligands and a lone pair on the phosphorus) are poorly characterized. The crystalline crown‐ether‐stabilized salts (1) and (2) have now been isolated.
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Ureas as Solvents for Chemical Investigations
Authors: Barker Barbara J. , Rosenfarb Joseph , Caruso Joseph A.
Published: December 2003

N‐Alkylated ureas, including cyclic derivatives, are readily obtained pure. These stable compounds are already used as industrial solvents owing to their considerable solvent power, their wide liquid range, and their favorable dielectric constants and dipole moments. They are being increasingly employed as reaction media for electrochemical and analytical studies.
The Chemistry of Iodine Azide
Authors: Dehnicke Kurt
Published: December 2003

Whereas chlorine azide and, to a lesser extent, bromine azide have long been used as preparative reagents in spite of their explosive nature, little is known about the properties of iodine azide although it was actually discovered before the other two compounds. Hantzsch's warning to beware fo this material, uttered in 1900, still seems to be widely observed. Only recently has iodine azide been isolated as a pure substance, thus promoting its more detailed investigation. Proper use of this highly labile reagent opens up new vistas in synthetic chemistry.
Tetrakis(ethylene)irondilithium and Bis(η4‐1,5‐cy‐clooctadiene)irondilithium
Authors: Jonas Klaus , Schieferstein Ludwig , Krüger Carl , Tsay Yi‐Hung
Published: December 2003

New FeLi2‐olefin complexes, e.g. (1), have been obtained from ferrocene by directed replacement of both C5H5 ligands. (1) reacts with COD to give (COD)2FeLi2 (2) [isolated as (2)·2 DME or (2)·2TMEDA]. which completes the series (COD)2Ni…(COD)2CoLi…(COD)2FeLi2
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Existence and Bond Energy of the Cesium Auride Molecule
Authors: Busse Bernd , Weil Konrad G.
Published: December 2003

Detection of cesium auride (CsAu) by mass spectrometry represents the first success in the study of systems of two metals with a large difference in electronegativity. The fragmentation energy yields a value of D (CsAu) ≈ 460 ± 30 kJ/mol for the bond energy. The stability of CsAu is determined mainly by an ionic bonding component.
Criteria for the Efficiency, Stability, and Capacity of Abiotic Photochemical Solar Energy Storage Systems
Authors: Scharf Hans‐Dieter , Fleischhauer Jörg , Leismann Hans , Ressler Ingrid , Schleker Wolf‐gang , Weitz Robert
Published: December 2003

The utilization of simple photochemical reactions for the storage of solar energy in the form of chemical energy in energy‐rich products has often been considered in the further development and improvement of e. g. simple thermosolar techniques. The hitherto proposed criteria for the qualification of an abiotic photochemical system are, however, mostly of a qualitative nature, so a mutal comparison of the systems is not precise enough. In this article it is shown how a useful correlation on the basis of time‐independent experimental data can be achieved and how, from the viewpoint of photochemistry, a comparative classification of known reactions is possible. The following reactions are compared: the [2 + 2]‐photocycloadditions of norbornadiene, dimethyl 2,3‐norbornadienedicarboxylate, and dicyclopentadienone, the photoisomerization of trans‐ to cis‐diacetylindigo, the photodissociation of nitrosyl chloride as well as a photocatalytic redox reaction. The quantity of material required and storage efficiency are by far the most favorable in the case of trans‐diacetylindigo. The main disadvantage of the latter however, is that the energy‐rich cis‐from rapidly reverts to the stable trans‐form at elevated temperatures.
A New Synthesis of Carbonyl Selenide
Authors: Kondo Kiyoshi , Yokoyama Satoshi , Miyoshi Noritaka , Murai Shinji , Sonoda Noboru
Published: December 2003

SeCO is obtained almost quantitatively from the selenolcarbamate (1), readily produced in situ, and sulfuric acid. Earlier procedures required high temperatures and complicated apparatus, and also gave only poor yields.
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Complexes with Chiral Alkylcyclopentadienyl Ligands for Homogeneous Catalytic Asymmetric Hydrogenation of 2‐Phenyl‐1‐butene
Authors: Cesarotti E. , Ugo R. , Kagan H. B.
Published: December 2003

