bluuebunny/crossref_metadata_2025_split huggingface dataset:
1,3‐Dipolar Cycloreversions
Authors: Bianchi Giorgio , De Micheli Carlo , Gandolfi Remo 
Published: December 2003

AbstractThe 1,3‐dipolar cycloreversion reaction represents a general scheme of fragmentation of pentaatomic heterocycles to produce 1,3‐dipolar systems and dipolarophiles. This review summarize cycloreversions which give rise to octet‐stabilized 1,3‐dipoles. The reaction can be either thermal or photochemical or electron impact induced. The aim of the article is to survey the published results, to emphasize the synthetic potential of this reaction, and to stimulate the study of its several not yet unambiguously defined mechanistic aspects.
Applications of SEPIL to the Solid State Defect Chemistry of Fluorites and Ultra‐trace Inorganic Analysis [New analytical methods (16)]
Authors: Wright John C. , Tallant D. R. , Gustafson F. J. , Johnston M. V. , Miller M. P. , Moore D. S. , Porter L. C. , Akse J. R. 
Published: December 2003

AbstractAlthough it has been recognized for many years that the spectra of lanthanoid ions can provide useful information about short range phenomena in the neighborhood of these inos in a solid material, lanthanoid spectroscopy has only infrequently been used for studying complex materials because of the problem of line‐sorting the complex spectra that are obtained. The advent of convenient tuneable lasers has eliminated this problem. By selectively exciting probe ion luminescence (SEPIL), it is possible to obtain fluorescence and excitation spectra from a single kind of crystallographic environment. Two applications of this method are dicussed in this paper. The first application is the study of the defect chemistry of fluorite materials (compounds with CaF2 lattice). It is shown how this method can provide unique information about the solid state chemistry, thus clarifying many of the unexplained behaviors of this important class of material. The second application shows application shows how ultra‐trace analysis can be carried out by causing an association between an analyte ion and a fluorecent probe ion. The unique crystal field levels of a probe ion associated with a particular analyte can be selectively excited so that traces of the ion to be analyzed can be detected with very high selectivity and with very low detection limits.
Determination of Morphological Properties of Swellable Solids by Size Exclusion Chromatography
Authors: Halász István , Vogtel Peter 
Published: December 2003

AbstractMany technically interesting porous solids, e.g. ion exchangers or adsorbents for catalysis, are swellable polymers, i.e. the pore structure depends on the solvent medium. A method based on exclusion chromatography, permits determination of the pore size and pore size distribution in the swollen state.—Size exclusion chromatography, also referred to as gel permeation, gel filtration, or molecular sieve chromatography, is a widely employed method for the separation of dissolved substances—mostly polymer mixtures—according to their molecular size. Porous solids are used as stationary phase. Conversely, pore sizes and other structural data can be determined by exclusion chromatography. This application requires a series of standards (polymer samples) of known molecular weight. As a simple and rapid method, it has already proven valuable for such determinations in the case of rigid solids; in the case of swellable solids, this constitutes the sole method by which the pore structure can be characterized: classical methods require dry samples.
Developments in the Field of Inorganic Pigments
Authors: Bittler Knut , Ostertag Werner 
Published: December 2003

AbstractThe specific properties of inorganic pigments result from an interplay of solid‐state properties, particle size, and particle shape. However, phenomena occurring at the pigment interfaces also have implications for the use of the pigment. The interrelations for individual classes of pigments are indicated, and two selected examples, namely transparent colored pigments and magnetic pigments, are subsequently discussed with particular attention being paid to industrial developments.
Trimethylphosphane Complexes of Nickel, Cobalt, and Iron—Model Compounds for Homogeneous Catalysis
Authors: Klein Hans‐Friedrich 
Published: December 2003

AbstractOne of the greatest achievements of organometallic chemistry in the last ten years has been the experimental proof that transition metal‐to‐carbon bonds are thermodynamically about as stable as those between main group elements and carbon. The present contribution demonstrates how simply constituted alkylnickel, ‐cobalt, and ‐iron complexes are obtained by means of a kinetic stabilization using suitable neutral ligands and what information these model compounds can provide with respect to the course of processes in homogeneous catalyses.
The Principle of Minimum Chemical Distance (PMCD)
Authors: Jochum Clemens , Gasteiger Johann , Ugi Ivar 
Published: December 2003

