bluuebunny/crossref_metadata_2025 huggingface dataset:
The Physical Mechanism of the Chemical Bond
Authors: Kutzelnigg Werner
Published: December 2003

First the interplay of kinetic and potential energy via the uncertainty relation is described with the aid of a variational function for the ground state of the H atom. The H ion is used to illustrate the physical mechanism of the occurrence of the chemical bond. The formation of the chemical bond can be divided into three steps: 1. the quasi‐classical (electrostatic) interaction of the unchanged electronic charges of the separate atoms; 2. the interference of the atomic orbitals, which (in the case of positive interference) leads to a displacement of charge into the bonding region and to a decrease in the kinetic energy; 3. deformation of the molecular orbitals to restore the correct balance of kinetic and potential energy. In simple models, it is often sufficient to consider just the second step. A two‐electron bond is not fundamentally different from a one‐electron bond. In larger molecules it is possible to distinguish between long‐range and short‐range interatomic contributions to the chemical bond. If the former are small, i. e. in molecules with non‐polar bonds, a one‐electron molecular orbital theory can be justified. Finally, the possibility of describing molecules by localized bonds is discussed.
Structure and Function of Nucleosides and Nucleotides
Authors: Saenger Wolfram
Published: December 2003

The nucleosides participating in biological processes consist of a sugar and a heterocyclic nucleobase; the nucleotides, which occur as monomers and as building units of polymeric nucleic acids, contain an additional phosphoester group. The complexity of the molecules leads to a complex stereochemistry with which the present progress report is concerned. Particular attention will be devoted to conformational considerations at the sugar groups, the syn‐anti conformation, the position of the C(5′)O(5′) bond relative to the sugar group, and the conformation of the phosphoester bonds. The article touches upon base pairing and base stacking, as well as forces stabilizing the syn conformation, and also deals with the reaction mechanism of the enzyme pancreatic ribonuclease as established from the stereochemistry of nucleotides and the mechanisms of action of the antileukemia drug 6‐azauridine and the antibiotic actinomycin D. Views on the effects of the unusual structures of the “rare” nucleosides 4‐thiouridine, isopentenyladenosine, and dihydrouridine on the structure of transfer ribonucleic acid are also presented.
Zintl Phases: Transitions between Metallic and Ionic Bonding
Authors: Schäfer Herbert , Eisenmann Brigitte , Müller Wiking
Published: December 2003

Experimental studies on compounds of alkali and alkaline earth metals with semi‐ and metametals have considerably broadened the basis for a discussion of the transition from metallic to ionic bonding. Current interest is focused mainly upon the elucidation of the principles governing the structure of such compounds which are subject to a wide range of variation within this class of materials. A new definition of the term Zintl phase is proposed after consideration of available findings.
α‐Peroxyamines
Authors: Hawkins E. G. E.
Published: December 2003

α‐Peroxyamines contain the group , which may also be incorporated into a ring. Numerous compounds of this type are accessible, inter alia, from ketones, hydrogen peroxide, or alkyl hydroperoxides and ammonia, as well as by autoxidation or photo‐oxidation of amines or imines. Apart from decomposition reactions, the chemistry of these compounds is characterized by interesting cyclizations to give lactams, imides, oxaziridines, tetroxanes, etc.
Electronic Transitions in Transition Metal Compounds at High Pressure
Authors: Drickamer H. G.
Published: December 2003

Very high pressure is becoming increasingly important for investigating electronic structure. The relative shift in energy of electronic orbitals which is commonly observed at high pressure can frequently lead to a new ground state for the system. These electronic transitions may result in changes in electrical, optical, or magnetic properties as well as changes in chemical reactivity. Electronic transitions in metals and insulator‐metal transitions have been widely studied by physicists. Recently, it has been found that electronic transitions in aromatic hydrocarbons and their electron donor‐acceptor complexes can induce chemical reactivity and lead to the formation of new classes of hydrocarbons.

Electronic transitions in transition metal complexes may lead to changes in spin state; both increase and decrease in multiplicity with increasing pressure have been observed. In addition, it has been shown that Fe(III) and Cu(II) reduce at high pressure in a variety of compounds. The behavior of these transition metal ions is described in some detail in relation to the general area of high pressure and electronic structure.
Phase‐Transfer Catalyzed Two‐Phase Reactions in Preparative Organic Chemistry
Authors: Dehmlow Eckehard V.
Published: December 2003

Quaternary ammonium and phosphonium salts catalyze reactions between substances located partly in an aqueous and partly in an organic phase. Use of such phase‐transfer catalysts simplifies and accelerates numerous reactions traditionally conducted in nonaqueous media. These reactions include carbene reactions, nucleophilic substitutions, alkylations of ketones and nitriles, Wittig and Darzens reactions, formation of ethers and esters. Other reactions such as hydrolysis and oxidation can be accelerated.
Photochemistry with Circularly Polarized Light
Authors: Buchardt Ole
Published: December 2003

