bluuebunny/crossref_metadata_2025 huggingface dataset:
Force Constants and Bond Orders of Nitrogen Bonds
Authors: Goubeau J.
Published: December 2003

The force constants and the corresponding bond orders of nitrogen bonds have been calculated from the vibrational spectra (infrared and Raman spectra) of a great number of nitrogen compounds. Plotting the maximum bond order of stable nitrogen bonds against the sum of Pauling's electronegativities of the bonding partners (Σx) leads to one continuous curve for the NX bonds where X represents elements of the first and the second short period of the periodic table. Furthermore, when the bonds formed between these elements are arranged in a coordinate system in such a way that the position of each bond is determined by the difference between the electronegativities of the bonding partners (Δx along the ordinate) and the sum of the electronegativities of the bonding partners (Σx along the abscissa), the bonding partners capable of forming multiple bonds all lie within a closed domain, where their position can be correlated with their polymerizability and other reactivities of the multiple bonds. Also discussed are the orders of bonds between nitrogen and some transition elements. In an appendix, the present methods used to calculate force constants and bond orders are surveyed.
Acrylonitrile from Propylene, Ammonia, and Atmospheric Oxygen
Authors: Schönbeck R. , König H. , Krzemicki K. , Kahofer L.
Published: December 2003

Acrylonitrile was produced in pilot plant from propylene, ammonia, and atmospheric oxygen in a fixed‐bed reactor in the presence of Bi/Mo/Si oxide shell catalyst. The propylene conversion, which can amount to about 70% under optimal conditions, was studied as a function of structural properties and the chemical composition of the catalyst, and of the composition of the starting mixture. Acrylonitrile of adequate purity for use in polymerizations could be obtained by multi‐stage processing of the crude product.
Aryl‐Δ2‐pyrazolines as Optical Brighteners
Authors: Wagner Annemarie , Schellhammer C.‐W. , Petersen S.
Published: December 2003

Di‐ and triaryl‐Δ2‐pyrazolines and their derivatives can be used as optical brighteners for synthetic fibers and plastics. The heterocycles are readily obtainable by several methods, e.g. condensation of β‐halogeno‐ or β‐dialkylaminopropiophenones with phenylhydrazine. A number of relationships can be detected between substitution and optical properties.
The Hormonal System of Plants
Authors: Linser H.
Published: December 2003

Higher plants generate active substances, termed phytohormones, having the character of tissue hormones. Some of these compounds have been isolated and identified, namely ethylene, heteroauxins, and gibberellic acids. Cell‐elongation inhibitors have been detected, but not yet isolated or identified. Natural and synthetic substances with hormone‐analogous effects and those with a hormone‐antagonistic effect have become known; evidently, they act on the hormonal system of plants which regulates growth, differentiation, and development and can serve as model substances for as yet unknown phytohormones. Certain physiological phenomena suggest the existence of additional phytohormones.
Complex Formation and Flower Colors
Authors: Bayer Ernst , Egeter H. , Fink A. , Nether K. , Wegmann K.
Published: December 2003

The pigment of the blue cornflower, protocyanin, is a complex of high molecular weight. Iron(III) and aluminum ions combine with the anhydro base of the cyanin to form deep‐blue complexes, which are stable in the physiological pH range. Complexes of this type also have been synthesized. Alkali metal salts play no part in blue flower pigments. Formation of blue complexes can be prevented by sequestration of the metal ions with stronger complexing agents, e.g. flavonols. The variation of flower colors can be explained to a large extent on the basis of the complex formation of anthocyanins. In delphinidin glycosides, the color base or anhydro base is stable even in slightly acidic media.
Evolutionary Aspects of the Structure of Proteins
Authors: Acher R.
Published: December 2003

The evolution of protein structures is discussed using cytochrome c, hemoglobin, and neurohypophyseal hormones as examples. Although these substances have different biological functions, their evolution is controlled by the same general rules: their primary structures vary at the level of the species, order, or class, but this variation is restricted by the fact that the biological activity of the protein must not be impaired. Alterations (i.e. substitutions, deletions, or additions of amino acid residues) can therefore occur only in certain positions of the peptide chains, although with different frequencies. The total number of alterations thus represents only the final state of a protein and does not take into account successive substitutions which may have taken place at the affected sites. It can therefore give only a rough indication of the phylogenetic distance between two species. The nature of the substituting residues, on the other hand, is a useful guide to zoological cognateness, since it allows the identification of transition molecules which simultaneously contain amino acid residues from the protein of the protein of the evolutionary ancestor and from the protein of the evolutionary descendant.
A New Group of Antischistosomal Compounds
Authors: Schmidt Paul , Wilhelm Max
Published: December 2003

A number of compounds containing the 5‐nitro‐2‐thiazolyl group are suitable for the treatment of schistosomiasis; 1‐(5‐nitro‐2‐thiazolyl)‐2‐imidazolidinone is particularly effective. The compounds are taken up selectively by the schistosomes causing the disease and by their eggs, and destroy both. – A review of earlier attempts to control this tropical disease is also presented in this communication.
Recent Syntheses and Reactions of Cyclic Imidic Esters
Authors: Seeliger W. , Aufderhaar E. , Diepers W. , Feinauer R. , Nehring R. , Thier W. , Hellmann H.
Published: December 2003