AbstractThe principle of minimum chemical distance (PMCD) allows one to formulate the isoprene rule, the conversion of tetrahydrodicyclopentadiene into adamantane, five syntheses of colchicine, and the syntheses of C16‐hexaquinacene, morphine and strychnine as optimization problems which can be solved by computers in less than a second. The principle of minimum chemical distance is based on an algebraic theory of constitutional chemistry. The PMCD, a corollary to the well known principle of minimum structure change, is a quantitative heuristic rule which serves as the foundation of the computer‐assisted combinatorial solution of a great variety of chemical problems, particularly in substructure analysis, the study of reaction mechanism, and the design of syntheses.
The Synthesis of Unusual Organic Molecules from Azoalkanes. New analytical methods (33)
Authors: Adam Waldemar , De Lucchi Ottorino 
Published: December 2003

AbstractThe thermal or photochemical denitrogenation of azoalkanes constitutes an effective and convenient method for the preparation of unusual organic molecules, including highly ringstrained, sterically crowded, fluxional, antiaromatic and other interesting structures. The importance of this synthetic approach is that the azo linkage serves as a means of introducing the critical (usually last) bond in the complex target molecule. This article presents a cross‐section of such elegant synthetic utilization of azoalkanes for fused‐, bridged‐ and spiro‐cyclization. Our coverage of the large body of literature has been directed by the complexity and novelty of the products. Azoalkanes are usually prepared via cycloaddition of azo dienophiles to appropriate substrates.
1,5,‐Electrocyclizations—An Important Principle of Heterocyclic Chemistry
Authors: Huisgen Rolf 
Published: December 2003

AbstractThe principle of orbital control of pericyclic reactions has deepened our understanding of reaction phenomena and provided an excellent classification of these one‐step processes. The electrocyclic reaction of the pentadienyl anion ⇌ cyclopentenyl anion type is relatively unimportant in all‐carbon systems and has not even been verified in the case of the parent compound. In the heterocyclic series, however, where up to five C‐atoms of the pentadienyl anion are replaced by heteroatoms, a multitude of ring closures and ring openings find their ordering principle in the mentioned electrocyclic reaction. The replacement of the carbon atoms by heteroatoms can take place isoinically, i. e., with retention of the anionic character, or isoelectronically. An isoelectronic replacement of CR2 in position 1 by NR2 OR, and or CR in position 3 by NR or O leads to a charge‐free resonance structure for the open‐chain species; the migration of the charge during the electrocyclization results in a correlation with a cyclic zwitterion. Conversely, isoelectronic exchange of CR in position 2 by NR or O produces a conjugated 1,3‐dipole, which cyclizes to a charge‐free unsaturated five‐membered ring. Twofold isoelectronic exchange allows the whole process to take place in a cation. Selected examples are to shed light on the classification and the thermodynamics of this electrocyclic reaction.
Production of High Temperatures in the Chemical Laboratory: Examples of Application in Lanthanoid Oxo‐Chemistry
Authors: Müller‐Buschbaum Hanskarl 
Published: December 2003

AbstractHigh‐temperature reactions have always been a fascinating although difficult field of experimentation for the chemist. In the case of solid‐state reactions the problems with apparatus increase exponentially with rising temperature, so that especially in this area of inorganic chemistry the modern techniques of producing high temperatures—from the solar furnace to the high‐power CO2 laser—have yielded new and interesting possibilities, particularly in the field of metastable high‐temperature compounds.
Biliproteins
Authors: Scheer Hugo 
Published: December 2003

AbstractBiliproteins, covalently bonded complexes of proteins and bile pigments, serve as light‐harvesting pigments in photosynthesis and light‐sensory pigments of photosynthetic organisms. Recent developments in the biochemistry and biophysics of these pigments are reviewed and an attempt is made to describe their functions of light‐harvesting and of information transduction on a molecular level.
Photoelectron Spectra and Molecular Properties: Real‐Time Gas Analysis in Flow Systems
Authors: Bock Hans , Solouki Bahman 
Published: December 2003