The reactions induced by circularly polarized light are reviewed and a general discussion of the induction of optical activity by circularly polarized light is presented. It is concluded that three different mechanisms, or their combinations, can cause asymmetric induction. In each case the optical yield is dependent on the optical anisotropy factor g, the ratio between the circular dichroism (Δϵ) and the extinction coefficient (ϵ). The results are discussed in terms of the presumed mechanisms, and particular attention is paid to the asymmetric synthesis of helicenes. It is concluded that this kind of photochemistry may have analytical importance.
Analysis of Herbicides
Authors: Thier Hans‐Peter
Published: December 2003

Herbicides, like other pesticides, leave undesirable residues on the treated plants. To analyze them, the plant material is extracted and the herbicidal residues are separated from the bulk of the co‐extractives of natural origin, about which too little is known. Quantitative determinations at the ppm level are best performed by gas chromatography with highly sensitive, specific detectors. In food control, where the history of the sample is unknown, the herbicide residues are identified and determined quantitatively together with the residues of other pesticides.
X‐Ray Absorption Spectroscopy on Free Molecules
Authors: Schwarz W. H. Eugen
Published: December 2003

The most recent spectroscopic method that can be applied to chemical problems is X‐ray absorption spectroscopy, in which the excitation of individual core electrons of an atom is studied. The analysis of the spectra with the aid of simple theoretical models yields information both about the core orbitals of the atom and about the unoccupied molecular orbitals, from which various molecular properties can be deduced. These not only include charge distribution, electronic configuration, geometry, and spatial and energy characteristics of orbitals of the molecule under investigation; one can also obtain parameters of radicals (such as stability, bond length, ionization potential, and electronic excitation energy) that differ from the molecule under investigation in that the nuclear charge of one atom is one unit higher.
Halovinylene Carbonates in Organic Synthesis. New synthetic methods (2)
Authors: Scharf Hans‐Dieter
Published: December 2003

Monohalo‐ and dihalovinylene carbonates constitute a new class of cyclophiles which permit simultaneous introduction of masked α‐hydroxyketo and α‐diketo functions, respectively, into the cycloadducts. Demasking can be performed by simple hydrolysis. Solvolytic opening of the carbonate ring leads to glycolic acid derivatives in the case of the monohalo compounds and to glyoxylic acid derivatives with the dihalo compounds. Preparation of the title compounds, their potential as synthetic reagents, and the chemistry of their simple reaction products are surveyed from a preparative viewpoint.
A Hundred Years of Stereochemistry—The Principal Development Phases in Retrospect
Authors: Weyer Jost
Published: December 2003

The theory of the arrangement of atoms in space was initiated in 1874 by van't Hoff and Le Bel. The starting points were mainly in the fields of structural chemistry and optical activity. After early difficulties, stereochemistry gained acceptance in the last quarter of the 19th century and led to many interesting investigations and discoveries: the investigation of geometrical isomerism, the Baeyer strain theory, the stereochemistry of nitrogen, the determination of the configurations of carbohydrates, Walden inversion, and the beginning of inorganic stereochemistry all fall in this period. Theoretical verification of the principal stereochemical hypotheses and the exact determination of the steric arrangement of atoms by physical methods were achieved only in the 20th century.
Modern Methods for the Study of Electrode Processes
Authors: Heitbaum Joachim , Vielstich Wolf
Published: December 2003

The investigation of electrode processes calls for the use of methods that yield information on the reaction mechanism and the reaction rate, on the nature and stability of intermediates, and on adsorption processes at the electrode. It is no longer enough to record current‐voltage curves or charging curves. In addition to the potentiostatic scan method, other methods that have proved useful for the investigation of electrode kinetics are the rotating disc electrode in particular, and to a smaller extent AC polarography. Intermediates can be identified with rotating double electrodes and by ESR spectroscopy or mass spectrometry. Adsorption processes on electrode surfaces can be studied by optical methods or by radioactive tracer methods.
Kinetics and Mechanism of Radical Polymerization
Authors: Mehnert Peter
Published: December 2003

Low molecular reactions are frequently accompanied by side reactions producing a whole spectrum of by‐products whose removal in purification operations generally causes little difficulty because the major and side products usually differ sufficiently in their properties. Hence detailed kinetic studies in low molecular chemistry can claim industrial interest only insofar as they aim to reduce the rate of formation of side products. The situation is completely different in polymer chemistry, where the terms major and side product no longer apply. Instead, one obtains mixtures of similar and/or isomeric molecules which differ so little with regard to molecular weight and structure that resolution into pure substances or isolation of pure substances becomes practically impossible. However, since all partial reactions exert a direct influence on the product spread, i.e. the composition and properties of a product mixture are modified by any change in operating conditions, detailed kinetic analyses embracing all relevant partial reactions are an essential prerequisite for the production of defined polymeric products on any scale. This progress report illustrates the importance of kinetics for radical polymerization with the aid of selected examples.
High Pressure Kinetic Investigations in Organic and Macromolecular Chemistry
Authors: Jenner Gérard
Published: December 2003

High pressure kinetics appears to be a valuable tool in investigating the mechanism of specific organic reactions. For instance, in pericyclic, Mentshutkin, cage, and polymerization reactions, such studies reveal various features of the transition state, in particular its localization along the reaction coordinate and its nature. However, precise conclusions require separation of the different effects (electrostatic, steric, orbital, etc.) which may contribute to the structure of the transition state.
Chemistry of Phosphorylcarbenes
Authors: Regits Manfred
Published: December 2003

