bluuebunny/crossref_metadata_2025 huggingface dataset:
Scope of Application of the Isoselective Relationship
Authors: Exner Otto , Giese Bernd
Published: December 2003

Comparison of activation parameters requires a statistically correct treatment in order to prove the validity of the isoselective relationship in specific cases, and to calculate the isoselective temperature for pairs of series of reactions.
High‐Resolution, Higher‐Order UV/VIS Derivative Spectrophotometry
Authors: Talsky Gerhard , Mayring Lothar , Kreuzer Hans
Published: December 2003

Derivative spectrophotometry has gained increasing importance in the past two years and is currently experiencing vigorous development. Following and introduction the present article provides a review of this extremely effective method. In particular, the advantages ofhigher‐order derivative spectrophotometry (HODS method,n> 2) are discussed on the basis of practical examples from a wide range of analytical fields. The results are achieved with the aid of a newly developed analog computer unit, whereby for the first time readily reproducible, low‐noise, on‐line spectra can be obtained up to the 7th order and even, in favorable cases, up to the 9th order. In practice it has proved valuable to work with spectra of the 3rd to 5th order; but even higher derivations could be profitable for the separation of strongly superposed signals or for “fingerprinting”.
Facile New Synthesis of Chloroarsinidene Complexes
Authors: von Seyerl Joachim , Moering Ute , Wagner Adalbert , Frank Albin , Huttner Gottfried
Published: December 2003

An extremely facile entry to functionalized chloroarsinidene complexes such as (1) is provided by the reaction shown below. The expected trigonal‐planar coordination of the arsenic was confirmed by X‐ray studies.
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Superacid‐Catalyzed Oxygenation of Alkanes. [New synthetic methods (26)]
Authors: Olah Georg A. , Parker David G. , Yoneda Norihiko
Published: December 2003

Owing to the ready availability of the starting materials, the functionalization of saturated hydrocarbons for preparing chemical intermediates and products represents an attractive goal. The possibility of converting alkane in a controlled way into alcohols, ketones etc., i.e. to oxyfunctionalize them, is particularly challenging. After a short account of previous methods used for the oxidation of alkanes, particular emphasis will be given to recently developed reactions of alkanes with oxygenating agents in superacidic media.
Dipotassium Hexaisobutyldialuminate, a Complex Containing an AlAl Bond
Authors: Hoberg Heinz , Krause Siegfried
Published: December 2003

The new dialuminum complex (1) is formed by the route shown below (hexane, 20°C, 63% yield, brown crystals). A σ‐interaction of the A1 atoms is deduced from the spectra and properties of (1).
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The Art of Titration. From Classical End Points to Modern Differential and Dynamic Analysis
Authors: Winkler‐Oswatitsch Ruthild , Eigen Manfred
Published: December 2003

Titration represents the quantitative determination of a chemical change in response to the variation in concentration of a standrad. Information on reaction parameters is usually obtained from an analysis of the shape of the titration curve. In this paper the derivatives of titration functions with respect to concentration variables and with respect to equilibrium parameters are compared with one another. The latter can be determined directly from amplitudes and time constants of the dynamic responses to equilibrium perturbations, brought about by fast alterations of temperature, pressure or electirc field.

Three general situations have to be distinguished: 1. If the interaction is very strong (i.e. the complex stability is high: K → ∞), the (average) number of sample praticles can be counted directly by means of their reaction with a calibrated number of standard particles.—2. If, on the contrary, the interaction is weak (i.e. the complex stability is low), the sample will react quantitatively only in the presence of a large excess of standard; the half‐way point of which provides a direct measure of the binding constant.—3. Only for moderate interactions can individual curves characteristic of the binding strength be observed. The limiting cases 1 and 2 yield titration curves which reflect only the general class to which the system belongs.

The dynamical procedures are fairly insensitive in case 1, which represents the classical end‐point situation and is most suitable for quantitative anlaysis, i.e. for a determination of sample concentrations. For case 2, the classical and dynamical techniques yield comparable information: mass‐action parameters are obtained from the extrema of the curves, which occur only in the presence of an excess of the standard. In case 3 the dynamical treatment provides a more direct access to the equilibrium constants, and also to the enthalpies or volumes of reaction as well as to the rate constants. The advantage of the dynamic method is due to the fact that in the two derivatives of the titration function d Ti/d ln q and d Ti/d ln p (where q is the titration variable, i.e. the ratio of standard and sample concentration, and p the mass‐action parameter, i.e. a reduced binding constant) the terms resulting from a differentiation with respect to p are more closely related to the reaction parameters than those following from a variation of q.

The dynamic analysis is generalized for applications to multiple‐step titration processes, where it allows for the measurement fo equilibrium and rate parameters of individual steps. A uniform representation utilizing trigonometric functions was chosen which expresses clearly the singualr character of the end‐point. The relations are summarized intabular form. They provide in conjunction with the illustrations the basis for a comparative discussion.
Plastics as Optical Materials
Authors: Dislich Helmut
Published: December 2003

The Principal material used in optics is glass. Plastics can only gain acceptance in optics if they have properties not encountered with glass or if a desired article can be produced more rationally from a plastic. An example of the first case is provided by UV light guides consisting of a quartz glass core surrounded by a plastic cladding; there is no glass with a sufficiently low refractive index. Examples of the second case are viewfinder optics for camerás and lenses for sunglasses and industrial safety spectacles.
Cyclooligocondensation of Amino Acids: Macrocyclic Amides of β‐Alanine
Authors: Rothe Manfred , Mühlhausen Dietger
Published: December 2003