Chiral hydrocarbon groups appear very promising as ligands in hydrogenation catalysts: thus enantiomeric excesses of 14.9[S‐(+)] and 10%[R‐(−)] were recorded for the test system (1) → (2) when the catalyst contained (η5‐(−)‐menthylcyclopentadieny1)2 TiCl2 and (η5‐(+)‐neomenthylcyclopentadienyl)(η5‐Cp)TiCl2 respectively.
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Catalytic Reactions with Hydrosilane and Carbon Monoxide [New synthetic methods (30)]
Authors: Murai Shinji , Sonoda Noboru
Published: December 2003

The reagent hydrosilane/carbon monoxide opens up new possibilities for organic synthesis. Four cases will be discussed: 1. The reaction of olefins with hydrosilane (trialkylsilane) and carbon monoxide in the presence of Co, Ru, and Rh complexes leads to enol silyl ethers having one more carbon atom that the olefins. 2. Cyclic ethers underto carbonylative ring opening to ω‐siloxyaldehydes when reacted with hydrosilane and carbon monoxide in the presence of Co2(CO)8 as catalysts 3. Aldehydes are catalytically converted into the next higher α‐siloxyaldehydes or 1,2‐bis(siloxy)alkenes depending on the reaction conditions used. 4. The reaction of alkyl acetates proceeds in various ways depending on the nature of the alkyl group; enol silyl ethers or alkenes are optained.–Mechanisms of these Co2(CO)8 catalyzed reactions using hydrosilane and carbon monoxide are discussed in which HCo(CO)n or R3SiCo(CO)nL function as catalytically active agents. With these species there are four types of catalytic cycles.–The synthetic possibilities of these catalytic reactions have still not been fully explored.
Nodal Nomenclature–General Principles
Authors: Lozac'h Noël , Goodson Alan L. , Powell Warren H.
Published: December 2003

A new, comprehensive graph‐based nomenclature system for chemical substances is proposed. Substances are named by using nodal nomenclature to name graphs derived from their structures by ignoring chemical details such as atom identities, bonding, charges, etc. After the fundamental graph is named, these chemical details are introduced by modifications and additions to the name of the graph to yield the name of the actual substance. Although development of nodal nomenclature originated with problems in naming some organic systems, it is not limited to organic substances. In this paper, only general principles for naming the graph are described; applications to specific substances will be discussed in future papers.
Direct Removal of Functional Groups by Catalytic Hydrogenolysis
Authors: Maier Wilhelm F. , Grubmüller Peter , Thies Irina , Stein Peter M. , McKervey M. Anthony , von Ragué Schleyer Paul
Published: December 2003

Transformation of derivatives into the parent hydrocarbon by conventional methods often requires several steps and frequently gives poor yields. The direct removal of functional groups by catalytic (30% Ni/Al2O3) hydrogenolysis is demonstrated for adamantane derivatives; the procedure is suitable for number ous groups, yields are excellent, and the reaction can sometimes be controlled by change in temperature.
Synthesis and Properties of the First Organosilyl‐Gallium Compounds
Authors: Rösch Lutz , Neumann Heinrich
Published: December 2003

Tris(trimethyl)silyl compounds of all GroupIIIB metals are known now that the synthesis of Ga(SiMe3)3 has been accomplished. The tetrahydrofuran adduct (1) initially obtained can be freed from solvent by sublimation in a high vacuum. Ga(SiMe3)3 resembles the indium derivative more closely than the (associating) aluminum derivative.
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Tetrakis(trimethylsilyl)borate and Other Trimethylsilylborates
Authors: Biffar Werner , Nöth Heinrich
Published: December 2003

Formation of silylborates appears to be the rule and that of silylboranes the (sterically determined) exception: attempts to synthesize B(SiMe3)3 from LiSiMe3 and B(OMe)3 in hexane yielded tetrakis(trimethylsilyl)borate. Accordingly, LiSiMe3 forms the strongly nucleophilic anion SiMe in hexane.—Li[B(tBu)4] is unknown.
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New Technologies for the Filmless Manufacture of Printing Forms
Authors: Vollmann Hansjörg W.
Published: December 2003