Phosphorylcarbenes, which have become known only recently during synthetic experiments in the field of phosphoryldiazoalkanes, have twofold preparative value. In the first place, they can be used to introduce phosphoryl groups into organic compounds, as in the phosphoryl‐cyclopropanation of alkenes or arenes and in the phosphorylcyclopropenation of alkynes. Secondly, phosphorylcarbenes readily undergo rearrangements; hydride, alkyl, aryl, or acyl shifts lead to phosphorylated alkenes. The phosphorylcarbene/methylenephosphane oxide rearrangement provides access to the short‐lived P analogs of the ketenes. Finally, the vinylcarbene/allene rearrangement was first discovered in this connection; it competes with ring closure to the cyclopropene.
Three‐Dimensional Structure of the Actinomycins
Authors: Lackner Helmut
Published: December 2003

Many complicated three‐dimensional structures can be formulated for the actinomycins, red chromopeptide antibiotics distinguished by pronounced antineoplastic activity, because of their unique constitutional type. Since these structures largely determine the specific activity of the actinomycin molecules in the host cells, knowledge of the structural forms occurring naturally in solution is a decisive prerequisite for detailed insight into the mode of biological action of the actinomycins. Investigations by several methods have shown that, in spite of their deviating primary structures, all important actinomycins assume only one very characteristic, pseudo‐C2‐symmetrical, and remarkably stable three‐dimensional structural type.
Ternary Cu2+ Complexes: Stability, Structure, and Reactivity
Authors: Sigel Helmut
Published: December 2003

The driving forces leading to the formation of ternary Cu2+ complexes are outlined; they are (i) statistical reasons, (ii) neutralization of charge in the mixed‐ligand complexes, (iii) steric factors (bulky groups, ring size of chelates), and (iv) formation of π bonds. The last point is important for achieving a large stability, as well as for the observation of discriminating qualities. An additional stability increase may possibly be achieved through a direct interaction between the two ligands bound to the same metal ion, i.e. Schiff base formation, hydrogen bonding or a charge‐transfer relation. The latter leads to distinct structures, i.e. metal ion‐bridged charge‐transfer complexes. The relation between stability and structure on the reactivity of mixed‐ligand complexes is emphasized. The relevance of the results for mixed‐ligand complexes containing metal ions other than Cu2+ is briefly outlined.
Field Desorption Mass Spectrometry
Authors: Beckey H. D. , Schulten H.‐R.
Published: December 2003

Field desorption (FD) enables mass‐spectrometric investigation of large organic molecules without their vaporization. The present state of our theoretical understanding of the ionization of these molecules in the adsorbed state on organic emitters is described. The special problems of the technique and prospective developments in the apparatus for future analytical problems are outlined. The present progress report concentrates on analytical studies of biochemical model compounds and degradation products from environmental chemicals and drugs. The method is particularly suitable for the detection and identification of submicrogram quantities of underivatized polar substances present in complex mixtures or pre‐purified extracts from biological materials.
Ring Contractions and Expansions of Vicinally Disubstituted Cyclobutanes and Cyclopropylmethyl Compounds
Authors: Conia J. M. , Robson M. J.
Published: December 2003

Cyclobutanes and cyclopropylmethyl compounds vicinally disubstituted in appropriate manner by one electron‐donating group and one leaving or electron‐receiving group undergo extremely facile ring contractions and expansions respectively. Unlike many rearrangements of small‐ring compounds and most rearrangements of larger‐ring compounds, these reactions usually give a single product in high yield and thus possess real synthetic interest. The subject matter of this progress report is classified according to the substituents in question since the nature of these groups largely determines the conditions under which rearrangement takes place.
Organic Compounds in Nature: Limits of Our Knowledge
Authors: Blumer Max
Published: December 2003

Current geochemical and environmental research reveals the presence in soils and sediments of extremely complex assemblages of organic compounds. Their recognition has long been delayed by both conceptual and analytical limitations. Even today the best techniques cannot fully resolve these mixtures into their individual components. Yet, the knowledge of their structures and abundances is needed in geochemistry, and especially for the assessment of their potential biological effect and ecological impact. The classical “natural products approach” is unlikely to provide this information; therefore, I foresee the need for a more realistic assessment of nature, that acknowledges the limitations of our present analytical powers and of our knowledge.
Methods for the Preparation of Bridgehead Olefins
Authors: Keese Reinhart
Published: December 2003

During the past eight years, bridgehead olefins have attracted rapidly increasing attention. In view of their significance with regard to the stereochemistry of alkenes, the study of certain reaction mechanisms, and the nature of the double bond, detailed research into this structural type appears highly desirable. Bridgehead olefins represent connective linkages between olefins in the ground state and species which can arise in the deactivation of photochemically excited alkenes and cycloalkenes and also contribute to our understanding of the structural conditions prevailing during cis‐trans isomerization of alkenes.
Chemical Nickel Plating
Authors: Niederprüm Hans
Published: December 2003