Nitrogen analogs of crown ethers of type (2) have recently atracted much attention. The reaction β‐alanine → (1) → (2) provides the simplest entry yet to these compounds. The tendency to form large rings in macrocyclization equilibria could be estimated for β‐alanine → (1).
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Catalytic Alkylation of Benzene with CO and H2: A Homogeneously Catalyzed Fischer‐Tropsch Synthesis
Authors: Henrici‐Olivé G. , Olivé S.
Published: December 2003

The synthesis of alkylbenzenes from benzene, CO, and H2 constitutes the first demonstration of true Fischer‐Tropsch chain growth on a soluble mononuclear catalyst [W(CO)6(+AlCl3)]. Reaction is performed at 200°C under pressure. No xylene is formed.
Chemical Vapor Deposition of Silicon Carbide and Silicon Nitride—Chemistry's Contribution to Modern Silicon Ceramics
Authors: Fitzer Erich , Hegen Dieter
Published: December 2003

Pure silicon carbide and silicon nitride have valuable properties in bulk pore‐free form; however, their industrial exploitation has hardly been possible so far. Neither compound can be melted or sintered in pure form; hot pressing or sintering at normal pressure requires the presence of additives; and the reaction‐sintering process in which only Si and C or Si and N are employed as additives affords porous materials.–The novel process of chemical vapor deposition has partly overcome the drawbacks of the previous methods. In the new process SiC is produced, e.g., by pyrolysis of CH3SiCl3, and Si3N4 by reaction of SiCl4 with NH3. This technique can also be used for pore filling in objects made of SiC and Si3N4 (gas phase impregnation) and for producing extremely fine SiC and Si3N4 (gas phase impregnation) and for producing extremely fine SiC and Si3N4 powder and SiC monofilaments suitable as components for SiC composites. Moreover, gas phase impregnation can also give fiber composites.
Effects of Long‐Chain Branches on the Degradation Kinetics of Polymers
Authors: Ebert Klaus H. , Ederer Hanns J. , Basedow Arno Max
Published: December 2003

Degradation of polymers in solution is greatly influenced by long side chains. Quantitative information about the number of branches and the length of the side chains etc., can be obtained from the molecular weight distribution by mathematical simulation.
Novel Titanium Halides Containing Metal‐Metal Bonds: Ti7Cl16 and Ti7Br16
Authors: Schäfer Harald , Laumanns Reinhard , Krebs Bernt , Henkel Gerald
Published: December 2003

The discovery of two new titanium halides came as a surprise. The isotypic compounds Ti7Cl16 and Ti7Br16 are produced by chemical transport (via gaseous complexes); X‐ray analysis shows them to contain TiTi bonds.
Photochemical Behavior of N2‐Complexes: Photoluminescence of trans‐(N2)2W(diphos)2 and trans‐(CO)2W(diphos)2
Authors: Caruana Albert , Kisch Horst
Published: December 2003

The first photoluminescing dinitrogen complex trans‐(N2)2W(diphos)2 (1) is also the first transition‐metal(o) compound to show a structured emission spectrum. These finding are of considerable significance for the photochemical reduction of complexed N2.
A New Lithium‐Nickel Polynuclear Complex: Ni(C12H17NiLi)2(THF)4
Authors: Jonas Klaus , Krüger Carl , Sekutowski Janine C.
Published: December 2003

Three linearly arranged nickel atoms and two coordinatively unsaturated Li and two pentacoordinated C atoms present in the new complex (2) (C12H18 = all‐cis‐1,5,9‐cyclododecatriene). Compound (2), formed as by‐product in the lithiation of C11H18Ni0, was obtained from (1) in 30% yield.
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Synthesis and Biosynthesis of Alkoxylipids
Authors: Mangold Helmut K.
Published: December 2003

Chromatographic methods have shown that lipids with long alkyl or 1‐alkenyl chains–called alkoxylipids or ether lipids–are widely distributed in human and animal tissues. These compounds comprise neutral alkoxylipids, i. e. 1‐O‐alkyl or 1‐O‐(1‐alkenyl)‐2,3‐di‐O‐acylglycerols, and alkoxylipids which are linked by a phosphate residue at C‐3 to aminoethanol, choline or serine. 1‐O‐Alkylglycerols, 1‐O‐(1‐alkenyl)glycerols and other natural alkoxylipids can be synthesized in high yields. 2‐Alkyl, 1,3‐dialkyl and trialkylglycerols which are not found in nature are also accessible by synthesis. The neutral alkoxylipids are employed in biomedical investigations, e.g. as substrates in acyl‐hydrolase systems or in fat absorption studies. The principal features of alkoxylipid biosynthesis have been elucidated. The alkyl residue is derived from a saturated or monounsaturated fatty acid via the corresponding alcohol. 1‐O‐(1‐alkenyl)‐2‐O‐acylglycerophosphoryl aminoethanols (“plasmalogens”) are apparently formed from the appropriate 1‐alkyl compounds; this is not possible in the case of the choline series. Both “aminoethanol” and “choline” plasmalogens are, nevertheless, present in most tissues.
Stereochemistry of [2,3]Sigmatropic Rearrangements
Authors: Hoffmann Reinhard W.
Published: December 2003

