bluuebunny/crossref_metadata_2025 huggingface dataset:
Proton Transfer, Acid‐Base Catalysis, and Enzymatic Hydrolysis. Part I: ELEMENTARY PROCESSES
Authors: Eigen M.
Published: December 2003

The proton occupies a special position as a promoter and mediator in chemical reactions occurring in solution. Many reactions in organic chemistry are catalysed by acids or bases; likewise, most enzymes contain active groups which promote acid‐base catalysis. To understand the reaction mechanisms involved, it is necessary to identify the elementary steps as well as their course in time. Systematic investigation of these elementary steps as well as their course in time. Systematic investigation of these elementary steps has become possible only with the development of new methods for studying very fast reactions. The present paper reviews the information obtained in this type of investigation. The result is a relatively complete picture of the elementary proton transfer mechanisms and a comprehensive description of the modes and laws of acid‐base and enzymatic catalysis.
Recent Developments in the Study of Lysozymes
Authors: Jollès P.
Published: December 2003

Lysozymes are widely distributed enzymes. They split the chemical skeleton of bacterial cell walls by hydrolysing the β (1 → 4) linkages between N‐acetylmuramic acid and N‐acetylglucosamine. the amino acid sequence of lysozyme from hen's egg‐white is known (129 amino acid residues). Lysozymes of different origins frequently differ in their primary structures although they exhibit qualitatively the same biological activity. The results obtained from investigations with lysozymes allow conclusions to be drawn regarding the chemical structure of the “backbone” of bacterial cell walls.
Reversibility of Energy Transformations in the Respiratory Chain
Authors: Klingenberg M.
Published: December 2003

In oxidative phosphorylation, the energy from the combustion of substrate hydrogen can be reversibly transformed into phosphate‐bond energy. This is the reason that oxidation‐reduction reactions in the respiratory chain can take place against the redox potential gradient if energy is supplied. The latter can come from ATP or directly from energy‐rich intermediates arising in the course of oxidative phosphorylation. – At the center of the present considerations is the postulate that there is an equilibrium prevailing in the respiratory chain that results from the reversibility of the reactions. At the same time this postulate provides a unifying approach to various phenomena related to the process of oxidative phosphorylation. Such an equilibrium may involve several components of the respiratory chain. Respiration thus corresponds to a dynamic equilibrium in the respiratory chain which deviates increasingly from the static equilibrium the greater the rate of respiration. Consequently, respiration can be considered as being regulated by the phosphorylation potential. – The stationary redox state of the components of the respiratory chain can be viewed as a simulataneous function of the phosphorylation potential and of the redox potential that effects both ends of the respiratory chain. The latter reacts to either extreme, i.e. to minimum or maximum differences in the redox potential, by forming characteristic patterns of the state of reduction of its components. Differences in redox potential amounting to as much as 280 mV can be over‐come by the phosphorylation potential for a single phosphorylative step. – The conditions for an equilibrium in the respiratory chain are also fulfilled from a kinetic viewpoint as the rates of the reverse reactions involving either electron or proton transfer are of the same order of magnitude as those of the forward reactions.
The Valence Tautomerism of Cyclooctatetraene
Authors: Huisgen R. , Mietzsch F.
Published: December 2003

The Diels‐Alder adducts of cyclooctatetraene and its derivatives are derived from the bicyclo[4,2,0]octane structure. A kinetic investigation shows that the Diels‐Alder addition of dienophiles to cyclooctatetraene and phenylcyclooctatetraene is preceded by a valence tautomerism equilibrium with bicyclo[4,2,0]octa‐2,4,7‐triene or its 7‐phenyl derivative.
Structure and Aromatic Character of Non‐benzenoid Cyclically Conjugated Systems
Authors: Hafner K.
Published: December 2003

The chemistry of aromatic compounds was originally confined to benzenoid hydrocarbons and their derivatives but has been enriched in the last decade by the discovery of numerous non‐benzenoid, cyclically conjugated systems that are more or less like benzene in their properties. This has necessitated a new conception of “aromatic character”. Theoretical and experimental studies have been applied to this problem. In this connection, several selected representatives of this class of compound are described, mostly from studies by the author's own group, and relationships between structure and “aromatic character” are indicated.
Aliphatic Thioketones
Authors: Mayer Roland , Morgenstern J. , Fabian J.
Published: December 2003

The methods described in the literature for the synthesis of aliphatic thioketones are examined critically in the light of the authors' own work; new practical methods of preparation are reported, and characteristic properties of thioketones are described.
Three‐Membered Rings Containing Two Hetero‐Atoms
Authors: Schmitz Ernst
Published: December 2003

Since their discovery five years ago, the diaziridines have become an extensive and easily accessible class of compounds. Hydrolysis of these compounds effects a simple synthesis of hydrazine, alkylhydrazines, and N,N′‐dialkylhydrazines. They are also powerful oxidizing agents. The rigidity of the three‐membered ring gives rise to a few stereoelectronic peculiarities. Investigations on the mechanism of formation of the three‐membered rings led to a new synthesis of oxaziranes and to discovery of the isomeric oximes with a three‐membered ring structure. The latter decompose readily to form diimide. Diazirines are cyclic isomers of the aliphatic diazo compounds and are surprisingly easy to obtain by dehydrogenation of suitable diaziridines; they are chemically much more stable than the linear isomers. Grignard reagents add onto the NN double bond without destruction of the three‐membered ring. Thermal decomposition yields carbenes.
Complexes of Tetradentate Ligands Containing Phosphorus and Arsenic
Authors: Venanzi L. M.
Published: December 2003

