Über hochverzweigte aliphatische Verbindungen, 4. Mitt.: Ergiebigere Synthesen des Triisopropylamins

Zusammenfassung Während Diisopropylformamid weder mit Methylmagnesiumjodid noch mit dem-bromid tertiäre Base liefert, konnte mit Methylmagnesiumchlorid Triisopropylamin erhalten werden. Diisopropylamin läßt sich mit Diisopropylsulfat, aber nicht mit den Isopropylhalogeniden oder mit Triisopropylphosphat, zum Triisopropylamin alkylieren. Schließlich wird diese Base auch durch Anwendung einer vonBruylants gefundenen Reaktion — Einwirkung von Alkylmagnesiumhalogenid auf Dialkylaminonitrile — erhalten, und zwar mit über 50% Ausbeute.Einige pK^*-Werte werden in Methylglykol—Wasser bestimmt.     

Complete Racemization in the Base Hydrolysis of Optically Active mer-[Chloro(diethylene triamine) (1,3-diaminopropan-2-ol-N,N′) cobalt (III)]tetrachlorozincate

The base hydrolysis of the optically active title compound proceeds with full racemization whilst the meridional arrangement of the diethylenetriamine ligand is fully retained. The optically active hydroxo complex prepared independently with retention of configuration racemizes ? 10⁴ times slower. This unique result is discussed in terms of the classical π-stabilization hypothesis for the base hydrolysis mechanism.     

Synthesis of Alkenyl-Substituted Allenecarboxylates

The Wittig olefination of decanoyl chloride by using the phosphonium salt 1 in the presence of two equivalents of Et₃N represents a one-step synthesis of the racemic form of the naturally occurring pheromone (–)- 2 which contains an alkenyl-substituted allenic moiety (ef. Scheme 1). It is also shown, that unsaturated acyl chlorides which contain at least one γ-H-atom undergo the Wittig reaction with an appropriate phosphorane yielding γ-alkenyl-substituted α-allenic esters and α-allenic γ-lactones, respectively (ef. Schemes 2 and 3).     

Über den Zusammenhang von Interpolation und diskreterT-Approximation mit rationalen Funktionen

Ohne Zusammenfassung     

Possible alternatives to tri-bimaximal mixing

Possible alternatives to tri-bimaximal mixing are presented based on other symmetry principles, and their predictions for |U _e3|, sin ² θ ₁₂ and sin ² θ ₂₃ are compared to the present neutrino mixing data. In some cases perturbations are required to give better agreement with the data, and the use of a minimal approach is illustrated. Precise experimental determinations of the mixing parameters will be required to decipher the correct mixing pattern and to pin down the appropriate flavor symmetry.     

First-principles modelling of scanning tunneling microscopy using non-equilibrium Green’s functions

The investigation of electron transport processes in nano-scale architectures plays a crucial role in the development of surface chemistry and nano-technology. Experimentally, an important driving force within this research area has been the concurrent refinements of scanning tunneling microscopy (STM) techniques. The theoretical treatment of the STM operation has traditionally been based on the Bardeen and Tersoff-Hamann methods which take as input the single-particle wave functions and eigenvalues obtained from finite cluster or slabs models of the surface-tip interface. Here, we present a novel STM simulation scheme based on non-equilibrium Green’s functions (NEGF) and Wannier functions which is both accurate and very efficient. The main novelty of the scheme compared to the Bardeen and Tersoff-Hamann approaches is that the coupling to the infinite (macroscopic) electrodes is taken into account. As an illustrating example we apply the NEGF-STM method to the Si(001)-(2×1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods.     

Effect of masker-frequency variability on the detection performance of infants and adults

The effect of masker-frequency variability on the detection performance of 7-9 month-old infants and adults was examined. Listeners detected a 300-ms 1000-Hz pure tone masked by: (1) A random-frequency two-tone complex; (2) a fixed-frequency two-tone complex; or (3) a broadband noise. Maskers repeated at 300-ms intervals throughout testing at 60 dB SPL. The signal was presented simultaneously with one presentation of the masker. Thresholds were determined adaptively using an observer-based method. Infants' thresholds were higher than adults' in all conditions, but infants' and adults' thresholds changed with masker condition in qualitatively similar ways. The fixed two-tone complex produced masking for both age groups, but more masking for infants than for adults. For infants and adults, the random two-tone complex produced more masking than broadband noise, but the difference was greater for infants than for adults. For infants and adults, the random two-tone complex produced more masking than the fixed two-tone complex, and the difference between these conditions was similar for both age groups. These results suggest that infants are more susceptible to informational masking than adults in the absence of spectral variability. Whether infants are more susceptible to the effects of masker-frequency variability than adults remains to be clarified.