Schnelle Reaktionen organischer Verbindungen in L?sung

Zusammenfassung Es wird eine einfache Apparatur beschrieben, die die Bestimmung der Geschwindigkeit schneller Reaktionen in Lösung und die Aufnahme der Spektren von instabilen Zwischenprodukten hierbei gestattet.

---

Summary A simple apparatus is described for determining the kinetics of fast solution reactions and for measuring the spectra of unstable intermediates.

---

---

Der Deutschen Forschungsgemeinschaft danken wir sehr für die Mittel zum Bau der beschriebenen Apparatur.     

Die gas-chromatographische Untersuchung der Pyrolyseprodukte von Kautschuken

Ohne Zusammenfassung     

Lösungsmitteleffekte in Kernresonanzspektren gesättigter Kohlenwasserstoffe

Proton NMR solvent effects ν(CCl₄) – ν(C₆H₆) have been measured for the methyl groups in 25 saturated cycloalkanes. Magnitude and sign of the Δ values are correlated with the molecular shape. The results are discussed with particular respect to stereochemistry, and they provide a new method for distinguishing between geometrical isomers.     

Staudinger reaction at in-bridgehead positions of phosphorus macrobicyclic compounds

Reaction of in,in-phosphite 1 with thiophosphoryl azide 2 affords in,in-dithiophosphate 3, in,in-thiophosphate-imidophosphate 4, and in,in-phosphite-imidophosphate 5. Compounds 4 and 5 are the first examples of the modification of in-bridgehead positions in macrobicyclic compounds with groups larger than methyl. The benzaldehyde arms of the in-substituent in 4 and 5 jut out of the cage bars. In 4 they are trapped between the macrocyclic arms to give the NMR spectra of a Cs-symmetric solution-state structure. In contrast, in 5 the benzaldehyde arms can move between the gaps of the cage. This results in 1H and 13C NMR spectra which are consistent for a compound with C3v symmetry. In,out-diimidophosphate 7 is obtained in moderate yield by reaction of in,out-phosphite 6 with thiophosphoryl azide 2. Its in-benzaldehyde moieties are not fixed between the cage arms, but can freely move from one gap to the next as is indicated by NMR measurements.     

The high-pressure <Emphasis Type="Bold">α/β</Emphasis> phase transition in lead sulphide (PbS)

The high-pressure behaviour of PbS was investigated by angular dispersive X-ray powder diffraction up to pressures of 6.8 GPa. Experiments were accompanied by first principles calculations at the density functional theory level. By combining both methods reliable data for the elastic properties of rock-salt type α- and high-pressure β-PbS could be obtained. β-PbS could be determined to crystallise in the CrB-type (B33), with space group Cmcm. The reversible ferro-elastic α/β transition is of first order. It is accompanied by a large volume discontinuity of about 5% and a coexistence region of the two phases. A gliding mechanism of {001} bilayers along one of the cubic 〈110〉 directions governs the phase transition which can be described in terms of group/subgroup relationships via a common subgroup, despite its reconstructive character. The quadrupling of the primitive unit cell indicates a wave vector (0, 0,π/ a ) on the Δ-line of the Brillouin zone. Received 11 October 2002 Published online 14 February 2003 RID="a" ID="a"Also at: Institute of Physics of the Czech Academy of Sciences, Cukrovarnicka 10, 16253 Praha 6, Czech Republic e-mail: knorr@min.uni-kiel.de RID="b" ID="b"Present address: University of Cambridge, Cavendish Laboratory (TCM), Madingley Road, Cambridge CB3 0HE, UK RID="c" ID="c"Present address: Johann-Wolfgang Goethe Universit?t, Mineralogisches Institut, Kristallographie, Senckenberganlage 30, D 60054 Frankfurt a.M., Germany     

Intrinsic tunneling spectra of Bi2(Sr(2-x)Lax)CuO(6+delta)

We have measured intrinsic-tunneling spectra of a single CuO-layer La-doped Bi2(Sr(2-x)Lax)CuO(6+delta) (Bi2201-Lax). Despite a difference of a factor of 3 in the optimal superconducting critical temperatures for Bi2201-La0.4 and Bi2212 (32 and 95 K, respectively) and different spectral energy scales, we find that the pseudogap vanishes at a similar characteristic temperature T* approximately 230-300 K for both compounds. We find also that, in Bi2201-Lax, pseudogap humps are seen as sharp peaks and, in fact, even dominate the intrinsic spectra.     

Present and future experiments with stored exotic nuclei at the FRS-ESR facility

High accuracy mass and lifetime measurements are performed with the combination of the in-flight separator FRS and the cooler-storage ring ESR at GSI. Exotic nuclei are produced via projectile fragmentation and fission at (400–900) MeV/u. This energy range is the basis for unique experimental conditions with bare and few-electron fragments and allows for the first time investigations for decay channels which are rare or strictly forbidden in neutral atoms. New experimental developments and data including the discovery of new isotopes are presented. The comparison of the experimental results with theoretical predictions indicates the potential for improvements of nuclear models. A new generation of experiments will be possible with the advent of the proposed international Facility for Antiproton and Ion Research (FAIR).     

Status of the energy-buncher in the low-energy branch of the Super-FRS

An ion-optical study on the layout of the so-called energy-buncher stage in the low-energy branch of the planned fragment separator Super-FRS is presented. The main purpose of the energy-buncher is a significant reduction of the energy spread of the `hot' fragments at the exit of the separator. Alternatively, the central unit of the buncher—a large dispersive dipole system—can be used as a high-resolution spectrometer for secondary products of nuclear reactions. The proposed design provides a large degree of flexibility for different experimental scenarios with slowed-down low-energy or stopped exotic isotopes.