bluuebunny/crossref_metadata_2025_split huggingface dataset:
Absolute Konfiguration von Azafrin
Authors: Eschenmoser Walter , Hans Eugster Conrad 
Published: December 2004

AbstractBy using complementary and selectively acting reagents (TiCl4 and sulfurane 16), azafrin, the main carotenoid in the rhizomes of Escobedia scabrifolia, has been shown to have the (5R:6R)‐configuration. Reaction of azafrinaldehyde (4) with (Ph3P)3RhCl leads to a mixture of 5 and 6, the latter arising probably through elimination of acetylene and recarbonylation.
Tetrakis (methylidene)cyclobutane (‘[4]Radialene’): Electronic states of the molecular ion
Authors: Bally Thomas , Buser Urs , Haselbach Edwin 
Published: December 2004

AbstractThe photoelectron spectrum of tetrakis (methylidene)cyclobutane (1, ‘[4]radialene’) is reported. The electronic states of 1+ are assigned on the basis of model calculations and with reference to related systems. Jahn‐Teller activity in the degenerate states is discussed. A failure of the simple LCBO‐model for the π(eg)‐orbital of 1 is noted and traced to the fact that this orbital, though having a symmetry‐equivalent π*‐counterpart, does not interact with it. This feature is confined to [4n]radialenes; their total π‐energies are therefore higher than those of the other members. It is shown that radialenes, in principle, do not constitute a class analogous to that of the linear polyenes as inferred earlier.
The Photoelectron Spectrum of Tetrafluorobutatriene
Authors: Basch Harold , Bieri Gerhard , Heilbronner Edgar , Jones Taylor B. 
Published: December 2004

AbstractThe He(Iα) and He(IIα) spectra of tetrafluorobutatriene 3(F) have been recorded for comparison with those of butatriene 3(H). Ab initio double‐zeta basis self‐consistent field (SCF) and configuration interaction calculations on butatriene show that, contrary to previous assignment, no shake‐up band is expected to appear in the 9–10 eV energy range of the photoelectron spectrum. Further, such SCF calculations on tetrafluorobutatriene support the use of the perfluoro effect in assigning the purely π orbital ionizations. It is argued that 3(F) is a key compound for the study of the perfluoro effect. This is supported by a qualitative comparison of its photoelectron‐spectroscopic results with those of other perfluoro systems.
Cryptates. XXV. Stability and selectivity of cation inclusion complexes of polyaza‐macrobicyclic ligands. Selective complexation of toxic heavy metal cations
Authors: Lehn Jean‐Marie , Montavon François 
Published: December 2004

AbstractWe have measured the stability constants of the cryptate complexes formed by ligands 1–4 with alkali, alkaline‐earth, transition metal and toxic heavy metal cations. Stabilities and selectivities of complexation of the alkali and alkaline‐earth cations are less pronounced in 1–4 than in the parent compounds 5 and 6 and decrease as the number of nitrogen sites increase. Remarkable complexation properties are found towards transition metal and toxic heavy metal cations. The intramolecular cavity of ligands 1–3 is too large for small cations like Co2+, Ni2+, Zn2+ so that the complexes formed are comparatively weak; however these cations are strongly complexed by ligand 4 whose intramolecular cavity has a much smaller size, compatible with their ionic radius. On the other hand, ligands 1–4 all form highly stable cryptates with Cd2+, Hg2+, Pb2+. Thus by the combined operation of the two structural parameters, cavity size and nature of the binding sites, cryptands 2 et 3 present very high selectivities for the complexation of these toxic heavy metal cations with respect to the biologically important ones Na+, K+, Mg2+, Ca2+, Zn2+. The selectivities of ligand 2 for Cd2+, Hg2+ and Pb2+ with respect to Zn2+ are as high as 106, 1018 and 109 respectively. They are much more pronounced than those of previously known complexing agents. Cryptands like 2 and 3 thus present a unique selectivity sequence of special interest in detoxication (decorporation, depollution). Further structural elaboration may allow to design ligands which present a given selectivity pattern of potential use in “cryptatotherapy” and “environment pollution control”. The results also provide evidence for the existence, at low pH, of protonated complexes which probably participate in an acid catalysed process for dissociation of the complexes.
8. Azidiniumsalze. 20. Mitteilung [1]. Einführung der Diazogruppe mit Azidiniumsalzen in Hydroxy‐arene und Hydroxy‐hetarene
Authors: Balli Heinz , Müller Volkmar , Sezen‐Gezgin Ayten 
Published: December 2004