The economic reproduction of graphic information was first made possible in the western world by Gutenberg's invention of movable type. In the printing methods of that time, mechanical transfer processes played the major role, while chemical processes were of secondary importance. When Alois Senefelder invented planographic printing (lithoprinting) at the end of the 18th century he called the new process “chemical printing”. Since then, chemistry has attained great importance in the production of printing forms: Thus the manufacture of surface (litho‐) printing forms with light required temporary storage materials and image reproduction processes based on chemical reactions. Since the advent of electronic processing of information, however, several former temporary storage media have become obsolete; newer, more sensitive image reproduction processes are increasingly making less use of chemical principles than of the electrical properties of materials.
Structural Changes on Oxidation: Flattening of the C4‐Cluster of Tetrahedrane
Authors: Bock Hans , Roth Bernhard , Maier Günther
Published: December 2003

As a cluster with a “balanced” number of electrons, tetra‐tert‐butyltetrahedrane surprisingly affords the same radical cation as tetra‐tert‐butylcyclobutadiene on electron removal. The spontaneous valence isomerization can be explained on the basis of the calculated charge distribution.
Heterocyclic Analogues of Methylenecyclopropanes
Authors: L'abbé Gerrit
Published: December 2003

Heterocyclic three‐membered rings with an exocyclic double bond merit special interest in view of their ring strain and their fascinating chemistry. Their synthesis, thermal decomposition, ring opening, and cycloaddition reactions will be discussed in this review. α‐Lactams, alkylideneaziridines, diaziridinones, and diaziridinimines belong to the best known classes, but the chemistry of alkylideneoxiranes and ‐thiiranes, α‐lactones, α‐thiolactones, thiiranimines, and aziridinimines has also been studied to some extent. Two elusive three‐membered rings are oxiranimines and thiaziridinimines; the former were postulated as reactive intermediates in the thermal decomposition of α‐lactams, whereas the latter were trapped efficiently with double and triple bonds during thermolysis of N‐sulfonyliminothiatriazolines. In spite of many attempts to prepare thione derivatives of the title compounds, they are still unknown. Included in this review are also some open‐chain dipolar species which are isomeric with the heterocyclic three‐membered rings.
Dimerization of S6O to S12O2: Crystal Structure Analysis of S12O2·2SbCl5·3CS2
Authors: Steudel Ralf , Steidel Jürgen , Pickardt Joachim
Published: December 2003

The first complex of a homocyclic sulfur oxide—itself formed from S6O in an otherwise unprecedented dimerization—is the title compound, which arises from S6O, SbCl5, and solvent CS2 at −50 °C. In the crystal, the SbCl5 groups together with the bridging O atoms have approximately octahedral geometry. The conformation of the S12 ring in the complex differs drastically from that in cyclo‐S12.
Cyclodextrin Inclusion Compounds in Research and Industry
Authors: Saenger Wolfram
Published: December 2003

α‐, β‐, and γ‐Cyclodextrins are cyclic oligosaccharides consisting of six, seven, or eight glucose units, which can be obtained on a large scale from starch. They form inclusion compounds with smaller molecules which fit into their 5—8 Å cavity. These (crystalline) complexes are of interest for scientific research as, contrary to the classical clathrates, they exist in aqueous solution and can be used to study the hydrophobic interactions which are so important in biological systems. Cyclodextrins also serve as models both for polymeric starch and, in the form of their polyiodide complexes, for “blue iodine‐starch”. As cyclodextrins catalyze several chemical reactions they and their functionalized derivatives provide useful enzyme models. Cyclodextrins can be used to advantage in the production of pharmaceuticals, pesticides, foodstuffs, and toilet articles—the (micro‐encapsulated) active and aromatic substances enclosed within them are protected from the effects of light and atmosphere and can be easily handled and stored in powder from. Substances which are not very soluble in water become more soluble in the presence of cyclodextrins—creams and emulsions can be stabilized, and the growth and yield of grain harvests can be increased. Cyclodextrins can be chemically modified for many different purposes; polymerized cyclodextrin or cyclodextrin bound to a polymer carrier have already been employed in gel inclusion and affinity chromatography.
New Aspects of the Reaction of Difluorosulfur Imides with Fluorine
Authors: Stahl Ingo , Mews Rüdiger , Glemser Oskar
Published: December 2003

A good entry to the highly reactive fluorine compound (2) is provided by reaction of (1) with fluorine in Pyrex vessels with UV irradiation. In metal autoclaves, (3), (4), and other products are obtained (R = C2F5) without irradiation.
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