bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recent Advances in the Theory of Liquids
Authors: Ree Teresa S. , Ree T. , Eyring H. 
Published: December 2003

AbstractIn this paper, the methods of calculation of liquid properties using cluster integrals or the radial distribution function are not discussed. Rather, the theories using a model approach are presented. The basic principles involved in the cell theory, tunnel theory, and significant structure theory are reviewed, and the merits of the three theories are examined by comparing theoretical and experimental values of the pressures, molar volumes, compressibility factors, and excess entropies of real liquids. ‐ The thermodynamic properties of two‐and three‐ dimensional arrays of hard discsand spheres are also calculated, and compared with the machine calculation.–One finds that the significant structure theory gives the best results in every case.
Thermal Fragmentation and the Determination of the Structure of Organic Compounds
Authors: Simon W. , Giacobbo H. 
Published: December 2003

AbstractA pyrolysis apparatus with high‐frequency induction heating has been developed, which, owing to the small dead volume in the pyrolysis zone (≥ 5 μl), can be used for pyrolysis gas chromatography utilizing capillary columns without a sample split system. Thin films of the samples are deposited on ferromagnetic conductors, and can be reproducibly heated in routine operation to an accurately defined temperature (the Curie point) in from 20 to 40 msec. Microgram quantities of natural amino acids can be identified by this method with the aid of standard pyrolysis gas chromatograms. When a thin film of the sample is used on the ferromagnetic conductor, the gragments are closely related to the structure of the original compound.
Heterocycles Containing Phosphorus
Authors: Märkl G. 
Published: December 2003

AbstractThe preparation of heterocycles containing phosphorus is described. The chemical behavior of ring systems containing trivalent phosphorus is mainly determined by their phosphine character; heterocyclic behavior in the ordinary sense is shown by rings containing functional groups. Syntheses and reactions of cyclic compounds of pentavalent and hexavalent phosphorus are particularly interesting.
The Structural Chemistry of Condensed Inorganic Phosphates
Authors: Thilo E. 
Published: December 2003

AbstractAfter it had become known that three types of condensed inorganic phosphates, i.e. metaphosphates, polyphosphates, and ultraphosphates, exist, attempts were made to elucidate their formation, properties, and mutual relationships. Metaphosphates and polyphosphates containing up to eight or ten monomer units can be separated chromatographically. In the melts, equilibria exist between the various types of phosphate anions. Annealing of the glasses leads to crystalline products, sometimes containing only one type of anion. The glass‐crystal transition proceeds via monomeric XO anions. This has been shown in the case of polyarsenatophosphates, in which the As atoms are randomly distributed over the chains in the vitreous state, but are located at preferred positions in the crystalline state. The maximum degree of dissociation of polyphosphates and polyphosphoric acids in water is 30%, which accounts for the ion exchange and the chelating effects. The cation‐catalysed decomposition of polyphosphates can take place either by hydrolytic degradation from the chain ends, or by rearrangement within the chains to form metaphosphates.
Novel Approaches to the Synthesis of Some Heterocycles Containing Nitrogen
Authors: de Stevens G. , Blatter H. M. , Carney R. W. J. 
Published: December 2003

AbstractSome syntheses of heretofore unknown pyrimidines, tetrahydroquinazolines, and quinazolines are described. These methods are uniquely simple one‐ or two‐step reactions, general and versatile in scope, and give high yields. Some interesting chemistry associated with these heterocyclic systems is discussed.
Contributions to the Chemistry of the Binary Compounds of the Transition Elements
Authors: Haraldsen Haakon 
Published: December 2003

AbstractPhase and structural relationships of the sulfur, selenium, and tellurium compounds of the 4d and 5d transition elements of groups IV to VII of the periodic system are discussed. Homologous elements behave very similarly with respect to the chalcogens, and this is particularly the case for niobium and tantalum, and for molybdenum and tungsten. However, zirconium, niobium, and molybdenum have a greater tendency towards formation of chalcogen‐poor phases than their homologues hafnium, tantalum, and tungsten. Subchalcogenides are known only for zirconium and niobium. The number of phases and the tendency towards formation of solid solutions are considerably smaller among the tellurides than among the sulfides and selenides. The crystal structures of the telluride phases also differ from those of the sulfide and selenide phases of analogous composition. In addition, a review of the phase and structural relationships of the arsenic and antimony compounds of the 4d and 5d transition elements of groups V to VII is given.
Color Centers in Alkali Borate Glasses Containing Cobalt, Nickel, or Copper
Authors: Juza R. , Seidel H. , Tiedemann J. 
Published: December 2003