Stereoselective synthesis is attracting more and more attention. Successful stereoselective syntheses require the availability of reactions of known stereochemistry which give maximum yields of the desired products. This is particularly so with reactions proceeding via cyclic transition states. Of these, the stereochemistry of [3,3]sigmatropic processes has long been known. This article now summarizes the factors determining the stereoselectivity of [2,3]sigmatropic rearrangememts.
Hexamethyldisilane/Iodine: Convenient In Situ Generation of Iodotrimethylsilane
Authors: Olah George A. , Narang Subhash C. , Gupta B. G. Balaram , Malhotra Ripudaman
Published: December 2003

Organic syntheses involving iodotrimethylsilane, e.g. cleavage of esters, ethers, snd carbamates under mild conditions, have advantages but Me3SiI is not readily obtainable and is also a sensitive compound. These difficulties are overcome by the Me3SiSiMe3/I2 reagent which can be used for convenient in‐situ generation of Me3SiI.
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August Kekulé—The Architect of Chemistry Commemorating the 150th Anniversary of His Birth
Authors: Hafner Klaus
Published: December 2003

Imagination, daring, and critical understanding are the sources of the impulses still felt today which chemistry received from the theoretical studies ofKekulé.“Let us learn to dream, gentlemen, then perhaps we shall discover the truth; but let us beware of publishing our dreams abroad before they have been scrutenized by our vigilant intellect … Let us always allow the fruit to hang until it is ripe. Unripe fruit brings even the grower but little profit; it damages the health of those who consume it; it endangers particularly the youth which cannot yet distinguish between ripe and unripe.” (Kekulé1890).
New Synthetic Reactions Based on the Onium Salts of Aza‐Arenes [New synthetic methods (29)]
Authors: Mukaiyama Teruaki
Published: December 2003

Effective syntheses employing 2‐halogenated pyridinium, benzoxazolium, benzothiazolium, and pyridinium salts have been accomplished in the absence of strong acids and bases. Activation of carboxylic acids or alcohols with these onium salts leads to 2‐acyloxy and 2‐alkoxy intermediates which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides isocyanates, isothiocyanates, nitriles, and isocyanates. The possibility of performing stereospecific syntheses (involving configurational inversion) with onium salts deserves attention.
Multidentate Acyclic Neutral Ligands and Their Complexation
Authors: Vögtle Fritz , Weber Edwin
Published: December 2003

The properties of cyclic crown ethers are approximated by acyclic neutral ligands (popdands), which are compared and contrasted with open‐chain bioionophores and acidic chelating agents in this article. Variations of the endo‐polarophilicity/exo‐lipophilicity balance, complex stability, ion slectivity can often be accomplished more easily, with greater versatility, and at less expense with acyclic polyethers than with their cyclic counterparts; complexation and decomplexation are generally faster in acyclic systems; and the pseudocavity usually has greater conformational flexibility. Acyclic crown ethers and open‐chain cryptands stiffened by rigid “terminal groups” containing donor atoms readily form crystalline complexes of alkali and alkaline earth metals. Some oppen‐chain neutral ligands form helical conformations in their crycstalin complexes. The observed coordination numbers and geometries are of theoretical interst. Attractive terminal group interactions lead to pseudocyclic species occupying a position intermediate between cyclic and acyclic ligands. It has recently proved possible to isolate crystalline complexes of alkali and alkaline earth metal ions with weakly donating oligo(ethylene glycol ethers) and with glycols; such complexes have also been obtained with sugars. Acyclic neutral ligands can serve as simple models of nigericin‐type bioionophores and be used analytically in microelectrodes. The recently discoverd crystalline stoichiometric complexes formed by some acyclic neutral ligands with guest molecules such as urea, thiourea, and water provide a fresh insight into weak interactions between neutral molecules and for the development of urea receptors.
Isopropyl Carboxylates—A New Class of Insect Pheromones
Authors: Francke Wittko , Levinson A. R. , Jen T.‐L. , Levinson H. Z.
Published: December 2003

The pheromone bouquet of the hide beetle consists of isopropyl carboxylates formerly unknown in insects. The principal component is isopropyl Z‐5‐dode‐cenoate.
Bonding Properties of Cyclopropane and Their Chemical Consequences
Authors: de Meijere Armin
Published: December 2003

Among the cyclic compounds of carbon, cyclopropane and its derivatives are outstanding by virtue of their unusual structural, spectroscopic, and chemical properties. The cyclopropane ring more closely resembles the CC double bond than the cyclobutane ring: it is a small ring with “double bond character”. Cyclopropyl and vinyl groups interact with neighbouring π‐electron systems and p‐electron centers; both cyclopropane derivatives and olefins form metal complexes, and add strong acids, halogens, and ozone; they both undergo catalytic hydrogenation and cycloadditions. While distinct differences in reactivity do exist–the double bond usually being more reactive than the three‐membered ring–there are no fundamental differences in behavior.–Although cyclopropane derivatives have been known for more than 90 years, intensive studies have been limited to the past 25 years. The development of carbene chemistry has rendered cyclopropane derivatives far more readily accessible. In recent years, the synthetic potential of the small‐ring function has been increasingly exploited. A considerable number of newly developed methods utilizing this approach clearly demonstrates that the reactivity of the cyclopropene ring, like that of the CC double bond, qualify it as a “functional carbon group”. This development is in full swing; we may therefore justifiably devote considerable effort to the study of cyclopropane chemistry.
Neurophysins: Molecular and Cellular Aspects
Authors: Acher Roger
Published: December 2003