AbstractFor the analysis and optimization of numerous gas phase reactions in flow‐systems, photoelectron spectroscopy has proven most valuable. This real‐time measuring probe allows one to determine—with millimol quantities and within a few hours—the temperatures for different decomposition channels. Simultaneously, main products are characterized and, if need be, their yield can be improved. By careful performance of the experiment, short‐lived and/or reactive molecules such as P2, thioformaldehyde or silabenzene can be detected. PE‐spectroscopic gas analysis is of particular advantage in the search for heterogeneous catalysts; they can be tested within a day using gas mixtures of varying composition over the temperature range from 300 K to 1300 K. In addition, PE‐spectrometers are well‐suited for on‐line connection to computers; portable instruments for laboratory use are under development.
The Kinetics of Intramolecular Reactions from Relaxation Time Measurements
Authors: Lambert Joseph B. , Nienhuis Ronald J. , Keepers Joe W. 
Published: December 2003

AbstractAnalysis of spin‐lattice relaxation (T1) provides alternatives to the standard line shape procedures for the investigation of intramolecular reactions; furthermore it expands the NMR range at both the high and the low energy barrier limits. Dipole‐dipole‐ and quadrupole‐relaxation times are sensitive to very rapid processes such as methyl rotation. Analysis of relaxation in the rotating frame(T1ρ) provides kinetics for many sorts of processes, particularly those in the dynamic range that is too rapid for line shape methods. Saturation transfer and the coalescence of relaxation times at high temperatures can be used to measure high energy barriers. The scope and limitations of these methods are described.
Benzvalene—Properties and Synthetic Potential
Authors: Christl Manfred 
Published: December 2003

AbstractToday, thanks to the versatile synthesis developed by Katz et al., benzvalene is not only the most extensively studied valence isomer of benezene but also one of the most easily synthesized bicyclo[1.1.0]butane derivatives. The double bond in this highly strained hydrocarbon is particulary reactive owing to interactions between the σ system and the double bond. Benzvalene is one of the most reactive olefins toward electron deficient substrates. Furthermore, the compound is bifunctional, since after addition to the π system the ring strain of the σ system provides the driving force for rearrangement or further addition reactions. This paper summarizes the spectroscopic properties and the reactivity of benzvalene. In order to demonstrate the importance of benzvalene and its derivatives as building blocks in organic synthesis the chemistry of compounds arising from benzvalene is also discussed. The article concludes with a summary of substituted benzvalenes.
Mass Spectrometry of Negative Ions
Authors: Budzikiewicz Herbert 
Published: December 2003

Abstract“It appears that negative ion mass spectra measured with a commercial instrument and the electron energies used (20–70 eV) are not suitable either for molecular weight or for structure determination—”. This was the conclusion of a paper appearing in 1965 which expressed the then almost universal opinion on the importance of negative ion mass spectrometry in the structure analysis of organic compounds[8]. The fact that quinones and aromatic nitro compounds were exceptions to this rule was rather taken as substantiation of this opinion. The potential value of the work originating from the laboratories of Manfred von Ardenne was first realized with the development of chemical ionization. This technique gave a firm foundation to negative ion spectrometry in the area where it is complementary to that of positive ions.
Pyramidal Carbocations
Authors: Schwarz Helmut 
Published: December 2003

AbstractPyramidal cations are discussed with reference to their role as the connecting link between organic and inorganic chemistry. The electronic structure of these ions is treated with respect to their physical and chemical properties, namely charge distribution, geometry, and quenching reactions with nucleophiles. The chemistry in the gas phase of certain carbenium ions, in particular the scrambling of carbon atoms, is readily explicable by invoking transition states or intermediates of pyramidal structure. Moreover, the behavior of unimolecular processes can be understood in terms of transition states in which a hydrogen molecule is positioned as a “side‐on” or an “end‐on” ligand.
Physical Methods for the Microanalysis of Solids—General Significance, Recent Developments, and Limitations
Authors: Grasserbauer Manfred 
Published: December 2003