Metal layers can be deposited from aqueous solutions not only by electric current as in electroplating but also by strong reducing agents. Chemical deposition of nickel on metallic and nonmetallic substrates, together with the long‐known silvering of glass, are the most widespread examples. This remarkable reaction has recently found a variety of industrial applications mainly in the preparation of corrosion‐resistant, hard, and wear‐resistant protective layers, in the metallizing of plastics, and in electronics.
Aminyl Free Radicals
Authors: Danen Wayne C. , Neugebauer Franz A.
Published: December 2003

Recent interest in aminyl free radicals, especially in their electronic structure, has led to many investigations in this area. This report reviews the main features of the generation of aminyls, their reactivity, and electronic properties.
Synthetic Applications of Heteroaromatic Betaines with Six‐Membered Rings
Authors: Dennis Nicholas , Katritzky Alan R. , Takeuchi Yoshito
Published: December 2003

The cycloadditions of 3‐hydroxy‐1‐methylpyridinium betaines with electron‐deficient olefins have been extended to a variety of 1‐substituents in place of methyl. Application of resonance theory and later of quantum chemical methods led to rationalization of preceding results and prediction of new reactions. Thermal additions of 2π‐ and 6π‐electron addends at the 2,6‐positions and of 4π‐electron addends at the 2,4‐positions are described. The cycloadducts are highly interesting potential synthetic building blocks.
Sequence Analysis of Polypeptides and Proteins by Combined Gas Chromatography‐Mass Spectrometry
Authors: Nau Heinz
Published: December 2003

A new method for determining the amino acid sequence of polypeptides consists in initial partial hydrolysis to yield a complex mixture of oligopeptides. After derivatization to enhance its volatility, the mixture is analyzed by combined gas chromatography and mass spectrometry. The sequence of the polypeptide is established by a computer from the identified oligopeptides. So far polypeptides having up to 40 amino acids have been analyzed by this method. The advantages and disadvantages of the new method compared with the stepwise procedure of the Edman degradation are considered. Since the two methods are based on fundamentally different principles they may prove to be complementary.
The Fischer‐Tropsch Synthesis: Molecular Weight Distribution of Primary Products and Reaction Mechanism
Authors: Henrici‐Olivé G. , Olivé S.
Published: December 2003

An evaluation of literature data concerning the production of hydrocarbons and alcohols by the Fischer‐Tropsch procedure indicates that the molecular weight distribution of the primary products can be described by the Schulz‐Flory equation (“normal” or “most probable” distribution). It follows that the highest attainable selectivity for a given molecular weight range can be calculated. A reaction mechanism is suggested.
Application of Catalyzed Reactions in Analytical Chemistry
Authors: Weisz Herbert
Published: December 2003

Catalyzed reactions are becoming increasingly improtant in analytical chemistry, and especially in trace analysis. The acceleration of a particular reaction (indicator reaction) promoted by the catalyst provides information about the catalyst concentration. Substances which lower or raise the activity of a catalyst (inhibitors or activators, respectively) can likewise be determined in this way. The course of a reaction is usually monitored by physical measuring techniques. Various methods of conducting these kinetic‐catalytic studies are discussed in this article.—Use of catalyzed reactions for end point detection in volumetric analysis is also feasible.
The Concept of Allopolarization. Effects of Substituents on the Reactions of Ambifunctional Anions
Authors: Gompper Rudolf , Wagner Hans‐Ulrich
Published: December 2003

The chemistry of ambifunctional anions is of great importance in organic preparations. Planning of syntheses requires a set of rules correlating structure and selectivity. The concept of allopolarization permits a description of substituent effects on kinetically controlled reactions: the change in selectivity is a function of the change in polarity of the ambifunctional anions. The relative charge density P = lx/ly serves as “polarity index”; X and Y are the potential sites of reaction. An attempt is made to illustrate the utility of this principle by means of examples taken from various classes of compounds.
Glass—A Continuing Challenge to Chemistry
Authors: Britton Marvin D.
Published: December 2003

This review of the modern chemistry of glass shows that silicate glasses are extremely reactive materials. Compositions, phases, surfaces, and structures can be manipulated in endless variety, and there is no foreseeable limit to the benefits of research in this area.
Penetration and Crosslinking of Macromolecules
Authors: Braun Dietrich
Published: December 2003

One of the topical problems of macromolecular chemistry is the question of the extent to which macromolecules in solution or in the amorphous solid state can engage in mutual interpenetration. The present article is concerned primarily with recent investigations on cross‐linking copolymerization and with inter‐and intramolecular reactions of polymers as a contribution to the study of molecular shape.
Solid State Chemistry of Ionic Fluorides
Authors: Portier Josik
Published: December 2003

The results of intensive pure research into the chemistry and physics of fluorides can be pieced together to give an overall picture whose discernible outlines hold promise of numerous new compounds having unusual and in some cases unique properties. Modern technology is called upon to exploit them.
Predictive Molecular Orbital Calculations in Organic Chemistry
Authors: Dannenberg Joseph J.
Published: December 2003

