bluuebunny/crossref_metadata_2025 huggingface dataset:
Diels‐Alder‐Reactions Part I: New Preparative Aspects
Authors: Sauer J.
Published: December 2003

Cycloadditions of conjugated dienes, named after their discoverers, have claimed preparative and mechanistic interest for nearly 40 years. The almost inexhaustible variability of the components of these one‐stage reactions offers entry to important classes of compounds. The systematization of the preparative uses of these reactions which is offered in this paper relates predominantly to recent results. The mechanistic aspects of the Diels‐Alder reactions will be discussed later in the second part of this contribution.
Specification of Molecular Chirality
Authors: Cahn R. S. , Ingold Christopher , Prelog V.
Published: December 2003

The topological analysis of chiral molecular models has provided the framework of a general system for the specification of their chirality. The application, made in and before 1956, of this system to organic‐chemical configurations is generally retained, but is redefined with respect to certain types of structure, largely in the light of experience gained since 1956 in the Beilstein Institute and elsewhere. The system is now extended to deal, on the one hand, with organic‐chemical conformations, and, on the other, with inorganic‐chemical configurations to ligancy six. Matters arising in connexion with the transference of chiral specifications from model to name are considered, notably that of the symbiosis in nomenclature of expressions of the general system and of systems of confined scope.

For corrigendum see DOI:10.1002/anie.196605111
Spectroscopy with Polarized Light
Authors: Dörr F.
Published: December 2003

Polarized light is used in electronic spectroscopy not only to obtain information about the positions. Intensities, and fine structures of absorption and luminescence bands, which can be obtained by normal electronic spectroscopy of solutions, but also to determine the orientation of the transition moments in relation to the molecular framework. The theoretical and experimental principles of molecular optical anisotropy are briefly described, and the three most successful methods (spectroscopy after mechanical alignment of the molecules on films and in crystals, or after electrical alignment in solution, and luminescence polarization of solid solutions) are discussed in detail and illustrated by typical examples. In connection with luminescence polarization, special emphasis is placed on triplet‐singlet phosphorescence. Reference is made to the importantce of polarization measurements on liquid solutions in biochemistry (study of intermolecular interactions of macromolecules by measurement of the rotational relaxation times).
Technology of the Microbiological Preparation of Organic Substances
Authors: Müller R. , Kieslich K.
Published: December 2003

The preparation of organic substances with the aid of the enzyme systems of micoorganisms has become competitive as a result of recent progress in the technology of fermentation. The relatively high cost of apparatus and the lower production capacity of microbiological plants in relation to the plants used in purely chemical processes are offset in many cases by the advantages of biological methods (reactions at conventionally inactive positions in the molecule, stereospecific substitutions, coupling of several reactions, mild reaction conditions, possible use of waste products).
Synthesis of Isocyanates and Carbodiimides
Authors: Ulrich H. , Sayigh A. A. R.
Published: December 2003

The reaction of 1,3‐disubstituted ureas and 1‐arylsulfonyl‐3‐alkylureas with phosgene permits the preparation of a number of isocyanates and sulfonyl isocyanates that had not previously been described, or that were difficult to prepare. 1,3‐Disubstituted thioureas and 1‐aryl‐(or alkyl)sulfonyl‐3‐alkylthioureas give carbodiimides. Thionyl chloride and phosphorus pentachloride react with the urea derivatives in the same way as phosgene. Oxalyl chloride reacts with ureas to form parabanic acid derivatives, whereas with thiourea it gives 2‐imino‐1,3‐thiazolidine‐4,5‐diones, which can isomerize to parabanic acid derivatives.
The Chemistry and Biochemistry of Insulin
Authors: Klostermeyer H. , Humbel R. E.
Published: December 2003

The protein hormone insulin occurs widely in the animal kingdom. Although its biological function is always the same, its amino‐acid composition varies widely. Insulin consists of two polypeptide chains, which are linked by three cystine residues to form a bicyclic system with a 20‐membered and an 85‐membered ring. The protein crystallizes in various forms with foreign ions. In solution, insulin normally forms aggregates of 2n molecules. The hormone can be regenerated from the separated polypeptide chains, and its total synthesis has been achieved in a similar manner from synthesized peptide chains. In the biosynthesis of insulin, the two chains are evidently built up separately and subsequently linked together. Insulin promotes the synthesis of glycogen, fat, and protein in the organism; insulin deficiency leads to an increase in the blood‐sugar level. At the molecular level, the mechanism of action of the hormone is still unknown. Current hypotheses are discussed. No specific active center has so far been detected in the insulin molecule, which contains several antigenic regions.
Relation of Microbes to Blood‐Group Active Substances
Authors: Springer G. F.
Published: December 2003