The effect of ligand shape on coordination numbers and geometry of coordination compounds has been studied using two tetradentate ligands containing phosphorus and arsenic. These tend to form five‐coordinate complexes with trigonal bipyramidal structure [Fe(II), Co(I), Co(II), Rh(I), Ni(II), Pd(II), Pt(II)], but can also form six‐coordinate complexes with octahedral structure [Fe(II), Ru(II), Os(II), Co(III), Rh(III), Pd(IV), Pt(IV)]. The magnetic properties and the stereochemistry of the complexes are explained by ligand field theory which predicts that, for metal ions with d6‐electronic configuration, a low overall field strength should favor the formation of five‐coordinate paramagnetic complexes while a high overall field strength should favor the formation of six‐coordinate diamagnetic complexes. – This work provides further indication that the tendency of polydentate ligands to use all the potential donor atoms is not as pronounced as is generally believed. This is shown by the isolation of chromium(III) complexes in which the tetradentate ligands are, in fact, acting as tridentate, and by the isolation of mercury(II) complexes where only two of the four donor atoms of the polydentate ligand are actually bonded to the central metal atom.
The Chemistry of New Heat‐Resistant Films and Fibers
Authors: Wallenberger F. T.
Published: December 2003

This survey is principally concerned with papers published since 1959 on hydrocarbon polymers, aliphatic poly(terephthalamide) fibers, poly(hydroxybenzoic acid) films, poly(oxadiazole) fibers, poly(benzimidazole) films, poly(phenyltriazole) films, poly(pyromellitimide) films, and fibers from cyclized poly(acrylonitrile). All these materials have extremely high melting points and satisfactory in‐use characteristics at high temperatures.
The Phenomenon of Phototropy
Authors: Luck W. , Sand H.
Published: December 2003

A short survey of the present status of our knowledge in the field of “phototrophy” is presented. The laws which govern this phenomenon are described, taking parafuchsin and N,N′‐di‐methyl‐1,4‐diaminoanthraquinone as examples. Phototropy and thermotropy are related. The acceleration of the regression of phototropically induced states by irradiation with light is discussed in some detail. An understanding of phototropy promises insight into the mechanisms of photochemical reactions and into the prerequisites for the preparation of light‐fast dyes.
The Photochemical Decomposition of Alkyl Azidoformates in Aliphatic Alcohols
Authors: Kreher R. , Bockhorn G. H.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196406601
The Structure of the Proton and the Neutron
Authors: Schopper H.
Published: December 2003

A short survey is given of the present state of our knowledge of the structure of the proton and the neutron. The results so far obtained have been derived from studies of the scattering of fast electrons.
Electron Affinity of Organic Molecules
Authors: Briegleb G.
Published: December 2003

The formation of organic radical ions by direct electron exchange between a donor molecule D and an acceptor molecule A is becoming increasingly important, particularly with regard to reaction mechanisms involving intermediate radical ions. All redox processes also involve electron exchange. Finally, the knowledge of electron affinities and ionization energies of organic molecules is necessary for a quantitative theoretical interpretation of intermolecular resonance and of the semiconductor properties of crystalline organic compounds and molecular compounds.
Old and New Processes of Multiplicative Distribution (Liquid‐Liquid Extraction). A Comparison of the Methods of aterial Flow and the Mode of Action
Authors: Fischer Werner , Biesenberger K. , Heppner J. , Neitzel U.
Published: December 2003

A new process is described for the separation of mixtures of materials by multiplicative distribution, which is characterized by repeated addition of the mixture throughout the whole process and by material exchange during the countercurrent flow of finite amounts of one, and infinitesimally small amounts of the other phase. The intrinsic features of the mode of action of the old distribution processes and the new one are developed, and their relationship to one another is discussed. In this connection, an attempt is made to clarify the confused situation in the terminology of this field by introducing clearer definitions. Reflux and “displacement distribution”, another new distribution process, are treated briefly in two final sections.
Eliminations from Olefins
Authors: Köbrich G.
Published: December 2003