Δ2‐Oxazolines and 4H‐5,6‐dihydrooxazines are readily obtainable from carboxylic acids and 2‐ or 3‐amino alcohols by gas‐phase dehydration, and 4H‐dihydrooxazines can also be obtained by condensation of N‐(hydroxymethyl) carboxamides with olefins. These cyclic imidic esters undergo reactions in which the ring is cleaved; these reactions include a new type of polymerization. The behavior of alkyl groups in position 2 and the cyclodditions in the 2,3‐position also have been studied. Reactions in side chains on position 2 and addition experiments on the sulfur analogues of the cyclic imidic esters are also reported. A table shows the principal infrared bands of substituted Δ2‐oxazolines.
Syntheses and Derivatives of Squaric Acid
Authors: Maahs G. , Hegenberg P.
Published: December 2003

Squaric acid (dihydroxycyclobutenedione), the dianion of which may be regarded as a novel aromatic system, has recently become readily accessible by simple syntheses. The acidic character of squaric acid manifests itself in the formation of salts and of lower alkyl esters, which can be converted into the amides. Squaric acid dichloride shows in its reactions typical acyl chloride behavior. Condensation of squaric acid with pyrrole, phenol, and azulene derivatives yields cyclotrimethine dyes.
Progress in the Chemistry of Allene
Authors: Griesbaum K.
Published: December 2003

Considerable progress has been made in the past decade in the preparation and chemistry of allene. The present article is a critical review of this progress, and shows that owing to the particular structure of allene (two double bonds situated in mutually perpendicular planes), the chemistry of this compound is unique in many respects.
Spin Density Distribution in 2,4,6‐Triphenylphenoxyl
Authors: Dimroth K. , Berndt A. , Bär F. , Schweig A. , Volland R.
Published: December 2003

The distribution of the unpaired electron over the oxygen and the 24 carbon atoms in the free 2,4,6‐triphenylphenoxy radical was determined by electron spin resonance spectroscopy and quantum‐mechanical approximation methods. The hyperfine splitting was evaluated with the aid of the spectra of triphenylphenoxyls deuterated in some or all of the substituent phenyl groups. The results of the quantum‐mechanical approximations were checked by recording the ESR spectra of triphenylphenoxyls labeled with 13C in positions 1,2,3, or 4 of the central ring. The spin density distribution permits a first discussion of the 17O‐coupling constants of correspondingly labeled triphenylphenoxyl and other organic free radicals.
Chemistry of Stable α‐Halogenoorganolithium Compounds and the Mechanism of Carbenoid Reactions
Authors: Köbrich G. , Akhtar A. , Ansari F. , Breckoff W. E. , Büttner H. , Drischel W. , Fischer R. H. , Flory K. , Fröhlich H. , Goyert W. , Heinemann H. , Hornke I. , Merkle H. R. , Trapp H. , Zündorf W.
Published: December 2003

Some years ago we found that α‐halogenoorganolithium compounds (carbenoids) previously postulated as transient intermediates in organolithium‐initiated α‐eliminations can be obtained in a stable form. The present paper is a review of the methods for their preparation and of their reactivity. They possess both nucleophilic and electrophilic properties, which can be utilized singly or combained for the synthesis of substances of very different types. Their thermolability, which is considerably reduced (with only one known exception) by the solvent tetrahydrofuran, is due to electrophilic secondary reactions, in which carbenes evidently do not occur as intermediates. A mechanism is proposed which fits the experimental data for various carbenoid reactions.
Chemistry of the Incandescent Lamp
Authors: Rabenau A.
Published: December 2003

Halogen lamps have been on the market for some time; they are replacing the conventional lamp in many fields except general service (domestic) applications. Their relatively small bulbs contain small amounts of halogen is addition to an inert gas. The mode of action of the iodine lamp, which depends on the presence of traces of oxypgen, has been elucidated. Tungsten evaporating from the filament is returned to it by a cyclic process involving a tungsten oxide and WO2I2. No tungsten is ever deposited on the bulb wall of such a lamp. A regenerative cycle in which the vaporized tungsten is deposited on the hottest (and hence most vulnerable) parts of the filament can, in principle, be realized by the use of fluorine compounds.
Chemical Effects of Nuclear Transformations in Solids
Authors: Müller Horst
Published: December 2003

Nuclear reactions and radioactive transformations offer the possibility of investigating the chemical reactions of “bare” nuclei. The interest in such chemical processes following nuclear transformations has already led to two international symposia[1,2]. In solids, the chemical reactions of recoil nuclei having energies lower than 1 keV proceed not via molten states, but via regions of little disorder.
Hydrophobic Interactions
Authors: Némethy G.
Published: December 2003

Recent advances in theoretical and experimental studies of hydrophobic interactions are reviewed. The theory of water structure as applied to hydrophobic bonding, theoretical estimates for the free energy of unfolding of proteins, and the statistical mechanical theory of hydrophobic bonding in polyamino acids are summarized. Experimental estimates of the thermodynamic parameters of the hydrophobic bond can be obtained from solubility and dimerization data of low molecular weight compounds. Recent studies of the interaction of proteins with nonpolar solutes are discussed. Hydrophobic bonds can also be important in various other kinds of interactions involving proteins. The observed effect of urea is mentioned, although no theoretical interpretation of this effect is available yet. In conclusion the methods available for the detection of hydrophobic interactions are reviewed.
Synthesis and Reactions of Cyanic Esters
Authors: Grigat E. , Pütter R.
Published: December 2003