Substances with blood‐group ABH(0) specificity are not confined to human red blood cells. Rather, such substances are ubiquitous antigenic surface structures which Nature has preserved throughout the phylogenetic development from microbes to man. — It could be shown experimentally that so‐called “pre‐existing natural” antibodies can result from inapparent immunization by these widely distributed antigens. — The blood‐group specific structures of bacteria are chemically closely related to the determinant structures of the human blood‐group ABH(0) glycoproteins. The situation is more complicated for the blood‐group active substances from higher plants; these give extraordinary immunochemical reactions and two of their blood‐group specific monosaccharides precipitate antibodies. — Recently the nature of the M and N blood‐group antigens of erythrocyte surfaces has been elucidated. They are the main antigens of the second of at least 14 human blood‐group systems. These substances, which are glycoproteins, are also excellent myxovirus receptors and inhibitors. The NN antigen is the first reported physically homogeneous, chemically defined and highly blood‐group active cell surface structure of human origin. As surface structures, blood‐group active substances appear to be frequently endowed with receptor properties in addition to those for blood‐group antibodies.
Heterolytic Fragmentation. A Class of Organic Reactions
Authors: Grob C. A. , Schiess P. W.
Published: December 2003

Heterolytic fragmentation is a widespread but neglected class of organic reactions. It involves the regulated cleavage of molecules containing certain combinations of atoms such as carbon, oxygen, nitrogen, sulfur, phosphorus, silicon, boron and halogens. Fragmentation reactions are useful in degradation and structure elucidation, some are also of preparative value. A knowledge of the structural and electronic requirements makes it possible to predict and influence the course of reactions. From a theoretical viewpoint the recognition of heterolytic fragmentation has lead to the classification and correlation of a large number of apparently diverse reactions. Selected cases are reviewed in this article.
Trifluorophosphine Complexes of Transition Metals
Authors: Kruck Th.
Published: December 2003

The present paper deals with a new class of inorganic coordination compounds, the first member of which, tetrakis(trifluorophosphine)nickel(0), was discovered in 1951. Not only have the neutral metal(0) trifluorophosphines been prepared, but also a number of their derivatives (trifluorophosphinemetal hydrides and trifluorophosphinemetallates, as well as nitrosyl, carbonyl, halogeno, and aromatic trifluorophosphine complexes). These compounds have been characterized by their chemical behavior and by spectroscopic and magnetochemical studies. Trifluorophosphine has the strongest π‐acceptor properties of all neutral ligands, and is therefore particularly suitable for the stabilization of unusually low oxidation states (zero and negative) of transition metals.
Sulfines and Sulfenes – the S‐Oxides and S,S‐Dioxides of Thioaldehydes and Thioketones
Authors: Opitz G.
Published: December 2003

Four sulfines have so far been prepared by elimination of HCl from sulfinyl chlorides with triethylamine and by oxidation of diaryl thioketones with peracid. They are colored, crystalline compounds, which slowly decompose at room temperature. Attempts to prepare sulfenes have not yet been successful, but mesylsulfene[1] has been isolated as the trimethylamine adduct. It can be shown by interception reactions that sulfenes are formed as intermediates by the action of trialkylamines on aliphatic sulfonyl chlorides and by the action of sulfur dioxide on diazoalkanes. They react with ROD to form monodeuterated sulfonates, with diazoalkanes to give three‐membered rings, with enamines, dienamines, ketene O,O,O,N‐, and N,N‐acetals, and chloral, and in some cases with vinyl ethers, to give four‐membered rings. They also react with nitrones to give five‐membered rings, and with β‐aminovinyl ketones and dienamines to give six‐membered rings.
Syntheses of Thiocarbamates
Authors: Walter W. , Bode K.‐D.
Published: December 2003

The methods suitable for the preparation of thiocarbamates are described and illustrated by examples and procedures. They are grouped under the following headings:

Addition of Alcohols and Thiols to Isothiocyanates

Thioacylation of Amines

with chlorothioformates

with O,S‐diesters of dithiocarbonic acid

with trithiocarbonates

Thioacylation of Alcohols, Phenols, and Thiols

with thiocarbamoyl chlorides

with N,N‐dialkylmercaptochloroformimidium chlorides

with N,N′‐thiocarbonyldiimidazole

Reaction of Thiocyanates and Cyanates with Hydrogen Sulfide

Alkylation of Metal Dithiocarbamates

Additions to Thiocyanic Acid
The Solvent Dimethyl Sulfoxide
Authors: Martin D. , Weise A. , Niclas H.‐J.
Published: December 2003

The dipolar aprotic solvent dimethyl sulfoxide is liquid over a wide range of temperatures, is a strong electron donor, and has a high polarity. It is therefore an excellent and selective solvent for many organic and even polymeric compounds, and can enter into H‐bonding and dipole‐dipole association. The structure of dimethyl sulfoxide, with a “hard” oxygen atom and a “soft” sulfur atom, leads to good solvation of cations and poor solvation of anions. Mixtures of alkoxides with dimethyl sulfoxide are therefore among the most strongly basic systems in organic chemistry, and are excellently suited for the deprotonation of weakly acidic OH, NH, and CH bonds, for eliminations, and for the initiation of polymerizations.
Benzene Oxide‐Oxepin Valence Tautomerism
Authors: Vogel E. , Günther H.
Published: December 2003

Benzene oxide and the potential 8π‐electron system oxepin exist in valence‐tautomeric equilibrium with each other, to which both components contribute to approximately the same extent. NMR spectroscopic measurements show that the equilibrium is rapidly established (activation energies of the forward and reverse reactions 9.1 and 7.2 kcal mole−1, respectively). The present knowledge of the properties of oxepin justifies its classification as a “heterotropilidene”. Benzene oxide‐oxepin represents a system having fluctuating bonds, the equilibrium of which can be displaced from one extreme to the other by means of suitable substituents. The oxide component determines the reactions of the system with most agents.