Neurophysins are linear cystine‐rich proteins containing 93–95 amino acid residues which like the neurohypophysial hormones oxytocin and vasopressin are formed in the hypothalamus and travel from there to the hypophysial posterior lobe. A species usually contains two (or three) neurophysins which differ only slightly in chain length and/or sequence. Many observatios suggest that both oxytocin and one of the neurophysins as well as vasopressin and the other neurophysin have a common precursor whose long chain is split into neurophysin and hormone. It can be shown on rats having considerable diabetes insipidus that a single gene controls the biosynthesis of the vasopressin and one of the neurophysins.
Quantitative Trace Analysis of Thallium in Biological Material
Authors: Achenbach Christoph , Ziskoven Rolf , Koehler Ferdinand , Bahr Ute , Schulten Hans‐Rolf
Published: December 2003

The pharmacokinetics of the poisonous element thallium have been examined directly by field desorption mass spectrometry from very small tissue samples. After oral administration of 160 mg/kg to mice, concentrations of 10−4 mol/1 were found in organs. While the teratogenic dose 50% is lower than the lethal dose 50% by a factor of 40, some 12.5% of fetal malformations still occur at 1/1000 of the lethal dose.
Developments in Arylnitrene Chemistry: Syntheses and Mechanisms [New synthetic methods (31)]
Authors: Iddon B. , Meth‐Cohn O. , Scriven E. F. V. , Suschitzky H. , Gallagher P. T.
Published: December 2003

Aryl‐ and heteroaryl‐nitrenes can take part in intra‐and intermolecular reactions in both of their possible electronic states (triplet and singlet). In this review we have endeavored to high‐light recent synthetic uses of these reactive intermediates as well as draw attention to avenues open to further exploration in this field. Singlet arylnitrenes will interact with suitable ortho‐positioned substituents to give a variety of fused azoles, some in excellent yield. In suitable solvents and in presence of amines and alcohols, phenylnitrenes undergo ring expansion to azepines which can also occur in nitrenes of certain fused bicyclic aromatics (naphthalene, quinoline, isoquinoline, benzo[b]thiophene). The latter nitrenes may also give rise to o‐diamines which are useful starters for further heterocyclic synthesis. Triplet arylnitrenes (usually regarded as having only a nuisance effect in synthetic work) may also be utilized in practicable heterocyclic syntheses within a suitable molecular framework. Decomposition of aryl azides in a mixture of an organic and polyphosphoric acid leads to fused oxazoles. The mechanism is discussed for all the reactions considered.
Capto‐dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]
Authors: Viehe Heinz Günter , Merényi Robert , Stella Lucien , Janousek Zdenek
Published: December 2003

The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto‐dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd‐Substitution has synthetically useful applications: cd‐substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross‐conjugated cd‐substituents are “radicophilic” and permit twofold carbon radical addition. cd‐Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd‐substituted molecules appear to involve radicals.
The Homologous Series of Cyclic Polysilanes from (Me2Si)5 to (Me2Si)35
Authors: Brough Lawrence F. , Matsumura Koichi , West Robert
Published: December 2003

Permethylsilicon rings having 5 through 35 members arise on slow addition of Me2SiCl2 to Na/K alloy in boiling tetrahydrofuran. After removal of the major products (Me2Si)5 and (Me2Si)6 (recrystallization and fractional sublimation) the cyclic polysilanes can be detected by high pressure liquid chromatography.
Reaction Paths on Multidimensional Energy Hypersurfaces
Authors: Müller Klaus
Published: December 2003

Theoretical investigation of a chemical reaction requires detailed knowledge of the potential energy of the molecular system. As a first step in such a study, minimum‐energy reaction paths have to be mapped on a generally multidimensional molecular potential surface. Even at this stage problems are encountered that have only recently been solved satisfactorily. The difficulties involved and various ways to handle them are discussed in connection with a two‐parametric model potential. Three chemical reactions examined illustrate the usefulness of such theoretical investigations as well as their current limitations.
A Model of Hydrogen‐Bonded Liquids
Authors: Luck Werner A. P.
Published: December 2003

The orientation defect model can be used for quantitative estimates and for understanding the properties of H‐bonded liquids, such as water and alcohol. The defect concentrations can be determined by vibrational spectroscopy, and the applicability of the approximation procedure derives from considering H‐bonds as chemical equilibria. Possible extensions of the simple model are critically discussed.
Chromium(II)‐catalyzed Electrochemical Dehalogenation of β‐Hydroxyhalides—Convenient Entry to Deoxynucleosides
Authors: Wellmann Josef , Steckhan Eberhard
Published: December 2003

The dehalogenation of β‐hydroxyhalides (halohydrins), as is often required in natural product syntheses, can be achieved by electrochemical reduction, especially by “indirect‐electrolysis”. Chromium(II) perchlorate in the presence of butanethiol can be used as catalyst. The OH groups must be protected. This method avoids elimination to give the olefin.
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Lithium Nitride Halides—New Solid Electrolytes with High Li+ Ion Conductivity
Authors: Hartwig Peter , Weppner Werner , Wichelhaus Winfried , Rabenau Albrecht
Published: December 2003

Solid ionic conductors are a treasure trove for modern technology. Among the lithium nitride halides which have now been thoroughly studied, the thermally stable Li1.8N0.4Cl0.6 can be utilized as thin low‐resistance layers, e.g. in printed circuits. Transfer experiments and EMF measurements confirmed that the electrolytic current flow is due to Li+ ions.
Chemistry and Function of Human Plasma Proteins
Authors: Schwick Hans‐Gerhard , Haupt Heinz
Published: December 2003