AbstractThe characterization of solid systems by physical methods (“physical analysis”) is one of the most important future‐orientated areas of analytical chemistry. Important developments are the increase of the informational content of analytical signals by application of mathematical methods, the investigation of extremely small amounts (microanalysis), as well as concentrations (trace analysis). New developments in analytical methodology and strategy in micro and surface analysis permit, for example, the direct identification of compounds in individual phases in the solid state, the quantitative elemental analysis of aerosol particles in the submicrometer region (identification of asbestos fibers), and highly sensitive distribution analysis of trace elements in semiconductors. Important technological‐scientific problems can be explained in this way.
The Bacterial Ribosome: A Programmed Enzyme
Authors: Gassen Hans Günter 
Published: December 2003

AbstractRibosome‐dependent protein synthesis in bacteria represents a complex sequence of reactions involving more than 150 compounds. The ribosome, constructed from 53 individual proteins and 3 nucleic acids, functions as the enzyme which catalyzes peptide bond formation. In contrast to most known enzymes the ribosome is “programmed” by the mRNA–the short‐lived transcript of DNA. The ribosome reads the nucleotide message of the mRNA and transforms its information into the amino acid sequence of a protein. In the course of this process, chemical bond energy is converted into directed mechanical motion. The model of protein biosynthesis on the programmable ribosome provides answers to the following questions: how is the mRNA framed into information units, how is the substrate specificity of the ribosome modulated by the codon of the mRNA, and how does the mRNA move with respect to the ribosome by one trinucleotide per peptide bond formed?
Palladacycloalkanes by Oxidative Coupling of 3,3‐Dimethylcyclopropene with Palladium(0) Compounds
Authors: Binger Paul , Büch Holger Michael , Benn Reinhard , Mynott Richard 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 153. DOI:10.1002/anie.198201530
Evolution of Hydrogen from Photochemically Reduced Water‐Soluble Tin(IV)‐Porphyrins
Authors: Krüger Wolfgang , Fuhrhop Jürgen‐Hinrich 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 193. DOI:10.1002/anie.198201930
The Dianion 1,2,3,4‐Tetraphenylcyclobutadienediide
Authors: Boche Gernot , Etzrodt Heinz , Marsch Michael , Thiel Walter 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 355. DOI:10.1002/anie.198203550
Cyclopropenes as Complex Ligands: Fe2(CO)9‐Induced Ring‐Opening of a Spirocyclopropene and Reversible CO‐Addition to the Vinylcarbene Ligand
Authors: Klimes Jörg , Weiss Erwin 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 477. DOI:10.1002/anie.198204770
The Cycloaddition of Carbonyl‐Flanked Methylene Bridges—A Novel Method for the Synthesis of Metallacycles
Authors: Bauer Christine , Guggolz Ernst , Herrmann Wolfgang A. , Kriechbaum Gangolf , Ziegler Manfred L. 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 434. DOI:10.1002/anie.198204340
Ph(Me3Si)CPCl as Educt for Methylenephosphanes with Alkyl‐, Amino‐, Phosphino‐, Alkoxy‐, or Alkylthio‐Groups on Phosphorus
Authors: Appel Rolf , Kündgen Ursula 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 549. DOI:10.1002/anie.198205490
Hexagonal Ferrites from Melts and Aqueous Solutions, Magnetic Recording Materials
Authors: Hibst Hartmut 
Published: December 2003