Eliminations from olefins are very often initiated by bases, and usually lead to formation of acetylene derivatives. In view of the numerous side‐reactions and subsequent additions or rearrangments observed, the nature of the base used is of considerable significance. Organometallic bases are very versatile. In addition to dehydrohalogenation, dehalogenation by metals, and also thermolytic and photolytic eliminations. (e.g. the retrodiene reaction with exchange of substituents) are discussed. Elimination from low‐membered cyclic olefins yields cycloalkynes having strained ring‐systems, and the existence of these can be demonstrated by trapping them. The mechanisms known for β‐elimination (E2, E1 and E1cB) occur also in the case of olefins; however – due to the sp2‐hybridization of the carbon atoms taking part – they are realized with different rates of reaction relative to saturated compounds. α‐Eliminations from olefines having aryl residues in the β‐position lead to formation of arylacetylenes by rearrangement of the carbon skeleton. The mechanism of this reaction, which is known as the Fritsch‐Buttenberg‐Wiechell rearrangement, is discussed in considerable detail, and several variations of the reaction are considered. According to present‐day knowledge carbenes are involved in α‐eliminations only when both β‐positions of the olefin are occupied by aliphatic substituents, or when they are occupied by aromatic residues where rearrangement to acetylenes is impossible for steric reasons (as for example with 9‐chloromethylenefluorene). With organolithium compounds a number of dehydrohalogenations, which are formally β‐eliminations, actually proceed via deprotonation on the halogenbearing carbon atom (α‐metallation). α‐Metallations are the rate‐determining steps when ether is used as solvent, but proceed quickly in tetrahydrofuran even at low temperatures. Compounds of the type \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$\raise1pt\hbox{$>$}{\rm C}\raise1pt\hbox{=\kern-3.45pt=}{\rm C(Li)Cl}$\end{document} may be prepared by this method and are recognized as intermediates in α‐eliminations.
Recent Development in the Chemistry of Heterosiloxanes
Authors: Schmidbaur H.
Published: December 2003

Progress in the chemistry of organoheterosiloxanes is reviewed in the light of the latest preparative and spectroscopic results. Attention is focussed on the heterosiloxane structural unit SiOX, the bonding in which – depending on the hetero‐atom – differs characteristically from that in the siloxane bridge SiOSi.
Exchange Rates of Ligands in Complex Ions
Authors: Pearson R. G. , Anderson Mary M.
Published: December 2003

It is possible to study the very rapid exchange rates between molecules or ions, L, coordinated to paramagnetic ions and the free molecules or ions, L*, in the body of the solution by measuring the line width of the NMR signal of L*.

Lifetimes of coordinated ligands that can be measured fall into the range of milliseconds to microseconds. The lifetime, or an upper limit to the lifetime, can be measured directly.
Recent Results in the Catalytic Oligomerization and Co‐oligomerization of Butadiene
Authors: Müller Herbert , Wittenberg D. , Seibt H. , Scharf E.
Published: December 2003

A number of new catalyst systems based on transition‐metal compounds have been developed for the oligomerization and co‐oligomerization of butadiene. These catalysis promote dienylations and the formation of other CC linkages, and make possible the synthesis of new open‐chain and cyclic compounds from butadiene.
N‐Substituted Tetrahydro‐1,4‐oxazines – A New Class of Fungicidal Compounds
Authors: König K.‐H. , Pommer E.‐H. , Sanne W.
Published: December 2003

Tetrahydro‐1,4‐oxazines with large alicyclic or long alkyl groups

Compounds of this type are the subject of German and other patent applications.

attached to the nitrogen exhibit good or very good fungicidal activities against fungus diseases of crops, particularly against the true mildew varieties. ‐ By examining several hundred compounds, the relations between chemical constitution and fungicidal action were investigated in an attempt to find the most effective compounds. The factors varied were the nature, chain length, and ring size of the N‐substituent, and the nature, number, and positions of the C‐substituents on the heterocyclic system. Furthermore, the lone electron pair at the nitrogen atom was incorporated by alkylation, formation of amine oxides or salts, or by complexing with heavy metal salts, and the resulting changes in the fungicidal activity were determined.
Mechanization of Chemical Documentation
Authors: Meyer Ernst
Published: December 2003

The principal reasons for the failure of mechanized documentation to gain wide acceptance in chemistry are the inflexibility fo the systems used and the difficulties encountered in precisely formulating all search questions. The present paper describes documentation methods for structural formulae, reaction types, and other data; these methods are more flexible than those commonly used. To avoid the use of electronic computers for simple enquireies, it is suggested that small card files should be supplied ready‐encoded from a central store, and mechanically sorted in accordance with the code which best suits the particular case.
Sequence Distribution in Copolymers. Chemical Studies
Authors: Harwood H. James
Published: December 2003

Various chemical procedures are available for studying the sequence distribution in copolymers, but none can be applied routinely. The run‐number approach permits the results of such studies to be treated with ease; all results obtained to date are consistent with classical copolymerization theory.
Sensitivity of Pyrimidines and Purines towards Neutron Irradiation
Authors: Wacker A. , Chandra P.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196508793
Synthesis of Bis(diaziridin‐1‐ylmethylene)‐hydrazine
Authors: Neidlein R. , Haussmann W.
Published: December 2003

No Absract.
The Hetarynes
Authors: Kauffmann Th.
Published: December 2003

Investigations carried out during the last six years have shown that, as in the case of benzene, an extra bond can be introduced into heteroaromatic rings. Since this possibility does not appear to be confined to exceptional cases, the heterocyclic arynes (hetarynes) promise a much wider variety than the carbocyclic arynes. Hetarynes occur mainly as intermediates in nucleophilic substitutions on halogenated heterocyclic compounds. Since the replacement of a CH group in dehydrobenzene by a nitrogen atom and the condensation of benzene rings have stabilizing effects, the stability of hetarynes is expected to increase with the number of N atoms and with the number of condensed aromatic rings.
Anaplerotic Sequences in Microbial Metabolism
Authors: Kornberg H. L.
Published: December 2003

