bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulfinato Complexes
Authors: Vitzthum Günther , Lindner Ekkehard
Published: December 2003

Sulfinatometal complexes exhibit unusual features in their structure, preparation, and use, and have attracted rapidly growing interest. Their structures are determined by the ability of the RSOgroup both to act as a monodentate ligand (sulfinato‐S or sulfinato‐O) and to add to coordination centers as a bidentate ligand, either intramolecularly or intermolecularly, via the two oxygens atoms (sulfinato‐O,O′) or via the sulfur atom and one of the oxygens (sulfinato‐O,S).
Gamma Resonance Spectroscopy and Chemical Bonding
Authors: Mössbauer Rudolf L.
Published: December 2003

Gamma resonance spectroscopy makes it possible to observe directly hyperfine interactions in solids. In the field of chemistry the feature of greatest interest is the measurement of isomeric shifts of gamma lines because these shifts are proportional to the electron density at the nucleus and can thus give detailed information about the electronic structure of the chemical bond. After a brief introduction to gamma resonance spectroscopy, this paper deals with the fundamental problem of the interpretation of measured isomeric shifts in terms of electron densities and then gives representative examples of chemical information that can be obtained for transition elements from the shifts and the splitting of the gamma lines.
Pulse Fourier Transform 13C‐NMR Spectroscopy, Principles and Applications
Authors: Breitmaier Eberhard , Jung Günther , Voelters Wolfgang
Published: December 2003

As a result of the development of pulse Fourier transform NMR spectroscopy 13C resonance has become accepted as a means of elucidating the structures of organic compounds having the natural 13C abundance. Assignment of the signals is facilitated by broad‐band and off resonance proton decoupling and by knowledge of longitudinal relaxation times. The pulse Fourier technique, which is more sensitive and faster than conventional NMR spectroscopy because of multi‐channel excitation, allows 13C measurements within a short time even on dilute samples of high molecular weight compounds without prior enrichment in 13C.
Vanadium and Chromium Catalysts for Polymerization of Ethylene
Authors: Henrici‐Olivé G. , Olivé S.
Published: December 2003

In the present progress report literature data concerning homogeneous catalyst systems based on vanadium and chromium are reviewed and complemented by a combined study of the magnetic properties and the polymerization activity of such systems. The results show that vanadium forms active species as V (III) and as V (II), but chromium only as Cr (II); models are suggested for the polymerization process. — A comparison with heterogeneous systems (Phillips catalyst) allows the establishment of some general principles concerning the activity of the catalyst and the properties of the polymers.
Application of Ligand Field Spectroscopy to Problems of Chemical Bonding in Solids
Authors: Reinen Dirk
Published: December 2003

Selected examples (dn systems) are presented to illustrate the interpretation of ligand field spectra (remission spectra) of solid inorganic compounds. In particular, this article demonstrates possible means for the investigation of weak cooperative interactions between transition metal coordination polyhedra and for the determination of the cation distribution in crystal lattices. The information value of the spectroscopic method to the chemist is critically discussed.
Vibration‐Spectroscopic Studies on Solid Compounds
Authors: Becher Hermann J.
Published: December 2003

Considerably improved possibilities are now available for the investigation of the optical vibrations in lattice compounds by Raman and IR spectroscopy. These spectra can be interpreted on the basis of the models and findings of molecular vibration spectroscopy. For simple lattice types simple frequency equations are found for the optical lattice vibrations with in‐phase vibration motions in all unit cells (wave vector k = 0). As an approximation, the force constants that occur in these equations may be interpreted as stretching force constants. For typical ionic lattices, the influence of Coulomb forces due to the lattice polarization that occurs during the vibrational motion must be taken into account. As is shown by the example of some spinels, the assignment of lattice vibrations can be facilitated by model calculations.
X‐Ray Spectroscopic Investigation of Chemical Bonding in Solids
Authors: Faessler Alfred
Published: December 2003

When an atom is incorporated into a molecule or a crystal, its X‐ray spectrum undergoes characteristic changes, the study of which leads to important information on the nature of the chemical bonding and on the electronic structure in a substance. A number of examples are given to illustrate the possibilities of the X‐ray spectroscopy of bonded atoms. Special attention is given to the displacement of the Kα lines, from which conclusions can be drawn regarding the charge on a bonded atom, as well as to the investigation of the emission bands resulting from valence electron transitions, which yields information on the energy band structure of the solid. X‐ray spectroscopic studies on free molecules and theoretical work on the calculation of the molecular orbitals of simple molecules are finally reported.
Structure of Ion Pair Solvation Complexes
Authors: Smid Johannes
Published: December 2003

In solvents of low polarity, salts containing a carbanion, e.g. fluorenylsodium, or a radical anion, e.g. coronenesodium, can exist as contact ion pairs or as solvent separated ion pairs. Particular interest attaches to the complexes of ion pairs with the strongly solvating, polydentate polyglycol dimethyl ethers (glymes) and with crown compounds. These systems can be studied by optical spectroscopy, NMR spectroscopy, and other methods.
Chemistry and Biochemistry of Branched‐Chain Sugars
Authors: Grisebach Hans , Schmid Rolf
Published: December 2003

