bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recent Developments in Organotin Chemistry
Authors: Neumann W. P. , Burkhardt G. , Heymann E. , Kleiner F. , König K. , Niermann H. , Pedain J. , Schick R. , Sommer R. , Weller H. 
Published: December 2003

AbstractNew synthetic methods developed in the field of organotin compounds since 1959 are reviewed. The use of alkyl aluminum compounds brings an advance in the preparation of tetraalkyltin derivatives, alkyltin halides, and alkyltin hydrides. Organotin hydrides offer new possibilities for the production of monomeric and polymeric organotin compounds. Diethyltin and diphenyltin, which are obtained by catalytic dehydrogenation of the respective dialkyltin dihydrides, are cyclic compounds. – The literature since 1959 is reviewed.
Chemistry and Biochemistry of Insect Hormones
Authors: Karlson P. 
Published: December 2003

AbstractInsect hormones attracted the interest of endocrinologists only comparatively recently. This is partly due to the fact that an equivalent of sex hormones – the classical hormones of vertebrate physiology – is unknown in insects. Castration has no marked effect on the secondary sexual characters. Insect hormones act primarily on developmental processes; the metamorphosis hormone, ecdysone, is the best studied. Recent investigations have shown that ecdysone has the empirical formula C27H44O6 and belongs to the streroids. The mechanism of its action is seen in its influence on the chromosomes. – Other hormone‐like substances, the pheromones, are outstanding for their high activity; a few molecules are sufficient to trigger the characteristic behavioural response.
Fast Gas Reactions in Shock Waves and Detonations
Authors: Jost W. , Just T. 
Published: December 2003

AbstractShock waves provide a simple means of achieving high temperatures and hence of studying the kinetics of endothermal processes, e.g. dissociation reactions, above 100 °K. Detonations can also be used for this purpose, but are restricted to a few exothermal mixtures. The production and properties of shock waves and detonations and the most important analytical methods used for kinetic investigations are described, and some typical results are discussed.
Emulsion Polymerization of Vinyl Monomers under the Influence of Ionizing Radiation
Authors: Hummel D. 
Published: December 2003

AbstractIonizing radiation induces the polymerization of some vinyl monomers in aqueous emulsion with high radiation yields. With identical emulsion compositions, the kinetics of this reaction and the kinetics of emulsion polymerization induced by water‐soluble initiators are very similar. The rate of reaction in emulsion polymerization is about one hundred times greater than in bulk polymerization. The initiation of emulsion polymerization by means of ionizing radiation permits uniform “illumination” of the reacting volume, as well as almost any desired variation in the frequency of initiation during the reaction. The sharp decrease in the overall rate of reaction when initiation is interrupted during emulsion polymerization of styrene induced by γ‐rays contradicts the earlier concept of sharply separated reaction zones.
Principles and Techniques of Diffuse‐Reflectance Spectroscopy
Authors: Kortüm G. , Braun W. , Herzog G. 
Published: December 2003

AbstractThe prerequisites for applicability of the Kubelka‐Munk theory of diffuse reflectance for obtaining characteristic color curves of powders are discussed, and some experimental support for the theory is given. Methods are described for eliminating surface reflection, which is always superimposed upon the diffuse reflection and which therefore distorts the spectrum. The effect of interactions with the adsorbent on the reflection spectra of adsorbed molecules is demonstrated by means of examples, and the special suitability of the method for investigating chemisorption and for following reactions at phase boundaries is pointed out. By analogy to the Beer‐Lambert law, the Kubelka‐Munk function can be used for quantitative photometric analysis. The reflectance curves of white standards are presented, and measurements relating to the conditions for “infinitely thick layers” are reported. The scattering coefficient of the Kubelka‐Munk functions has been estimated for several samples of color‐filters as a functions of grain‐size and wavelength. The effect of moisture on diffuse reflectance spectra is discussed, and details of the measuring techniques are presented.
Formation and Cleavage of Dihydroxydiarylmethane Derivatives
Authors: Schnell H. , Krimm H. 
Published: December 2003