In 1963, it was found that sterically unhindered esters of cyanic acid, which had previously been considered unobtainable, could be easily prepared from phenols and cyanogen halides. Another synthesis, involving the thermolysis of thiatriazole derivatives, was discovered in 1964. The aryl cyanates in particular have since been found to have many uses as starting materials for the preparation of numerous new classes of compounds [e.g. derivatives of esters of imidocarbonic acid (esters, amides, imides, hydrazides, hydroxylamides, sulfamides, sulfhydrazides, semicarbazides); esters of imidocarboxylic acids; s‐triazines, pyrimidines, tetrazoles, triazoles, triazolones, oxadiazoles, thiadiazoles, benzoxazinones, etc.], mainly by addition of nucleophilic or 1,3‐dipolar reactants, or as aids e.g. in the elimination of H2O or H2S or in the transfer of CN groups.
The Action of Carbon Disulfide and Sulfur on Enamines, Ketimines, and CH Acids
Authors: Mayer Roland , Gewald K.
Published: December 2003

The reaction of sulfur, carbon disulfide, and enamines at room temperature leads mainly or exclusively to 3H‐1,2‐dithiole‐3‐thiones; these are occasionally accompanied by 2H‐1,3‐dithiole‐2‐thiones, which can also be prepared by a modified procedure. Many enamines react with sulfur at room temperature to form thioamides. At about 50°C, enamines of acetophenone give 2‐benzylidene‐4‐phenyl‐2H‐1,3‐dithiol. The action of isothiocyanates and sulfur on enamines leads to the formation of thiazolidine‐2‐thiones. 2H‐Thiopyran‐2‐thiones can be prepaAred from enamines or dienamines with carbon disulfide at room temperature. The reaction of ketimines (Schiff bases) with carbon disulfide and sulfur yields 3H‐1,2‐dithiole‐3‐thiones or isothiazoline‐5‐thiones. The reaction of alkynes with sulfur and carbon disulfide leads to 2H‐1,3‐dithiole‐2‐thiones. Nitriles containing active methylene groups react with carbon disulfide and sulfur to form 5‐amino‐3H‐1,2‐dithiole‐3‐thiones. When isothiocyanates are used instead of CS2, the reaction leads to δ4‐4‐amino‐thiazoline‐2‐thiones.
The Formation of CC Bonds with the Aid of α‐Halogeno Ethers, Sulfides, and Amines
Authors: Gross H. , Höft E.
Published: December 2003

α‐Halogeno ethers, sulfides, and amines are reactive compounds which can be used for the formation of new CC bonds, either as nucleophilic or as electrophilic reagents, or by α‐elimination. The use of these compounds in the synthesis of many classes of organic compounds is reviewed.
Electron‐Impact Induced Rearrangement Reactions of Organic Molecules
Authors: Brown P. , Djerassi C.
Published: December 2003

Hydrogen migrations accompany many mass spectrometric fragmentation processes and a detailed study of these migrations, largely by means of deuterium labeling, has shed much light on electron‐impact induced bond fissions. More recently, it has been found that groups other than hydrogen, such as alkyl, aryl, hydroxyl, etc., also can migrate after electron bombardment and the present article is concerned with a discussion of such molecular rearrangements among organic compounds. These observations are not only of intrinsic mechanistic interest, but a detailed knowledge of the occurrence of such migration reaction is crucial to the proper interpretation of mass spectra and to the avoidance of misinterpretations in “element mapping”.
The Chemistry of Bunte Salts
Authors: Distler H.
Published: December 2003

Bunte salts can be obtained, not only from alkyl halides and sodium thiosulfate, but also from compounds containing activated multiple bonds, and sodium thiosulfate. The Bunte salts prepared by the new method, contrary to earlier observations, are cleaved by alkalis into the unsaturated starting compounds and sodium thiosulfate. This reaction, which is used for the fixation of unsaturated compounds (e.g. to cellulose), and other reactions of the Bunte salts are discussed. The industrial applications and biological properties of the Bunte salts are also mentioned.
Investigation of Inorganic Systems at High Temperature by Mass Spectrometry
Authors: Drowart J. , Goldfinger P.
Published: December 2003

High‐temperature mass spectrometry (hitherto at temperatures between 1000 and 2500 °K and at pressures between 10−3 and 10−12 atm) has already made possible the identification of many previously unknown and unpredicted diatomic and polyatomic molecular species. The present paper deals with the investigation of many oxides, of halides, and of carbon molecules and intermetallic molecules. An apparatus for the production and investigation of molecular beams is described. Knudsen cells permit the production of molecular beams under equilibrium conditions; in special cases the “double‐oven” type of Knudsen cell is used. Thermodynamic and kinetic quantities such as ΔH values, dissociation energies, and ionization cross sections of the species investigated are given.
Acetylcholinesterase
Authors: Engelhard N. , Prchal K. , Nenner M.
Published: December 2003

Acetylcholinesterase plays a vital part in the functioning of nerves, and serious physiological damage arises from its blockage by esters of phosphonic and phosphoric acid used e. g. in pesticides. The properties and the mechanism of action of acetylcholinesterase, which show many similarities to those of other hydrolases, are described. Therapeutic agents (reactivators) for the toxic phosphorus compounds specified are also discussed.
A Topological Approach to the Problem of Ring Structures
Authors: Fugmann R. , Dölling U. , Nickelsen H.
Published: December 2003