In addition to catabolic and anabolic pathways, which enable nutrients to enter and to be withdrawn from the central routes of metabolism, enzymic sequences operate to ensure that intermediates, removed from these central routes in the course of biosynthesis, are replenished. These obligatory pathways of replenishment are generically designated “anaplerotic sequences”. The nature of these sequences, operative in micro‐organisms growing on C3‐ and C2‐compounds, is discussed in outline, and the mode of regulation of one of them (the glyoxylate cycle) is examined in detail.
Synthesis and Reactions of Organic Fluoro Compounds
Authors: Machleidt H.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196507173
New Reactions of Alkylidenephosphoranes and their Preparative Uses. Part II. Alkylidenephosphoranes and Halogen Compounds
Authors: Bestmann H. J.
Published: December 2003

The reaction of alkylidenephosphoranes with compounds containing halogens can be used to prepare ylides, which can be converted in to useful products, e.g. by hydrolysis, by thermal decomposition, or by other reactions. Examples of such products are ketones including cyclic, unsaturated, and branched‐chain ketones (including cyclic, unsaturated, and branched‐chain ketones), carboxlic esters (including those of unsaturated, branched‐ chain, polyenecarboxylic, acetylenecarboxylic, and allenecarboxylic acids), and aldehydes.
New Reactions of Alkylidenephosphoranes and their Preparative Uses III. Alkylidenephosphoranes and Reagents Containing Multiple Bonds
Authors: Bestmann H. J.
Published: December 2003

A few examples of preparatively useful syntheses using alkylidenephosphoranes and substances containing a CN or CC double bond are the preparations of olefins, allenes, pyran derivatives, and cyclopropane derivatives. Olefins, ketones, and monocyclic compounds can be obtained by autoxidation of alkylidenephosphoranes; α, β‐dioxo compounds (including cyclicones) can be prepared by oxidation with peroxy‐acids. Alkylidenephosphoranes can also be used for the synthesis of azines and Schiff bases. Of the many possibilities offered by the Wittig reaction, only the preparation of tritiated aldehydes and olefins will be considered.
The Use of Electron Paramagnetic Resonance in Organic Chemistry
Authors: Schneider F. , Mobius K. , Plato M.
Published: December 2003

The more recent applications of electron paramagnetic resonance (EPR) to organic chemistry include the investigation of triplet states, donor‐acceptor complexes, short‐lived free‐radical intermediates, and reaction kinetics. The principles of the theoretical calculations required to obtain the maximum information from EPR spectra are outlined for free radicals containing π‐electron systems. EPR intensities, line widths, hyperfine splitting, and g factors permit the determination of free‐radical yields, ionic charges, rotation frequencies in rotamers, electron density distributions, electronegativities, intramolecular torsion angles, solvent effects (resulting from hydrogen bonding), and π‐orbital energies. – The production of free radicals with the aid of initiation reaction in flow systems, by irradiation, and by electrolysis seems particularly promising.
Synthesis of Transcurium Elements by Nuclear Reactions with Heavy Ions
Authors: Keller C.
Published: December 2003

Experimental techniques are described for the preparation of transcurium elements. Nuclear reactions with heavy ions appear to be most promising for the preparation of new transcurium elements and isotopes. Since these nuclear reactions have extremely small cross‐sections, only few atoms will be produced. Owing to their short half‐lives, the heaviest nuclei can presumably be identified only indirectly through the probabilities of their formation and distintegration.
Phosphorescence Spectroscopy as an Analytical Method for Aromatic and Heterocyclic Compounds
Authors: Zander M.
Published: December 2003

The phosphorescence of aromatic and heterocyclic compounds at low temperatures can be utilized for their identification and determination. The theoretical and experimental basis of phosphorimetry, which represents a valuable addition to the better‐known analytical methods, is described, and examples of its application to coal‐tar chemistry are discussed.
New Products of Reaction of Organometallic Compounds with Sulfur, Selenium, Tellurium, and Phosphorus
Authors: Schumann Herbert , Schmidt Max.
Published: December 2003

Bond fission of molecular sulfur, selenium, and tellurium by lithiotriphenylmetal compounds (of Ge, Sn, Pb) is summarized. The products are suitable as starting materials for synthesis of new “ether analogues”. Transphenylation with tetraphenylstannane is interpreted as a high‐temperature variant of the usual fission of chalcogen molecules by nucleophilic reagents. In principle, transphenylation can be applied also to other elements, as is illustrated for phosphorus. In the syntheses achieved, many of the tin‐phosphorus compounds arising as intermediates can be isolated.
The Chemistry of Silicon‐Sulfur Compounds
Authors: Haas A.
Published: December 2003

The preparations, properties, structures, and chemical reactions of silicon‐sulfur compounds are reported. The chain structure of the polymeric silicon disulfide is used as a basis from which the various classes of compounds can be derived: cyclothiasilanes, disilyl sulfides, silanethiols, and organothiosilanes. Infrared data and force constants of the Si‐S bond are discussed.
Electronic Structure and Properties of Non‐Alternant Hydrocarbons
Authors: Zahradník R.
Published: December 2003

The present paper is concerned mainly with studies on the electronic structure of nonalternant hydrocarbons by quantum‐chemical methods. The references to original publications are by no means exhaustive, but an attempt has been made to cover the entire field. (Analogues and derivatives of non‐alternant hydrocarbons are only touched.) The intention is to outline the present situation with regard to quantum‐mechanical studies on non‐alternant hydrocarbons, and to indicate to the chemist the use of the theoretical characteristics obtained by various approximations of the MOLCAO method.