Branched‐chain sugars have recently been isolated in larger numbers from microorganisms and higher plants as glycoside components of antibiotics or phenolic compounds. They also occur in plants in cell wall polysaccharides. Sugars with methyl, hydroxymethyl,formyl, hydroxyethyl, and glycoloyl branches have so far been found in nature. Many new methods have been developed for the synthesis of these sugars. With one exception, the branched sugars known at present can be divided biogenetically into three groups. Sugars with methyl branches are formed by C1 transfer, sugars with hydroxyethyl branches by C2 transfer to a hexose chain, and sugars with hydroxymethyl or formyl branches by rearrangement of a hexose or pentose chain.
Chemistry of the Positron and of Positronium
Authors: Ache Hans J.
Published: December 2003

In this progress report, the properties and behavior of the positron (“positive electron”, anti‐electron) and of the positronium, a “hydrogen atom” containing a positron instead of a proton, are considered from the chemist's viewpoint. Examples are given to demonstrate the development of positronium chemistry, in aqueous solution and in the gaseous, liquid, and solid phases, with its problems and possibilities.
Carrier‐Bound Biologically Active Substances and Their Applications
Authors: Orth Hans Dieter , Brümmer Wolfgang
Published: December 2003

Stable catalysts can be obtained by fixation of enzymes on suitable supports. The principal methods for their preparation and their properties are described. The use of supported enzymes in routine biochemical analysis as “insoluble reagents” for automatic analyzers and for enzyme electrodes appears particularly interesting. For preparative transformations and syntheses, the supported enzymes offer the advantage that many processes that were formerly operated batch‐wise can be run continuously to give protein‐free products. The use of supported proteinases as specific adsorbents provides a simple method for the isolation of various naturally occurring inhibitors. This principle, which is the basis of affinity chromatography, has now also been adapted to the purification of enzymes and other biologically active substances on suitable supported effectors.
Structure of Porous Adsorbents
Authors: Unger Klaus
Published: December 2003

Porous solids are gaining in importance as adsorbents and catalysts both for scientific investigations and for industrial applications. Adsorbents having predetermined pore structure can be prepared by specific synthesis. This pore structure can be described in detail and comprehensively by specific parameters, which can be determined by gas adsorption measurements and by other means. Information concerning the bonding state and the concentration of the functional groups on the surface is obtainable by the use of chemical and physical methods of investigation. Other functional groups can be attached to the surface by chemical reactions. It is possible in this way to prepare selective adsorbents.
Perspectives in Nonsteroidal Anti‐inflammatory Agents
Authors: Shen T. Y.
Published: December 2003

Among numerous nonsteroidal anti‐imflammatory agents synthesized in the past few years, various analogs of indomethacin, phenylacetic acid and heteroarylacetic acid have reached the stage of clinical evaluation. Their biochemical mechanisms of action are exemplified by the broad activity profile of indomethacin which includes inhibition of mediators and enzymes, effects on cell membranes, and, most recently, inhibition of prostaglandin biosynthesis. The importance of pharmacodynamic properties to clinical efficacy was clearly demonstrated in some cases. Several candidates were eliminated because of their side‐effects. A group of α‐methylarylacetic acids showed a high degree of stereospecificity in their potency and metabolisms in vivo, as well as inhibition of prostaglandin synthetase and albumin binding in vitro. Extrinsic Cotton effect provides a sensitive technique in the study of interactions of these drugs with biopolymers. Competitive binding and antagonistic interactions between nonsteroidal drugs, particularly salicylate, were observed in vitro and in vivo. Progress in salicylate research was marked by the synthesis of flufenisal as a new derivative with enhanced potency and longer duration of action. Several fenamate analogs and new chemical types have shown promise in preliminary clinical trials. Various immunological approaches are under investigation for the treatment of rheumatoid arthritis. Newer concepts are still needed to achieve more effective control of arthritic disorders.
Fluorinated β‐Sultones
Authors: Knunyants I. L. , Sokolski G. A.
Published: December 2003

Fluorinated (β)‐sultones are formed on addition of sulfur trioxide to fluorinated olefins. Tetrafluoroethanesultone has been studied particularly thoroughly. The title compounds are characterized by the ease with which they undergo ring cleavage to give, e.g., derivatives of α‐sulfo carboxylic acids, of sulfonic acids, of carboxylic acids, and of sulfuric acid. Fluorinated compounds of this type containing an α‐hydrogen atom are especially valuable in preparative work.
Basic Behavior of Epoxides in the Presence of Halide Ions
Authors: Buddrus J.
Published: December 2003

Epoxides behave as bases in the presence of catalytic quantities of halide ions. They convert halogenated hydrocarbons into olefins, suitable phosphonium salts into ylides, and haloforms into dihalocarbenes. Kinetic studies with the aid of JR and NMR spectroscopy show that the species that functions as the proton acceptor is neither the epoxide ion nor the halide ion, but the 2‐haloethoxide ion.
Biochemistry of the Pteridines
Authors: Rembold Heinz , Gyure William L.
Published: December 2003