In the mechanized documentation of chemical literature, the definition of structural concept is very important. The usual for definitions for ring structures are inadequate. Essential ring structures are sometimes not recognized on the basis of these definitions and are therefore missed in a literature search. This is particularly true of bridged ring systems. The ring concept and ring condensation types are now redefined on a topological basis in the closest possible analogy to the intuitive approach of the chemist. In complicated molecular structures, these “fundamental rings” can be easily determined, either manually or by means of a programmed computer. The concept of the “ring complex” is defined and suggested as a preliminary screen in literature searches for ring structures. This will save machine time, and so reduce the cost of searches.
Synthesis and Reactions of the Alkynylamines
Authors: Viehe H. G.
Published: December 2003

Alkynylamines RCCNR have been known for only a few years. They are stable compounds, some of which have now become commercially available. Their high reactivity toward electrophiles as well as toward nucleophiles (particularly on acid catalysis) makes them very versatile starting materials. An interesting practical application is their use as condensing agents in peptide syntheses. They are superior to dicycloexylcarbodiimide as dehydrating agents for organic acids. They condense with polar multiple bonds and dipolar systems to form cyclic structures.
The Active Species in Homogeneous Ziegler‐Natta Catalysts for the Polymerization of Ethylene
Authors: Henrici‐olivé G. , Olivé S.
Published: December 2003

Cp2TiCl2 and Cp2TiEtCl (Cp = cyclopentadienyl, Et = ethyl), in combination with aluminum alkyls, have been studied as model catalyst systems for the polymerization of ethylene in toluene. The activity of these systems resides in the presence of a complex molecule involving an alkylated Ti(IV) and an alkylated Al species, linked together by chlorine bridge bonds. The environment of the Ti is of octahedral symmetry with one vacant site available for the coordination of ethylene. The bridged Al‐alkyl causes a destabilization of the Ti‐alkyl bond (“trans effect”), thus rendering it active for polymerization. The reduction Ti(IV) → Ti(III), inevitable in these systems, involves the irreversible change from octahedral to tetrahedral symmetry with loss of the catalytic activity. Polymerization and reduction are supposed to occur at the same catalyst site. Magnetic methods (susceptibility and EPR) as well as the kinetics of polymerization were used in the investigation of these catalyst systems.
Electron‐Pair Repulsions and Molecular Shape
Authors: Gillespie R. J.
Published: December 2003

The theory described in this article emphasizes the importance of interactions between the electron pairs in the valence shell of a central atom in determining stereochemistry and it assumes that interactions between the ligands are generally of lesser importance although sufficiently bulky groups, or chelate ligands, may play an important role in determining the stereochemistry. If lone‐pair electrons are present in the valence shell of the central atom then the two theories (the theory of interaction of electron pairs and the theory of interaction between ligands) predict different structures. In the great majority of cases the determined structures are those expected if it is assumed that lone pairs are stereochemically active, i.e. if repulsions between electron pairs in the valence shell determine stereochemistry.
Potential and Charge Distribution at Semiconductor‐electrolyte Interfaces
Authors: Memming R. , Schwandt G.
Published: December 2003

The present article deals with the basic concepts of charge and potential distribution at semiconductor‐electrolyte interfaces. The authors use examples to show how external polarization and the variation of the electrolyte composition can change the potential drop across the space‐charge region in the semiconductor and in the Helmholtz double layer at the interface. The article also contains a detailed discussion of the effects exerted by surface properties and by injection of carries on the distribution of charge and potential.
Syntheses with ketones, sulfur, and ammonia or amines at room temperature
Authors: Asinger F. , Offermanns H.
Published: December 2003

A large number of preparatively interesting compounds have become readily available by the simultaneous action of sulfur and ammonia or amines on ketones. Direct syntheses of Δ3‐thiazolines, Δ3‐imidazoline‐5‐thiones, 5,6‐dihydro‐4H‐1,4‐thiazines, and the 1,2,3,4,5,6‐hexathiocane system from ketones, sulfur, and ammonia or amines, and further possibilities for the synthesis of these heterocyclic systems have been proposed. Other heterocycles containing N or N and S (thiazoles, thiophenes, thiazolidines, tetrahydrothiazolo[2,3‐c]‐1,4‐thiazines, thiomorpholines, 4‐amino‐2H‐imidazoles, etc.) are readily obtainable by further reactions of these compounds. Hydrolysis of the Δ3‐thiazolines yields α‐mercapto ketones, which are the starting materials for other syntheses. Most of the syntheses described proceed at room temperature and at normal pressure.
The Concept of Hard and Soft Acids and Bases as Applied to Multi‐Center Chemical Reactions
Authors: Saville B.
Published: December 2003