AbstractThe absorption spectra and the magnetic moments of Co2+, Ni2+, and Cu2+ in alkali borate glasses of various compositions and in halide‐containing glasses have been explained from the point of view of the ligand field theory. Spectra and magnetic moments are highly dependent on the composition of the base glass; this must be ascribed to the change in the coordination of the transition‐metal ions. There are far‐reaching analogies with corresponding complexes in solution or in the crystalline state.
The Quaternary Structure of Proteins
Authors: Sund H. , Weber K. 
Published: December 2003

AbstractMany protein molecules, particularly those with high molecular weights, consist not of a single polypeptide chain, but form a complex made up from several polypeptide chains. This structure, which can be reversibly broken down, is known as the quaternary structure. A number of metabolic phenomena can be explained on a molecular basis by invoking the quaternary structure.
Some Advances in the Inorganic Chemistry of Bromine
Authors: Stenger V. A. 
Published: December 2003

AbstractRecent advances in the chemistry of bromine and its inorganic compounds are covered under the headings of technology, properties and reactions, liquid bromine as an inorganic solvent, analysis, and new or newly studied compounds. Much of what is new is bromine chemistry is characteristic also of what is new in inorganic chemistry as a whole. That is, more detailed information about compounds and reactions is becoming available from the application of new instrumental and theoretical techniques.
Functional Groups on the Surfaces of Solids
Authors: Boehm H.‐P. 
Published: December 2003

AbstractAtoms or groups foreign to the structure of a solid are often bonded to its surface. On diamond, graphite, and even silicon dioxide, the foreign atoms are bonded covalently, whereas the bonding of the structural groups to titanium oxide and alumina is predominantly ionic. Oxides are normally covered with a monomolecular hydroxide layer. Changes in the valence of the metal atoms lead to changes in the acidity of the surface; for example, reduction of surface Ti4+ions gives the surface of TiO2 an acidic nature.
New Methods and Results in the Study of Polyacids
Authors: Jahr K. F. , Fuchs J. 
Published: December 2003

AbstractThe present status of research on condensed vanadic, molybdic, and tungstic acids is reviewed. Information about the structure and formation of polyanions can be obtained by X‐ray analysis and from nuclear magnetic resonance, infrared, and Raman spectra, as well as from complex formation in aqueous solution. Salts of the polyacids can be prepared in organic solvents by hydrolysis of esters of the metal oxoacids.
Some Recent Developments in the Chemistry of Transition Metal Oxocations
Authors: Selbin J. 
Published: December 2003

AbstractThe range of stability of transition metal oxocations in aqueous solution is discussed. Species with a metal‐oxygen bond of order higher than unity are particularly interesting. Bond orders can sometimes be determined from bond lengths and angles, but generally only by infrared spectroscopy. – The frequency range of the metal‐oxygen stretching vibration, previously assumed as about 900–1100 cm−1, must according to these investigations be extended at least to 780 cm−1 if all multiple bonds, particularly those in trans‐dioxo complexes, are to be included. Broad bands down to 650 cm−1 are ascribed to metal‐oxygen bridges. — The existence of cations such as ZrO2+ and VO, or of the “well‐known” titanyl ion, TiO2+, has never been proved. In many cases polynuclear, oxygen‐bridged oxometal species must be assumed.
Silicon‐Nitrogen Heterocycles
Authors: Fink W. 
Published: December 2003

AbstractGreat progress has recently been made in the chemistry of the silicon‐nitrogen bondC. Eaborn: Organosilicon Compounds. Butterworths, London 1960, p. 339.
R. Fessenden and J. S. Fessenden, Chem. Reviews 61, 361 (1961).
K. A. Andrianov, I. Haiduc, and L. M. Khananashvili, Uspekhi Khim. 32, 563 (1963); Chem. Abstr. 59, 8782 (1963).
U. Wannagat, Advances inorg. Chem. Radiochem. 6, 265 (1964).
I. Haiduc: Westep do Chemii Nieorganicznych Zwiazkow Pierscieniowyrh. WPN, Warsaw 1964, Chap. 10 (in Polish).
. Whereas attention was formerly concentrated on open‐chain silazanes and silylamines, growing interest is now being shown in the cyclic SiN compounds. A major factor which has contributed to the rapid development in this field is the need for better polymers and liquids for use above 350 °CCf. E. G. Rochow, Chim. et Ind. 85, 897 (1961).
. The present article deals with monomeric cyclic compounds containing at least one silicon‐nitrogen bond in the ring, as well as the polycyclic compounds derived from these.
Methods and Applications of Quantum Chemistry. Part I: Physical and Mathematical Basis
Authors: Kutzelnigg W. 
Published: December 2003