Biochemical information about the ubiquitous pteridines has become generally available only within the last fifteen years. This delay can be traced to the chemical lability of these compounds and their small concentrations in organisms. New methods of isolation and isotopic techniques have provided data on the biosynthesis, anabolism, and catabolism of this class of compounds. Hydrogenated pteridines are recognized today as cofactors for various mixed function oxygenases and are involved in cellular electron transport. Further unknown catalytic functions for pteridines in cellular metabolism are indicated by their physiological activity, negative redox potentials, and histoautoradiographic data.
Hereditary Diseases—Causes, Cures, and Problems
Authors: Brady Roscoe O.
Published: December 2003

The nature of the biochemical abnormalities in over a hundred inherited diseases of humans is now convincingly established. This impressive achievement has provided numerous practical benefits, amongst which are: 1. accurate methods for the diagnosis of patients with these diseases; 2. identification of symptom‐free heterozygous carriers of the defective genes; and 3. procedures for the antenatal detection of a large number of these disorders in fetuses. It is anticipated that equally impressive advances will be made in the future regarding the therapy for patients with these diseases who escape prenatal detection, or in cases when an affected fetus is identified but is carried to term in compliance with the decision of the parents. The current concepts regarding the therapy of heritable metabolic diseases are outlined and potential innovations for future corrective procedures are indicated in this report.
Chemistry and Biochemistry of Azaquinones
Authors: Knackmuss Hans‐Joachim
Published: December 2003

The azaquinones are a new class of bacterial secondary metabolites. Investigations were necessary on the chemistry of the azaquinones, their imides, and 2,3,6‐pyridinetriols and 3‐aminopyridine‐2,6‐diols in order to obtain information about the structure and biogenesis of these natural products.
The Origin of Life
Authors: Paecht‐Horowitz Mella
Published: December 2003

The theory of the evolution of the species, which is today widely accepted, requires a starting point. It is postulated that the biological starting point could have emerged only if chemical evolution had preceded it. Experiments are described which show the formation of organic substances from inorganic gases under conditions which prevailed on earth in the prebiotic era; also demonstrated is the polymerization of such organic substances into biological macromolecules. Hypotheses are discussed whereby these macromolecules could be transformed into dynamic structures which might finally lead to self‐reproduction.
Elemental Sulfur—A Challenge to Theory and Practice
Authors: Schmidt Max
Published: December 2003

Surprisingly little is still known about many aspects of the system “elemental sulfur”, in spite of its being one of the longest known and common “chemical substances” and today available cheaply and in great purity. This paper summarizes some of the newer investigations that have increased our understanding of this system.
Anomalies in the Structural Chemistry of Silicon
Authors: Bürger Hans
Published: December 2003

In contrast to carbon, silicon fails to form multiple bonds that are stable at room temperature. Consequently molecules in which silicon exhibits coordination numbers (CN) of 1, 2, and 3 may only be obtained at very high or low temperatures. Under these conditions their structural features, including multiple bonds, resemble those of carbon. On the other hand, silicon is capable of forming various hexacoordinated compounds making use of its d orbitals. Nitrogen and oxygen bonded to silicon develop an unusual stereochemistry: planar nitrogen, nearly or completely linear oxygen, and considerable shortening of SiN, SiO, and SiF bonds are specific examples. N(SiR3)2 and CH2SiR3 ligands permit stabilization of unusually low CNs of many metals and give rise to amino and alkyl derivatives of unexpectedly high stability due to the particular electronic, the R3Si group.
Thermodynamics of Addition Polymerization Processes
Authors: Ivin K. J.
Published: December 2003

The polymerizability of compounds such as 1,l‐disubstituted ethylenes, aldehydes, ketones, isocyanates, and five‐ and six‐membered ring compounds is determined largely by thermodynamic considerations. The transition from non‐polymerizability to polymerizability, correspondlng to a change in the sign of ΔG, is often quite sharp. Factors which generally make the free energy of polymerization more negative, and which therefore favor polymerization, are low temperature, high pressure, and high monomer concentration. Additional driving force is sometimes available if the monomer is in the supercooled (glassy) state rather than the crystalline state, or if the polymer crystallizes on formation. Alkyl substituents have an unfavorable effect on polymerizability; halogen substituents have a favorable effect. Many monomers which do not homopolymerize for thermodynamic reasons will copolymerize with a second monomer to the extent of forming copolymers containing 50 or even 66 mol per cent of the first monomer.
Sesquiterpenes
Authors: Rücker Gerhard
Published: December 2003

Of the 4000 or so terpenoid natural products known today, whose carbon skeleton can be divided up into isopentane units by the “isoprene rule” (C10, monoterpenes; C15, sesquiterpenes; C20, diterpenes; C25, sesterterpenes; C30, triterpenes; steroids; carotenoids; polyprenes), the sesquiterpenes, numbering about 1000, represent the largest single class. According to the well founded concepts developed in recent years for the biogenesis of their highly diverse carbon skeletons, the present report is divided into nine sections dealing respectively with farnesanes, bicyclofarnesols (drimanes, iresanes), bisabolanes, cadinanes, humulanes and caryophyllanes, germacranes, “hydroazulenes”, selinanes and eremophilanes, and maalianes and aristolanes. Further groups of sesquiterpenes can be derived from each of these structural types.
Syntheses of Seven‐ and Five‐Membered Rings from Allyl Cations
Authors: Hoffmann H. M. R.
Published: December 2003