Many chemical bonds of differing types and strengths have recently been regarded by Pearson[1] as representing partnerships between (Lewis) acids and (Lewis) bases. Most acceptor molecules or ions (acids) can be placed in one or other of two categories, graphically termed “Hard” and “Soft”. There are also two broad categories of donor molecules or ions (bases) which can also be termed Hard and Soft. On the whole, strong chemical bonds are partnerships between either a Hard base and a Hard acid or a Soft base and Soft acid, whereas weaker bond types most usually result in cases of either Hard base‐Soft acid or Soft base‐Hard acid interactions. The present paper shows how this concept of acidity and basicity can be applied in the interpretation of multi‐center chemical reactions involving interconnected acid‐base relationships. In particular, fourcenter substitutions and additions involving cooperative attack by nucleophiles and electrophiles at various chemical bonds have been examined, and a conclusion is reached that especially reactive patterns of reactants can be developed if the substrates contain bonds between either a hard acid and a soft base, or a soft acid and a hard base. Indeed, the arguments can be elaborated to provide two distinct Rules which should be of interest in the interpretation of metal‐ion assisted reactions and in the design of novel syntheses.
Nucleophilic Reactivity of the Thiophosphoryl Group
Authors: Teichmann H. , Hilgetag G.
Published: December 2003

The difference in the nucleophilic reactivities of the and groups can be satisfactorily explained on the basis of Pearson's acid‐base concept[21]. The thiophosphoryl sulfur is a typical “soft base”, and reacts preferentially with sub‐group B metals, halogens, and sp3 hybridized carbon, whereas it is largely inert to “hard acids” such as protons, carbonyl carbon, and tetrahedral phosphorus. Since a nucleophilic attack by the thiophosphoryl sulfur leads to a decrease in the charge density of the phosphorus atom, the latter (or the α‐carbon atom in O‐alkyl esters) becomes more open to nucleophilic attack. This reaction principle forms the basis of sulfur exchange, dealkylation, isomerization, and the Pistschimuka and Michalski reactions.
Structure and Mechanism of Action of the Active Center of Yeast Pyruvate Decarboxylase
Authors: Schellenberger A.
Published: December 2003

Kinetic studies have shown that the two low molecular‐weight components of yeast pyruvate decarboxylase (thiamine pyrophosphate and Mg2⊕ ions) first add rapidly and reversibly to the apoenzyme in binary equilibria. The resulting adduct then “cyclizes” in a rate‐determining, practically irreversible reaction to form the thermodynamically stable holoenzyme. These results were supplemented and extended by the testing of numerous analogues of thiamine pyrophosphate in enzyme experiments and then used for the interpretation of the enzyme reaction.
Hexamethylphosphoramide
Authors: Normant H.
Published: December 2003

Growing interest is being shown in the role of the solvent (particularly polar solvents) in chemical reactions[1–4]. The most remarkable polar aprotic solvent appears to us to be the hexamethylated triamide of orthophosphoric acid, OP(N(CH3)2)3, which is known as hexamethylphosphoramide or tris(dimethylamino)phosphine oxide. Hexamethylphosphoramide[5–7] has recently been studied with respect to its solvent properties for gases[5], for many organic and inorganic salts[7], and for polymers[5], as well as its use as a polymerization co‐catalyst. However, these aspects are not considered in the present paper, which deals with the physical and chemical properties of hexamethylphosphoramide, and in particular with its use as a reaction medium. Our own work on hexamethylphosphoramide began in 1961, and until then very little work had been done on this compound. Even in a paper published by Parker[1b] in 1965, very little reference is made to hexamethylphosphoramide.
The Photolysis of Iodoaromatic Compounds
Authors: Sharma R. K. , Kharasch N.
Published: December 2003

Under appropriate conditions, the photolysis of iodoaromatic compounds yields derivatives of biphenyl and phenanthrene, as well as organometallic compounds. Ring closures of o‐terphenyls to triphenylenes and of benzanilides to phenanthridones are described. The formation of dehydrobenzene (benzyne) on photolysis of 1,2‐diiodobenzene in solution has been established. The photolysis of various substituted iodoaromatic compounds or of substances such as CH3I, ICN, ICH3, COOH, or RCCI, provides a general method for the generation of a large variety of free radicals in solution. The potential uses of photochemically initiated exchanges of iodine in ArI for 131I, Li, D, Cl, or Br are noted.
Methods and Results of Optical Investigations on Semiconductor Interfaces
Authors: Beckmann K. H.
Published: December 2003

Measurement of the state of polarization of reflected light (ellipsometry) permits the determination of the thickness and refractive index of thin layers formed on a surface. The IR absorption spectra of such thin layers, which can be measured by means of internal reflection spectroscopy (IRS), provide information about their chemical composition. These methods have been used to study adsorption processes and the formation of reaction layers at semiconductor interfaces, and may also be used for measurements of free charge carriers in the space‐charge region and in surface states. Results of such investigations are given in this article.
Reactions with N‐Carbonylsulfamoyl Chloride
Authors: Graf R.
Published: December 2003

N‐Carbonylsulfamoyl chloride (NCSA) is an intermediate that can be obtained from cyanogen chloride and sulfur trioxide, and which reacts with many compounds, via electrophilic substitution, much more readily than other isocyanates. Reactions with compounds containing hydroxyl, amino, or carboxyl groups lead to N‐chlorosulfonylurethanes, ‐ureas, and ‐amides, respectively. This group of products also includes the parent substance sulfamoyl chloride (amidosulfonyl chloride). The reaction of N‐carbonylsulfamoyl chloride with olefins provides an easy route, not only to derivatives of β‐amino acids and unsaturated carboxylic acids, but also to many β‐lactams. New, very reactive sulfonylisocyanates of several types can be obtained by further reactions of primary products obtained from N‐carbonylsulfamoyl chloride and by the reaction of N‐carbonylsulfamoyl chloride with olefins in the presence of free‐radical formers. When allowed to react with a number of compounds, NCSA undergoes loss of carbon dioxide to form products containing the grouping = NSO2Cl.
The Discovery, Isolation, Elucidation of Structure, and Synthesis of Antamanide
Authors: Wieland Th. , Lüben G. , Ottenheym H. , Faesel J. , De Vries J. X. , Prox A. , Schmid J.
Published: December 2003