The utility and importance of predictive, rather than correlative, molecular orbital calculations in organic chemistry are discussed. Examples of the predictive approach to organic synthesis and the study of organic reaction mechanisms are presented.
Molecular Complexes and Oxygen Adducts of Tetrapyrrole Pigments
Authors: Fuhrhop Jürgen‐Hinrich
Published: December 2003

Metalloporphyrins not carrying functional groups and the π‐radicals of these species form comparably stable coplanar π‐π‐dimers by means of various types of weak interactions. Chlorophyll a and other derivatives containing carbonyl groups add water and aggregate into molecular complexes by means of hydrogen bonds. Such aggregates are of special interest in connection with a new hypothesis for the photo‐oxidation of water to oxygen during photosynthesis. Finally, Some new discoveries concerning the structure and reactivity of heme‐oxygen complexes are discussed.
Processing of Plastic Waste and Scrap Tires into Chemical Raw Materials, Especially by Pyrolysis
Authors: Sinn Hansjörg , Kaminsky Walter , Janning Jörg
Published: December 2003

An account of the occurrence of pyrolyzable material and the state of development of pyrolysis processes in the USA and Japan is followed by a description of laboratory and pilot‐scale experiments designed to exploit the raw material content of pyrolyzable substances rather than the heating value. Plastic waste and scrap tires can be pyrolyzed to give up to 40% by weight of aromatic compounds in fluidized sand beds which are surprisingly insensitive to the unit size of the feed material.
Hormone Receptors
Authors: Lübke Klaus , Schillinger Ekkehard , Töpert Michael
Published: December 2003

Hormone receptors are proteins located on the cell membrane or in the cell cytoplasm. Their function is to recognize and bind the respective hormone; the biological action of the hormone originates from the hormone‐receptor complex. Specific receptors have been found for all known hormones. Monitoring the equilibration between hormone, receptor, and hormone‐receptor complex (“determination of receptor binding”) permits quantitative determinations of hormones, allows the characterization of endocrinal disturbances, and contributes to the elucidation of structure‐affinity relationships.
Molecular Aspects of Sickle Cell Disease
Authors: Waterman Michael R. , Cottam G. Larry
Published: December 2003

Sickle cell hemoglobin (hemoglobin S) contains valine instead of glutamic acid in position 6 of the β‐chain. Few detectable conformational differences exist between hemoglobin S and normal adult hemoglobin (hemoglobin A). Following loss of oxygen, sickle cell hemoglobin (hemoglobin S) self associates to form a liquid crystal phase which distorts the erythrocyte into the sickle shape thereby resulting in the clinical symptomology associated with sickle cell anemia. This gel contains deoxyhemoglobin S monomers and polymers in equilibrium. The polymerization process is known to have a negative temperature coefficient, to be pH dependent, and to be extremely dependent on hemoglobin S concentration. The polymerization of deoxyhemoglobin S appears to be entropically driven and occurs in two kinetic phases, a delay period and a rapid polymerization process. The polymer consists of tubules containing six or eight strands of deoxyhemoglobin S tetramers which align with one another. Each strand is would around the tubule with a pitch of about 3000 Å, but the precise nature of the intermolecular hemoglobin S contacts is not known. Subsequent alignment of the tubules occurs and results in the tactoids observed in (S/S) erythrocytes. While many of the details of polymer formation and structure remain to be elucidated, several attempts to chemically alter the sickling phenomenon have been carried out. As yet, however, no satisfactory chemical treatment has been discovered.
Stereoselective Hydride Elimination from Organo‐Lithium and ‐Magnesium Compounds
Authors: Reetz Manfred T. , Stephan Wilfried
Published: December 2003

Hydride acceptors effecting elimination of β‐hydrogen atoms from organo‐lithium and‐magnesium compounds have been found in triphenylmethyl tetrafluoroborate, tricyclohexylborane, and tri(sec‐butyl) borane.
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Preparation of Halogen‐Bridged Cationic Dinuclear Complexes of Manganese and Rhenium
Authors: Mews Rüdiger
Published: December 2003

Cationic carbonyl complexes (1) with a halogen bridge between two manganese or ruthenium atoms have now been prepared by several routes. They are stable up to temperatures exceeding 100°C.
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Poly(organophosphazenes)—Unusual New High Polymers
Authors: Allcock Harry R.
Published: December 2003

An inorganic‐backbone high polymer system based on alternating phosphorus and nitrogen atoms promises to solve many of the problems hitherto associated with conventional organic polymers. The chemistry, structure, biomedical, and technological aspects of these polymers are reviewed.
Analytical Applications of Chemiluminescence
Authors: Mendenhall G. D.
Published: December 2003

Most organic compounds react very slowly with atmospheric oxygen at room temperature. The weak chemiluminescence accompanying this autoxidation can be amplified and measured by sensitive instruments. Emission of light from many materials can also be induced mechanically and photochemically. The intensity‐time curves are so characteristic that they can be used to establish whether the composition and history of two samples are identical. Moreover, numerous physical properties can be correlated with emission and thus measured.
Stereoisomeric Quinhydrones of the [2.2](1,4)Naphthalenophane Series
Authors: Staab Heinz A. , Herz Claus P.
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.
Photodielectric Polymers for Holographic Use
Authors: Reich Shimon
Published: December 2003