AbstractAfter an introduction to the fundamental concepts of quantum mechanics it is shown how to describe a chemical system in the language of theoretical physics. The equations which one obtains can not, in general, be solved in closed form. Approximate numerical methods that furnish sufficiently accurate solutions for many problems of interest are, however, available. The most important of these are presented briefly, and are given physically visualizable interpretations as far as this is possible. Special attention is devoted to more modern methods of quantum chemistry, to the basis assumptions underlying them, their scope, and their limitations. Treatment of the theory of the chemical bond is reserved for Part II.
Isotope Effects in Organic Chemistry and Biochemistry
Authors: Simon H. , Palm D. 
Published: December 2003

AbstractThe present article shows the extent to which isotope effects are likely to be encountered in the use of isotope techniques and what problems are studied with primary and secondary isotope effects. By way of example, the results of studies on E2 reactions, particularly in the Hofmann degradation, are discussed, followed by a discussion of some “analytical isotope effects”. Finally, the problems encountered and the information that can be obtained from isotope effects studies on enzyme reactions, and the advantages and disadvantages of competitive and non‐competitive techniques are described. In addition to a survey of isotope effects in dehydrogenase reactions, new isotope effects encountered in the dehydrogenation of T‐labeled alcohols are reported.
Polymers Containing Lactone Groups
Authors: Palm R. , Ohse H. , Cherdron H. 
Published: December 2003

AbstractPolymers containing intact lactone groups are a new class of macromolecules with reactive groups, which are relatively easy to obtain by polymerization, polycondensation and polyaddition, as well as by reactions on existing macromolecules. Polymers with β‐lactone Groups in particular can enter into numerous addition reactions, which can be used, for example, to obtain macromolecules containing hydroxy acid or amino acid groupings. The reactions proceed under mild conditions, and can even be carried out in aqueous media, frequently giving water‐soluble polymers. The polymers can be cross‐linked at low temperatures, even from the aqueous phase, by the addition of bifunctional or oligofunctional reagents. Polymers containing β‐lactone groups can also be used as a basis for graft co‐polymers; polyester or polyether branches can be grafted on, depending on whether monomeric lactones or monomeric epoxides are used.
Inorganic, Organometallic, and Organic Analogues of Carbenes
Authors: Nefedov O. M. , Manakov M. N. 
Published: December 2003

AbstractThis review deals with inorganic, organometallic, and organic compounds, as well as with elements, that on the basis of their electronic structure and their reactions can be regarded formally as analogues of carbenes. These “carbene analogues” include in particular the compounds of monovalent boron, aluminum, nitrogen, and phosphorus; those of divalent silicon, germanium, tin, and lead; atomic oxygen; atomic sulfur; and atomic selenium. The preparation and chemical properties of the carbenes and their analogues are compared.
Nickel‐Catalysed Reactions of Allyl Halides and Related Compounds
Authors: Chiusoli G. P. , Cassar L. 
Published: December 2003

AbstractAllyl compounds react with carbon monoxide, or with carbon monoxide and acetylene, in the presence of tetracarbonylnickel as catalyst. These catalysts are involved also in coupling reactions and addition reactions of activated olefins and ketones. Reactions of this type can be used for the preparation of unsaturated aliphatic acids, esters, nitriles, hydrocarbons, alicyclic ketones, keto acids, keto esters, diketones, lactones, phenols, and other compounds. The reactions proceed via π‐allylnickel complexes.
The Bucherer Reaction and the Preparative Use of its Intermediate Products
Authors: Seeboth H. 
Published: December 2003

AbstractThe study of purified intermediate products of the Bucherer reaction has shown that this reaction proceeds, not via bisulfite addition compounds of the keto form of the naphthols and the ketimine form of the naphthylamines, but via tetralonesulfonic acids and tetraloniminesulfonic acids. The intermediates lead to compounds that are otherwise difficult or impossible to obtain, and some of which are new. The mechanism of the Bucherer reaction is discussed in detail.
The Norcaradiene Problem
Authors: Maier G. 
Published: December 2003