Diazo‐Group Transfer to Hydroxy‐arenes and Hydroxy‐hetarenes Using Azidinium SaltsDie Einführung der Diazogruppe mit 1‐Äthyl‐2‐azido‐pyridinium‐tetrafluoroborat und 2‐Azido‐3‐äthyl‐benzthiazolium‐tetrafluoroborat in Hydroxybenzole, Hydroxynaphthaline und einige Hydroxy‐hetarene wird beschrieben. Der Anwendungsbereich dieser Methode im Vergleich mit der Tosylazid‐Methode wird diskutiert.
12. Anil‐Synthese. 17. Mitteilung. Über die Herstellung von styryl‐derivaten des 2‐phenyl‐4H‐1,2,4‐triazolo [1,5‐a]pyridins
Authors: Pauchard Jean‐Paul , Siegrist Adolf Emil 
Published: December 2004

Preparation of styryl derivatives of 2‐phenyl‐4H‐1,2,4‐triazolo [1,5‐a]pyridine7‐Methyl‐2‐phenyl‐ and 2‐(3‐chloro‐4‐methylphenyl)‐4H‐1,2,4‐triazolo[1,5‐a]‐pyridines react with anils of aromatic aldehydes in the presence of dimethyl‐formamide and potassium hydroxide at 20–45° to yield the 2‐phenyl‐7‐styryl‐ and 2‐(2‐chloro‐stilben‐4‐yl)‐4H‐1,2,4‐triazolo [1,5‐a]pyridines respectively (‘Anil Synthesis’). Further, the Schiff's bases derived from o‐chloroaniline and 2‐(p‐formyl‐phenyl)‐ and 7‐formyl‐2‐phenyl‐4H‐1,2,4‐triazolo [1,5‐a]pyridine yield, with methyl‐ and with p‐tolyl‐substituted heterocycles, the corresponding heterocyclic substituted styryl and stilbenyl derivatives.
Free Radical Formation from Excited States of Aliphatic Carboxylic Acids and esters in solution as studied by electron spin resonance
Authors: Kaiser Tony , Grossi Loris , Fischer Hanns 
Published: December 2004

AbstractDuring UV.‐irradiation of aliphatic carboxylic acids and esters in aqueous and nonaqueous solutions various alkyl and acyl type radicals derived from parent compounds and solvents have been observed by ESR.‐spectroscopy. The structures of the radicals point to α‐cleavage, β‐dehalogenation and photoreduction as major photolytic processes of carboxylic acids and esters. The relative contributions of these processes to the overall photodecompositions depend on the carboxyl substituents, on solvent and temperature. Similarities of carboxyl and carbonyl group photochemistry are discussed.
Zur strahlungslosen Desaktivierung des tiefsten angeregten Singulett‐Zustandes von 2‐Alkyl‐indazolen in neutraler und protonierter Form
Authors: Heinzelmann Willy 
Published: December 2004

On the Mechanism of Radiationless Deactivation of the First Excited Singlet State of 2‐Alkyl‐indazolesThe temperature dependence of the quantum yields of fluorescence (ΦF), intersystem crossing (ΦT) and photoreactions (ΦR) have been measured for several neutral and protonated 2‐alkyl‐indazoles. The experimental data (Fig. 1 and 3) can be interpreted in terms of the reaction schemes 1 and 2 with temperature independent constants for fluorescence emission and intersystem crossing and temperature dependent photochemical primary processes. Whereas at low temperatures the sum of the quantum yields of fluorescence and intersystem crossing equals 1, at higher temperatures a very efficient radiationless deactivation process takes place (Table). Based on kinetic and photochemical data it is concluded that this deactivation proceeds via a hypersurface crossing (Fig. 2) or hypersurface touching (Fig. 4) in the course of the photochemical rearrangements 1 → 2 and 4 → 5 respectively.Similar mechanisms are expected to be responsible for the unusual internal conversion in other heterocyclic compounds.
Die Synthese von Actinioerythrol, Violerythrin und anderen 2,2′‐Dinor‐carotinoiden
Authors: Kienzle Frank , Minder Rudolf E. 
Published: December 2004