The use of polymeric materials as “thick” recording media for holographic applications is discussed. These materials offer some interesting applications owing to their high diffraction efficiency, high storage density, excellent angular and spectral discrimination, as well as in situ real‐time recording. The present state of art is outlined, as are prospects for the future.
Halogenonitrosylmolybdates—Isolation of the First Classical MoI Complex
Authors: Sarkar Sabyasachi , Müller Achim
Published: December 2003

A “classical” complex chemistry of lower valent molybdenum (Mo0, MoI, MoII) can be systematically developed now that the first NO‐stabilized complex (1) of Mo in the formal oxidation state I has been obtained.
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Reaction of Dicyanocobyrinic Heptamethyl Ester with Ascorbic Acid
Authors: Gossauer Albert , Grüning Burghard , Ernst Ludger , Becker Wulf , Sheldrick William S.
Published: December 2003

Stable yellow corrinoids can arise as by‐products in reactions of vitamin B12 involving a change in the oxidation state of the cobalt. The structure of the pigment from a vitamin B12 analog and ascorbic acid has now been elucidated by X‐ray structure analysis.
The Role of Birth Control in the Survival of the Human Race
Authors: Wiechert Rudolf
Published: December 2003

Analysis of the growth of the world's population shows that if no trenchant measures are taken, the number of the earth's inhabitants is likely to double to 8 billion people within as few as 35 years. Hormonal contraception is presently the best method available which would be capable of counteracting this trend. 6.5 tons of estrogen and 32 tons of progestogen would in theory be sufficient to protect the 500 million women of child‐bearing age from unwanted pregnancies for one year.—In addition, the history, industrial methods of synthesis, mode of action and side effects of steroid contraceptives as well as the possible future developments are briefly mentioned.
Detection of an Orthonitrate by Vibrational Spectroscopy: Na3NO4
Authors: Jansen Martin
Published: December 2003

The existence of the NO ion has now been proved by Raman spectroscopy. X‐ray structure analysis has so far been precluded by the non‐availability of single crystals of the extremely moisture‐ and CO2‐sensitive compound Na3NO4.
Electrocyclic Ring Opening Reactions of Ethylene Oxides
Authors: Huisgen Rolf
Published: December 2003

Substituents capable of stabilizing negative charge endow ethylene oxides with the ability to undergo electrocyclic ring opening at the CC bond; heating or irradiation generates small equilibrium concentrations of carbonyl ylides which can engage in 1,3‐dipolar cycloadditions. Apart from the normal conrotatory mode of ring opening, predicted by the Woodward‐Hoffmann rules, the disrotatory process, forbidden by orbital symmetry, also appears to occur in the case of α‐cyano‐cis‐stilbene oxide. Kinetic studies on α‐cyano‐trans ‐and ‐cis‐stilbene oxide permit construction of the energy profile for electrocyclic ring opening to give the stereoisomeric carbonyl ylides and for their recyclization and rotation.
Principles of Osmotic Desalination
Authors: Böddeker K. W.
Published: December 2003

Salt solutions can be separated into pure water and concentrated salt solution by reverse osmosis using semipermeable membranes. The distinct features and limitations of osmotic separations are developed from a consideration of the pertinent solution properties and the conditions inherently to be met by the membranes, seen as interacting barrier phase in a process which substantially separates water from water.
Repetitive Peptide Synthesis with Insoluble Polymer‐Bound Reagents and Solubilizing Macromolecular Peptide Carriers
Authors: Heusel Gerhard , Bovermann Günter , Göhring Walter , Jung Günther
Published: December 2003

A new reaction cycle for chain elongation of peptides utilizes soluble peptide carriers and solid polymeric reagents. In the actual coupling step no side products are formed, nor do excess reagents have to be removed.
[η5‐C5H5Mo(CO)3HgMo]4, a Metal Cluster with Cubane Structure
Authors: Deutscher Josef , Fadel Suheil , Ziegler Manfred L.
Published: December 2003

A cubane skeleton composed of alternant Hg and Mo atoms is shown by X‐ray structure analysis to be present in complex (1). Bimetallic clusters with a cubane structure were not previously known.
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Synthesis and Reactions of N‐Chlorocarbonyl Isocyanate
Authors: Hagemann Hermann
Published: December 2003

ClCONCO (N‐chlorocarbonyl isocyanate) is prepared in 90% yield by partial hydrolysis of the addition product of phosgene and cyanogen chloride. Many derivatives of the iminocarboxylic acid parent compound can be obtained from this highly reactive species. Both the acid chloride and the isocyanate group are amenable to reactions exhibiting overall selctivity, and this opens the way, inter alia, to a simple preparative synthesis of isocyanates from alcohols, phenols, thiols, and thiophenols. Combination of the two functional groups and their peculiar symmetry, which becomes evident, e.g. in the HCl adduct, facilitates ready cyclization of N‐chlorocarbonyl isocyanate under very mild conditons.
A Novel Transformation of Diphenylcyclopropenone: Double Bond Cleavage in the Reaction with Platinum Complexes
Authors: Carrol W. Eamon , Green Michael , Howard Judith A. K. , Pfeffer Michel , Stone F. Gordon A.
Published: December 2003