Human blood plasma contains a large number of proteins. New analytical and preparative techniques have so far permitted the isolation of more than one hundred such proteins; about ninety percent of these were first characterized in the last 30 years. The plasma proteins include components of the clotting and complement systems as well as proteinase inhibitors, immunoglobulins, lipoproteins, and carrier proteins. The biological function of some of the plasma proteins is not yet known. Deficiency of one or more plasma proteins usually causes serious health disorders, the best known example being hemophilia. Several biologically active proteins can be gained from blood plasma; these proteins—for example the blood clotting factors—are of great prophylactic and therapeutic importance and allow a better exploitation of the valuable plasma than can be obtained by means of transfusion.
Heterogeneously Catalyzed Gas‐Phase Bromination of Trifluoromethane
Authors: Bock Hans , Mintzer Jan , Wittmann Jörg , Russow Jürgen
Published: December 2003

The optimization of a heterogeneously catalyzed gas‐phase reaction by PE spectroscopy is demonstrated for the production of F3CBr, an extinguishing agent used in automatic fire extinguishing installations. A specially developed (PE spectroscopic) gas‐analysis technique permits screening of catalysts (and conditions). The best results were obtained with FeCl3/KBr/activated charcoal.
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Electrophilic Reagents—Recent Developments and Their Preparative Application
Authors: Effenberger Franz
Published: December 2003

The most widely known electrophilic agents are protic acids and compounds with an electronsextet partial structure. Recent research has aimed at the development of new electrophilic reagents, with greater reactivity on the one hand and higher selectivity on the other, which would largely obviate the addition of Lewis acids (Friedel‐Crafts catalysts), and also allow control of the isomer ratio in reactions with ambivalent substrates. Compounds with “super‐leaving groups”, such as trifluoromethanesulfonate and fluorosulfate, have been demonstrated as most advantageous in this respect since they are sufficiently polarized or dissociated for reactions to take place even in the absence of Friedel‐Crafts catalysts. Heterocycles such as pyridones or imidazole are likewise suitable leaving groups; they are employed for their high selectivity, and also because they allow working under non‐aqueous conditions.
1H‐NMR Investigations on the Mutarotation of N‐Acetyl‐D‐neuraminic Acid
Authors: Friebolin Horst , Supp Martin , Brossmer Reinhard , Keilich Gunda , Ziegler Dietmar
Published: December 2003

Enzymatic liberation of N‐acetyl‐α‐D‐neuraminic acid in an NMR spectrometer permitted the first determination of the mutarotation of this biochemically important sugar derivative which was formerly considered to be too fast to measure. Until recently it was assumed that only the β‐form is present in aqueous solution.
1,3‐Bis(1‐lithio‐3‐methyl‐1‐phenylpentyl)benzene, an Organodilithium Compound Soluble in Aromatic Hydrocarbons
Authors: Schulz Günther , Höcker Hartwig
Published: December 2003

A bifunctional initator suitable for anionic 1,4‐polymerization of 1,3‐dienes is the title compound (1), because it is the first representative of its kind to be soluble in aromatic hydrocarbons.
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Influence of Isomerism of Alkanes on the Thermodynamic Properties of Cyclohexane/Alkane Mixtures
Authors: Heintz Andreas , Lichtenthaler Rüdiger N. , Schäfer Klaus
Published: December 2003

The differing thermodynamic behavior of straight‐chain and branched hydrocarbons in mixtures with other compounds is particularly important in separation processes. An extension of the Flory theory now permits a consistent description of the excess quantitites for mixtures of isomeric alkanes with cyclohexane and prediction of these quantities for regions of pressure and temperature not yet examined experimentally.
Direct Photolysis of Uranium Hexafluoride as a Preparatively Utilizable Endothermic Reaction
Authors: Becker Frank S. , Jacob Eberhard
Published: December 2003

Laser isotopic separation of uranium could profit from UF6 photodissociation. Direct cleavage of UF6 (50 g) by UV light into UF5 and highly pure fluorine was achieved almost quantitatively (39 h) in a new apparatus. It should be possible in principle to accomplish laser isotope separation without scavengers and to recover fluorine in the nuclear fuel cycle.
Viroids: A Class of Subviral Pathogens
Authors: Gross Hans J. , Riesner Detlev
Published: December 2003

Infectious RNA molecules lacking a protein coat have recently been shown to be the cause of several diseases in higher plants. These molecules, termed viroids, have been characterized as circular chains composed of about 360 nucleotide residues. They therefore comprise a class of infectious pathogens even smaller than viruses or bacteriophages. As a result of work on viroids it is now possible for the first time to give a complete description of the structure of a eukaryotic pathogen. Viroids possess structural and dynamic properties which have not as yet been observed with other nucleic acids. This article summarizes and discusses the results of predominantly biochemical and physicochemical studies on viroids.
Polarized Low‐Temperature Crystal Spectra of Inorganic Complexes
Authors: Day Peter
Published: December 2003

The electronic spectra of complexes are especially informative if they are recorded for crystals at low temperature or at varying temperature with polarized light. This straightforward technique frequently permits reliable band assignment. Such assignments, being independent of the assumptions of any particular theoretical model, then provide a basis for testing theories of electronic structure.
Amorphous Silver Silicates, Storage Elements with Low Switching Field Strength
Authors: Jansen Martin , Käs Hans Herbert
Published: December 2003

