bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclic Compounds as Configurational Models for Stereoregular Polymers
Authors: Farina M. , Peraldo M. , Natta G. 
Published: December 2003

AbstractIt is possible to draw analogies between linear polymers and cyclic compounds. Stereochemical considerations developed in this connection led to the recognition of new aspects of importance for the systematic classification of both classes of compounds; for example, asymmetric structures can be predicted which had hitherto never been suspected. – The concept of “diasteric centers” is introduced, and the definition of an “asymmetric center” is expressed in more general terms.
New Methods in the Chemistry Pyridazones
Authors: Dury K. 
Published: December 2003

AbstractA new synthesis of mucochloric acid by chlorination of butynediol has facilitated the preparation of a series of 4,5‐dichoropyridazones. The high reactivity of these compounds has been investigated and applied in several ways. New classes of compounds, some with biological activity, were obtained by displacement of the chlorine atoms. New heterocyclic systems were prepared by condensation and rearrangement reactions.
The Chemistry of Vinylsulfonic Acid
Authors: Distler H. 
Published: December 2003

AbstractVinylsulfonic acid and its derivatives can be prepared from β‐chloroethanesulfonyl chloride or carbyl sulfate (β‐hydroxysulfonyloxyethanesulfonic anhydride). The chemistry of vinylsulfonic acid has assumed industrial importance since the discovery of a simple synthesis of β‐chloroethanesulfonyl chloride from chloroethane or ethane, sulfur dioxide, and chlorine by the Reed process. Carbyl sulfate is as important a starting material as β‐chloroethanesulfonyl chloride, and surpasses the latter in some respects, e.g. on account of the low price of its components ethylene and sulfur trioxide. Vinylsulfonates undergo addition reactions with alcohols, phenols, thiols, sulfinic acids, carboxylic acids, amides, imides, and hydrazides, as well as with amines, ureas, diazonium salts, and nitroparaffins. Furthermore, they undergo halogenation, nitration, olefination, and the Diels‐Adler reaction. – Methods for the preparation of the free vinylsulfonic acid are described. Alkyl vinylsulfonates are excellent alkylating agents. The derivatives of vinylsulfonic acid are used e.g. as plasticizers, emulsifiers, and fungicides.
Formation of Free Radicals in Polyamide Fibers during Drawing
Authors: Matthies P. , Schlag J. , Schwartz E. 
Published: December 2003

AbstractThe formation of free radicals during the process of drawing of spun fibers was observed for the first time with two polyoxamides. The fibers turn red, and an ESR signal can be detected. Both, color and ESR absorption are not permanent. The decrease in the intensity of the ESR absorption and the change in the optical reflectance with time, as well as the dependence of the decoloration on temperature were investigated. The action of high‐energy radiation on the polyoxamides also leads to a red coloration and gives rise to ESR signals. It is concluded that the red color is due to free radicals associated with the oxamido group.
The Function of the promotors in the Technical Ammonia Catalyst
Authors: Krabetz R. , Peters Cl. 
Published: December 2003

AbstractAn attempt is made to give a phenomenological description of the relationships between the catalytic activity and the distribution of the promotors in the reduced ammonia catalyst. Investigations were carried out on series of catalysts whose compositions were gradually brought closer to that of technical ammonia catalysts by the addition to iron of one new activator (Al2O3, K2O, CaO, MgO, SiO2) at a time.
New Finding in the Chemistry of the Lower Oxides of Sulfur
Authors: Schenk P. W. , Steudel R. 
Published: December 2003

AbstractImportant advances have recently been made in the chemisty of the lower oxides of sulfur, both in the preparative sphere and by the application of modern physical methods of investigation. In this paper the knowledge gained to date on the compounds SO, S2O2, S2O, S2O3, and the polysulfur oxides is reviewed and critically appraised.
The Prostaglandins
Authors: Samuelsson B. 
Published: December 2003