The novel dinuclear platinum complex (1) is doubly bridged by ring‐opened diphenylcyclopropenone. Neither the cleavage of the CC double bond of a small ring by a transition metal complex nor bridging ligands of this kind (X‐ray structure analysis) were formerly known.
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Thermal and Photochemical Cycloelimination of Nitrogen
Authors: Meier Herbert , Zeller Klaus‐Peter
Published: December 2003

Cyclic azo compounds including heteroaromatics with a NN bond of strong double‐bond character can eliminate molecular nitrogen on addition of sufficient thermal energy or on electronic excitation. Some substrates decompose spontaneously, others are moderately or even extremely resistant to N2‐elimination. From a preparative point of view this type of reaction opens a variety of interesting possibilities, e.g. the synthesis of small carbocycles or heterocycles, strained bi‐ and polycycles, as well as cage compounds. From a theoretical mechanistic viewpoint, current importance attaches to the primary fragments such as carbenes, diradicals, trimethylene, trimethylenemethane, dipoles, ylides, antiaromatic 4π‐systems, unstable cycloalkynes, and arynes.
Carbonyl Olefination with (Triphenylstannyl)methyllithium
Authors: Kauffmann Thomas , Kriegesmann Reinhard , Woltermann Annegret
Published: December 2003

A modified alternative to the Wittig reaction utilizes (triphenylstannyl)methyllithium. Yields are good; the alcohol does not have to be isolated.
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Solid Ionic Conductors: Principles and Applications
Authors: Rickert Hans
Published: December 2003

Solid ionic conductors, also called solid electrolytes, transport electric current by means of ions. The best known examples of these usually crystalline compounds include doped ZrO2, as well as AgI, β‐Al2O3, and CaF2. Ionic conduction in solid electrolytes reaches its maximum value if a partial lattice of a solid compound undergoes transition at elevated temperature to a quasimolten state. The ionic conductivity in such solid compounds is then as high as in molten salts. Solid electrolytes have found many scientific and technological applications; thus, they can be used to study thermodynamic and kinetic problems, and to build fuel cells, batteries, sensors, and chemotronic components.
Reactive Derivatives of Aliphatic N‐Sulfinylamines—Alkylation of N‐Sulfinylalkylamines and Bis (tert‐butyl)‐sulfur Diimide
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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Restriction Endonucleases
Authors: Arber Werner
Published: December 2003

Restriction endonucleases are enzymes commonly found in bacteria which can fragment DNA. Cleavage of the DNA molecule takes place after recognition of a nucleotide sequence which is specific for each restriction endonuclease. Some of the enzymes split the DNA within the recognition sequence. This property allows these enzymes to be used for the systematic fragmentation of DNA molecules in structural and functional analyses of genetic material. The biological function of restriction endonucleases could be to provide a sort of primitive immune system which enables the cells to destroy foreign genetic material. Methylation of nucleotides lying within the recognition sequence serves to protect the cell's own DNA from being degraded by its restriction endonucleases. Restriction endonucleases were discovered during the investigation of the restriction of viral growth observed on changing hosts.
Synthesis and Crystal Structure of a Methylenebis(diphenylphosphane) Complex of Silver Bromide Containing a Trigonal Bipyramidal Ag3Br2 Central Unit
Authors: Aly Aref A. M. , Neugebauer Dietmar , Orama Olli , Schubert Ulrich , Schmidbaur Hubert
Published: December 2003

The novel structural unit Ag3B lies at the center of the complex formed from equimolar amounts of AgBr and the dpm ligand. The Ag…Ag distances are just too long for metal‐metal bonding.
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A New Preparation of Symmetrical γ‐Diketones
Authors: Stetter Hermann , Bender Hans‐Jürgen
Published: December 2003

Transformation of aldehydes into diketones of type (1) is possible by thiazolium salt‐catalyzed addition to α, β‐unsaturated sulfones. The products can be readily separated on use of divinyl sulfone (R1CH2CH).
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Nitrogen as Leaving Group: Dediazoniations of Aromatic Diazonium Ions
Authors: Zollinger Heinrich
Published: December 2003

On heating, aromatic diazonium salts eliminate nitrogen by two fundamentally different mechanistic pathways, i.e. heterolysis and homolysis. Among these pathways a series of variants are known, giving rise to a whole variety of mechanisms. This article considers the effect of specific solvation, apparently characteristic of diazonium ions, by various solvents (fluorinated alcohols, methanol, water, dimethyl sulfoxide, pyridine, and hexamethylphosphoric triamide) on the mechanism. Apart from the donor properties of the solvent, the oxidation potential and the presence of additives play a major role in determining what reaction type will predominate.
Selective Reactions with Organoaluminum Compounds
Authors: Yamamoto Hisashi , Nozaki Hitosi
Published: December 2003