With 1,6‐oxido[10]annulene, which is formally a 2,7‐bridged oxepin, the oxepin character is completely suppressed by the formation of a delocalized 10π‐electron system extending over the C10 perimeter. The existence and aromatic character of 1,6‐oxido[10]‐annulene give rise to the conception of a homologous series of oxygen bridged annulenes (1,6; 8,13‐bisoxido[14]annulene, 1,6; 8,17; 10,15‐trisoxido[18]annulene etc.), which, like the parent acenes, possess a (4n + 2)π‐electron system. Molecular models demonstrate that a considerable flattening of the C4n+2 perimeter is achievable in the case of a syn or all‐syn arrangement of the oxygen bridges, and that the requirement for aromaticity is thus satisfied. This is confirmed in a striking manner by the synthesis and properties of syn‐1,6; 8,13‐bisoxido[14]annulene.
Recent Chemistry of Bullvalene
Authors: Schröder G. , Oth J. F. M.
Published: December 2003

The essential structural element of bullvalene is the homotropilidene system. Thus in any discussion of the chemistry of bullvalene, all bridged homotropilidenes must also be considered. The present article deals with new syntheses and with the thermal behavior of the homotropilidene system and of bullvalene. Emphasis is also placed on the syntheses and the NMR‐spectroscopic behavior of complexed bullvalene, of monosubstituted, disubstituted, and fused bullvalenes, and of some benzobullvalene derivatives.
Separation of the Isotopes of Uranium by the Separation Nozzle Process
Authors: Becker E. W. , Bier K. , Bier W. , Schütte R. , Seidel D.
Published: December 2003

The separation nozzle process is based on the partial spatial separation of components of different mass in an expanding supersonic jet stream. The process is of especial interest for the separation of uranium isotopes. Details of a systematic experimental determination of the most favorable operating conditions for such a separation are given and the construction and testing of a closed circulation system, the basic unit of a ten membered pilot cascade separator for uranium isotope separation, is described. The optimum values of the specific cost factors obtained experimentally for the separation nozzle process are compared with the corresponding values estimated for the gaseous diffusion process.
Siloxane Compounds of the Transition Metals
Authors: Schindler F. , Schmidbaur H.
Published: December 2003

Heterosiloxanes of transition metals contain the characteristic grouping SiOX; in the compounds known so far, X may be Au, Zn, Cd, Hg, Ti, Zr, Hf, V, Nb, Ta, Cr, U, Re, Fe, Co, Ni, or Pt. Most of these compounds are obtained from silanols, metal silanolates, acyloxysilanes, disiloxanes, or alkoxysilanes, i.e. from compounds that already contain an SiO bond. The transition metal may be introduced e.g. as a halide, as an organometailic compound, as an alkoxy compound, or as an oxide. Heterosiloxanes are also formed on reaction of many silicon compounds that do not contain oxygen with transition metal compounds containing oxygen. Some of these compounds, e.g. some titanosiloxanes, are very stable, whereas others decompose explosively. Oligomeric and polymeric heterosiloxanes exist in addition to the monomeric compounds.
Electrochemical Processes for the Enrichment of Isotopes
Authors: Freyer H. D. , Wagener K.
Published: December 2003

The principles of electrochemical methods of isotope separation and the results obtained are described. The migration of ions in salt melts and solutions, complex formation in the homogeneous phase, electrolysis, ion‐exchange equilibria, and exchange electrolysis are discussed in detail.
Mitochondrial Oxidative Phosphorylation
Authors: Schatz G.
Published: December 2003

Mitochondria can form ATP from ADP and inorganic phosphate, the required energy being supplied by respiration. This coupled process, which in sufficiently aerated normal animal cells furnishes the bulk of the cellular ATP, is termed oxidative phosphorylation. The overall reaction is intimately associated with the mitochondrial inner membrane and proceeds via a primary high‐energy intermediate. This intermediate, in a manner as yet unknown, energizes the anhydride formation between ADP and inorganic phosphate. The coupling between respiration and ATP synthesis is mediated by proteins of the mitochondrial inner membrane which are known as “coupling factors”. The mechanism of oxidative phosphorylation is at present being discussed in terms of three hypotheses which are generally referred to as “chemical”, “chemiosmotic”, and “conformational” hypotheses. None of these hypotheses has as yet been experimentally verified.
Circular Dichroism and Optical Rotatory Dispersion — Principles and Application to the Investigation of the Stereochemistry of Natural Products
Authors: Snatzke G.
Published: December 2003

The principles of circular dichroism and of optical rotatory dispersion are described. Examples are given to illustrate the use of these methods for the determination of the configurations and conformations of natural and synthetic products. Some limitations of the octant rule are mentioned.
α‐Lactams (Aziridinones)
Authors: Lengyel I. , Sheehan J. C.
Published: December 2003

α‐Lactams have often been postulated as intermediates in numerous processes. The isolation of the first α‐lactam, N‐tert‐butyl‐3‐phenylaziridinone, was accomplished in 1962. Since then, further N‐ and C‐3‐substituted α‐lactams have been synthesized. Most of these very reactive compounds undergo easy thermal decomposition; remarkable is the relative stability of 1,3‐di‐tert‐butylaziridinone, which does not start to decompose below 140°C. The α‐lactam ring is opened by nucleophilic reagents. — The correlation of stability and substituents is discussed in the last section. An acyclic, planar or almost planar, charge‐delocalized intermediate is suggested to explain the observed effects.
The Cool Flames of Hydrocarbons
Authors: Fish A.
Published: December 2003