The cycloaddition of allyl cations to conjugated dienes offers an efficient and general tool for the construction of seven‐membered carbocycles. The silver salt route is highly suitable for generating allyl cations and can be used even in most difficult cases, i. e. for elusive and intractable allyl cations such as 2‐methylallyl, 2‐methoxyallyl, and the parent allyl cation. Cycloadditions to the 2‐methoxyallyl cation come very close to the prototype of a 6π, 7C reaction, since the carbonyl group introduced into the new ring can either be used for further transformations or be removed altogether. The combination of an allyl cation with π reactants, especially conjugated dienes, is a powerful and strongly convergent synthetic method since it permits one‐step assembly, from a C3 and a C4 unit, of a cluster of up to four chiral centers in a ring which is larger than six‐membered. Allyl cations combine with electron‐rich 2π systems to form novel five‐membered rings. The nature of the organometallic intermediates has been elucidated in many cases.
Methylchlorophosphanes and Their Reaction Products
Authors: Staendeke Horst , Kleiner Hanss‐Jerg
Published: December 2003

Methyldichlorophosphane and dimethylchlorophosphane can be prepared only with considerable difficulty. The ease with which they yield numerous reaction products is an indication of the pronounced reactivity of these organohalophosphanes. Possible applications of such organophosphorus compounds exist inter alia in the fields of plant protection, corrosion prevention, and flame retardants, as well as in the catalysis of gas phase reactions, for instance the desulfurization of gas mixtures.
Possibilities and Limitations of Delegated Literature Searches by Computer
Authors: Fugmann Robert , Ploss Gottfried
Published: December 2003

The present‐day chemist is constantly on the lookout for information which may be useful to his work. If he is able to define his interests precisely enough then he can avail himself of information scientists and of specialized literature stores. However, retaining access to such information, which only he himself can subjectively judge for relevance to his work, and which most often constitutes a powerful incentive to his creative thinking, will always require his own “browsing” literature studies or personal contacts. These are the limitations of any delegated literature search.
Chemical Applications of Raman Spectroscopy
Authors: Schrader Bernhard
Published: December 2003

Raman spectorscopy is—like infrared spectroscopy—a method for the study of vibrations of molecules and crystals. The two methods are complementary: if a vibration results in a change of the polarizability of a molecule, it is Raman active; if a change in the molecular dipole moment results, it is infrared active Vibrations of nonpolar groups and totally symmetrical vibrations of molecules are often only Raman active. IR and Raman spectra together give information about the symmetries and structures of molecules and crystals and about the properties of chemical bonds and intermolecular interactions. Until about 10 years ago Raman spectra could only be recorded on relatively large amounts of essentially colorless substances. After the advent of laser light sources the situation changed completely. The amount of sample substance required is now in the region of milli‐ and micrograms. Gases, liquids and solid samples, especially air‐sensitive and reactive substances, single crystals, crystal needles and filaments as well as aqueous solutions can be readily investigated. The identification of molecules and the elucidation of molecular structures, biochemical analysis, and control of evnivornmental pollution are important aplications of Raman spectroscopy. Raman spectroscopy now constitutes an additional powerful tool in instrumental analysis
Structures of the Intermediate Complexes in Friedel‐Crafts Acylations
Authors: Chevrier Bernard , Weiss Raymond
Published: December 2003

Addition compounds of Lewis acids MXn and acyl halides RCOX occur as intermediates in Friedel‐Crafts acylations. IR and NMR studies on these intermediates have indicated the probable existence of structural isomers. In X‐ray structural analysis, it is possible to distinguish two forms, i.e. the molecular form, in which the compounds are present as donor‐acceptor complexes RCXO→MXn, and the ionic form, in which they can be formulated as oxocarbenium salts [RCO]+[MXn+1]−. The compounds of the donor‐acceptor type RCXO→MXn are characterized by the formation of a coordinate oxygen‐metal bond; the transfer of electrons from the oxygen to the metal of the acceptor is always due to a weak donor‐acceptor interaction. The positive charge of the aryloxocarbenium ions is partly delocalized over the aromatic nucleus. The positive charge in alkyloxocarbenium ions, on the other hand, is essentially localized on the carbon atom of the carbonyl group, as is confirmed by electron density distribution calculations.
Biochemistry of Natural Proteinase Inhibitors
Authors: Tschesche Harald
Published: December 2003

The natural inhibitors of proteolytic enzymes are proteins. These inhibitors associate reversibly with the enzymes to form stoichiometric protein‐protein complexes, in which substrate‐analogous association at the active center of the enzyme results in competitive inhibition of all catalytic functions. The very widespread occurrence of inhibitors in the animal and plant kingdoms underlines their biological importance in the intermediate metabolism, which can be understood as an extension of the possibilities for temporary and local limitations of enzyme activities. Existing knowledge includes a series of covalent structures, detailed kinetic data on the reversible protein‐protein interaction, the processes involved in inactivation, and chemical methods for the modification of these proteins. Early X‐ray structural data for an inhibitor and its enzyme complex provide an insight into the molecular structure of the latter and the interactions involved in the association to form the complex.
Activation of Molecular Oxygen
Authors: Henrici‐Olivé G. , Olivé S.
Published: December 2003