The Synthesis of Actinioerythrol, Violerythrin and other 2,2′‐Dinor‐carotenoids2,2′‐Dinor‐carotenoids including the naturally occurring actinioerythrol (1) and the blue carotenoid violerythrin (2), as well as 2,2′‐dinor‐rhodoxanthin (25) and 2,2′‐dinor‐zeaxanthin (27) and others have been obtained by total synthesis.
Physikalisch‐chemische Eigenschaften deuterierter Verbindungen. 4. Mitteilung. Deuterierung von Kohlenwasserstoffen durch heterogen katalysierten Isotopenaustausch im Gegenstrom
Authors: Gäumann Tino , Öz Hami , Piringer Otto 
Published: December 2004

The Deuteration of Hydrocarbons by Heterogeneous Catalysis in a Counter‐current ColumnA counter‐current method for the perdeuteration of liquid hydrocarbons by heterogeneously catalysed isotope exchange with deuterium gas is described. The efficiency of the column which was developed for this purpose has been investigated and optimised as a function of the experimental variables. The limits of the applicability of this method are discussed.
Rh(I)‐katalysierte Umlagerungen von 3,4‐Diacycloxy‐1,5‐hexadiinen; synthese von (E)‐4‐acyloxymethyliden‐2‐cyclopenten‐1‐onen
Authors: Pürro Serge , Pryde Andrew , Zsindely Janos , Schmid Hans 
Published: December 2004

Rh(I)‐Catalysed Rearrangements of 3,4‐Diacyloxy‐1,5‐hexadiynes; Synthesis of (E)‐4‐Acyloxymethyliden‐2‐cyclopenten‐1‐onesThe 3,4‐diacyloxy‐1,5‐hexadiynes3, 6and8which were synthesized according to a known, slightly modified procedure react with [Rh(CO)2Cl]2at 100° in chloroform with formation of the (E)‐4‐acyloxymethyliden‐2‐cyclopenten‐1‐ones4, 7and9(Schemes 2, 3and4), respectively.DL‐ andmeso‐3as well astrans‐ andcis‐8, give the same (E)‐isomers4and9, respectively. 3,4‐Diacetoxy‐3, 4‐dimethyl‐1, 6‐diphenyl‐1,5‐hexadiyne (10) produces with the same catalyst 2,6‐diacetoxy‐3, 4‐dimethyl‐1,6‐diphenylfulvene (11)(Scheme 5). A mechanism for the formation of the cyclopentenones is proposed inScheme 6.
Spektroskopische Untersuchungen über die Rolle des Käfig‐Effektes bei der Prädissoziation aromatischer Nitroverbindungen
Authors: Lippert Ernst , Kelm Jürgen 
Published: December 2004

AbstractPhotolysis of the bond Rar–NO2 contributes to quenching of the fluorescence of aromatic nitro compounds. Since no nitro compound is known which fluoresces above 20,000 cm−1 photolysis must occur via a predissociation process. Either a fluorine‐substituted nitro compound or fluorobenzene as the solvent was used for the irradiation experiments so that 19F‐NMR. spectroscopy could be used to analyse the reaction products. Cage effects play an important role. With a large distance between the radicals Rar and NO2, the phenyl radical forms a diphenyl compound with a benzenetype solvent molecule, and with small distance recombination will occur. For medium to long distances geminal recombination will also occur, not to the initial nitro compound, but to the corresponding nitrite, which in the presence of oxygen forms o‐nitrophenol. Mass spectrometry showed that the added oxygen atom is located in the nitro group.
CIDNP.‐Investigation of Photoinduced Polymerization
Authors: Borer Armand , Kirchmayr Rudolf , Rist Günther 
Published: December 2004

