Über Ränder in elektronenmikroskopischen Abbildungen

Ohne Zusammenfassung Der Verfasser hat der Forschungsgemeinschaft für die Unterstützung der Arbeit und Herrn Prof. Dr. L. Ebert für interessante Diskussionen zu danken.     

Osmotische Molekulargewichtsbestimmungen an Polystyrollen. (Vorläufige Mitteilung)

Ohne Zusammenfassung     

Die Keimbildung an Ionen in übersättigten Dämpfen

Zusammenfassung In der vorliegenden Arbeit ist die Keimbildung an Ionen in übers?ttigten D?mpfen theoretisch und experimentell untersucht worden. Mit Hilfe eines einfachen kinetischen Ansatzes ist es gelungen, die Zahl der sekundlich entstehenden Keime bzw. Tr?pfchen theoretisch festzustellen. Die Prüfung der Theorie erfolgte auf zwei verschiedenen Wegen. 1. Wurde die Abh?ngigkeit der kritischen übers?ttigung von der jeweiligen Ionenintensit?t, 2. die Abh?ngigkeit der Tr?pfchenzahlen vom Expansionsgrad bei konstanter lonenintensit?t experimentell untersucht.     

Beobachtungen an Mercurijodidfällung in Gallerten und Glyzerin

Ohne Zusammenfassung     

Walking metals in d8···d8 hetero-bimetallic complexes: an original dynamic phenomenon

In the course of our investigations on polymetallic complexes derived from 1,3-bis(thiophosphinoyl)indene (Ind(Ph(2)P=S)(2)), we observed original fluxional behavior and report herein a joint experimental/computational study of this dynamic process. Starting from the indenylidene chloropalladate species [Pd{Ind(Ph(2) P=S)(2)}Cl](-) (1), the new Pd(II)···Rh(I) hetero-bimetallic pincer complex [PdCl{Ind(Ph(2) P=S)(2)}Rh(nbd)] (2; nbd=2,5-norbornadiene) was prepared. X-ray crystallography and DFT calculations substantiate the presence of a d(8)···d(8) interaction. According to multinuclear variable-temperature NMR spectroscopic experiments, the pendant {Rh(nbd)} fragment of 2 readily shifts in solution at room temperature between the two edges of the SCS tridentate ligand. To assess the role of the pincer-based polymetallic structure on this fluxional behavior, the related monometallic Rh complex [Rh{IndH(Ph(2) P=S)(2)}(nbd)] (3) was prepared. No evidence for a metal shift was observed in that case, even at high temperature, thus indicating that inplane pincer coordination to the Pd center plays a crucial role. The previously described Pd(II)···Ir(I) bimetallic complex 4 exhibited fluxional behavior in solution, but with a significantly higher activation barrier than 2. This finding demonstrates the generality of this metal-shift process and the strong influence of the involved metal centers on the associated activation barrier. DFT calculations were performed to shed light onto the mechanism of such metal-shift processes and to identify the factors that influence the associated activation barriers. Significantly different pathways were found for bimetallic complexes 2 and 4 on one hand and the monometallic complex 3 on the other hand. The corresponding activation barriers predicted computationally are in very good agreement with the experimental observations.     

Li+(TMPAND)Na−: The first alkalide prepared from an azacage complexant

The new lithium-selective complexant 5,12,17-trimethyl-1,5,9,12,17-pentaazabicyclo[7.5.5]nonadecane (TMPAND) was used to synthesize Li⁺(TMPAND)Na–, the first alkalide prepared from an azacage complexant. This sodide was characterized by a variety of methods. Differential scanning calorimetry experiments showed a reversible, endothermic, solid-solid phase transition at an onset temperature of –75 ± 3°C and with H = 3.3 ± 1 kJ/mol.²³Na NMR spectra showed a peak at –61 ppm, characteristic of a sodium anion, and a second minor peak at –10 ppm, probably due to the interaction of Na- with trapped electrons. The quadrupole coupling constant of the complexed lithium cation was found to be 0.19 MHz at –100°C, and⁷Li NMR spectra showed a discontinuity in the line width of the⁷Li NMR peak and in the quadrupole coupling constant at the phase transition.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Über neue Pyrimidine und deren Überführung in 6-Sulfanilamidopyrimidine Vorläufige Mitteilung

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The first step in layer-by-layer deposition: electrostatics and/or non-electrostatics?