AbstractDihydroxydiarylmethane derivatives are formed by condensation of aromatic hydroxy and carbonyl compounds in the presence of acidic condensing agents at low temperatures or in the presence of bases at elevated temperatures. This article deals with formation and cleavage mechanisms in acid and basic media. As a result of the investigations reported, new methods of preparing unsymmetric dihydroxydiarylmethane derivatives and p‐alkenylphenols have been developed.
Production of Polyhydric Alcohols from Wood Polysaccharides
Authors: Sharkov V. I. 
Published: December 2003

AbstractBy hydrolysis and hydrogenolysis, plant polysaccharides, i.e. mainly cellulose and hemicelluloses, can be converted with high yields into polyhydric alcohols (hexitols, pentitols, glycerol, ethylene glycol, propylene glycol). Procedures which have been developed in the U.S.S.R. are described. Of particular interest is the simultaneous hydrolysis and hydrogenolysis of plant polysaccharides with noble metal catalysts. Here yields are almost quantitative.
Oligomers and Pleionomers of Synthetic Fiber‐Forming Polymers
Authors: Zahn H. , Gleitsman G. B. 
Published: December 2003

AbstractThe term “oligomer” is defined, and a survey of methods for the isolation and synthesis of cyclic and linear oligoesters, oligourethanes, oligo(acrylonitriles), and oligoamides is presented. The oligomers serve a valuable function as model substances for the investigation of many properties of the corresponding high polymers. This is shown using several examples (infrared spectroscopy, X‐ray spectroscopy, viscosity).
Permethylation of Oligomeric and Polymeric Carbohydrates and Quantitative Analysis of the Cleavage Products
Authors: Wallenfels K. , Bechtler G. , Kuhn Richard , Trischmann H. , Egge H. 
Published: December 2003

AbstractMethylation of mono‐, oligo‐, and polysaccharides with methyl iodide/barium oxide or dimethyl sulfate/barium hydroxide in dimethyl sulfoxide as solvent rapidly leads to high degrees of methylation. Depending on the structure and solubility of the substrate, permethylation can be achieved either in one operation or by repetition of the same treatment. Procedures of permethylation of various carbohydrates are given. The methyl glycosides obtained on methanolysis can be separated and determined quantitatively by gas chromatography. The preparation of separating columns with minimum retention for this purpose is described. Pullulan was shown to have the structure of a completely linear polymer of maltotriose units connected by α‐1→6‐linkages. – In addition the gaschromatographic identification of methyl ethers of glucosamine and galactosamine is reported.
Preparation of N‐Alkoxyureas and Their Use as Selective Herbicides
Authors: Scherer O. , Hörlein G. , Härtel K. 
Published: December 2003

AbstractN‐(4‐Chlorophenyl)‐N′‐methoxy‐N′‐methylurea (Aresin®)‐ and N‐(3,4‐dichlorophenyl)‐ N′‐ methoxy‐N′ ‐methylurea (Afalon®) are two new herbicides with characteristic selective activity. A simple and convenient method for their preparation is described.
Recent Developments in the Chemistry of Aminoboranes
Authors: Niedenzu K. 
Published: December 2003

AbstractThe isosterism of BN and CC grouping invites comparisons. Recent investigations on substituted aminoboranes R1R2NBR3R4 have been attempted in order to evaluate this concept of isosterism. Some of the latest results include evidence for geometric isomerism due to hindered rotation about the BN bond, isolation of isomeric compounds which can be considered as formal analogues of cyclohexanes, and the incorporation of BN groups into aromatic systems.
Equilibrium and Nonequilibrium in the Glycolysis System
Authors: Bücher Th. , Rüssmann W. 
Published: December 2003

AbstractThe relationship between the metabolic throughput within the network of energy‐furnishing metabolism and the deviation of its composite reacting units from equilibrium is discussed. Measurements have been made of the steady‐state relaxation times, and, following a suggestion by Alberty, their application is described. The results confirm and extend the concepts of intracellular redox relationships which the authors' research group outlined five years ago in this journal. The maximum difference between the redox potentials of the lactate/pyruvate and of the DPN/DPNH systems was calculated to be 2 mV. Deviations of the α‐glycerophosphate/dihydroxyacetone phosphate system measured in vivo are correlated with the rate of flow in the glycerophosphate cycle.
Amides of the Alkali and the Alkaline Earth Metals
Authors: Juza R. 
Published: December 2003