AbstractThe photochemistry and some initiator characteristics of the polymerization initiators ω,ω‐dimethoxy‐ω‐phenyl‐acetophenone (A), ω,ω‐diethoxy‐acetophenone (B) and ω,ω‐diisopropoxy‐acetophenone (C) have been studied by 1H‐ and 13C‐chemically‐induced nuclear polarization (CIDNP.) experiments. The primary reaction of initiator A is a Norrish‐type I cleavage, while for B and C Norrish‐type I and Norrish‐type II cleavages are of comparable importance. Three different recombination products could be detected for initiator A which correspond to the three canonical resonance forms of the substituted benzyl radical.In a number of polymerization experiments the competition between reactions among initiator radicals and reactions of initiator radicals with the monomer acrylic acid methyl ester was studied at low concentrations of the monomer. These experiments give insight into the first steps of the polymerization process.The positive sign of the α‐hydrogen hyperfine couplings of the dimethoxy‐methyl‐ and the diisoproproxymethyl‐radicals could be established, in agreement with the deviation of these radicals from planarity.A slow square‐wave light‐modulation technique has been employed in 13C‐FT.‐experiments to measure absolute CIDNP.‐intensities.
Rubidium‐Pentafluoromanganat(III) und dessen Monohydrat, strukturelle Daten und Topotaxiebeziehungen
Authors: Günter John Ralph , Matthieu Jean‐Pierre , Oswald Hans Rudolf 
Published: December 2004

Rubidiumpentafluoromanganate (III) and its monohydrate, crystal data and topotaxyThe unit cells and most probable space groups of the new compounds Rb2MnF5 · H2O and Rb2MnF5 have been determined from single crystal X‐ray diffraction data and the powder diffraction patterns indexed.

.By analogy to the stoichiometrically similar phases high temperature K2MnF5 · H2O, the unit cell of which has also been determined and its powder diffraction pattern indexed, and (NH4)2MnF5, model structures for the rubidium salts are proposed. Both structures consist of infinite chains of corner sharing coordination octahedra [MnF6], between which the rubidium ions and in the case of the hydrate additional water molecules are located. X‐ray diffraction and scanning electron microscopical investigations of the dehydration of the hydrate clearly point to a chain controlled topotactic reaction mechnism. This supports the proposed model structures and confirms the possibility of predicting topotactic reaction mechanisms.
Macrocarpamin, ein neues Bisindolalkaloid aus Alstonia macrophylla WALL. 167. Mittelung über organische Naturstoffe
Authors: Mayerl Friedrich , Hesse Manfred 
Published: December 2004

Macrocarpamine, a new bisindole alkaloid from Alstonia macrophylla WALL.A new bisindole alkaloid give the name (−)‐macrocarpamine (3) was isolated from the bark of Alstonia macrophylla WALL. Under pyrolytic conditions 3 is cleaved into the two known bases (+)‐pleiocarpamine (2) and (−)‐anhydro macrosalhin‐methin (5) (Scheme 1). The structure of 3 (including relative configuration) was deduced on the basis of chemical evidence and from its UV.‐, IR.‐, NMR.‐ and mass spectroscopic data.
Chemical Reactions in Electrical Discharges: Preparation of perfluorinated acetylenes and nitriles. Preliminary communication
Authors: Bieri Gerhard , Stadelmann Jean‐Pierre , Thommen Fritz , Vogt Jürgen 
Published: December 2004

AbstractSeveral fluorinated acetylenes and nitriles have been isolated from the reaction mixture obtained from Tesla excited fluorinated aromatic compounds. Differences in product distributions using Tesla or radio frequency discharges are discussed.
Inhaltsstoffe des Osmanthus‐Absolues. 1. Mitteilung: 2,5‐Epoxy‐megastigma‐6,8‐dien
Authors: Kaiser Roman , Lamparsky Dietmar 
Published: December 2004