Molecular oxygen as a ligand in transition metal complexes is of interest for biochemistry, and for inorganic and organometallic chemistry. Several examples of O2 complexes, as well as the kinetics and mechanism of their formation are presented. The influence of other ligands on the activation of O2 is discussed on the basis of a MO description of the electronic structure of the oxygen molecule and of the bonding within the metal‐oxygen complexes. Reactions of coordinated oxygen are described.
Results and Problems of O‐Glycoside Synthesis
Authors: Wulff Günter , Röhle Gerbard
Published: December 2003

Considerable problems attend the synthesis of biologically important natural products whose carbohydrate components display a greater or lesser degree of complexity. The present progress report surveys recent developments in the formation of O‐glycosidic bonds starting from 1‐halo sugars and from sugar 1,2‐orthoesters. Particular emphasis is placed on attempts to reach a better understanding of the steric course of glycosylation reactions on the basis of mechanistic considerations. Studies on the silver‐salt dependence of the Koenigs‐Knorr synthesis led to improvements in preparative applications and to new concepts concerning the reaction course. The introduction of sugar 1,2‐orthoesters as glycosylation components has greatly enriched our preparative armoury for the synthesis of trans glycosides. Remarkable progress has also been made in the synthesis of cis glycosides, in part by exploiting novel neighbouring group effects.
Trialkoxycyclopropenylium Ions
Authors: Dehmlow Eckehard V.
Published: December 2003

For corrigendum see DOI:10.1002/anie.197407452
Chemically Produced Excited States
Authors: White Emil H. , Miano Jeffrey D. , Watkins Carol J. , Breaux Eves J.
Published: December 2003

Electronically excited states of organic molecules are formed in many chemical reactions. Such chemically produced excited states are (with one exception) identical to light produced excited states, and they undergo the molecular transformations expected of such states (“photochemistry without light”). The excited states can also be used in energy transfer experiments. This review covers the generation of chemically produced excited states, the chemical reactions they undergo, and the possible role of chemically produced excited states in biology.
Mass Spectral Interaction between the Functional Groups of Multiply Substituted Alkanes
Authors: Bosshardt Herbert , Hesse Manfred
Published: December 2003

The mass spectral decomposition of di‐ and polyfunctional alkanes is characterized essentially by two, fundamentally different reactions: On the one hand the structures of the fragment ions are determined by separated degradation of each functional group; on the other hand, however, a relatively large number of fragment ions result from the combined action of two or even more functional groups. This special type of fragmentation has become an important topic in today's mass spectral research. In the present progress report an attempt has been made to summarize the results obtained so far.
Beech Lignin—Proposal of a Constitutional Scheme
Authors: Nimz Horst
Published: December 2003

The high molecular weight material lignin consists of phenylpropane units linked together by a variety of bond types. During the past eight years, two newly developed degradation procedures have permitted the first direct determinations of the nature of these bonds. The first procedure affords a very mild partial hydrolysis of benzyl ether bonds. Eleven dimeric, trimeric, and tetrameric degradation products were obtained in this way from spruce and beech lignin: they exhibited three different kinds of bonds between the C9 structural units, and their structures have all been elucidated. In the second procedure, the most important kind of bond in lignin, i. e. the arylglycerol‐β‐aryl ether bond, can be subjected to directed cleavage under mild conditions after introduction of a suitable neighboring group. On application to beech lignin, 91 % of the material was degraded giving monomeric to tetrameric phenols. Complete structural elucidation of the twenty dimeric phenols isolated and a knowledge of their relative yields and the yields of the other fractions obtained by gel filtration permitted a structural scheme to be set up for beech lignin in which the C9 structural units are linked together by no less then ten different kinds of bonds. The structural scheme, which can be readily explained biogenetically, has the same elemental composition as natural beech lignin. Further support for the structural scheme comes from a comparison of the 13C‐NMR spectrum of natural beech lignin and a 13C‐NMR spectrum calculated for the proposed structure on the basis of about fifty lignin model substances.
Mass Transport in Solids
Authors: Frischat Günther Heinz
Published: December 2003

Two aspects are especially important in connection with mass transport in solids; these are the phenomenological description of the diffusion process and the discussion of the transport mechanism. In addition to the self‐diffusion of the constituent ions or atoms of a solid, which can be followed only with the aid of radioactive or stable isotopes, other known types of diffusion are the diffusion of trace elements, which can in principle be treated in the same way as self‐diffusion, and chemical diffusion, in which the diffusion partners differ in their chemical composition. Processes of this type are being increasingly studied with the electron beam microprobe. Regardless of the crystallinity and the type of bonding, problems concerned with diffusion in solids can be discussed from a single standpoint by slight adaptation to suit the particular situation in question.
The Cyclobutadiene Problem
Authors: Maier Günther
Published: December 2003

Cyclobutadiene has recently become the center of reawakened interest. By use of the matrix isolation technique, cyclobutadienes can now be prepared as monomers frozen in matrices. Thus both the unsubstituted parent compound and its alkyl‐substituted derivatives are amenable to study. The present progress report surveys the entire field; however, particular emphasis is placed on the author's own results from investigations concerning this classical problem of organic chemistry.
Equilibrium and Transport Properties of Low‐Melting Salts
Authors: Richter Joachim
Published: December 2003