AbstractProstaglandins occur in many animal species and tissues. They are C20‐carboxylic acids contining one five‐membered ring, one keto group, two or three hydroxy groups, and one to three CC double bonds. Their structures were elucidated by chemical, radiochemical, and physical methods in combination with gas chromatography and mass spectrometry. The prostaglandins are biosynthesized from essential fatty acids. By their action smooth muscles are stimulated and lipid metabolism is affected.
Isonitrile Syntheses
Authors: Ugi I. , Fetzer U. , Eholzer U. , Knupfer H. , Offermann K. 
Published: December 2003

AbstractIn spite of the large number of reactions which involve the formation of isonitriles, the only preparative routes to these compounds, until recently, were the classical isonitrile syntheses discovered about one hundred years ago by Gautier and Hofmann. These methods are not generally applicable, and give satisfactory yields only in exceptional cases. Isonitriles have recently become readily available by the elimination of water from N‐substituted formamides, using acyl halides of Group IV–;VI elements in the presence of bases as dehydrating agents. A dehydrating system with a particularly wide range of application consists of phosgene with tertiary amines. This system generally provides the easiest and most productive route to isonitriles, particularly where large quantities (> 1 mole) are to be prepared.
The Structure of Sugar Phenylosazones
Authors: Mester L. 
Published: December 2003

AbstractThe open‐chain chelate structure of sugar osazones, first proposed by Fieser and Fieser, has now been confirmed by chemical methods, X‐ray analysis, and NMR spectroscopy. These investigations showed that the properties of sugar osazones are best described by a formula containing a quasi‐aromatic chelate ring.
Melting and Crystal Structure — Some Current Problems
Authors: Ubbelohde A. R. 
Published: December 2003

AbstractThe “classical” definition of liquid and solid phases acording to mechanical criteria is unsatisfactory. It is now know that “premelting” effects occur in crystals, and in many liquids the formation of clusters is observed near the melting point, with structures which can correspond to the short‐range order of the crystals from which the melt is derived.–In particular, the implications of the theories of Lennard‐Jones and Devonshire and of Mizushima and Ookawa are discussed.
Valence‐Bond Isomers of Aromatic Systems
Authors: van Tamelen E. E. 
Published: December 2003

AbstractThe prefix xn is proposed for the classification of valence‐bond isomers of aromatic systems, where n is the change in the number of rings or in the number of π‐bonds on isomerization. Representatives of the x1‐series are Dewar benzene and 9, 10‐dihydronaphthalene. Benzvalene and prismane belong to the x2 and x3 series, respectively. Various derivatives of such valence‐bond isomers have recently become known.
Valence‐Bond Isomers of Substituted Benzenes
Authors: Viehe H. G. 
Published: December 2003

AbstractDewar benzene, Ladenburg benzene (prismane), and a combination of these bond systems (benzvalene) have variously been discussed as planar limiting structures of benzene, although they have no physical reality. If, however, we regard these systems as non‐planar structures (as did their originators), they become chemical individuals, derivatives of which have recently been isolated. In addition to being a valance‐bond isomer of benzene, benzvalene is also the first member of a still largely hypothetical series of molecules (the valenes), in which the skeleton atoms can change places with their neighbors to produce the valencebond isomers. The best‐known representative of this class is bullvalene.
On the Analysis of Photosynthesis by Flashlight Techniques
Authors: Witt H. T. , Rumberg B. , Schmidt‐Mende P. , Siggel U. , Skerra B. , Vater J. , Weikard J. 
Published: December 2003

AbstractDirect information regarding the primary process in photosynthesis is obtained by measurement of the very short‐lived primary and intermediate products with the aid of (1) flash photometry, (2) periodic flash photometry, and (3) flash manometry. The analysis of the primary process using these methods on normal plant cells and chloroplasts and on those which have been chemically or physically modified has led to the formulation of a reaction scheme for the transport of electrons in photosynthesis.
Structure Determination of Free Molecules by Electron Diffraction
Authors: Almenningen A. , Bastiansen O. , Haaland A. , Seip H. M. 
Published: December 2003