AbstractCompounds having the norcaradiene structure are stable if one of the double bonds of the norcaradiene also belongs to a benzene ring or if C atoms 1 and 6 are fixed in position by a bridge. A similar effect that favors the norcaradiene form is produced by the incorporation of nitrogen atoms in positions 3 and 4. Cycloheptatriene and most of the simply substituted tropilidenes exist exclusively in the monocyclic triene form. It has been possible in some cases to detect a valence‐tautomeric equilibrium between the norcaradiene and the cycloheptatriene ring system. Non‐classical stabilization of compounds having norcaradiene or cycloheptatriene structure in the sence of a pseudoaromatic “homobenzene” is only very slight, if it occurs at all.
Eliminations in Cyclic cis‐trans‐Isomers
Authors: Hückel W. , Hanack M. 
Published: December 2003

AbstractSolvolytic El eliminations from cis‐alkylated p‐toluenesulfonates of cycloalkanols (particularly menthols and decalols) lead almost exclusively to “Saytzeff hydrocarbons”; this fact is accounted for by the increase in the rate of solvolysis that results from the participation of the tertiary trans‐hydrogen. The corresponding trans‐alkylated compounds give mixtures. The solvolysis of these compounds is compared with the deamination of stereoisomeric primary amines and with the proton‐catalysed dehydration of tertiary alcohols. E2 reaction of vicinally alkylated cycloalkane derivatives involves attack on the secondary hydrogen, and in the case of the trans isomers leads to pure “Hofmann hydrocarbon”; with the cis‐isomers, competition occurs between the E1 and E2 reactions. The fact that the tertiary hydrogen is not attacked is explained by its anionic character. Reference is made to the competition of E1 and E2 reactions in exhaustive methylation.
Aromatic Fluorine as a Chemical Label for Detecting Reaction Mechanism
Authors: Suschitzky H. 
Published: December 2003

AbstractThis article explains how nucleophilically activated fluorine can be used for the detection of ion‐pair formation during the decomposition of various aryl radical generators. Thus a concurrent dual mechanism for the breakdown of certain aryl radical sources can be experimentally demonstrated by fluorine labeling. The bearing of this information on the mechanism of diazo coupling is also discussed.In addition, labeling with aromatic fluorine is applied to the thermolysis of aryl azides, the aminolysis of 3‐aryl‐4‐bromosydnones, and the hydrolysis of 3‐arylsydnone imines. Finally some mechanistic problems are posed which may possibly be solved by this labeling technique.
Neighboring‐Group Effects and Rearrangements in Reactions of Cyclopropylmethyl, Cyclobutyl, and Homoallyl Systems
Authors: Hanack M. , Schneider H.‐J. 
Published: December 2003

AbstractThe neighboring‐group effect produced by a double bond in the homoallyl position or by a cyclopropane or cyclobutane ring leads to interesting rearrangements, which are discussed in this paper mainly from the point of view of mechanism, but also from that of preparative work. The question of the postulated non‐classical carbonium ions acquires a special significance in this connection.
New Methods of Preparative Organic Chemistry. Transfer of Diazo Groups
Authors: Regitz M. 
Published: December 2003

AbstractWhen an arenesulfonyl azide, particularly p‐toluenesulfonyl azide, reacts, in the presence of a base, with a compound containing an active methylene group, the two hydrogen atoms of the active methylene group are replaced by a diazo group to form a diazo compound and an arenesulfonamide. The method may be used for the synthesis of the diazo derivatives of cyclopentadienes, cyclohexadienes, 1,3‐dicarbonyl, 1,3‐disulfonyl, and 1,3‐ketosulfonyl compounds, ketones, carbonic acid esters, and β‐iminoketones. Secondary reactions can lead to azo compounds and heterocycles such as 1,2,3‐triazoles, 1,2,3‐thiadiazoles, and pyrazolin‐4‐ones. Azidinium salts react in the same way, but in this case an acidic reaction medium is necessary, a fact that is sometimes advantageous.
Higher Coordination Numbers of the Typical Elements
Authors: Hudson R. F. 
Published: December 2003