An understanding of the physical and chemical phenomena and the structure of salt melts calls not only for kinetic and spectroscopic data but also for systematic studies on the equilibrium and transport properties of individual systems. The present article deals with the activity coefficients, transport numbers, and self‐diffusion and interdiffusion coefficients of salt melts, and the results of consistent measurements of these quantities are reported.
Transition to Nonmetallic Behavior in Expanded Liquid and Gaseous Metals
Authors: Hensel Friedrich
Published: December 2003

At high temperatures and pressures, liquid and gaseous metals exhibit a steady transition from metallic to nonmetallic behavior when the density is sufficiently reduced. All the properties are influenced by this transition, as is shown by measurement (on mercury, cesium, and potassium) of the electric conductivity, the density, the thermoelectric power, and in some cases the Hall effect, as well as the optical absorption. The continuous variation of the density over a wide range is achieved by compression or expansion above the critical temperatures of the metals, i. e. 14900C for mercury, 17500C for cesium, and 19250C for potassium.
1,3‐Anionic Cycloadditions of Organolithium Compounds: An Initial Survey. New synthetic methods (4)
Authors: Kauffmann Thomas
Published: December 2003

In the field of [3 + 2]‐cycloaddition reactions, 1,3‐anionic cycloadditions have now joined 1,3‐dipolar cycloadditions as a second reaction type of major general importance. The cycloaddition in question has been found to occur with 2‐azaallyllithium compounds, allyllithium compounds (with an electron acceptor located on C2), and 1,3‐diphenylpropargyllithium. Compounds with CC, CN, NN, and CS double bonds and those with CC and CN triple bonds were found to be 1,3‐anionophilic. 1,3‐Anionic cycloaddition opens new routes to 1‐aza‐, 1,2‐diaza‐, 1,3‐diaza‐, 1,2,4‐triaza‐, and 1‐thia‐3‐azacyclopentane derivatives, to pyrroles and imidazoles, as well as (and this appears to be of special importance) to cyclopentane derivatives. Currently available data attribute stereospecificity to the 1,3‐anionic cycloadditions, which occupy an interesting intermediate position between 1,3‐dipolar cycloadditions and transition‐metal‐catalyzed cyclizations. A two‐step mechanism has been demonstrated in one case.
The Theory of Pericyclic Reactions
Authors: Epiotis Nicoloas D.
Published: December 2003

Pericyclic reactions include thermal and photochemical cycloadditions and cycloreversions, electrocyclic reactions and sigmatropic shifts. Configuration interaction analysis can be used for making predictions about preferred reaction pathways, about reaction rates, about the nature of possible intermediate steps, and above all about the stereochemistry of such reactions.
Mechanisms of Photochemical Air Pollution
Authors: Pitts J. N. , Finlayson B. J.
Published: December 2003

Selected aspects of the chemistry of photochemical air pollution is discussed and some important, unresolved problems dilineated. The reactive species considered include NO2, O3, O(3P), O(1D), O2(1Δg), OH and HO2. Both the kinetics and mechanicsms of the reactions constituting the major tropospheric sources and sinks of these species are treated where available. The application of this information in both computer and smog chamber simulations of photochemical smog is discussed.
The Wolff Rearrangement of α‐Diazo Carbonyl Compounds
Authors: Meier Herbert , Zeller Klaus‐Peter
Published: December 2003

The readily accessible α‐diazo carbonyl compounds are distinguished by their high reactivity, which opens up a variety of preparative applications under modified conditions. Wolff rearrangements of these compounds, induced thermally, photochemically, or catalytically, afford ketenes. Free and complexed carbenes, 1,3‐dipoles, 1,3‐diradicals, and the antiaromatic oxirenes have been considered as intermediates or transition states. The present progress report attempts to integrate preparative and theoretical aspects.
Preparation, Structure, and Reactions of Halomalondialehdes
Authors: Reichardt Christian , Halbritter Klaus
Published: December 2003

The present progress report provides a survey of the synthesis, structure, and reactions of halomalondialdehydes, including “cyanomalondialdehyde” (diformylacetonitrile), the only pseudohalogen compound so far known in this series. Halomalondialdehydes are reactive compounds, applicable in a variety of ways, and are characterized particularly by their cyclizations with bifunctional compounds. Many of the reactions discussed below can be applied to substituted malondialdehydes other than those specified.
Formation of Ad‐Layers and Clusters on Condensation of Metal Vapors on Solid Surfaces
Authors: Niedermayer Rolf
Published: December 2003

Synthesis of organometallic materials can be accomplished in many cases by cocondensation of metal atoms and organic molecules at low temperatures. The reaction kinetics is determined by the competition between metal cluster growth and formation of the organometallic compound. Interesting compounds may contain one or more metal atoms; the latter type could be obtained by reaction between a cluster containing the desired number of metal atoms and an organic molecule. A precise knowledge of the events occurring on condensation of metal atoms and cluster formation can therefore be of value in the control of chemical synthesis. These phenomena have been investigated in connection with the study of the growth of thin metallic films, both experimentally and theoretically. Direct observation of the formation of very small clusters is difficult. The good agreement between experimental results and recent calculations for the development of large clusters, however, allows reliable theoretical conclusions for the first stages of adsorption and cluster formation. The present contribution describes experimental work on film growth and relevant theoretical concepts, and an attempt is made to develop applications to organometallic synthesis.
Sulfur Atoms as Ligands in Metal Complexes
Authors: Vahrenkamp Heinrich
Published: December 2003