Materials for digital information storage are in demand. Amorphous silver silicates, prepared by fusion of Ag2O and SiO2 under ≥ 1800 bar of O2 at 600°C, exhibit bistable switching behavior after a forming process. A given storage state is conserved without any need for a holding current; “silver clusters” are presumably involved.
Distribution of Terminal and Bridging CO‐Groups in an Anionic Carbonylmetal Cluster as a Result of Ion‐Pair Formation. Crystal and Molecular Structure of LiCo3(CO)10 · i‐Pr2O
Authors: Adams Hans‐Norbert , Fachinetti Giuseppe , Strähle Joachim
Published: December 2003

Drastic structural changes in an anionic carbonylmetal cluster can be evoked by slight changes in the acid/base properties of the system. In the crystalline title compound (X‐ray structure analysis) edge‐bridging CO groups are present in the cluster units. In contrast, the IR spectrum recorded in ether indicates an equilibrium between (a few) clusters of this kind and (mainly) clusters having terminal CO groups.
The Kinetic and Mechanistic Evaluation of NMR Spectra. New analytical methods (18)
Authors: Binsch Gerhard , Kessler Horst
Published: December 2003

In addition to the static parameters of the chemical shifts and coupling constants, which serve as a source of knowledge for molecular structure and stereochemistry, an NMR spectrum can frequently furnish dynamic quantities characterizing relaxation and exchange phenomena. The information about nuclear switching processes has proved to be particularly useful in practice for the detection of internal molecular motions and for the estimation or determination of the corresponding energy barriers. A plethora of studies of this nature has in the past been performed on simple proton spectra. Methodological developments of recent years have led to a significant reduction of the effort required for the quantitative dynamic evaluation of NMR spectra arising from complex spin systems or involving other nuclei. In many cases it has, moreover, become possible to extract detailed mechanistic information inaccessible by other means. The practical execution of such analyses will be explained and illustrated by a selected number of applications.
Towards an Understanding of the Carbon‐Carbon Bond
Authors: Rüchardt Christoph , Beckhaus Hans‐Dieter
Published: December 2003

In this essay, the classical question of “the influence of the number and kind of substituents on the strength of the CC bond”, is pursued with the modern tools of contemporary physical organic chemistry. Based on the work of Karl Ziegler, the products and kinetics of thermolysis of a large number of highly branched aliphatic hydrocarbons and phenyl‐ or cyano‐substituted derivatives were investigated. For each class of compounds, a linear relationship was found between the free enthalpy of activation of the homolytic cleavage of the weakest CC bond and the strain energy in the ground state. These relationships permitted a quantitative separation of steric and electronic effects on the cleavage of CC bonds. The influence of the size of the substituent groups on bond angles, bond lengths, and the conformational behavior of model compounds was studied by means of experimental structure determinations and force field calculations. CC bond lengths up to 164 pm, bond angles at tetracoordinate carbon as large as 126°, and unusual eclipsed and gauche preferred conformations were found.
Brominations with N‐Bromosuccinimide: Solvent and Selectivity
Authors: Offermann Werner , Vögtle Fritz
Published: December 2003

Correlations of the selectivity κ of a reaction with the refractive index n of the solvent used are new in physical organic chemistry. Such a relationship has been discovered on bromination of three toluene derivatives with NBS in ten different solvents; deviations were found for the eleventh solvent CCl4.
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Liquid Chromatography of Enantiomers: Determination of Enantiomeric Purity in Spite of Extensive Peak Overlap
Authors: Mannschreck Albrecht , Mintas Mladen , Becher Georg , Stühler Georgine
Published: December 2003

A new approach to the determination of enantiomeric purity P is based on the known technique of liquid chromatography on chiral phases, such as triacetyl‐cellulose. Interfering overlapping or fusion of peaks are overcome by simultaneous measurement of absorbance A and rotation α as functions of the volume eluted (υ)· C+ is determined graphically.
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Intercalation Complexes of Metallocenes in Iron Oxide Chloride
Authors: Schäfer‐Stahl Hartwig , Abele Raimund
Published: December 2003

Assumption of “free” electrons in the intercalation complex (1) of FeOCl and ferrocene rationalizes the finding that the high‐spin Fe3+ state of the FeOCl host lattice is retained on intercalation of the guest molecule (Mössbauer spectrum), while the Mössbauer absorptions of ferrocene disappear completely. The conductivity of the crystal also supports formulation as (1).
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N‐Isocyanoiminotriphenylphosphorane: Synthesis, Coordination Chemistry, and Reactions at the Metal
Authors: Weinberger Bernd , Fehlhammer Wolf Peter
Published: December 2003

A storage form of N‐isocyanides, e.g. isodiazomethane CNNH2, and a new complex ligand are two applications of the surprisingly stable N‐isocyaniminophosphorane (1). It is readily accessible by the route shown below.
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Hexakis(dimethylamino)cyclohexaborane, a Boron(I) Compound without Electron Deficiency
Authors: Nöth Heinrich , Pommerening Hans
Published: December 2003

A B6 ring with a chair conformation is present in the title compound (1) which crystallizes from distillation residues obtained on dehalogenation of [(CH3)2N]2BCl. (1) is the first homocycle of boron and also the first boron (I) compound not to exhibit electron deficiency.
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High‐Resolution Transmission Electron Microscopy Re‐examined as a Tool in Solid State Chemistry
Authors: Gruehn Reginald , Mertin Wilhelm
Published: December 2003