The simplest modification of the MO–LCAO method is the Hückel approximation (HMO), in which the molecular orbitals ψi are expressed as linear combinations of the atomic orbitals ϕj; in the π‐electron approximation only the 2pzatomic orbitals are considered. For the interaction of n orbitals we have:The π electron densities and the bond ordes can be calculated from the coefficients cij of the molecular orbitals. The energies Ei of the molecular orbitals are found by solving the determinantal equation' the n permitted levels are given by:where α is the Columb integral of the 2Pzorbital of carbon and β is the resonance intergral of the CC π‐bond (and also the unit of energy in the HMO theory). The occupied molecular orbital with the highest energy is denoted by k1 (normal state), and the unoccupied level with the lowest energy by k−1(valence state). The transfer of an electron from k1 to k−1is called N → V1 excitation.

The main difference between the HMO method and the more accurate MOLCAO methods is that electronic interactions are explicitly taken into account in the latter; these methods arePople'sSCF (self‐consistent field) method andPariserandParr'sLCI (limited configuration interaction) method.
Structure Formation and Molecular Mobility in Water and in Aqueous Solutions
Authors: Wicke E.
Published: December 2003

The study of the structure of water and of aqueous solutions has recently received new impetus from the efforts at commercial desalineation of sea water and from developments in molecular biology. The current view that, apart from single molecules, water contains only one type of structural element, namely “flickering” network structures with tetrahedrally hydrogen‐bonded water molecules (two‐states model) is proving inadequate in the interpretation of new experimental data and in the calculation of thermodynamic functions. After a critical discussion of the basis of this model and of the concept of hydrogen bonds, a second kind of structural element, i.e. a third state, is suggested: small aggregates of molecules containing mainly non‐tetrahedral hydrogen bonds as well as some tetrahedral ones, and packed more densely than allowed by the lattice‐like structure. These aggregates – dimers to hexamers – can be regarded as the primary products of disruption of the network structures, and displace the latter as structural components in water with increasing temperature or concentration of solutes. This “combined” model allows a consistent interpretation of the properties of water and of the various effects of dissolved substances.
The Biosynthesis of Cyclitols
Authors: Kindl H. , Scholda R. , Hoffmann‐Ostenhof O.
Published: December 2003

Information has recently been obtained, mainly with the aid of radioactive compounds, about the biosynthesis of various cyclitols. It was found that the most widely occurring cyclitol, meso‐inositol, is biosynthesized by a pathway probably common to all organisms, in which the cyclohexane ring is formed by ring closure between the two terminal carbon atoms of D‐glucose. Cell‐free extracts or enzyme systems that catalyse the conversion of D‐glucose into meso‐inositol can be prepared from various biological materials. The biosynthesis of the other hexahydroxycyclohexanes (inositols) involves meso‐inositol as an intermediate. A few steps in the conversion of meso‐inositol into other inositols have been studied.
The Passivity of Metals
Authors: Schwabe K.
Published: December 2003

After a survey of the various factors, depending both on the metal and on the attacking substance, that can influence the anodic dissolution of metals, the nature of the passive layer is discussed on the basis of electrochemical and optical studies. Passivation is characterized by a rapid decrease in the anodic current density as the Galvani tension is increased; this is due to the presence of a monomolecular layer, which prevents the metal ions from passing across the phase boundary. The growth of this layer is strongly influenced by transport processes, particularly with in the layer itself. The kinetics of the passivation and activation processes can be explained by the simultaneous occurrence of competing reactions which depend on the potential; exchange adsorption appears to play some part in the passive behavior of metals towards various acids.
Automation of Structure Analysis. Part II. Automation of the Evaluation
Authors: Hoppe W.
Published: December 2003

The extent to which it is possible to automate the determination of a structure from the data collected with automatic measuring equipment is discussed. The development of the automatic evaluation is synchronous with that of digital computer program.—Even the simple calculation of structure factors from the intensities (i.e. the analysis of the geometrical and physical intensity factors) takes several weeks when the many thousand reflections are processed “manually”, i.e. with a desk calculator. A large electronic computer, on the other hand, executes these calculations in a few seconds. Nevertheless, even the largest computers available at present are too small for many of the complex steps in the calculation and for the quantity of data involved. Evaluation methods which, owing to long computing times, can at present only be tested on relatively simple structures will become more attractive with the advent of machines with computing times in the nanosecond range.

