Synthese von Dibenzo[a,g]chinolizinen — Ein neuer Zugang zu Protoberberinen

Summary A novel synthesis to prepare dibenzo-8-quinolizinones8 is reported using the intramolecular cyclisation of the benzylated Reissert compounds6 for the key step. Methylation of8 by methyllithium gives partial deoxygenated coralynes10 which in turn can be reduced by NaBH₄ yielding the 8-methyltetrahydro-protoberberines11. The structures are assigned by NMR-spectroscopy.

     

Kapitza phonon transmission from clean H-silicon(111) surfaces into liquid helium

We have studied the phonon transmission from ultraclean Si(111) surfaces into liquid helium by the phonon pulse technique. Reflection experiments and angular resolving transmission experiments were performed to measure the absolute value of the transmission coefficient and its dependence on the phonon emission angle into the solid. Clean samples etched conventionally in dilute HF show a significant anomalous transmission. An additional etch step in highly buffered HF (i.e., NH₄F) with a pH-value of 7.8 reduces the transmission coefficient drastically. Local inhomogeneities of the transmission coefficient caused by the deposition of water molecules on the surface could be visualized by the enhanced transmission. We found that the observed anomalous transmission is caused by mass defects.     

Noisy one-dimensional maps near a crisis. II. General uncorrelated weak noise

The escape rate for one-dimensional noisy maps near a crisis is investigated. A previously introduced perturbation theory is extended to very general kinds of weak uncorrelated noise, including multiplicative white noise as a special case. For single-humped maps near the boundary crisis at fully developed chaos an asymptotically exact scaling law for the rate is derived. It predicts that transient chaos is stabilized by basically any noise of appropriate strength provided the maximum of the map is of sufficiently large order. A simple heuristic explanation of this effect is given. The escape rate is discussed in detail for noise distributions of Lévy, dichotomous, and exponential type. In the latter case, the rate is dominated by an exponentially leading Arrhenius factor in the deep precritical regime. However, the preexponential factor may still depend more strongly than any power law on the noise strength.     

Effect of shear-wave polarization on defect detection in stainless steel weld metal

Ultrasonic inspections of austenitic stainless steel weld metal are particularly difficult because of the dendritic structure and anisotropy of the material. The acoustic properties of stainless steel weld metal are discussed. Data on frequency spectra and variations in longitudinal and shear velocities with wave propagation direction are presented. Differences in shear velocities as great as 25% have been observed as the polarization direction is changed. The difference in detectability of artificial reflectors using shear waves of varying polarization is presented, and it is demonstrated in some cases that horizontally polarized shear waves can ‘detect’ a reflector in the weld metal where the traditional vertically polarized shear waves cannot.     

Zur Reaktion von Silylradikalen. Das Verh?ltnis Disproportionierung/Rekombination

Ohne Zusammenfassung     

1H-NMR- und ir-spektroskopische untersuchungen an erythro-2-brom-3-chlor-1,3-diarylpropanonen-1

By comparison of the ¹H-NMR- and IR spectra of erythro-2-bromo-3-chloro-1,3-diaryl- propan-1-ones (1) with those of analogous dihalogenides, the NMR signals of the AB part have been assigned to both the non-aromatic protons H_A or H_B and bands in the IR region 500–750 cm^?1 to the C-halogen vibrations, respectively. Hammett relations for NMR signals and IR carbonyl frequencies were found and problems connected with transmission of the effects of substituents were discussed.     

Ring-Ketten-Gleichgewichte bei der Methathese-Reaktion von Cycloolefinen

Ohne Zusammenfassung