Transmission electron microscopy (TEM) can be used with crystalline solids to obtain direct images of small structural groups comprising a few coordination polyhedra with resolution nearly down to atomic scale (“lattice imaging”). More exact knowledge of the conditions required for direct imaging, as well as improvements in the instruments themselves, have now made it possible to examine very small defect regions (microdomains), faults in the stacking sequence of structural groups or atom layers (planar or Wadsley defects), and isolated defects in narrowly delimited areas that may actually be below the dimensions of the unit cell. The structural principle of the very smallest ordered regions can even be determined when X‐ray structure analysis proves unable to do this. “Block structures” are particularly suitable as models for the testing and further development of the high‐resolution method; the detection of three‐dimensional, two‐dimensional, and one‐dimensional defects has been studied on such structures.
A New Variant of the Amphoterism of Tin(II) Hydroxide: Sn(OH)2 as Stannio Complex Ligand
Authors: du Mont Wolf‐Walther , Neudert Brigitte
Published: December 2003

A novel mode of fixing a transition metal to an amphoteric inorganic polymer has been accomplished in the complexes (2). Complexes having coordinative SnM bonds were formerly unknown. Sn(OH)2 is still highly associated in (2) (M = Cr, W; R = Ph, Me).
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Liquid Metals and Liquid Semiconductors
Authors: Hensel Friedrich
Published: December 2003

Numerous liquid systems have electrical properties which resemble those of crystalline and amorphous semiconductors. The existence of “semiconducting” behavior in these liquids is mostly related to a continuous transition from a metallic to a “semiconducting” state when a thermodynamic variable such as temperature, density or concentration is changed. Changes in the nature of the chemical interaction and the associated changes in the structure of the liquid are of fundamental importance for the transition to a “semiconducting” state. This will be demonstrated for the ionic liquid CsAu, for covalent liquid selenium, and for expanded liquid metals.
Solubility of Nonvolatile Biochemical Substances in Compressed Carbon Dioxide
Authors: Alwani Ziad
Published: December 2003

The extraction of natural products with compressed carbon dioxide has already found industrial application. Studies on the model substance α‐tocopheryl acetate showed that its solubility (i) increases in liquid and supercritical CO2 with increasing pressure and (ii) changes comparatively little when CO2 is warmed at constant pressure from subcritical to supercritical temperature.
13C‐NMR Spectroscopic Studies on [13C]methylated Bituminous Coal
Authors: Haenel Matthias W. , Mynott Richard , Niemann Klaus , Richter Udo‐Burckhard , Schanne Lother
Published: December 2003

13C‐NMR studies on bituminous coal require preparation of soluble derivatives largely retaining the original structure of the coal. Reductive methylation with solvated electrons/13CH3I satisfies these requirements. The spectrum reveals that the methyl groups are linked mainly to tertiary and quaternary (benzylic) C atoms.—This chemical derivatization with isotopically labeled groups should also be suitable for the study of polymers.
Structure and Function of the Energy‐Converting System of Mitochondria
Authors: von Jagow Gebhard , Engel Wolf Dieter
Published: December 2003

The main energy source for all endergonic processes occurring in living organisms is the phosphate bond energy of nucleoside triphosphates, especially adenosine triphosphate (ATP). In aerobic organisms, as for instance in mammals, more than 90% of ATP is formed during the process called oxidative phosphorylation. In this process, similar to that of muscle contraction and nerve excitation, nature works with vectorial processes taking place at a membrane separating distinct spaces from each other. The present article deals with the operation of a set of water‐insoluble membrane proteins and enzymes vectorially transporting electrons, protons and other ions, which finally leads to the formation of ATP. This machinery transforming substrate oxidation energy into chemical energy in the form of the phosphoric anhydride bond of ATP operates with a very high efficiency.

The structure and function of the machinery of mitochondrial oxidative phosphorylation are described. It consists of the electron transfer chain, the ATP‐synthetase, the adenine nucleotide translocase and the phosphate carrier. The electron transfer chain can be resolved into multiprotein complexes—at three of them energy conversion takes place—and into the electron carriers ubiquinone and cytochrome c. The substrate oxidation energy is converted into the chemical energy of ATP with an electrochemical proton gradient as intermediary form. The energetic aspects of the processes are analyzed by linear irreversible thermodynamics. Great success has been gained during the past few years on the structural characterization of the participating proteins. The function of the various systems is partially elucidated on the molecular level; this concerns especially the mechanism of proton and adenine nucleotide translocation, as well as ATP formation.
The Structure of Simple Molecular Liquids
Authors: Zeidler Manfred D.
Published: December 2003

Liquid structure is described by the pair‐correlation function. If the liquied particles are molecules then the respective correlation function depends on distance and several angular variables; hence, for the sake of simplicity a symmetry‐adapted representation must be used. The most important structural parameters of this molecular pair‐correlation function can be determined approximately by a combination of several scattering experiments, such as neutron (employing different isotopes), X‐ray and electron diffraction. Light scattering, dielectric, and nuclear magnetic relaxation experiments provide further, albeit less direct, access to such determinations. Some results obtained by measurements on chloroform are reported. Theoretical computations of these structural parameters are also discussed.
Characterization by Mössbauer Spectroscopy of Iron Carbide Phases in a Highly Active Carbon Matrix Catalyst for Medium Pressure Fischer‐Tropsch Synthesis
Authors: Schäfer‐Stahl Hartwig
Published: December 2003