This review describes the properties of the cool‐flame and two‐stage ignition processes that characterize the gaseous oxidation of hydrocarbons and discusses the chemical reactions that are responsible for these phenomena. Cool flames result from a chainthermal acceleration of reaction rate. It is probable that the free‐radical chain involved is propagated by the reaction of an alkyl radical with oxygen to give an alkyperoxy radical which isomerizes to a hydroperoxyalkyl radical. The decomposition of this radical produces a hydroxyl radical, which attacks the hydrocarbon rapidly and unselectively to regenerate an alkyl radical. Branching probably results from the pyrolysis of mono‐ and dihydroperoxides, from the oxidation of aldehydes, and from radical‐molecule reactions. This reaction scheme explains the existence of a low‐temperature ignition peninsula and the relation of the extent and shape of this peninsula to the molecular structure of the hydrocarbon. The chemical relevance of cool flames to abnormal combustion phenomena, such as knock, in gasoline engines is discussed.
The Structure and the Function of Gangliosides
Authors: Wiegandt H.
Published: December 2003

Gangliosides are found in the brain and other organs, and are composed of sphingosine, fatty acids, hexoses, and sialic acid. Types of gangliosides differ in the fatty acids and the sugar residues. The carbohydrate residue in the quantitatively predominating brain gangliosides is ganglio‐N‐tetraose, a tetrasaccharide. In these gangliosides, this residue combines with one or more molecules of sialic acid. The oligosaccharide part is a carrier of serologic properties. Gangliosides are characteristic lipid components of some neuronal membranes in the central nervous system, and can be localized on the synaptic apparatus of nerve cells in the cerebral cortex. Their site of occurrence and physiological action point to their participation in the transmission of impulses. It was in the brains of the mentally ill that gangliosides were first discoverd, and indeed their pathologic accumulation can possibly be attributed to congenital defect of enzymes involved in their synthesis or metabolism. Gangliosides are produced from their components by acceptor‐specific transferases.
Recent Results in the Field of Liquid Crystals
Authors: Saupe A.
Published: December 2003

Thermotropic mesomorphous phases such as occur in the melts of many organic substances are considered. Though mesomorphous melts were first observed by Reinitzer in 1888, fundamental structural problems regarding such melts have not, as yet, been completely solved. Part I of this article deals mainly with such structural problems and with the theories of crystalline organic liquids. Part II describes the use of nematic solvents for magnetic resonance studies on oriented molecules. Examples are given to illustrate the possibilities offered by this procedure, and some of the results obtained so far are reviewed.
The Degradation of Poly(ethylene terephthalate)
Authors: Buxbaum L. H.
Published: December 2003

The penetration of new markets by polyester fibers has emphasized the need for increased stability of the polyester toward a variety of degradative reactions. Extensive studies of the nature of the thermal, hydrolytic, oxidative, and radiation‐induced degradation reactions have been reported. The interpretation of kinetic investigations and the identification of the reaction products have been facilitated by using suitable esters as model compounds in place of the polymeric species.
Formation and Properties of Solvated Electrons
Authors: Schindewolf U.
Published: December 2003

In the formulation of many chemical reactions, electrons are regarded as readily transferable particles, though their participation in these reactions cannot be directly observed. However, the discovery that electrons can be produced in various ways in suitable solutions and that they are stabilized by solvation and can thus be studied directly has recently led to a rapid growth of interest in these, the simplest and most reactive particles of chemistry. The solvated electron has physical properties that permit its detection by various methods even at very low concentrations, so that it is also possible to follow its many reactions, most of which are extremely fast.
“Bicarburet of Hydrogen”. Reappraisal of the Discovery of Benzene in 1825 with the Analytical Methods of 1968
Authors: Kaiser R.
Published: December 2003

The historical background and the admirable analytical procedure that led Michael Faraday to the discovery of benzene in 1825 are discussed. Using modern techniques of instrumental analysis, the author retraces the isolation and analysis of benzene, and shows that the starting material used by Faraday must have been a very complex mixture of hydrocarbons, which would make severe demands even on present‐day preparative analytical techniques, since it contains more than 300 components at concentrations greater than 100 ppm. The magnitude of the changes in analytical techniques can be seen from the fact that it is no longer necessary to isolate individual compounds, and that a great deal of information can be obtained with a much smaller quantity of material and in a much shorter time. Nevertheless, Faraday's persistence, experimental skill, and accuracy of measurement remain an example to the analyst of today.
The Biosynthesis of Aromatic Amino Acids and its Regulation
Authors: Lingens F.
Published: December 2003

Microorganisms synthesize the aromatic amino acids phenylalanine, tyrosine, and tryptophan, as well as the related compounds p‐aminobenzoic acid, tetrahydrofolic acid, p‐hydroxybenzoic acid, ubiquinone, vitamin K, and nicotinic acid, by a highly branched route passing through shikimic acid. The biosynthesis is not regulated in the same way in all the organisms studied. The regulation is strongly dependent on the ability of the enzymes involved to be resolved into isozymes, their ability to be inhibited, and their activation, repression, and induction.
Soot Formation in Premixed Hydrocarbon Flames
Authors: Homann K. H.
Published: December 2003