AbstractFollowing preparative work, the behavior of amides towards excess ammonia (ammoniate formation) and on removal of ammonia (degradation to imides)was studied particularly with regard to the solid state (crystal structure) and the transition to the liquid phase (melting point). Energy relationships are discussed on the basis of enthalpies of formation. Studies on ternary amides and imides are still in the initial stage. – Emphasis is laid here on the establishment of parallels between amides and hydroxides as well as between the aquo and ammono systems, and also on the differences between the amides with their dipolar NH2‐ anion, and the halides. The results, although still incomplete, permit a survey to be given of experimental data with the aid of information obtained from the pertinent literature.
Intramolecular Free‐Radical Reactions
Authors: Heusler K. , Kalvoda J. 
Published: December 2003

AbstractIn the present article an attempt is made to summarize the steric requirements and the influence of neighboring groups which determine the course of intramolecular radical reactions. Steroids are used as substrates for these reactions, since here the spatial arrangement of the ring members and the distances between substituents are largely fixed. Furthermore, intramolecular free‐radical reactions are of practical importance in steroid chemistry in connection with substitution at non‐activated carbon atoms. Almost all the reactions discussed begin with the formation of an oxygen radical by oxidation of an alcohol with lead tetraacetate or by homolysis of the corresponding hypoiodite.
The Design of Phosphorylating Agents
Authors: Clark V. M. , Hutchinson D. W. , Kirby A. J. , Warren S. G. 
Published: December 2003

AbstractPhosphorylating agents are compounds capable of transferring the group (HO)2P(O) in free or esterified form. Numerous phosphorylating agents can be classified into PXYZ systems, in which the element or group Z must be capable of accommodating the electrons of the PX bond. Systematic classification of PXYZ compounds and numerous examples of phosphorylation in chemistry and biochemistry are given.
Fundamental Aspects of Diffusion Processes
Authors: Jost W. 
Published: December 2003

AbstractA simple description of diffusion processes and a derivation of the general laws of diffusion are given. The distribution with time of particles according to a random‐walk process is considered and compared with results derived from a differential equation. Diffusion coefficients for and examples of diffusion processes in various media (e.g. gases, solutions, solids, and high polymers) are given. “Uphill” diffusion, i.e. diffusion against the concentration gradient is also discussed. In addition, diffusion in anisotropic systems, in systems consisting of more than one phase and in multicomponent systems is treated.
Photochemical Substitutions on Metal Carbonyls and Their Derivatives
Authors: Strohmeier W. 
Published: December 2003

AbstractThe photochemical reaction of n‐ and π‐electron donors with metal carbonyls or their derivatives, which was discovered some years ago, provides a means of preparing a wide range of new metal‐carbonyl derivatives which are obtainable only in poor yields or not at all by thermal reactions. – Preparative methods are described. The mechanism of this photochemically induced substitution was elucidated for selected examples, and an attempt has been made to gain an insight into the polarity of the metal‐ligand bond. – This paper is intended as a survey of work published recently in this field.
Recoil Reactions of Tritium with Organic Compounds
Authors: Schmidt‐Bleek F. , Rowland F. S. 
Published: December 2003

AbstractAfter “cooling”, the hot tritium atoms formed above thermal energies by nuclear reactions abstract or replace hydrogen atoms, and replace substituents X (e.g. alkyl, NH2, NO2, OH, COOH, F, Cl, Br, or I) in organic compounds. Isotope effects have been observed for protonated vs. deuterated compounds in several hot reactions. Models and mechanisms are discussed for the abstraction and replacement, for specific reactions on certain carbon atoms, and for the isotope effects. These are based on steric, bond‐energy, and kinetic considerations.
Structure and Crystallization Behavior of Glasses
Authors: Vogel W. 
Published: December 2003

AbstractAlmost all optical and technical glasses contain micro‐heterogeneities which can be seen using an electron microscope. These heterogeneous regions are shaped like small drops, and their size (20 to 500 Å) depends on the construction of the glass, on its temperature‐history, on the field strength of the cations, and also on the adjacent gas atmosphere. ‐ Preparation of valuable ultramicrocrystalline ceramics for industrial use from ordinary and photosensitive glasses involves controlled phase‐separation processes and subsequent crystallization.
Reactions of Metal Acetylacetonates
Authors: Collman J. P. 
Published: December 2003