A critical discussion is presented on the properties and prerequisites of adsorbed polyelectrolytes that have to function as substrates for further layer-by-layer deposition. The central theme is discriminating between the roles of electrostatic and non-electrostatic interactions. In order to emphasize this feature we refrain from discussing practical problems sometimes incurred in polyelectrolyte adsorption like freezing-in of non-equilibrium situations, patchwise attachment, unclear chemistry and only consider solid substrates. Although it is in principle ambiguous to discriminate between coulombic and non-coulombic or "chemical" interactions, it will be shown that, as a rule, non-coulombic contributions to the interactions cannot be neglected. They are responsible for the familiar overcharging. For obtaining more insight, it is recommended to consider electrometric techniques such as electrokinetics, conductometry and potentiometry, in combination with other analytical techniques applied to well-defined systems, for which various parameters can be modulated in a systematic way.     

The first ionic liquid-promoted three-component coupling strategy for an expeditious synthesis of β-nitrocarbonitriles/thiocyanates

A novel and convenient three-component coupling reaction of nitromethane, aromatic aldehydes and trimethylsilyl cyanide (TMSCN) or ammonium thiocyanate has been developed for an expeditious synthesis of β-nitrocarbonitriles or β-nitrothiocyanates, respectively, via C-C and C-S bond-forming reactions. The synthetic protocol strategically involves a one-pot sequential Henry reaction and a Michael addition efficiently promoted by the same ionic liquid [bmim]OH. The main advantages of the present approach include the use of inexpensive simple substrates and an ionic liquid as an efficient reaction promoter for the mild synthesis in a one-pot procedure.     

Molecular iodine: a highly efficient catalyst in the synthesis of quinolines via Friedländer annulation

A mild and efficient route for the synthesis of quinolines and polycyclic quinolines via Friedl?nder annulation, utilizing molecular iodine (1 mol%) as a new catalyst, is described.     

The Microwave Direct Heating of Zeolite FAU in an Open System

Zeolite FAU was heated directly by microwave irradiation at 2450 MHz is in open system without special loading materials. It was discovered that zeolite X was heated to 1473K about 90 seconds at power output of 400W. HY type zeolite was also heated to 1373K although in needed relative long time (about 11 minutes). Influences of exchangeable cations and adsorbed substances on zeolite′s ability to absorb microwaves were also discussed.     

Imidazole-functionalized magnetic Fe3O4 nanoparticles: an efficient,green, recyclable catalyst for one-pot Friedländer quinoline synthesis

Research on Chemical Intermediates - An efficient and cost-effective procedure for preparation of Fe3O4 nanoparticles and supported Brønsted acidic ionic liquid...     

Brønsted acid-catalyzed enantioselective Friedländer condensations: achiral amine promoter plays crucial role in the stereocontrol

A highly enantioselective Friedl?nder condensation has been established by using chiral Br?nsted acids in combination with achiral amines to give quinolines in high yields (up to 99%) and with excellent enantioselectivities (up to 95%).     

The first synthesis of (±)-3α-acetoxy-15β-hydroxy-7,16-seco-trinervita-7,11-diene,defense substance from a termite soldier

The first total synthesis of defense substance from a termite soldier has been achieved in a route that allows the preparation of other stereoisomers.     

Silica sulfuric acid as an efficient catalyst for the Friedländer quinoline synthesis from simple ketones and ortho-aminoaryl ketones under microwave irradiation

The synthesis of quinoline derivatives via Friedländer method from ortho-aminoaryl ketones in the presence of a catalytic amount of silica sulfuric acid (SSA) under solvent-free condition and microwave irradiation was described. A good range of simple ketones such as cyclohexanone and deoxybenzoin were used.