The critical fuel‐oxygen ratio for soot formation and its dependence on temperature and pressure are discussed for various hydrocarbons. It is shown in the case of the Bunsen flame that the shape and structure of the flame front also have a decisive effect on soot formation. In the reaction zone of fuel‐rich hydrocarbon flames, unsaturated compounds are formed, and the concentration profiles of these products can provide quantitative information about their importance in soot formation. The “mechanism” of soot formation is discussed on the basis of the concentrations of higher hydrocarbons and the variation of the number and size of the soot particles. The effects of electric fields and foreign additives on soot formation have been given consideration.
SE(P): Electrophilic Substitution at Phosphorus
Authors: Warren S. G.
Published: December 2003

Reactions belonging to the formal category of electrophilic substitutions at phosphorus are classified according to mechanism and the coordination number of the phosphorus atom.
Antibiotics as Inhibitors of Nucleic Acid and Protein Synthesis
Authors: Hartmann G. , Behr W. , Beissner K.‐A. , Honikel K. , Sippel A.
Published: December 2003

The antibiotics of the rifamycin, actinomycin, chromomycin, and anthracycline groups have been found to be specific inhibitors for the DNA‐controlled synthesis of RNA in vitro. Streptomycin, chloramphenicol, and puromycin can specifically suppress certain steps in the biosynthesis of proteins. The investigation of the mode of action of such substances may help us to gain a better insight into the transmission of hereditary information.
Memory Effects and Stereochemistry in Multiple Carbonium Ion Rearrangements
Authors: Berson J. A.
Published: December 2003

The stereochemical configuration at the initial site of heterolysis in a carbonium ion process in solution controls the specificity of migration two steps later in many sequential multiple rearrangements. These “memory effects” are attributable to the presence on the potential energy surface of small, hitherto undetectable minima. A variety of structural, stereochemical, and isotopic marking techniques are used to demonstrate that memory effects are a general feature of the ring‐expansion route to bicyclic carbonium ions. The intermediates formed in these reactions, although necessarily symmetrical or quasi‐symmetrical at equilibrium, act unsymmetrically. The memory effect uses the rate of an intramolecular carbonium ion rearrangement as a calibration with which to compare the rate of symmetrization. In this way, the system functions as a sensor of sub‐species.
Dehydration of Alcohols on Aluminum Oxide
Authors: Knözinger H.
Published: December 2003

The dehydration of alcohols on γ‐aluminum oxide, which yields water, olefins, and/or ethers, was studied with the aid of kinetic methods and IR spectroscopy. The unimolecular olefin formation probably proceeds via a surface compound, in which an alcohol molecule is joined by two angular H‐bonds to an OH group and an oxygen ion on the surface. The ether formation (bimolecular reaction), on the other hand, requires OH groups and oxygen and aluminum ions on the surface. The ether is formed from a surface alkoxide group and molecularly adsorbed alcohol.
Olefin Alkylation in Biosynthesis
Authors: Cornforth J. W.
Published: December 2003

Stereochemical studies, made possible by asymmetric labeling with hydrogen isotopes, have led to the hypothesis that enzymic association of C5 units in polysoprenoid synthesis is not a concerted process but proceeds in two steps: a trans 1,2‐addition to an olefin followed by a trans 1,2‐elimination. It is shown that similar mechanisms can also explain the cyclization of squalene epoxide to tetracyclic and pentacyclic triterpenoids.
Crystallization during Polymerization
Authors: Wunderlich B.
Published: December 2003

Simultaneous as well as successive polymerization and crystallization is possible. While crystallization after polymerization usually produces folded chain lamellar crystals, crystallzation during polymerization frequently produces fibrillar extended chain crystals.
Planar Complexes Containing Metal‐Metal Bonds
Authors: Krogmann K.
Published: December 2003

Planar complexes, and particularly those of platinum, can form structures containing linear chains of heavy metal atoms with metal‐metal distances as short as 3.1 Å. The bonding in these chains can be strengthened by partial oxidation, and the bond lengths can be reduced to 2.8 Å in this way. Model structures for the novel nonstoichiometric products, such as K2[Pt(CN)4]Cl0·32 · 2.6 H2O, are considered. The bonding is also discussed on the basis of a one‐dimensional band model.
Catalase and Peroxidase Activity of Cu2+ Complexes
Authors: Sigel H.
Published: December 2003

The relation between the structure of Cu2+ complexes and their catalytic activity in the decomposition of H2O2 can be used as a “molecular probe”, since it allows the deduction of the number of coordinated ligand groups in a Cu2+ complex from its catalytic activity. Since only coordinated ligand groups are oxidized by H2O2, further information about the coordination sphere of the metal ion can be obtained from the oxidation of certain parts of a ligand, which can be followed spectrophotometrically. The Cu2+ complexes of amides, polyamino acids, nucleotides, RNA, and native and denatured DNA have been investigated in this way. Kinetic studies provide an insight into the mechanisms of catalase and peroxidase reactions.
Electrochromism and Solvatochromism
Authors: Liptay W.
Published: December 2003