For corrigendum see DOI:10.1002/anie.196605112
The Structure of Glasses
Authors: Krebs H.
Published: December 2003

A melt can readily solidify to a glass with a three‐dimensional or two‐dimensional network, or a chain structure, provided that an irregular bonding system can be formed by virtue of free rotation about the bonds between a central atom and the ligands which function as bridging atoms. Such an irregular structure can arise when the system contains a sufficient amount of bridging atoms such as O, F, and S, or bridging groups such as CH2, with bond angles less than 180°. When the network is formed predominantly by trivalent and tetravalent elements, such as As and Ge, the glasses – though they cannot be prepared by cooling of melts – can be obtained by other processes, e.g. by condensing the vaporized substances onto a surface (glasses in the wider sense of the word). As a result of extensive network formation, the bonding systems and, therefore, the short‐range order of the atomic arrangement in the melt differ from those in the glass or the crystal. A liquid mixture of substances having unlike molecular size and shape also can form a glass on solidification. Moreover, glasses can be formed even when the systems contains only one component opposing regular packing into a crystal lattice.
On the Secondary Structure of Soluble Ribonucleic Acids
Authors: Doepner H. , Seidel H. , Cramer F.
Published: December 2003

For corrigendum see DOI:10.1002/anie.196608472
Problems of Iron Metabolism with Special Reference to Biochemical, Physiological, and Clinical Aspects
Authors: Keiderling W. , Wetzel H. P.
Published: December 2003

A brief account of the functions and chemical structures of the principal iron compounds found in the human body is followed by a discussion of the physiology of iron metabolism, starting with its resorption, continuing with its transport and assimilation by the body cells, and concluding with its elimination. Special attention is paid to the problems of intracellular and extracellular transport of iron. A number of diseases with characteristic disturbances of the iron metabolism are also briefly described.
Electron Pyrolysis, a New Method of Organic Microanalysis
Authors: Schildknecht H. , Enzmann F. , Gessner K. , Penzien K. , Römer F. , Volkert O.
Published: December 2003

Organic compounds incubated with tritiated water of specific activity 5 Ci/ml are specifically fragmented. The β‐active fragments can be detected in very small quantities by chromatographic separation. Chemical identification of these fragments provides information about the original compounds, as has been shown by experiments with amino acids, esters, lactones, amides, quinones, terpenes, nitrogen‐sulfur heterocycles, and natural products.
Methods for the Synthesis of Uniform Polymers
Authors: Winter J. H.
Published: December 2003

The difficulties encountered in the preparation of polymers that are uniform chemically, structurally, and in their molecular weight are due mainly to the wide variety of possible polymers. This arcticle gives a review of attempts to synthesize homogeneous polymers by chain reactions and by stepwise synthesis. Syntheses on templates are extremely important in living cells; methods have recently been found for syntheses of this type that are independent of natural processes. Uniform polymers can also be obtained by reactions on existing polymers. In replicating polymers, this in principle requires the modification of only one polymer molecule.
Syntheses of Carboxylic Acids from 1, 1‐Dichloroehylene
Authors: Bott K. , Hellmann H.
Published: December 2003

Many β‐alkyl‐ and β‐arylpropionic acids are readily obtainable by the reaction of secondary or tertiary alcohols, esters of these, or olefins with the inexpensive 1, 1‐dichloroethylene in sulfuric acid. The success of the synthesis depends on the bulk and energy of the carbonium ion intermediate formed from the alcohols or olefins. With carbonium ions having one H atom attached to the carbonium C atom, electrophilic substitution of the 1,1‐dichloroethylene takes place to a small extent. Dicarboxylic acids and carboxylic acids with higher molecular weights are sometimes formed as a result of side reactions.
Reactions of the Carbonyl Group in Fluorinated Ketones
Authors: Gambaryan N. P. , Rokhlin E. M. , Zeifman Yu. V. , Ching‐yun Chen , Knunyants I. L.
Published: December 2003

The chemistry of polyfluorinated ketones has recently received a great deal of attention.

A. Ya. Yakoubovich, Usp. Chim. 25, 3 (1956).

H. P. Braendlin and E. T. McBee in: Advances in Fluorine Chemistry. Butterworths, London 1963, Vol. 3, p. 1.

The review by Braendlin and McBee [2] does not deal only with perfluorinated ketones; moreover, though published in 1963, it is already outdated. The papers discussed in [1,2] will not be reviewed in the present article.

. The carbonyl and imino groups of the fluorinated ketones and their imines react in many different ways. In particular, the electron‐attracting perfluoroalkyl groups intensify the electrophilic properties and weaken the nucleophilic properties of the carbonyl group. The perfluoroalkyl group also hinders the heterolytic removal of the hydroxyl group from adducts by reducing the stability of the carbonium ion . The increased electrophilicity of the carbonyl group and the increased stability of the addition products leads not only to a change in reactivity in the characteristic ketone reactions, but also to numerous new reactions which are not observed with non‐fluorinated ketones. Thus it is possible to synthesize a wide variety of fluoroorganic compounds from perfluorinated ketones.

We have been concerned mainly with hexafluoroacetone, since in addition to being the most readily available and simplest perfluorinated ketone, this is also a typical representative of this class of compounds.