AbstractThe intensity of electrons scattered by a gas can be calculated with classical as well as with quantum‐mechanical methods. The range of validity of the equations obtained can be found experimentally. Comparison of the calculated and empirical intensity or radial distribution curves allows the determination of the structure and amplitudes of vibration of a molecul. – For example, it has been found that the two bromine atoms in cis‐1, 3‐dibromocyclobutane occupy equatorial positions. The benzene rings in biphenyl derivatives are inclined at about 45° to each other. In biscyclopentadienylberyllium, the metal atom is not located midway between the two rings.
Chemistry and Biochemistry of α‐Lipoic Acid
Authors: Schmidt Ulrich , Grafen P. , Goedde H. W. 
Published: December 2003

AbstractThe principal physiological function of lipoic acid appears to be its action as coenzyme in the oxidative decarboxylation of α‐oxo acids. In order to find out whether lipoic acid is essential to higher organisms, structurally modified lipoic acids were prepared as potential antagonists. Only 4‐oxalipoamide promotes the growth of S. faecalis 8043; the other substances tested are inactive or else inhibit growth. In experiments to determine the substrate specificity of lipoamide oxidoreductase and its inhibition by structurally modified lipoic acids, no strong inhibitors were discovered. –; Ring strain, spectra, and ring cleavage of compounds containing the 1, 2‐dithiolane ring are discussed in relation to the biological function and the reactivity of lipoic acid.
Extreme Values of the Pressure Coefficient of Viscosity
Authors: Kuss E. 
Published: December 2003

AbstractThe pressure coefficients of viscosity of hydrocarbons and ethers containing two to four phenyl groups linked either directly, via methylene bridges, or via CH(CH3) bridges, were studied with a view to elucidating the reason for the extreme viscosity‐pressure behavior of certain mineral oils. Measurements were made in the range of 1 to 2000 atm at 25, 40, 60, and 80 °C. The results show the existence of a simple relationship between molecular structure and viscosity‐pressure coefficient, and suggest applications in control engineering and lubrication technology.
A Method for the Preparation of Methylmetal Compounds
Authors: Sundermeyer W. , Verbeek W. 
Published: December 2003

AbstractA new method has been developed for the preparation of methylmetal compounds from methyl chloride and the chlorides of boron, aluminum, silicon, tin, phosphorus, antimony, or mercury. Fused salts are used as solvents, and metals are suspended in these to act as halogen acceptors. The metals are recovered, together with chlorine, by electrolysis. This process, which can be carried out continuously and quantitatively, can be used for the preparation of technically important methylmetal compounds that cannot be obtained directly by the “Mülheim aluminum alkyl method”.
The Separation of Zirconium and Hafnium by Liquid‐Liquid Partition of their Thiocyanates
Authors: Fischer Werner , Deierling B. , Heitsch H. , Otto G. , Pohlmann H.‐P. , Reinhardt K. 
Published: December 2003

AbstractThe partition equilibria of zirconium and hafnium thiocyanates between water and methyl isobutyl ketone have been studied under various conditions. Since the system shows extremely marked deviations from Nernst's distribution law, the two elements cannot be prepared in a very pure state by a simple multi‐stage partition. By the use of suitable additives and a new scheme of material flow, however, a continuous process using 23 mixer settlers has been developed, by means of which ZrO2 containing less than 10 p.p.m. of HfO2 and HfO2 containing only 0.3% of ZrO2 can be obtained from a zirconium‐hafnium mixture (hafnium content: 1 to 2%).
The Chemistry of Protactinium
Authors: Keller C. 
Published: December 2003