Constituents of Osmanthus Absolute, Ist communication:2,5‐Epoxy‐megastigma‐6,8‐dienesBesides some further ionone derivatives we identified two new bicyclic oxacompounds (1a/1b) of the megastigmane type in the Osmanthus absolute. Isolation, special features of their spectral datas and synthesis starting from ethyl α‐safranate are described. The synthetic pathway choosen allowed the additional identification of four substances occurring in the same natural substrate, because some synthetic by‐products formed int he reaction sequence exhibited corresponding spectra and GLC. retention as the hitherto unknown components of the Osmanthus absolute.
Zur Photochemie von Allylaryläthern. 55. Mitteilung über Photoreaktionen
Authors: Waespe Hans‐Rudolf , Heimgartner Heinz , Schmid Hans , Hansen Hans‐Jürgen , Paul Henning , Fischer Hanns 
Published: December 2004

AbstractThe photochemical reactions of different allyl aryl ethers (Scheme 3) were investigated in hydrocarbons (Chap. 3.1) and in alcoholic solvents (Chap. 3.2). The composition of the photoproducts depended very much on the nature of the solvent. Irradiation (3–95 h) of different methyl substituted allyl aryl ethers (1, 3, 5, 7 and 11) with a low pressure mercury lamp (λEmiss. = 254 nm; 6 or 15 Watt) under argon (quartz vessel) resulted in the formation of 2‐, 3– and 4‐substituted phenols, dienones and products of consecutive reactions (Tables 1–4 and 6). The results suggested that all products were formed by homolytic cleavage of the CO bond in the singlet state of the ethers to intermediate radical‐geminates (Scheme 5) followed by radical recombination of the two fragments. No products were formed by concerted processes (Table 5, Schemes 5 and 6).Upon irradiation of allyl aryl ethers lacking alkyl substituents at position 4 (1 and 5) in protic solvents, mainly 2‐ and 4‐allylated phenols were obtained (Tables 1 and 4); 3‐allylated phenols were formed only in small amounts (0.02%). However, in aromatic hydrocarbons or cyclohexane 3‐allylated phenols were obtained from 1, 5 and 11 in significant amounts (3–11%; Tables 1, 4 and 6). E.g., upon irradiation of allyl‐2,6‐dimethyl‐2,4‐cyclohexadien‐1‐one (6) besides 3‐ and 4‐allyl‐2, 6‐dimethyl‐phenol (23 and 24). Irradiation of 5 in methanol afforded 23 and 6 only in traces, whereas 24 was the main product.
On Metal‐Atom Clusters IV. Photoionization thresholds and multiphoton ionization spectra of alkali‐metal molecules
Authors: Herrmann André , Leutwyler Samuel , Schumacher Ernst , Wöste Ludger 
Published: December 2004

AbstractThe investigation of electronic and structural parameters of metal molecules as a function of size may be decisive for understanding and control of heterogeneous catalysis with finely divided metals. Metal‐atom clusters can be prepared by several methods, most of which yield a molecular mixture only. Expansion of an atomic vapour into vacuum through a supersonic nozzle creates a complex cluster‐spectrum which has been investigated by photoionization using a mass‐spectrometer as selective detector. Broad band single photoionization (PI.) yields the abundances and ionization thresholds for Nax(x⩽16), Kx(x⩽12) and NaxKy(x+y⩽6). Rough indications about other deactivation channels of excited alkali‐molecules are obtained from an analysis of the photoionization efficiency (PIE.) curves. Two‐photon PIE. curves with narrow‐band (laser) light sources give an accurate photoionization threshold value and detailed information on ionization processes. Two‐photon ionization spectra via a real intermediate state reached by laser excitation are equivalent to normal absorption spectra, if the exciteation step is controlled by the true transition probabilities. By investigation of the power dependence of the ion current of Na as a function of the wavelength of the tunable cw dye laser (excitation) and of the ionizing Ar+‐ or Kr+‐laser, conditions under which true spectra are obtained have been clarified, in good agreement with a photon‐kinetic model of the processes involved. Vibronic and rovibronic spectra of several transitions in Na2 and K2 have been measured. Similarly a spectrum of Na3 has been determined mass‐selectively. The scope of the new method for an absorption spectroscopy in molecular beams is discussed.
Electrical Properties of the Organic Metallic Compound bis (tetrathiotetracene)‐triiodide, (TTT)2‐I3
Authors: Hilti Bruno , Mayer Carl W. 
Published: December 2004