Antamanide is the name we have given to a constituent of the fungus Amanita phalloides. This substance counteracts the lethal action of the Amanita toxins phalloidine and α‐amanatine if administered to the white mouse before, or simultaneously with, the poisons. Its concentration in the fungus is, however, so low that the toxic action of the latter predominates. Antamanide is a cyclic decapeptide formed from the L‐amino acids alanine, phenylalanine, proline, and valine in the molar ratio 1:4:4:1. The amino‐acid sequence was determined by a combination of gas chromatography and mass spectrometry. The structural formula assigned was confirmed by synthesis according to a classic route of peptide chemistry.
Problems and Possibilities of Modern Trace Analysis
Authors: Specker H.
Published: December 2003

As a result of the development of measuring techniques, analytical chemists can now determine very small quantities as well as trace concentrations of the order of 10−8% with good accuracy. In exceptional cases it is even possible to detect 105 atoms of an element. In this review, definitions of important analytical terms are outlined and a critical appraisal of the principal methods of trace analysis is given.
Conductance of Electrolyte Solutions
Authors: Barthel J.
Published: December 2003

The present article deals with methods and results of conductance studies with special reference to nonaqueous solvents, e.g. ethanol, dioxane, dimethylformamide, acetonitrile, nitromethane, and acetone, in some cases mixed with water, as well as NH3, SO2, I2, etc. On the basis of a model in which the ions are represented as charged spheres and the solvent as a homogeneous isotropic medium, the conductance theory can (at least for low electrolyte concentrations) give a more or less complete representation of the problem. A new statistical treatment of the transport problem confirms important results of this representation. The present state of the investigation is finally outlined in a review of recent publications.
Cycloadditions — Definition, Classification, and Characterization
Authors: Huisgen R.
Published: December 2003

The growing volume of publications on cycloadditions indicates that this general type of reaction merits a place beside the better‐known substitutions, eliminations, and additions. The world of phenomena does not provide us with definition and classification principles. These are created by the scientist and are not free from arbitrariness. A terminology[1] is suggested for cycloadditions. These reactions do not all proceed by the same mechanism. Since ideas about reaction mechanism can change with the introduction of new criteria, it is shortsighted to base definitions and classifications on mechanism alone. Consequently, the definition of cycloadditions will not be restricted simply to multi‐center processes with a cyclic electron shift.
Carbonylation of Olefins under Mild Temperature Conditions in the Presence of Palladium Complexes
Authors: Bittler K. , Kutepow N. V. , Neubauer D. , Reis H.
Published: December 2003

During a search for catalysts that allow carbonylation reactions on olefins to proceed below 100 °C, complex palladium(II) compounds having the formula LmPdXn were found to be catalytically active. L denotes a ligand such as a phosphine, nitrile, amine, or olefin, X is an acid residue, and m+n is 3 or 4. The catalysts permit the carbonylation of heat‐sensitive compounds, as well as selective carbonylation of polyunsaturated olefins. The new process can also be carried out on the industrial scale, as is shown by the carbonylation of cyclododecatriene
Nitrogen Oxide Fluorides
Authors: Schmutzler R.
Published: December 2003

Oxyfluorides of nitrogen, i.e. compounds containing the grouping FNO, have been known for many years in the form of simple compounds, such as NOF and NO2F. Detailed studies of physical, structural, and chemical aspects of this class of compounds have been conducted only in recent years, after the potential of NF compounds as rocket propellants had been recognized. Several novel types of oxyfluorides of nitrogen, such as difluorohydroxyl amines, RONF2, or trifluoroamine oxide, F3NO, have been discovered recently. A further major development in ONF chemistry is indicated by the discovery that compounds of great chemical potential are formed between HF and NOF or NO2F, respectively.

The compound O2NOF, although not an oxyfluoride of nitrogen, will also be discussed in this review, because of its particular chemical relationship to NO2F.
Free Radical Studies at Low Temperatures
Authors: Mile B.
Published: December 2003

Free radicals can be produced in the gas phase and then condensed together with the molecules of an inert gas; they can also be generated and trapped in isolated sites in rigid solids. IR and ESR spectra of trapped radicals provide information concerning their structure and chemical properties. The techniques employed for producing and studying radicals are reviewed and a number of recent IR and ESR investigations of trapped radicals are discussed. The last part of the article deals exclusively with the applications of the rotating cryostat to the study of the ESR spectra and reactions of trapped radicals at low temperatures.
Modification of the Orientation of Substitution Reactions on Thiophene and Furan Derivatives
Authors: Goldfarb Ja. L. , Volkenštein Ju. B. , Belenkij L. I.
Published: December 2003