AbstractProtactinium exhibits an ambivalent chemical behavior. In non‐aqueous solutions and in the solid state, both quadrivalent and quinquevalent protactinium has properties which characterize it as a typical actinide element. On the other hand, investigations in aqueous solution show quinquevalent protactinium to be a homologue of niobium and tantalum. It exhibits – except in hydrofluoric acid solutions – a marked tendency to undergo irreversible hydrolysis and condensation reactions, which leads to the situation that tracer amounts (ca. 10−12mole/l) and macroscopic amounts (10−3–10−6mole/l) of protactinium often behave differently. Reduction with strong reducing agents gives aqueous solutions of Pa(IV), the properties of which again correspond in general to those of Th(IV) and show no relation to Nb(IV). Our knowledge of the chemical behavior of this rare radioelement has been advanced, in particular, by the production in 1958–1960 of 100 g of pure protactinium – the largest amount so far – from residues of the British production of uranium.
The Kinetics of Crystal Growth
Authors: Heyer H. 
Published: December 2003

AbstractThe fundamentals of the theory of crystal growth comprise the two concepts of growth via two‐dimensional nuclei and growth with the aid of dislocations. Measurements of the relationship between rate of growth and supersaturation are particularly suitable for testing theoretical predictions. Experimental results are compared with predictions for crystal growth from the vapor phase, from solution, and from the melt. Depending on the experimental conditions, examples of both types of growth are met irrespective of the nature of the mother phase.
Kinetic Relationships between Reactions in the Gas Phase and in Solution
Authors: Martin H. 
Published: December 2003

AbstractSome recent examples of reactions proceeding both in the gas phase and in solution have been investigated to determine their kinetics and mechanisms. The ratio of the corresponding rate constants, kG and kL, of the elementary processes studied has been found to be about unity for unimolecular reactions and between 1 and 10 for bimolecular reactions. The mechanisms, overall rates, rate constants, and activation energies have been determined for the homogeneous gas reaction NOCl + Cl2O = NO2Cl + Cl2 and the reaction NOCl + N2O5 = NO2Cl + 2 NO2, carried out in C2F3Cl3.
The Synthesis of Oligo‐ and Polynucleotides
Authors: Cramer F. 
Published: December 2003

AbstractProblems and results of the synthesis of oligonucleotides are reviewed. The central role of the nucleic acids in biochemistry is a challenge to synthesize nucleic acids of known base sequence and chain length. Oligomers with various sequences of up to 12 members and homo‐oligomers with a maximum chain length of 30 nucleotides can be obtained by chemical synthesis. The enzymatic synthesis of ribonucleic acids can be directed in such a way that polynucleotides with definite sequences are produced.
Advances in Molecular Diamagnetism
Authors: Haberditzl W. 
Published: December 2003

AbstractAt the present state of instrumentation and quantum‐mechanical approximations, diamagnetic measurements can supply information on chemical structure which complements the result of other approaches, such as infrared and NMR spectroscopy. General applicability and relatively low cost of equipment are among the advantages of this technique. There is growing interest in the relation to chemical shifts in NMR spectra and in the possibility offered by this technique for testing quantum‐chemical approximations.
Structures and Reactions of Organic ate‐Complexes
Authors: Tochtermann W. 
Published: December 2003

AbstractSome years ago, WittigG. Wittig, Angew.Chem.70, 65 (1958).pointed out that ate‐complexes are characterized by anionic activation of the substituents attached to the central atom. The behavior of these compounds thus contrasts with that of the onium‐complexesCf.E. Müller: Neuere Anschauungen der organischen Chemie. Springer, Berlin 1957, p. 132–142studied by Meerwein, which are characterized by cationic activation of the ligands. These two types of complexes form together two complementary aspects of organic coordination chemistryMetal‐carbon π‐complexes are excluded from the following discussion..
The Chemistry of α‐Carbonyl Azo Compounds
Authors: Fahr E. , Lind H. 
Published: December 2003

Abstractα‐Carbonyl azo compounds such as diesters of azodicarboxylic acids, diacylazo compounds, and esters of arylazocarboxylic acids are highly reactive. They add e.g. to amines, aromatic compounds, olefins, CH acids, Grignard and diazo compounds, aldehydes, ketones, and ketenes. These reactions can be used for the preparation of triazanes, hydrazones, oxa‐diazoline, azomethinimine, and diazetidine derivatives, etc. α,α′‐Dicarbonyl azo compounds are among the strongest dienophiles known.
Reactions of Elementary Silicon
Authors: Bonitz E. 
Published: December 2003