The types of sulfur bonding—as sulfane or sulfide—encountered in the molecules of maingroup elements are almost unknown in the chemistry of metal complexes, where the sulfur atoms function instead as two‐electron donors by bridging two metal atoms, as four‐electron donors by bridging three or four metal atoms, or as six‐electron donors by incorporation between four metal atoms. In such complexes, the metal‐metal bond can be modified over a wide range by chemical or electrochemical variation of the number of electrons present. The readiness with which polynuclear complexes containing metals and sulfur undergo redox reactions is also utilized by Nature in the active sites of some redox proteins.
D‐Penicillamine—Production and Properties
Authors: Weigert Wolfgang M. , Offermanns Heribert , Degussa Paul Scherberich
Published: December 2003

The non‐naturally occurring amino acidD‐penicillamine, originally only of interest as a key substance in the structural elucidation and total synthesis of penicillins is gaining increasing importance as a therapeutic, particularly in the long‐term treatment of rheumatoid arthritis.D‐Penicillamine which previously was obtained semi‐synthetically by degradation of penicillins can now be totally synthesized using a new process which starts from isobutyraldehyde, sulfur, ammonia, and hydrogen cyanide and yields the racemate which is then selectively resolved. The biochemical behavior ofD‐penicillamine—chelate formation with heavy metal ions, cleavage of disulfide bridges, and condensation with aldehyde groups—affords information related to its therapeutic activity.
Properties of Sulfur‐Sulfur Bonds
Authors: Steudel Ralf
Published: December 2003

SS bonds are extraordinarily flexible and have properties that are observed only on isolated occasions for other homonuclear bonds: the bond lengths very between 1.8 and 3.0Å, the bond angles between 90 and 180° and the dihedral angles between 0 and 180°; the bond energies amount to up to 430 kJ/mol. The SS stretching frequencies can appear over the range 177–820 cm−1 and force constants of 1.4 to 6.3 mdyne/Å have been calculated. This variability is illustrated with examples containing isolated and cumulated SS bonds.
Detection of Fragment Genesis in the Mass Spectrometer: DADI Mass Spectrometry as an Aid in the Structure Analysis of Organic Compounds
Authors: Schlunegger Urs Peter
Published: December 2003

“Direct Analysis of Daughter Ions” (DADI) can be carried out with commercial mass spectrometers embodying the Nier‐Johnson inverse geometry. DADI measurements permit experimental detection of the consecutive formation of molecule fragments (fragment genesis). Knowledge of fragment genesis enables the chemist to clarify the fragmentation processes of molecule‐ions and provides information on the structure of fragments formed in the mass spectrometer. In combination with classical mass spectrometry such information makes it easier to determine the structure of compounds, to analyze mixtures, to determine the sequence in periodically constructed molecules, for example oligopeptides, and to study rearrangement reactions occurring in the mass spectrometer.
Substitution Reactions Which Proceed via Radical Anion Intermediates
Authors: Kornblum Nathan
Published: December 2003

A new type of substition process at a saturated carbon atom is described. These reactions, which proceed via a chain sequence in which radical anions and free radicals are intermediates, are noteworthy for providing novel and powerful means of synthesis: they occur readily under mild conditions, they give excellent yields of pure products, and, in contrast to SN2 displacements, they are rather insensitive to steric hindrance. As a consequence, radical anion processes are especially valuable for the preparation of highly branched structures. Many inorganic and organic anions readily enter into these displacements and, indeed, amines are also effective. Systems which undergo substitutions via this electron transfer mechanism include benzylic, cumylic, strictly aliphatic, and heterocyclic molecules. It is of interest that a number of groups which do not behave as leaving groups in SN2 displacements are readily displaced at room temperature from a satureted carbon atom via the radical anion‐free radical pathway, e.g., nitro, azide, sulfone, and ether groups.
Mechanism of Ozonolysis
Authors: Criegee Rudolf
Published: December 2003

The formation of ozonides (1,2,4‐trioxolanes) from alkenes and ozone can be described as a succession of three [2+3] cycloadditions or cycloreversions involving primary ozonides (1,2,3‐trioxolanes) and aldehyde or ketone oxides as decisive intermediates, all of which have finite lifetimes. There is no warranted experimental basis for assuming an alternative mechanism.
Intramolecular 1,3‐Dipolar Cycloaddition Reactions
Authors: Padwa Albert
Published: December 2003

The intramolecular 1,3‐dipolar cycloaddition reaction of suitably functionalized 1,3‐dipoles represents a general scheme for the synthesis of novel fused ring heterocycles. Such reactions of a number of 1,3‐dipoles are summarized and the general outline and potential analogies for these reactions noted. While the immediate aim of this review is to survey and correlate published work, it is hoped that general and specific points in need of study will be revealed and will stimulate further work in this fertile field.
A Synthesis of Prostaglandins: Strategy and Reality
Authors: Ernest Ivan
Published: December 2003