.
Conformational Aspects of Many‐Membered Rings
Authors: Dale J.
Published: December 2003

The stereochemistry of the various chemical grouping which constitute the structural units of ring systems is first reviewed. It is then shown that the strain‐free possibilities even of large rings are restricted, and that the ring conformation theoretically derived generally correspond to those found by physical methods. Variations of physical properties and of cyclization yield in homologous series are explained on a conformational basis.
New Methods of Preparative Organic Chemistry V: Organic Syntheses with Imides of Sulfur Dioxide
Authors: Kresze G. , Wucherpfennig W.
Published: December 2003

Cycloadditions and other reactions of compounds containing the groups NSO and NSN are reviewed.
Structures and Syntheses of Carboranes
Authors: Köster R. , Grassberger M. A.
Published: December 2003

Following a discussion of bonding, the structures of the known carboranes of the clovo type and of the incompletely condensed types are described; the recently discovered carboranes with high carbon contents, such as tetracarbahexaborane (“boracarbane”) are also discussed. The preparation of carboranes from polyboranes and the possibility of obtaining organo carboranes from organoboranes are then described. Some rearrangements which take place within the carborane skeleton are also mentioned.
Reactions with Molecular Oxygen
Authors: Fallab S.
Published: December 2003

Molecular oxygen is an important oxidizing agent both in industrial and in biological processes. In many of these processe, the O2 molecule reacts preferentially with free radicals, which are frequently paramagnetic metal ions. Homogeneous systems of this type that are described in the literature are discussed, and an attempt is made to establish the factors that determine the course and mechanism of the reaction.
Hexamethyl(Dewar Benzene) (Hexamethylbicyclo[2.2.0]hexa‐2,5‐diene)
Authors: Schäfer W. , Hellmann H.
Published: December 2003

Hexamethyl(Dewar benzene) was first obtained by bicyclotrimerization of 2‐butyne in the presence of aluminum chloride. This preparation provided a basis for a comprehensive study of the chemical reactivity of Dewar benzene derivatives. Interesting information concerning the reactivity of the permethylated Dewar benzene system can be deduced from its behavior on hydrogenation and oxidation, and, in particular, from the addition of H‐acidic compounds and from the substitution and elimination reactions of the resulting adducts.
Polymerization of Trioxane
Authors: Weissermel K. , Fischer E. , Gutweiler K. , Hermann H. D. , Cherdron H.
Published: December 2003

A survey of the possible modes of polymerization of trioxane is followed by a discussion of current ideas concerning the course of the polymerization. The polymerization, which involves ring cleavage, is characterized by a number of side reactions of the growing polyoxymethylene cations, such as chain transfer, transacetalization, and hydride shift. These reactions not only determine the nature of the end groups and the molecular weight of the resulting polyoxymethylenes, but are also responsible for their chemical and molecular uniformity. Special emphasis is placed on the role of the monomeric formaldehyde formed during the polymerization of trioxane.
Electrophilic Substitution of Heteroaromatic Compounds with Six‐Membered Rings
Authors: Katritzky A. R. , Johnson C. D.
Published: December 2003

The limited amount of quantitative data available on the electrophilic substitution of heterocycles is surveyed. Initial objectives are first to determine the species undergoing substitution and then to find out the amount by which the heterocyclic atom or group activates or deactivates the ring by comparison with the corresponding benzenoid compound. When sufficient data are available it is hoped to correlate this by means of a Hammett‐type treatment or by MO methods.
Formation and Properties of Carbosilanes
Authors: Fritz G.
Published: December 2003

The present paper describes the formation of silicon‐carbon compounds (carbosilanes), the molecular skeletons of which consist of alternate Si and C atoms, and which can be obtained by thermal decomposition of Si(CH3)4, CH3SiCl3, (CH3)2SiCl2, and (CH3)3SiCl. The description of the formation of carbosilanes is followed by a discussion of the reactions of polychlorinated carbosilanes with organometallic compounds.
Chemical Gamma‐Resonance Spectroscopy
Authors: Goldanskii V. I.
Published: December 2003

Two of the most important contributions that nuclear physics has made to modern science and technology have been in the fields of nuclear energy and isotope labeling. In recent years nuclear physics has stimulated the appearance and extremely rapid development of yet another new and equally important scientific discipline, namely gamma‐resonance spectroscopy. This new branch of spectroscopy, which is based on the Mössbauer effect[1–3] is playing an increasingly important role in physics, chemistry, biology, geology, and in the elucidation of various technical problems. – This paper deals briefly with the basic physics of the Mössbauer effect and the characteristics of Mössbauer (gamma‐resonance) spectra, and then considers various applications of this new type of spectroscopy. Particular attention is paid to the fundamentals and development of chemical gamma‐resonance spectroscopy [4–9] as a technique for the resolution of problems in various fields of chemistry and biology and to the range of problems tackled in recent years in our laboratory of nuclear and radiation chemistry at the Institute of Chemical Physics of the Academy of Sciences of the USSR. A number of reviews and monographs dealing with the application of the Mössbauer effect in chemistry have already been written [4–12]. The following work is based mainly on experimental results obtained by research workers in the Soviet Union.
Physical Causes of Aging in Plastics
Authors: Stuart H. A.
Published: December 2003

A number of physical changes that take place in a polymer below the glass transition temperature without the action of a medium are first described, and are then explained on the basis of changes in supramolecular order. Pure stress crazing with the characteristic self‐limitation of craze growth is then considered. Models are developed to explain stress crazing under the influence of a wetting medium. Attempts to reduce stress crazing are then treated and the article closes with a discussion of the influence of morphological structure on crazing and cracking.
Nitrenes and the Decomposition of Carbonylazides
Authors: Lwowski W.
Published: December 2003