The position and the intensity of electronic bands are influenced by an electric field. Pronounced changes in the position of absorption bands are mainly due to the dipole moment of the molecule in the ground state and the change in the dipole moment during the excitation process, and pronounced changes in intensity are due to the field dependence of the transition moment, which can be described by the transition polarizability. The effect of an external electric field on the optical absorption (electrochromism) of suitable molecules can be used to determine the dipole moment in the ground state, the change in dipole moment during the excitation process, the direction of the transition moment of the electronic band, and certain components of the transition polarizability tensor. These data largely determine the strong solvatochromism (solvent‐dependence of the position and intensity of electronic bands), which is observed in particular with molecules having large dipole moments. Smaller contributions to solvatochromism result from dispersion interactions, which predominate in the case of nonpolar molecules. The models developed have been experimentally checked and verified by a combination of electro‐optical absorption measurements (influence of an external electric field on absorption) and investigation of the solvent‐dependence of the electronic bands.
Cycloadditions with Polar Intermediates
Authors: Gompper R.
Published: December 2003

A discussion of the criteria that have been used to distinguish experimentally between one‐step and two‐step cycloadditions shows that in most cases useful information can be obtained only by isolation or interception of intermediates; the isolation of intermediates is also of preparative importance.
The Synthesis of Rare Sugars
Authors: Brimacombe J. S.
Published: December 2003

The use of new oxidation reagents, such as the Pfitzner‐Moffatt reagent, dimethyl sulfoxide‐acid anhydrides, and ruthenium tetroxide, has significantly improved the yields obtained on oxidation of a secondary hydroxyl group to a carbonyl group in suitably protected sugars. The application of these new oxidants in the carbohydrate field is briefly surveyed. The product ketones are convenient intermediates for syntheses of amino, branched‐chain, deoxy, and other rare sugars. Some representative syntheses are illustrated.
Sigma‐Pi Rearrangements of Organotransition Metal Compounds
Authors: Tsutsui M. , Hancock M. , Ariyoshi J. , Levy M. N.
Published: December 2003

σ‐Bonded organic groups in transition‐metal complexes can rearrange to π‐bonding ligands and vice versa: the classic example is the formation of π‐arenechromium complexes from σ‐arylchromium compounds. Rearrangements of this kind can be induced, inter alia, by reactions of the metal or of the ligand, as well as by migration or insertion of a ligand. Rearrangements play a role in many industrial processes, including the polymerization and isomerization of olefins and the hydroformylation of olefins.
Synthesis of Alkynes from Enol Esters
Authors: Craig J. Cymerman , Bergenthal M. D. , Fleming I. , Harley‐Mason J.
Published: December 2003

Eliminations leading from enol sulfonates, enol phosphates, and enol phosphonium salts to alkynes are reviewed. Olefin eliminations are usually the rate‐determining step in the formation of the triple bond. Enol esters may also play a role in the biosynthesis of alkynes.
Hydration Structure and Intermolecular Interaction in Polyelectrolytes
Authors: Zundel G.
Published: December 2003

In hydration, the intermolecular interaction is of decisive importance, since the ions modify the properties of the hydration water molecules, and the water molecules in turn have a strong influence on the interaction between the ions. These processes can be studied in detail with the aid of IR spectroscopy, which in addition provides a picture of the hydration structure. IR spectroscopy also shows that the excess protons are in energy bands and allows the detection of the proton dispersion forces acting between tunneling protons. The results of IR studies on polyelectrolytes contribute to our understanding of the many biological processes that depend on the behavior of ions.
Antioxidants
Authors: Mahoney L. R.
Published: December 2003

The free radical initiated liquid phase oxidation of hydrocarbons is inhibited by phenols and aromatic amines. In the present article the recent results of kinetic and thermodynamic studies of the inhibition are discussed.
Determination of the Structures of Organic Molecules and Quantitative Analyses with the Field Ionization Mass Spectrometer
Authors: Beckey H. D.
Published: December 2003

Field ionization and electron impact mass spectrometry complement each other well. Whereas bombardment of organic molecules with 70 eV electrons yields many characteristic fragment ions, which give valuable information about the structure of the molecules, the “soft” field ionization even of very unstable substances leads to the formation of relatively intense molecular ions which are often undetectable on ionization by electron bombardment. Field ionization also gives fragment ions that, though not very intense, are often very characteristic, and yield further information about the structure. The field desorption technique greatly reduces the degree of thermal decomposition of solid organic samples.

New activation methods for field ion emitters lead to more intense ion beams and prolong the life of the emitters. Quantitative analyses using the field ionization mass spectrometer are of interest for hydrocarbon mixtures containing a very large number of components (e.g. several hundred). Simplified analyses are possible in particular for high‐boiling petroleum fractions.
Phosphorus. From Elemental Light to Chemical Element
Authors: Krafft F.
Published: December 2003