The prostaglandin synthesis developed in the Woodward Research Institute at Basel serves to provide an unusual look behind the scenes. A candid account is presented of the sometimes tortuous chronological sequence of ideas and experiments during work on a challenging synthesis.
Mechanistic Aspects of Olefin Metathesis
Authors: Calderon N. , Ofstead E. A. , Judy W. A.
Published: December 2003

In this paper views regarding the nature of the transition state in olefin metathesis are discussed. Earlier concepts that assumed a pairwise scrambling mechanism have been recently challenged. Metathesis studies involving acyclic as well as cyclic olefins have been reported which strongly suggest a chain process that may involve a carbene‐to‐metallocycle interconversion as the pathway responsible for transalkylidenation. Catalytic systems that display a low apparent metathesis activity on terminal olefins display a unique specificity in cross reactions with internal olefins. Critical experiments indicate that terminal olefins rapidly undergo regenerative metathesis preferentially. Results suggest that in the transient metallocycle, the most stringent steric requirements occur at the β‐carbon, although the origin of this steric demand is not obvious.
New Developments in the Field of Vitamin B12: Reactions of the Cobalt Atom in Corrins and in Vitamin B12 Model Compounds
Authors: Schrauzer G. N.
Published: December 2003

Studies with vitamin B12 model compounds such as the cobaloximes provide a basis for the understanding of the mode of action of corrinoid coenzymes in enzymatic reactions. They also widen our knowledge of the properties and reactions of organocobalt compounds. The present article outlines the most important nonenzymatic reactions of cobalt in vitamin B12 and in model compounds of the cobaloxime type.
Vinamidines and Vinamidinium Salts—Examples of Stabilized Push‐Pull Alkenes
Authors: Lloyd Douglas , McNab Hamish
Published: December 2003

The name vinamidines has been proposed for 1,5‐diazapentadienes: these compounds can be regarded as vinylogous amidines and at the same time as push‐pull substituted (and thereby stabilized) alkenes. Vinamidine and vinamidinium structural elements may also form part of a ring system. Characteristic of this class of compounds are their reactivity toward electrophiles (at Cβ) and nucleophiles (Cα) and their regenerative character,i.e.their tendency to undergo substitution instead of addition reactions. Reactions of vinamidinium salts with nucleophiles are of special preparative value: they leade.g.to pyrazoles, oxazoles, pyrimidines, diazepines, quinolines, and quinolizines.
Orbital Correspondence Analysis in Maximum Symmetry
Authors: Halevi E. Amitai
Published: December 2003

The use of Orbital Correspondence Analysis in Maximum Symmetry (OCAMS) for determining the allowed course of a reaction is described in terms of the familiar “A, S” notation. Several well known thermal and photochemical reactions are used as examples: Polyene cyclization; the fragmentation and dimerization of cyclobutadiene; [π4 + π2] cycloaddition; the isomerization of Dewar‐benzene. The relation of OCAMS to the classical correlation procedures of Woodward and Hoffmann and of Longuet‐Higgins and Abrahamson is brought out, as are the sources of the occasionally contradictory predictions of OCAMS and of the classical procedures.
Is Gold Chemistry a Topical Field of Study?
Authors: Schmidbaur Hubert
Published: December 2003

The question raised in the title of this progress report is answered point for point with an emphatic “yes”: Ranging from metallic gold,viaclusters of gold atoms in low valence states, compounds of AuI, AuII, AuIII, and AuV, organogold derivatives, ylide and carbene complexes, to the catalytic activity of gold it embraces a long‐neglected area of chemistry holding promise of many a discovery.
Chiral Derivatives of Achiral Molecules: Standard Classes and the Problem of a Right‐Left Classification
Authors: Ruch Ernst
Published: December 2003

Chemistry judging by its applications, physics according to its methods, and heavily reliant upon the tools of mathematics—that is what makes theoretical chemistry. And yet that is where its strength lies—in the variety of these sciences. It is quite natural that, in answer to specific problems, results and methods can sometimes be developed whose scope extends far beyond the original application. Rather it is a mark of quality if consequences can be found in chemistry and physics and the pathway leads via new mathematical procedures and concepts. Regrettably, any publication aiming to present such aspects will usually encounter little resonance since the linguistic confusion in science, its disciplines, and subdisciplines, lies like a veil over our understanding. The author nevertheless wishes to attempt to present, in a series of articles, results of research into chemical themes in a manner designed to appeal to the interest of chemists, without neglecting interdisciplinary aspects. All that is required to understand the argumentation is a lively interest.

The first two articles are concerned with the chirality of molecules, and in particular with questions relating to the chirality phenomenon of molecules in the framework of molecular classes. In view of the algebraic nature of the mathematical methods adopted, it is not surprising that precise statements result. It appears of primary interest to establish the degree to which such statements can be considered valid for molecular models or molecules themselves.
Synthesis of Cyclodepsipeptides by Cyclooligomerization
Authors: Rothe Manfred , Kreiss Wolfgang
Published: December 2003

The antibiotic valinomycin is a cyclic depsipeptide of formula (2), n=3. All cyclodepsipeptides (2) can be prepared by cyclooligomerization of the linear subunits of type (1) in toulene or diethyl phosphite.
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