Under normal conditions, thiophene and furan derivatives are substituted in the α position, and no convenient alternative methods for the preparation of β‐substitution products have been available until now. The present article describes a method that permits the synthesis of many β‐substituted thiophenes and furans. In this method, the carbonyl group in α‐aldehydes or ketones of the thiophene and furan series is blocked by complex formation with an excess of aluminum chloride, so that electrophilic substitution takes place in position 4. In another useful method, the carbonyl group is blocked by acetalization. The acetals can be metalated in the ring by organolithium compounds.
Syntheses of Cyclopropylcarbonyl Compounds
Authors: Conia J. M.
Published: December 2003

There are three important direct routes to cyclopropylcarbonyl compounds: 1. Cyclization of chains of three carbon atoms, the first or third of which is adjacent to a carbonyl or potential carbonyl carbon atom (this type includes syntheses by intramolecular alkylation of γ‐halogeno ketones or related compounds in alkaline media); 2. insertion of a methylene group or substituted methylene group into the olefinic double bond of an α,β‐unsaturated carbonyl compound; and 3. introduction of an acetonyl group into the double bond of an olefin. However, cyclopropylcarbonyl compounds can also be obtained from 1,2‐epoxycyclobutane and 2‐bromocyclobutanone derivatives by ring contraction. Another possibility is the dehalogenation of α,α‐bis(bromomethyl) cycloalkanones. This review concludes with a discussion of these little known routes and of a particularly suitable method which involves the reaction of methylene iodide, a ZnCu couple, and α,β‐unsaturated ketones.
Observations on the Crystal Structures of Electron Donor‐Acceptor Complexes
Authors: Prout C. K. , Wright J. D.
Published: December 2003

The theoretical interpretation of electron donor‐acceptor complex formation in terms of charge transfer interactions has stimulated many structure determinations for these complexes. These fall into three classes, depending on the type of orbitals involved in charge transfer. In σ‐σ complexes, intermolecular bonds become shorter and intramolecular bonds become longer as charge transfer increases. Relative orientations correspond to overlap of donor and acceptor molecules in directions of “preferred polarizability”. Intermolecular bond lengths in σ‐π complexes show similar trends, and the axial orientation in the benzene‐halogen complexes is probably the result of the best compromise between orbital overlap and energy factors. π‐π Complexes contain stacks of alternate plane‐to‐plane donor and acceptor molecules, arranged in three characteristic ways. There is little correlation between interplanar spacing in these stacks and charge transfer properties. The relative orientations of donor and acceptor molecules within the stacks are determined by a combination of charge transfer interactions (maximized when aromatic rings of donor and acceptor molecules are displaced by half a ring diameter) and dipole‐induced dipole interactions (maximized, for example, when a polar bond of one molecule overlaps a polarizable region of another). Crystal packing requirements and dispersion forces modify these effects, and no satisfactory theoretical treatment of this complex combination of interactions is yet available.
On the Chemistry of Clay
Authors: Hofmann U.
Published: December 2003

Kaolinite, illite, chlorite, montmorillonite, and vermiculite are among the most important of the clay minerals. Cations are embedded between the silicate layers and on the basal faces of the crystals. Whereas only the cations on the outer faces are exchangeable in the first three of the above minerals, those between the layers can also be replaced by others in montmorillonite and vermiculite. These characteristics and the ability of montmorillonite and vermiculite to undergo intracrystalline swelling and to form inclusion compounds are responsible for the industrial importance of kaolin and clay. The structure of halloysite is particularly interesting, since the silicate layers in this case are rolled up to form tabes. The possible role of the clay minerals as catalysts in the formation of petroleum and in the beginning of life is finally discussed.
Replacement of Plasma by High Molecular Weight Substances
Authors: Appel W. , Biekert E.
Published: December 2003

In the course of the development work, natural and synthetic polymers were examined to see whether they were suitable for use as plasma substitutes. The criteria of a plasma substitute are discussed in this connection. The most important of the base substances used at present (dextran, modified gelatin, polyvinylpyrrolidone, and hydroxyethyl starch) are described, and a typical example of proven therapeutic value is discussed for each type.
The Cytogenetics of Human Tumors
Authors: Zang K. D. , Singer H.
Published: December 2003

Chromosome changes can be observed in many tumors, suggesting that a connection exists between chromosome aberrations and tumor formation. A general introduction to the techniques and objectives of research in cytogenetics is followed by a discussion of the modern theories of the etiology of tumors, using human meningioma as an example. Meningiomas are relatively benign, slowly growing tumors of the meninges.
Preparation, Properties and Reactions of Polychloroamine Derivatives
Authors: Holtschmidt H. , Degener E. , Schmelzer H.‐G. , Tarnow H. , Zecher W.
Published: December 2003

Highly chlorinated amine derivatives can be prepared by the high‐temperature chlorination of amines and amine derivatives. Essential for the success of this reaction is an adequate temperature control suited to the constitution of the amines. In many cases the chlorination products achieve stability by cleavage reactions with formation of the imidic acid chloride or isocyanide dichloride grouping. Cyclic compounds are formed under special conditions. The chlorination process described can be used to obtain e.g. polychloroaryl and polychloroalkyl isocyanide dichlorides, polychloroaryl and polychloroalkyl imidic acid chlorides, and polychloroheterocyclic compounds.
The Gabriel Synthesis of Primary Amines
Authors: Gibson M. S. , Bradshaw R. W.
Published: December 2003