With the aid of selected examples an overview is given of the development trends in highly discriminative reactions using organoaluminum compounds. (1) Isomerization of substituted oxiranes into allyl alcohols has been effected both stereo‐ and regioselectively by means of a new organoaluminum reagent, diethylaluminum 2,2,6,6‐tetramethylpiperidide (DATMP); this reaction which provides a new route for the regiospecific transformation of allyl alcohols into 1,3‐dienes. (2) A novel nonenzymic heterolysis of allylic phosphates of terpenoids has been effected by organoaluminum compounds and has enabled development of a new method for the selective synthesis of cyclic terpenes. (3) The reductive condensation of α‐haloketones with carbonyl compounds in the presence of diethylaluminum chloride and zinc affords β‐hydroxy‐carbonyl derivatives in good yields with exclusion of undesired self‐condensations products.
Triazene Transfer with Activated 2‐Tetrazenes
Authors: Stöldt Ernst , Kreher Richard
Published: December 2003

N‐Diazonium ions like (2) generally react in the same way as C‐diazonium ions by elimination of N2. The reaction of 2‐tetrazenium salts (1) with anionic nucleophiles Z⊖ shown below is new: the N3 sequence of (2) is retained in the products (3), formally the result of coupling between (2) and Z⊖.
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Ternary Rhenium Sulfides with [Re6S8]‐Clusters
Authors: Spangenberg Manfred , Bronger Welf
Published: December 2003

The first clusters to contain Re6 units are present in compounds (1) to (3). The six Re atoms form an octahedron with eight S atoms distributed over the faces. Other ternary sulfides of type AxMySz have chain or layer structures.
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Rearrangement of Tris‐σ‐homobenzenes to 1,4,7‐Cyclononatrienes
Authors: Spanget‐Larsen Jens , Gleiter Rolf
Published: December 2003

A better understanding of the rearrangements of tris‐σ‐homobenzenes was the goal of MINDO/3 calculations of parts of the multidimensional energy surface for the cis‐ and trans‐isomer and for diademane. Cyclononatriene is accordingly expected to be present in addition to trans‐tris‐σ‐homobenzene in equilibrium at elevated temperature.
Synthesis of N‐Methyliminosulfur Tetrafluoride, CH3NSF4, from the Cation CH3NSF
Authors: Mews Rüdiger
Published: December 2003

Stepwise addition of polar reagents  to NSF3 (1) was formerly impossible in the case of “methyl fluoride”; the salt (2) and the tetrafluoride (3) are stable compounds.
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Higher‐Order Derivative Spectrophotometry for the Fine Resolution of UV/VIS Spectra
Authors: Talsky Gerhard , Mayring Lothar , Kreuzer Hans
Published: December 2003

Low‐noise, reproducible UV/VIS spectra up to the 7th derivative can now be plotted on‐line with the aid of a novel analog computer unit. Optimum resolution is usually achieved up to the 4th derivative: all shoulders, terraces, and points of inflection of unipolar signals are generally transformed into bipolar signals. Numerous applications exist.
Spiroconjugation
Authors: Dürr Heinz , Gleiter Rolf
Published: December 2003

Spiro compounds having mutually perpendicular π‐electron systems (“spiro‐polyenes”) exhibit a new kind of homoconjugation, which is designated as spiroconjugation. Spiro‐polyenes are readily accessible,e.g.by cycloaddition, by elimination of dinitrogen from 1,2‐diazaspiro‐polyenes, and by cyclization of carbenium ions or carbanions. The magnitude of the effect exerted by spiroconjugation is estimated by model calculations. It can be detected, for instance, by comparison of the electronic and photoelectron spectra of spiro‐polyenes and analogous compounds which are unable to undergo such interaction.
Chromatography with Supercritical Fluids
Authors: Klesper E.
Published: December 2003

Chromatography with supercritical fluids unites the features of both gas chromatography and liquid chromatography, yet retains special characteristics of its own. The diffusion coefficient and particularly the viscosity of fluid phases may approach values for low‐pressure gases, while the solvent power may be similar to that of liquids. However, with supercritical fluids it is possible to control chromatographic separations very effectively by pressure programming, since the solubility increases with increasing density. Temperature programming, on the other hand, can have the opposite effect to that in gas‐ or liquid‐chromatography since the density decreases with increasing temperature at a given pressure. Supercritical fluid chromatography is primarily of interest for the separation of higher molecular weight compounds. The efficiency of this method of separation is demonstrated on several homologous series. Thus, a styrene oligomer with nominalMw=2200 can be resolved by a pressure and temperature program into 40 species.
Electrostatics, the Chemical Bond and Molecular Stability
Authors: Benson Sidney W.
Published: December 2003

Electrostatic models of the chemical bond are based on the Virial Theorem and hold promise for providing a reliable and accurate method for predicting heats of formation of molecules and free radicals. The Principle of Alternating Polarity which states that those compounds are most stable in which atoms of opposite polarity are bonded is shown to be quantitatively described by electrostatic models. Current fixed partial‐charge models account for ΔH of hydrocarbon molecules and radicals. With inclusion of polarization effects, whose energies are small, they also account for the dipole moments in hydrocarbons. A brief account is given of a more general model with significant polarization interaction which is under development and which appears to be able to account for both ΔH and dipole moments of polar molecules.