AbstractElementary silicon is normally treated “dry” with gaseous reactants in a fluidized bed. The apparent inertness of ordinary silicon is due to surface passivation. Non‐passivated silicon reacts as a strongly electropositive element. Finely divided silicon is pyrophoric and forms surface compounds with many substances (e.g. alcohol, water, and metal or organic halides) even at room temperature. An alternative to the “dry” process is a new suspension process, in which finely divided activated silicon, preferably suspended in its liquid reaction products (possibly in the presence of the soluble catalysts) reacts at elevated pressures, generally with liquids. The reactions in suspension can be easily controlled, and al the silicon is consumed. Polysilanes often are the only initial products, and these react further in the homogeneous liquid phase to give monosilanes. For example, dissolution of ordinary silicon in methanol leads smoothly to methoxysilanes, which can add to unsaturated hydrocarbons.
Snytheses and Reactions of O,N,N′‐Trisubstituted Isoureas
Authors: Däbritz E. 
Published: December 2003

AbstractThe CuCl2‐catalysed addition of alcohols to aliphatic caribodiimides (particularly diisopropylcarbodiimide) to form O,N,N′‐trialkylisoureas may, in the case of bifunctional hydroxy compounds (esters of α‐hydroxycarboxylic acids, diols, halogeno alcohols, amino alcohols, and cyclic hydroxy ethers), continue to give 5‐, 6‐, and 7‐membered 1,3‐O,N or 1,3‐N,N heterocycles. O,N,N′‐Trialkylisoureas are selective alkylating agents. Thus alcohols with allyl structures can be etherified with diisopropylcarbodiimide; a new method of esterification via O,N,N′‐trialkylisoureas has been applied to mesitylenecarboxylic acid.
Carbohydrates Containing Nitrogen or Sulfur in the “Hemiacetal” Ring
Authors: Paulsen H. 
Published: December 2003

AbstractIn 5‐amino‐5‐deoxy‐and 5‐thioaldoses, a 6‐membered hemiacetal ring can be formed by incorporation of a nitrogen or sulfur atom into the ring instead of the oxygen present in pyranoses. In the case of 5‐(N‐acylamido) ‐5‐ deoxyaldoses, the nucleophilic strength of the amide grouping is lowered, with the result that ring closure occurs only when sterically favored, or when a side reaction with formation of furanose is not possible. On the other hand, 5‐amino‐5‐deoxyaldoses containing a free amino group readily from 6‐membered “hemiacetal” rings. The resulting piperidinoses possess properties that are unusual in sugars, since they contain the 2‐hydroxypiperidine ring system. Piperidinoses are stable to alkalis and labile to acids; they rearrange in the presence of acids to give Amadori compounds, or lose three molecules of water to give derivatives of β‐hydroxypyridines. Owing to the high reactivity of the mercapto group, 5‐thioaldoses from only sugars with rings containing sulfur, the behavior of which resembles that of the oxygen analogues. 4‐Amino‐4‐deoxy‐ and 4‐thioaldoses can form 5‐membered rings containing nitrogen and sulfur.
Progress in the Chemistry of Casein
Authors: Jollès P. 
Published: December 2003

AbstractCasein from cow's milk is not a single substance, but can be resolved into numerous components. These include x‐casein, which is the only fraction that contains appreciable quantities of sugars. This component plays a very important role in the clotting of milk by rennin, when it is split into an almost sugar‐free fraction, para‐x‐casein, and a fraction containing sugars, x‐caseinoglycopeptide. Caseinoglycopeptides have been isolated not only from the casein of cow's milk, but also from the caseins of sheep. Goat, and human milk. The second part of the paper deals with the clotting of milk by rennin and the amino acid sequence in caseinoglycopeptides.
Force Constants and Bond Orders of Nitrogen Bonds
Authors: Goubeau J. 
Published: December 2003

AbstractThe 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

AbstractAcrylonitrile 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

AbstractDi‐ 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.