AbstractThe maximum of the d.c. conductivity of single crystals of the title compound ((TTT)2‐I3), grown by cosublimation, is shown to be at about 35K. The ratio of the b‐axis (needle axis) conductivity at the temperature of its maximum (Tm ≅ 35 K) and its value at T = 300 K (normalized conductivity σ(Tm)/σ(300)) is strongly sample dependent. Values for σ(Tm)/σ(300) as high as 8 have been obtained. From 300 K to about 120 K the conductivity σ is proportional to T−1.3. in the temperature interval 40K⩽T⩽120K we found: σ∝︁T−1. On the low temperature side of the maximum (6K⩽T⩽20K) the conductivity is proportional to Tα, with α ranging from 2 to 2,5. It is shown that impurities, misfit of the stoichiometry and/or physical sample quality (crystal perfection) drastically shift the minimum of the resistivity to higher temperatures (Fig. 5), thereby altering also the temperature dependence of the resistivity on both sides of the minimum. Our crystallographic data difference from the results published by Isett et al. and Buravov et al. (Table 1) with regard to the iodine spacings. We argue that the polarisability of the I ions in their chain direction contributes significantly to the high conductivity (σ=1000 to 1000 Ω−1 cm‐1) along the crystallographic b‐axis (needle axis).
Electronic Properties and Optical Activity of Oligopeptides. III. Some cyclohexapeptides with glycine, L‐ and D‐alanine
Authors: Iseli Max , Wagnière Georges , Brahms J. Georges , Brahms Sabine 
Published: December 2004

AbstractThe wavelength range of the CD. spectra of some cyclohexapeptides containing different sequences of glycine, L‐ and D‐alanine is extended down to 170 nm. This allows a relatively complete recording of the (n − π*) and (π° − π*) Cotton effects. Some striking spectral changes are observed on going from one molecule to another. The relative influence of L‐ and D‐alanyl residues is discussed: Some spectra may be qualitatively related to each other by considering the effect of an L‐residue at position q in the ring to cancel partially with the effect of a D‐residue at position q ± 3. Assuming these cyclopeptides to occur in a hydrogen‐bonded pleated sheet structure, certain dominant changes in the spectra are interpreted as reflecting a transition of the overall backbone conformation from one which is closer to the (optically inactive) symmetry Ci to another which is closer to the (optically active) symmetry C2. An attempt is made to relate the influence of L‐ and D‐substituents within hairpin bends of the pleated sheet structure to an amide sector rule.
Laserflash‐photolysis of thep‐Chloranil/naphthalene system: Characterization of the naphthalene radical cation in a fluid medium,
Authors: Gschwind Rudolf , Haselbach Edwin 
Published: December 2004

AbstractExcitation ofp‐Chloranil (CA) in propylcyanide (PrCN) at room temperature leads to rapid production of3CA* which decays predominantly toCAH· withk= 1.6 · 105s−1. Observation of a photoinduced current suggests simultaneous production ofCA−formed by electron transfer quenching of3CA* by the medium. Added naphthalene (NP) quenches3CA* withkq= 7.0 · 109M−1S−1;NP+is unambigously identified as product (besidesCA−) of the electron transfer process. Dissociation of the ion pair occurs with essentially unit probability. Higher concentrations ofNPlead to the formation of (NP)+2. Pertinent spectroscopic parameters established forNP+under the conditions used are λmax= 685 nm (ϵ = 2970) using the known parameters ofCA\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document}as reference.NP+andCA\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document}decay by charge annihilation withkr= 4.5 · 109M−1S−1. The deviation from the diffusion controlled rate constant expected for ionic species, is discussed in view of the spin characteristics of the process. Comparison with two other ion recombination reactions leads to the conclusion that ‘inverted behaviour’ as expected fromMarcus' theory does also not show up forbackwarde−‐transfer between two ions (produced by forward e−‐transfer between two neutrals). Residual absorptions in the system are ascribed toCAH·, tentatively proposed to originate from H+‐abstraction byCA\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{+ \atop \dot{}} $\end{document}from the solvent.NP+appears to be a rather stable species with respect to the medium if the latter is meticulously purified.