AbstractCertain metal acetylacetonates undergo reactions characteristic of aromatic systems. Outstanding among these are electrophilic substitutions and the formation of a stable diazonium fluoroborate. Unsymmetrically substituted chelates have been prepared by stepwise substitution of trifunctional complexes. Chemical and physical properties of such mixed‐ring complexes provide evidence for intramolecular interannular electronic effects transmitted through the metal ion.
The Chemistry of Diimine
Authors: Hünig S. , Müller H. R. , Thier W. 
Published: December 2003

AbstractThe presence of diimine in solution can be shown conclusively by the stereospecific cishydrogenation of symmetrical multiple bonds. Apart from reactions which have hitherto been attributed to hydrazine, this review deals primarily with the various sources and secondary reactions of diimine.
New Cotton Dyes
Authors: Hensel H. R. , Lützel G. 
Published: December 2003

AbstractThe present paper deals with new cotton dyes, approaching the subject from two directions. In the first section the synthesis of a new type of reactive dye from products of Peppeacetylene chemistry is reported. The second part describes a dyeing process which does not stat with reactive dyes. Instead, the homopolar bonding between dye and cotton is formed by linking the dye to the substrate via polyfunctional bridges. These two programs have led to the development of the ®Primazin P and ®Basazol dyes.
Relationships between Structures and Mass Spectra of Organic Compounds
Authors: Spiteller G. , Spiteller‐Friedmann Margot 
Published: December 2003

AbstractOur knowledge concerning the relationships between the structure and mass spectra of organic compounds has widened immensely during the past few years. It has become possible to alter the course of fragmentation in the mass spectrometer by changing certain substituents using simple chemical reactions. The fragmentation products formed are then entirely different from those of the starting material. A combination of controlled mass‐spectrometric decomposition with chemical microreactions often permits the solution of complicated structural problems with a minimum expenditure of time and material. One example for the alteration of the fragmentation pattern by a simple chemical reaction is discussed in connection with the elucidation of the structure of pleiocarpamine.
Color and Constitution of Azo Compounds
Authors: Bock H. , Rudolph G. , Baltin E. , Kroner J. 
Published: December 2003

AbstractAttempts to explain the surprising violet color of the new azobisphosphonic acid derivatives Y2OPNNPOY2 have led to the preparation and spectroscopic characterization of more than 60 azo compounds. The long‐wavelength n → π* transitions on which the color depends exhibit regularities which justify the assumption of substitutent‐specific absorption increments. The complex relation between color and constitution of azo compounds can be qualitatively explained with the aid of orbital models. Infrared and ultraviolet spectral data show that conjugation is inhibited by tetra‐coordinated phosphorus (V). the π‐system of these compounds therfore comprises only for atoms, P·N·N·P. The unexpected violet color of the phosphorus azo compounds can be ascribed to a π*/d orbital interaction. The substituent effects described have general significance, and n→π*transitions of other chromophores are similarly affected.
Automation of X‐Ray Structural Analysis Part I. Automation of the Measuring Process
Authors: Hoppe W. 
Published: December 2003

AbstractThe present paper is the first of two reports describing the principles which can be applied to the construction of automatic counter‐tube diffractometers for the X‐ray analysis of crystals. These instruments can reduce the time required for the analysis of an organic crystal (measurement of a few thousand intensities) from several months (by the photographic method) to a few days.
A Code for the Classification of the Ultraviolet Spectra of Organic Compounds
Authors: Pestemer M. , Bergmann G. , Perkampus H.‐H. , Schrader B. 
Published: December 2003

AbstractThe ultraviolet spectra of all organic compounds can be classified according to the chemical constitution with the aid of a simple code based on a ten‐digit decimal system, each digit indicating the “spectroscopic weight” of the encoded information. The code discussed here will shortly be used in the Atlas of Ultraviolet Spectra which appears in the Documentation of Molecular Spectroscopy Series.
Fluorosulfuric Acid as a Reaction Medium and Fluorinating Agent in Inorganic Chemistry
Authors: Engelbrecht A. 
Published: December 2003