Exactly 300 years ago in the city of Hamburg, a certain Hennig Brand, self‐styled doctor medicinae, and chymist, discovered a strange substance in human urine, which was later called phosphorus (light bearer), a name then common to various luminous substances, and which created much excitement in the latter years of the 17th century on account of its properties. However, it was not Brand who profited from the discovery but others: Johann Daniel Krafft, Johann Kunckel, and Gottfried Wilhelm Leibniz, men who knew only too well how to exploit the weaknesses of the discoverer. “Cold fire”, Brand's own name for the new substance, was originally regarded as elemental light or fire, and it was not until the conception of the antiphlogistic theory by Antoine Laurent Lavoisier that the proper position of phosphorus among the chemical elements was recognized. In fact, the element played a decisive role in the overthrow of the phlogiston doctrine, a little over one hundred years after its discovery and almost two hundred years ago.
Classification of Partition Reactions of Inorganic Cations
Authors: Specker H. , Kettrup A.
Published: December 2003

In partition reactions of inorganic cations, it is necessary to establish the composition of the extracted compounds. The methods used and the limits of their application are described and illustrated for the extraction of cobalt thiocyanates. The results obtained allow new analytical applications, e.g. the fractional extraction of Hg, Bi, Cd, In, and Zn.
Organogermyl, Organostannyl, and Organoplumbyl Phosphines, Arsines, Stibines, and Bismuthines
Authors: Schumann H.
Published: December 2003

The preparation, properties, and reactions of the compounds named in the title are described, with particular reference to the possible participation of (p→d)π components in the bonding between the group IVB and the group VB elements.
Crystal Structure Analysis by Neutron Diffraction II
Authors: Will G.
Published: December 2003

This second part of the article “Crystal Structure Analysis by Neutron Diffraction” deals with the diffraction of neutrons by magnetically ordered crystals. Neutron diffraction is at present the only reliable method for the determination of the magnitude, direction, and spatial distribution of magnetic moments in crystalline substances. Since the magnetic moments are essentially due to the unpaired electrons, the distribution of these electrons in the crystal can be measured in this way.
The Defensive Chemistry of Land and Water Beetles
Authors: Schildknecht H.
Published: December 2003

Wherever life forms have arisen, they have had to defend themselves, even on the lowest levels, against their own kind. Darwin called this the struggle for life. The following discussion shows that this struggle can be carried on chemically with compounds of widely differing classes. Examples of defensive substances found are hot quinones in bombardier beetles, and weak and strong carboxylic acids, phenols, terpenes, steroids, and alkaloids in other Adephaga.
From Planck to Bohr
Authors: Hermann Armin
Published: December 2003

The quantum theory, which is nowadays a fundamental basis of chemistry that is regarded as self‐evident, initially presented immense difficulties to human thought. An insight into many particulars of its fascinating evolution is provided by the correspondence of those involved in the development of the theory between 1899 and 1913, which has now been thoroughly sifted for the first time by the author.
Energy Production in Anaerobic Organisms
Authors: Decker K. , Jungermann K. , Thauer R. K.
Published: December 2003

Biological redox processes are required for the synthesis of “energy‐rich” compounds which are in an enzyme‐controlled equilibrium with the general energy carrier adenosine triphosphate (ATP). The basic mechanisms of biological energy transformation are substrate level (SLP) and electron transport phosphorylations (ETP). In anaerobic catabolism the numerous nutrients are channelled into only a few substrate level phosphorylations; the occurrence in chemotrophic anaerobes of energy conservation coupled to electron transport has not yet been demonstrated unequivocally. At present, the determination of the ATP turnover (YATP) in growing cells appears to be a promising method of approaching this problem. The existing knowledge of oxygen dependent enzyme reactions and their molecular evolution provides the basis for a biochemical definition of aerobic and anaerobic organisms.
Detection of Hindered Rotation and Inversion by NMR Spectroscopy
Authors: Kessler Horst
Published: December 2003

Rotations and inversions in organic molecules are readily recognizable from the temperature dependence of the NMR spectra. The study of the effects of substituents on the activation barriers of such processes permits the elucidation of reaction mechanisms, and the stability limits of isomers can also be determined. The knowledge of the stability limits is necessary for the specific synthesis of stable rotamers and invertomers.
Cooperative Conformational Transitions of Linear Biopolymers
Authors: Engel Jürgen , Schwarz Gerhard
Published: December 2003

Conformational transitions in proteins, nucleic acids, and other biopolymers evidently play a decisive role in many biological processes, particularly in control processes. They often proceed cooperatively, i.e. the elementary process of the transition of an individual segment of these macromolecules in influenced by the state of other segments via intramolecular interactions. In general, the segments favor the same state as their neighbours. The resulting equilibrium properties of cooperative systems, e.g. the sharpness of the transitions and their dependence on the chain length, can be quantitatively explained for linear systems by the linear Ising model. The molecular causes of the cooperativity can be explained for simple model polymers.
New Forms of Carbon
Authors: Vohler Otto , Reiser Peter‐Ludwig , Martina Renato , Overhoff Dieter
Published: December 2003

A number of novel carbon materials whose unique properties fit them for many uses have recently been developed. Pyrolytic graphites are excellent conductors of heat and electricity parallel to the surface, whereas they are semiconductors perpendicular to the surface. A similar anisotropy is found in graphite foils, which are impermeable, but also very flexible. Glasslike carbon, which is also impermeable, is, however, completely isotropic. Carbon foams and felts are extremely light and exhibit very good thermal insulation up to high temperatures. In addition to very high strength, carbon fibers have values of Young's modulus greater than that of any other fibers or wires. Carbon fiber/resin composites are therefore more rigid than any other known materials; their specific Young's modulus is five times that of steel.
Ion‐Selective Sensors
Authors: Simon Wilhelm , Wuhrmann Hans‐Rudolf , Vašák Milan , Pioda Lavinia A. R. , Dohner René , Štefanac Zlata
Published: December 2003