The decomposition of organic carbonylazides can lead to the formation of nitrenes. Ethoxycarbonylnitrene is formed in the photolytic and thermal decomposition of ethyl azidoformate and by α‐elimination from N‐(p‐nitrobenzenesulfonyloxy)urethan. Both of the possible electronic states of this nitrene take part in intermolecular reactions. Pure singlet nitrene is formed by α‐elimination from the urethan and on thermal decomposition of ethyl azidoformate, but changes so rapidly into the triplet form that the reactions of both forms are observed. Singlet ethoxycarbonylnitrene undergoes selective and stereospecific insertion into CH bonds and adds stereospecifically to olefins. Triplet ethoxycarbonylnitrene, however, does not undergo insertion into CH bonds, and adds to olefins with complete loss of the geometric configuration. By following quantitatively the stereospecificity of the addition reaction and by selective interception of the triplet and singlet forms of the nitrene, it can be shown that the photolysis of ethyl azidoformate leads directly to nitrene of which one third is in the triplet state. In the decomposition of aryl‐ and alkylcarbonylazides (acid azides), the removal of nitrogen is accompanied by a synchronous rearrangement to isocyanates (Curtius rearrangement). In this system, nitrenes are obtained only by photolysis. They add to double bonds and undergo very selective insertion into CH bonds, but do not rearrange at a measurable rate to isocyanates. The photolytic Curtius rearrangement is also a concerted reaction.
Hydration of cn bonds in heteroaromatic substances
Authors: Albert A.
Published: December 2003

Many aromatic N‐heterocycles add water across the CN double bond. Methods are described for recognizing this phenomenon and for diagnosis of the site of attack. These methods are extended to the determination of (a) the ionization constants of unstable states (whether hydrated or anhydrous), (b) the ratio of hydrated to anhydrous forms at equilibrium, and (c) the rate constants of hydration. The features that stabilize hydration in a molecule are discussed. The literature through 1965 and 1966 is reviewed with special reference to the emergence of new principles, such as di‐hydration and the shifting of hydration within a molecule.
Formation and Properties of Medium and High Molecular Weight Compounds of Elements of Groups 3, 4, and 5
Authors: Fritz G.
Published: December 2003

The differences between compounds of carbon and of silicon are discussed, and the role of silicon as a fundamental structural component in inanimate nature is described. Starting with silicic acid and silicates, the structure and properties of the silicones and of compounds having SiCSi skeletons are described. The possibilities for the formation of high molecular‐weight compounds between elements of Groups 3 and 5 of the periodic system are considered, with particular reference to boron nitride and to aluminum‐phosphorus compounds.
Directed Aldol Condensations
Authors: Wittig G. , Reiff H.
Published: December 2003

The present article describes the discovery of a new procedure for aldol condensations for the preparation of α,β‐unsaturated carbonyl compounds

G. Wittig, H. Pommer, and W. Stilz, German Patent 1199252 (April 5, 1963), BASF; Chem. Abstr. 63, P 1739c (1965).

. The scope of this process is demonstrated by many examples, including some from the natural products sector; at the same time, however, these examples also mark its limitations. The metalated Schiff's bases may be classified as ambident anions; this also explains acylations on the nitrogen. A comparison of the new directed aldol condensation with the formation of unsaturated carbonyl compounds through olefination via phosphorylids shows that the latter method fails when a ketone is used as the substrate. This is where the described procedure using metalated Schiff's bases proves its value.
The Mechanism of the Wolff‐Kishner Reduction, Elimination, and Isomerization Reactions
Authors: Szmant H. H.
Published: December 2003

The mechanism of the Wolff‐Kishner reaction is discussed in the light of accumulated information about the kinetics, thermodynamics, and solvent effects of the process. Wolff‐Kishner reduction under normal conditions is thought to involve the trans hydrazone anion, which, in the rate‐determining step, exhibits a more or less concerted proton capture at the carbanion terminal and undergoes a solvent‐induced proton loss at the nitrogen terminal. The stereochemistry of the Wolff‐Kishner reduction is believed to be affected by the presence of “ortho” substituents and by a change to a nonpolar, aprotic reaction medium. The mechanism elaborated for the Wolff‐Kishner reduction is extended to the Wolff‐Kishner elimination and isomerization reactions. Conformational analysis of the intermediates permits correlation of the competitive reduction and elimination processes with the structures of acyclic systems.
Ternary Nitrides, Phosphides, and Arsenides of Lithium
Authors: Juza R. , Langer K. , Von Benda K.
Published: December 2003

Ternary phases have been prepared from lithium, another metal, and nitrogen, phosphorus, or arsenic. The ternary compounds, in particular the nitrides, are thermally more stable than the binary compounds. The lithium gives rise to a relatively high polar bonding component. At high temperatures, lithium and the second metal are often randomly distributed among the interstices of the metalloid lattice. The ordering processes that take place with decreasing temperature are investigated by X‐ray and magnetic methods and by differential thermal analysis. The phases are classified on a structural basis into seven groups.