AbstractOwing to their particular crystallographic properties, ferrimagnetic hexagonal ferrites exhibit a far greater coercive force than the conventional magnetic pigments. They therefore appear to be suitable for use in magnetic information storage procedures, some of which are novel and are at the development stage. Thus, magnetic tapes of high coercive force containing barium ferrite could be used as master tapes for copying magnetic information or for producing forgery‐proof magnetic cards, if magnetic heads having high‐order write fields were successfully developed. Moreover, platelet‐like ferrite pigments in which the preferred direction of magnetic orientation is perpendicular to the plane of the platelet are of great interest for perpendicular magnetic recording.In this progress report, the crystal structures, magnetic characteristics of hexagonal ferrites, and chemical processes for their production are discussed. In particular, reactions in salt melts or under hydrothermal conditions produce finely divided pigments whose particles have a pronounced hexagonal, plate‐like habit, a narrow particle size distribution, and advantageous magnetic properties. The magnetic properties of the pigments crystallized from salt melts may be adjusted by cation exchange.
A Novel Anionic Five‐Coordinate Tris(trichlorostannato)platinum(II) Complex
Authors: Albinati Alberto , Nägeli Ralph , Rüegger Heinz , Pregosin Paul S. 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 755. DOI:10.1002/anie.198207550
2‐Methyl‐2‐triphenylphosphoniodithiopropionate–A Photosensitive Complex Ligand with Labile PC Bond
Authors: Kunze Udo , Merkel Reinhard , Winter Werner 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 711. DOI:10.1002/anie.198207110
The 1,3‐Dithian‐2‐ylmethoxycarbonyl (Dmoc) Moiety–A Protecting Group for the Amino Function in Peptide Synthesis
Authors: Barthels Regina , Kunz Horst 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 702. DOI:10.1002/anie.198207020
Influence of Conformational Rigidity on the Stabilization of α‐Ferrocenyl Carbocations: A cis‐Fixed Diferrocenyl Carbenium Ion
Authors: Mueller‐Westerhoff Ulrich T. , Nazzal Adel , Prössdorf Wolfram , Mayerle James J. , Collins Russell L. 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 686. DOI:10.1002/anie.198206860
Diels‐Alder Reactions of [5]Metacyclophane
Authors: Turkenburg Lucas A. M. , Blok Pieter M. L. , de Wolf Willem H. , Bickelhaupt Friedrich 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 744. DOI:10.1002/anie.198207440
Bicyclo[4.4.2]dodeca‐1‐ene– The First “Hyperstable” Bridgehead Olefin
Authors: Kukuk Hanspeter , Proksch Ehrhardt , de Meijere Armin 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 696. DOI:10.1002/anie.198206960
Synthesis, Structure, and Reactions of Primary Adducts of Sulfur or Selenium with Hexaphenylcarbodiphosphorane
Authors: Schmidbaur Hubert , Zybill Christian E. , Neugebauer Dietmar 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 590. DOI:10.1002/anie.198205900
Anomalies of Liquid Water
Authors: Lang Elmar Wolfgang , Lüdemann Hans‐Dietrich 
Published: December 2003

AbstractWater at low temperatures (T < 300 K) reveals a multitude of unusual physico‐chemical properties, which originate from the strong directivity of the hydrogen bonds. This directivity forces the molecules into a tetrahedral arrangement of first neighbors and thus leads to a poor packing efficiency. All anomalies of the liquid become more pronounced in the metastable range below the melting pressure curve. In the following article, methods for the investigation of the supercooled range are presented. A few anomalous static and dynamic properties are described and compared with the properties of normal liquids. The experimental results are discussed in the context of computer simulations and the more recent theories on cold water. It can be concluded that the anomalies of water, for instance the density maximum of the liquid phase and the initial decrease in viscosity with pressure, are confined to the pT‐range: T < 300 K, p ≲ 200 MPa. At these pressures, lowering the temperature leads to an unexpected behavior of almost all physical properties. They seem to approach a phase transition at T ≃ (TM − 50 K), the nature of which has not yet been fully characterized. This phenomenon has hitherto been observed only in supercooled water.—In the future it will be possible to use supercooled aqueous solutions for kinetic studies, thus expanding the available dynamic range for the investigation of aqueous solutions considerably.
Topical Problems in the Biosynthesis of Red Blood Pigment
Authors: Franck Burchard 
Published: December 2003

AbstractUroporphyrinogen III plays a key role in the biosynthesis of heme, the red pigment of blood. In vivo studies with specifically 14C‐ and 3H‐labeled precursors have revealed that the formation uroporphyrinogen III in the organism follows several primary and subsidiary pathways. Model experiments on the pattern of biosynthesis have led to simple and effective methods of synthesizing uroporphyrin analogs and have shown that their production is strongly favored thermodynamically. The biologically porphyrins important thus available permit a mechanistic explanation of the light‐induced dermatoses in porphyria diseases and suggest promising medical applications in diagnosis and therapy.
Influence of Ring‐Size of Cycloalkenes on the Activation Volume in the High‐Pressure Copolymerization of Maleic Anhydride
Authors: Jenner Gérard , Kellou Mohamed , Papadopoulos Mihalis 
Published: December 2003

AbstractThe complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 929. DOI:10.1002/anie.198209290