An improved understanding of the Fischer‐Tropsch synthesis (CO + H2 → hydrocarbons), and especially of the processes occurring at the catalyst, is of great topical interest. Reduction of an FeCl3‐graphite intercalation compound by biphenyllithium afforded an amorphous carbon layer matrix with embedded highly dispersed Fe particles. In the presence of CO and H2 (140°C, medium pressure range) the Fe particles are transformed mainly into iron carbide phases. This highly active catalyst has now been treated at various temperatures with gas mixtures having different H2 contents. It is deduced from the catalytic activity and the Müssbauer spectra that iron carbide phases are the actual catalyst, at least below 200°C.
Catalytic Synthesis of Magnesium Hydride under Mild Conditions
Authors: Bogdanović Borislav , Liao Shih‐tsien , Schwickardi Manfred , Sikorsky Peter , Spliethoff Bernd
Published: December 2003

Magnesium hydride, of potential use for reversible storage of hydrogen, has now been synthesized by a method proceeding under mild conditions and which can be performed on a large scale. Especially active catalysts are obtained by reaction of anthracenemagnesium with halides of chromium, titanium, or iron in THF. These solutions are catalytically active at 20°C and under normal pressure.
Geminal Dialkylation of Ketones with Grignard Compounds and Methyltitanium(IV) Chlorides
Authors: Reetz Manfred T. , Westermann Jürgen , Steinbach Rainer
Published: December 2003

The methylation of tert‐alkyl chlorides—obtained from ketones via the Grignard compounds and their chlorination—can be achived with Me2TiCl2, MeTiCl3, or even ZnMe2 and TiCl4 as catalyst under very mild conditions.
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Metalloporphyrin‐Catalyzed Hydroxylation of Cyclohexane by Alkyl Hydroperoxides: Pronounced Efficiency of Iron‐Porphyrins
Authors: Mansuy Daniel , Bartoli Jean‐François , Chottard Jean‐Claude , Lange Marc
Published: December 2003

The catalytic hydroxylation of non‐activated alkanes by hydroperoxides under mild conditions has been studied on the example of cyclohexane and cumyl hydroperoxide. Of the metalloporphyrin catalysts tested, Fe(TPP)Cl was strongly effective, Mn(TPP)Cl was weakly effective, Co(TPP) and Os(TPP)(CO)(py) suffered alteration during the catalysis, while Ni, Cu, Zn, Mg, Ti, and V derivatives proved to be inactive.—In Nature alkane oxidations with O2 are catalyzed by (iron‐containing) cytochrome P450.
Structure and Dynamic Behavior of syn‐1,6‐Ethano‐8,13‐methano[14]annulene
Authors: Günther Harald , von Puttkamer Henning , Deger Hans M. , Hebel Peter , Vogel Emanuel
Published: December 2003

Detailed structural information is obtainable from 3J(H,H) values in unsaturated ring systems. Accurate analysis of the 400‐MHz 1H‐NMR spectrum of the title compound revelated a temperature‐dependent equilibrium between the double bond isomers (1)⇌(2) (see previous communication).
Water Gas Shift Reaction with the Aid of Selenium/Platinum Catalyst
Authors: Kambe Nobuaki , Morimoto Fumihiko , Kondo Kiyoshi , Sonoda Noboru
Published: December 2003

A new catalyst for the water gas shift reaction is metallic selenium/platinum black. Conversion of CO into CO2 was at most 43% after 20 h at 200°C/ca. 30 bar CO. Both these elements are necessary for the catalytic formation of H2 and CO2. The reaction could proceed via H2Se: H2Se/platinum black is also suitable for use as a catalyst.
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Reduction of Carbonyl Compounds by Aluminum Telluride and H2O or D2O
Authors: Kambe Nobuaki , Kondo Kiyoshi , Morita Satoru , Murai Shinji , Sonoda Noboru
Published: December 2003

The reduction of carbonyl compounds with H2Te generated in situ leads conveniently and very mildly to alcohols. The method offers particular advantages in the production of deuterated alcohols with the aid of Al2Te3 and D2O, which is far more favorably priced than any deuterated reducing agent.
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Recent Progress in Oxo‐ and Fluorometalate Chemistry
Authors: Hoppe Rudolf
Published: December 2003

About a quarter of a century ago a review article having almost the same title appeared in this journal[1]. Since then many hundreds of new fluorides and oxides of metals have been synthesized, and repeatedly subjected to detailed investigation. Why, and to what end are such compounds still studied[2]? Has our knowledge been not only widened but also deepened? What advances have been made in synthetic chemistry in this sector? Have new ideas led to unforeseen results and have unexpected findings forced the revision of tested concepts? This area of research belongs to solid state chemistry, and in the meantime has become almost unsurveyable even for a committed researcher. In this paper, therefore, an attempt is made to outline any relevant advances that have been made and to present open questions and new aspects using selected examples, mainly from the chemistry of the first row of the transition metal series. Those not directly involved in this area may be surprised to find that even substances with a simple composition are also cited. They might ask whether such compounds mentioned in text books are not already understood. Although it is a widely‐held view that such compounds are well known, this is incorrect: Probably no‐one has ever prepared a sample of CrF2 or Na2O whose composition “adequately” exactly corresponded to the quoted formula[3]. Typical examples which demonstrate the considerable effort necessary for finally proving what others long ago already assumed to know, can be taken from the area of inorganic chemistry (e.g.: As2O) as well as from organic chemistry (e.g. C4[C(CH3)3]).