Numerous advances have recently been made in the development of ion‐selective (glass, solid, liquid) membrane electrode systems. The theoretical principles and practical requirements of such “sensors” are outlined in this article, and an attempt is made to review their possible applications.
Polarity of Covalent Bonds
Authors: Klessinger Martin
Published: December 2003

The concept of “partial ionic character” has proved exceedingly valuable and fruitful as a qualitative description of the electronic structure of molecules; however, the theoretical ideas underlying the empirical relations for the determination of the ionic character of a bond do not bear critical examination. Even Mulliken's population analysis fails in many cases as a means of interpreting quantum‐chemical calculations. On the other hand, a graphical representation of the spatial charge density distribution allows an intuitive interpretation even of complicated calculations, and (possibly in combination with an analysis of the forces acting on the atomic nuclei) yields very much farther‐reaching information on the polarity of a bond than can be expressed by the values of some parameters on the basis of excessively simplified models.
Recent Results on the Biochemistry of the Cell Wall Lipopolysaccharides of Salmonella Bacteria
Authors: Lüderitz Otto
Published: December 2003

Lipopolysaccharides, which are located in the cell wall of gram‐negative bacteria, are characterized by their biological versatility. They represent the O antigens of the bacteria, they are potent endotoxins, and they often function as the receptor sites for bacteriophages. The study of the mode of action of lipopolysaccharides and the search for structures in the macromolecules that are responsible for biological activity became promising when principles of the chemical fine structure of lipopolysaccharides were identified. The following review summarizes the results of recent investigations regarding the structure of lipopolysaccharides, their biosynthesis and its genetic determination.
Gel Chromatography
Authors: Heitz Walter
Published: December 2003

Gel chromatography can be regarded as a network‐limited partitioning of substances. The theory of this method and the preparation and properties of various gel systems are reviewed. Optimization of the method is illustrated for the separation of oligomers.
Chemistry and Logical Structures
Authors: Ugi Ivar , Marquarding Dieter , Klusacek Hans , Gokel George , Gillespie Paul
Published: December 2003

The utility of the basic structures of modern mathematics for chemistry is discussed; general set theory, topology, and group theory are shown to pervade almost all static and dynamic aspects of chemistry. Chemical analogy, the systematic classification of molecules and a corresponding nomenclature system, conformational transformations, polyhedral rearrangements, and the relations between starting materials, transition complexes, and final products of chemical reactions are examples of where we apply the elements of modern mathematics to the solution of chemical problems.
Degenerate Carbonium Ions
Authors: Leone Ronald E. , von R. Schleyer Paul
Published: December 2003

Carbonium ions are called “degenerate” when they rearrange through finite energy barriers to give products whose gross structures are identical with those of the starting ions. In such degenerate rearrangements (“automerizations”), individual atoms and groups become mixed but the overall structure is conserved. Automerizations can be observed by noting the dispersal of isotopic labels, the loss of optical activity, or the temperature dependence of NMR spectra. In certain cases, a combination of well‐known rearrangement processes results in complete mixing of all atoms, C or H. The 2‐norbornyl and 9‐barbaralyl cations are examples of fully degenerate systems; conditions can be found where both give but single‐line NMR spectra.
Valence Isomerism in Selected Heterocyclic Systems
Authors: Paquette Leo A.
Published: December 2003

Valence isomerization and the phenomenologically related principle of valence tautomerism, as they apply to several nitrogen‐containing heterocyclic systems, are discussed herein. Attention is called first to 1H‐azepines and the reluctance of such substances to isomerize to azanorcaradienes. The role of homo‐1H‐azepines in this context is then briefly outlined. Azocines (azacyclooctatetraenes) are seen to occupy an interesting position in the sense that pronounced shifts in the position of equilibrium (from almost entirely monocyclic to virtually completely bicyclic) occur with substitutional alterations of various types. The capability of azabullvalenes for degenerate valence isomerization is the next presented, and contrast is made with the properties of benzazabullvalenes and an azasemibullvalene derivative.
Radical Anion Intermediates in Organic Chemistry
Authors: Holy N. L. , Marcum J. D.
Published: December 2003

Radical anions are reactive intermediates in a variety of organic reactions. They make possible several unique synthetic conversions and provide an opportunity for investigating structural relationships. Examples of such reactions are given and current mechanistic views are discussed.
Biogenic Substances in Sediments and Fossils
Authors: Albrecht Pierre , Ourisson Guy
Published: December 2003

Most sedimentary rocks contain small concentrations of finely divided organic material. With the aid of modern analytical methods, samples of such rocks can be examined in detail, and conclusions can be drawn concerning the origin of the organic substances. Intact or modified biogenic compounds such as paraffins, isoprenoids, alcohols, ketones, carboxylic acids, steroids, triterpenes, and porphyrins have been isolated from the soluble fractions of the organic material of many sediments and from identified fossils of various geological ages. Even Precambrian rocks contain biogenic substances, so that life forms must have existed more than three billion years ago. The main component of the organic material is “kerogen”, the complicated polymeric structure of which has not yet been established.