AbstractFluorosulfuric acid is known both in aqueous solution and as the anhydrous compound. The anhydrous acid exhibits electrical conductivity which indicates its autodissociation. Even strong acids such as H2SO4 or HCIO4 behave as proton acceptors, i.e. as bases, in fluorosulfuric acid. Volatile inorganic acid fluorides can be readily prepared using fluorosulfuric acid as fluorinating agent.
Progress in the Chemistry and Molecular Biology of Flavins and Flavocoenzymes
Authors: Hemmerich P. , Veeger C. , Wood H. C. S. 
Published: December 2003

AbstractAn attempt is made to create a basis for the understanding of flavin‐ (Vitamin B2‐) dependent oxidations in terms of molecular structure. The main points of this survey can be summarized as follows: (a) The flavins must be differentiated according to their redox states (quinone state, radical state, hydroquinone state), since configuration, energy content of the tautomeric forms, metal affinity etc., alter drastically during reduction. – (b) The methyl group on C‐8 of the flavoquinone is reactive. – (c) The electron transfer properties of the flavin system frequently depend on the coupling of secondary redox systems to the apoprotein. This interaction thermodynamically stabilizes the half‐reduced state of the flavin. – (d) Numerous novel flavin types, among them stabilized free radicals, have become available through syntheses at the dihydro stage. – (e) Reaction of the flavin radical with O2 is slow as long as no disproportionation occurs, i.e. the fast flavin autoxidation proceeds via the dihydro state. – (f) The flavin nucleus gains affinity for heavy metal ions only by the acceptance of one, and only one, electron. – (g) Redox activity and contact with the flavin coenzyme have been confirmed for Fe and Mo, which occur in flavoproteins. The properties of the metal coordination sphere are determined primarily by sulfur‐containing groups of the apoprotein.
1,2‐Dehydrobenzene
Authors: Wittig G. 
Published: December 2003

AbstractThe historical development of the methods to generate dehydrobenzene is outlined. Dehydrobenzene readily adds nucleophilic as well as electrophilic partners. Diels‐Alder addition to dienes is moreover a valuable synthetic principle. The intermediacy of dehydrobenzene has been proved for polar additions by labeling with 14C or with a substituent. The same conclusion has been reached in Diels‐Alder additions by competition experiments. The considerable selectivity displayed by dehydrobenzene in both types of reaction is not caused by solvation, since recently the existence of dehydrobenzene in the gas phase has been established, where it reacts similarly as in solution.
Progress in Optical Circular Dichroism
Authors: Velluz L. , Legrand M. 
Published: December 2003

AbstractAn apparatus first described in 1961 for the measurement of circular dichroism down to 220 mμ has been improved and its range extended down to 185 mμ. Some examples are given in the field of dienes, conjugated ketones, and aromatic chromophores. A more extensive study of protein structures was developed with the following results: (a) helical polypeptides show a complex dichroism in the far ultraviolet with three components (192 mμ, 204 mμ, 225 mμ), characteristic of the helical array of peptide groups; (b) human serum albumin shows a very similar curve of dichroism and is 60% helical; (c) urea denaturation, as judged by dichroism, is a reversible phenomenon; (d) a solvent such as chloroethanol increases the helical content of human serum albumin and clupein and has only a very small action on poly‐L‐glutamic acid; (e) the rupture of SS bonds in human serum albumin favors the attack of denaturing agents such as urea; (f) detergents help to maintain the rigid structure of human serum albumin after the rupture of SS bonds.
The Alkylating Properties of Alkyl Thiophosphates
Authors: Hilgetag G. , Teichmann H. 
Published: December 2003

AbstractThiophosphate and phosphate esters have been synthesized in great variety since about 1945, and are being produced in increasing quantities, mainly for plant protection. An important property of alkyl phosphates and thiophosphates is their alkylating power, which is comparable with that of dialkyl sulfates and alkyl p‐toluenesulfonates. The chemistry of thiophosphates is largely determined by their alkylating properties, since the sulfur, both in the alkyl thiophosphate and in the thiophosphate anion formed on dealkylation, can act as a point of attack for self‐alkylation.