AbstractThe bonding in electron‐deficient molecules, e.g. the boron hydrides and certain metal alkyls, and in molecules which appear to violate the rare gas rule, e.g. hydrogen bonded complexes, interhalogen compounds and compounds of the typical elements with high coordination numbers such as PCI5 and SF6 can be described by a simple molecular orbital treatment involving delocalized α‐bonds. The contribution of d‐orbitals to the bonding in the interhalogen compounds and rare gas fluorides is very small. The stereochemistry and physical properties of the PX5 system are explained readily by the delocalization treatment and it is likely that here also the importance of spd hybridization has been overemphasized in the past.
Direct Synthesis of Organohalogenosilanes
Authors: Baźnt V. , Joklík J. , Rathouský J. 
Published: December 2003

AbstractThe direct synthesis of organohalogenosilanes, particularly methyl‐ and phenylchlorosilanes, is the main process for the production of the monomers required for silicone polymers. This complex heterogeneous catalytic reaction involves the interaction of a gaseous component (the organic halide) with two solid components (silicon and copper), the relative quantities of which change as the reaction proceeds. The mechanism of the direct synthesis has not yet been conclusively established. The free‐radical mechanism originally proposed supposes the formation of organic free radicals. On the other hand, the chemisorption mechanism suggested later postulates the dissociative adsorption of the organic halide on the silicon‐copper double center (the silicon and the copper being joined by a chemical bond). The results obtained so far indicate that the chemisorption mechanism is of decisive importance, but it is not impossible that both mechanisms operate simultaneously.
The Reduction of Organic Compounds with Chromium(II) Salts
Authors: Hanson J. R. , Premuzic E. 
Published: December 2003

AbstractChromium(II) salts can be used for a variety of reductions in organic chemistry; for example, alkyl halides and suitably substituted olefins may both be reduced to alkanes, and alkynes may be converted into trans‐olefins. Several epoxyketones are reduced to α,β‐unsaturated ketones or β‐hydroxyketones, and a nitro steroid was found to give a hydroxy(hydroxyimino) compound. The reduction of alkyl halides is reported to proceed by a free‐radical mechanism; the halogen atom that is set free forms a bridge between two chromium atoms.
Poly‐β‐amides
Authors: Bestian H. 
Published: December 2003

AbstractHigh molecular weight poly‐β‐amides with fiber‐forming properties (repeating unitNHCR2CR2CO) differ from the polyamides of the nylon series in that the amide groups are much more closely spaced. These polymers are thus the nearest of the synthetic polyamides to natural silk. The production of poly‐β‐amides was made possible by a recent synthesis of β‐lactams from olefins and chlorosulfonyl isocyanate. The anionic polymerization of the β‐lactams gives poly‐β‐amides containing up to 10 000 monomer units in the chain. The molecular weight can be controlled as desired by means of initiators and chain terminators, and the properties can be varied within wide limits by the choice of the β‐lactam or by copolymerization of several β‐lactams. Remarkable differences are observed between polymers containing structural units in the threo form and those containing erythro structural units. The poly‐β‐amides can be spun into fibers having valuable textile properties.
Sulfonyl Hydrazones of Cyclic Amides and Quaternary Azo Sulfones of Heterocycles as Reagents in Azo Chemistry
Authors: Hünig S. 
Published: December 2003

AbstractSulfonyl hydrazones of cyclic amides undergo oxidative coupling with phenols and reactive methylene components. The reaction proceeds via the azo sulfones, which may be used as such, and which, as ambident cations, enter into many reactions with nucleophiles and extend the scope of oxidative coupling. The reaction with phenols is a two‐step process, in which the limiting cases k1 ≪ k2, k1 ≈ k2, and k1 ≫ k2 can be realized by slight variation of the reactants.
Reactions of Electron‐Rich Olefins
Authors: Hoffmann R. W. 
Published: December 2003

AbstractOlefins are normally preferentially attacked by electrophiles. This trend is strengthened in enol ethers and enamines, and is particularly pronounced in tetramethoxyethylene and in tetraaminoethylenes. These electron‐rich olefins are accordingly also excellent reducing agents. In their reactivity, therefore, they behave as counterparts of tetracyanoethylene. This compound shares with the electron‐rich olefins a strong tendency to undergo cycloadditions, the electron‐rich olefins adding particularly readily to electrophiles.
Hereditary DNA Alterations
Authors: Freese Ernst 
Published: December 2003

AbstractMutations and recombinations are hereditary alterations of DNA, which is found mainly in the chromosomes of cells. They can occur spontaneously and they can be induced by high energy radiation or by chemicals. This article considers the developments following the discovery of the DNA structure that have led to a molecular explanation of point mutations, of large chromosome alterations, and of recombination. In conclusion, consequences for human society are drawn from the knowledge gained.