Reaction of potassium phthalimide with halogenoalkanes and with a variety of other alkylating agents leads to the N‐alkylphthalimide. N‐Substituted phthalimides may be converted into the corresponding primary amine by hydrolysis or hydrazinolysis. The scope and limitations of these reactions, which together constitute the Gabriel Synthesis of primary amines, are reviewed.
Mechanistic Organic Photochemistry
Authors: Zimmerman H. E.
Published: December 2003

Organic photochemical reactions can be understood as transformations of the electronically excited states of the reactant molecules. By considering Lewis structure or molecular orbital representations of these excited states it is possible to outline the several possible reactions available in the case of a given reactant. A number of different types of photochemical transformations are now reasonably well understood. In these cases one finds the same common controlling feature, namely the tendency for an excited state species to follow mechanistic pathways of minimum energy and the requirement for continuous electron redistribution in following these pathways. These preferred transformations can often be selected by inspection of relative bond orders for different types of bonding, by comparison of the potential energy surfaces available to the excited state molecules, and by use of correlation diagrams. The reactions derive from both singlet and triplet states, and one of the more reliable methods now available for identifying excited states reacting is termed the “fingerprint method”. Examples of the author's mechanistic approach are given both for ketone and for hydrocarbon photochemistry.
Reactions of Isocyanide Dihalides and their Derivatives
Authors: Kühle E. , Anders B. , Klauke E. , Tarnow H. , Zumach G.
Published: December 2003

The readily obtainable isocyanide dichlorides can be used as starting materials for the preparation of many types of substances. Exchange reactions yield numerous derivatives of formic and carbonic acids, while heterocyclic products have been obtained by reaction with bifunctional partners. The present article deals not only with reactions that are known from the literature but also with the author's own work, some of which has not been published before.
The Chemistry of Hypervalent Molecules
Authors: Musher J. I.
Published: December 2003

Molecules formed from atoms of Groups V–VIII of the periodic table in their higher valences are studied and a general theory for their electronic and geometric structure is presented. These molecules, which we call hypervalent molecules, are unique in that a donor atom can possess two identical monovalent ligands which are bonded by different types of chemical bonds. The present study provides a simple theoretical description of such molecules using doubly‐occupied lone‐pair orbitals to form hypervalent bonds, and these bonds are divided into two classes as to whether they involve p electrons alone or utilize s electrons as well. While the theoretical classification is of some interest in itself, there are even more interesting problems concerning the physico‐chemical properties of these molecules and the syntheses of new molecules and polymers. We thus present a brief description of the energetics, possibilities for intermolecular inversion and site‐exchange, and synthetic paths for the preparation of hypervalent molecules, as well as indicate a number of new molecules which can probably be synthesized using these ideas.

For corrigendum see DOI:10.1002/anie.196901311
Reactions of Aromatic Nitro Compounds with Bases
Authors: Buck P.
Published: December 2003

Aromatic nitro compounds can react in many ways with bases. The reaction path followed depends mainly on the degree of nitration (with a sharp jump from mononitro to di‐ and trinitro compounds) and the base used. Redox reactions or nucleophilic aromatic substitutions predominate with mononitro compounds, whereas Meisenheimer additions together with nucleophilic aromatic substitutions are preferred by dinitro and trinitro compounds; deprotonations are less common. The bromine in nitrobromobenzenes can be replaced by metal at low temperatures. Very weak bases generally give electron donor‐acceptor complexes.
The Composition and Conformation of Sugars in Solution
Authors: Angyal S. J.
Published: December 2003

The conformations of the aldoses in solution, and the compositions of the equilibrium mixtures formed from aldoses after dissolution in water, have been determined by NMR spectroscopy. Calculations based on non‐bonded interactions and on the anomeric effect account for the observed conformations, and allow an approximate prediction of the α:β ratio of pyranoses in equilibrium and of the extent of anhydride formation from sugars in acid solution. In certain circumstances the furanose forms are more stable than the pyranose forms.
Steps in Precipitation Reactions
Authors: Lieser K. H.
Published: December 2003

The combined application of various methods of investigation (e.g. nephelometry, conductivity measurements, electron microscopy, isotope exchange, BET surface area determinations, paper chromatograhy, coprecipitation) lead to a refined insight into the course of precipitation reactions. The formation of a new solid phase within a solution can, in the case of ionic crystals, be formally described as proceeding via a number of steps – nucleation, growth, ripening, and recrystallization (aging) – which overlap in time. The precipitation of hydroxides is a more complex process since additional chemical reactions (e.g. hydrolysis, condensation reactions) take place within the newly formed solid phase.
Biosynthesis of Lichen Substances, Products of a Symbiotic Association
Authors: Mosbach K.
Published: December 2003

Lichens are composed of algae and fungi living together in symbiotic association and forming characteristic, often polycyclic lichen substances that are rarely encountered in other organisms. While the cultures of the unassociated individual constituents of the lichens can live for an unlimited time some doubt surrounds their viability in nature; their biosynthetic powers are not additive in the lichens. The results concerning the biosynthesis of the lichens that are discussed in the present article were obtained mainly with 14C‐labeled compounds.
The Chemistry of Enol Ethers
Authors: Effenberger F.
Published: December 2003

Enol ethers (vinyl ethers) are intermediate in their reaction behavior between olefins and enamines. This article presents a survey of reactions leading to bond formation at the βC atom of enol ethers; polymerizations and additions of acidic HX compounds are not reviewed.