On the application of homonuclear NOE difference spectroscopy as a convenient tool for configurational assignment of compounds with a C=N bond

Summary The applicability of homonuclear NOE difference spectroscopy for configurational assignment of compounds characterized by a -CH=N-R substructure is evaluated employing phenylhydrazones, benzenesulfonylhydrazones, (thio)semicarbazones, and oxime ethers derived from heteroaromatic carbaldehydes.Dedicated to Prof. Dr. F. Sauter with cordial wishes on the occasion of his 60th anniversary     

Trading relations in the perception of /r/-/l/ by Japanese learners of English

The role of language-specific factors in phonetically based trading relations was examined by assessing the ability of 20 native Japanese speakers to identify and discriminate stimuli of two synthetic /r/-/l/ series that varied temporal and spectral parameters independently. Results of forced-choice identification and oddity discrimination tasks showed that the nine Japanese subjects who were able to identify /r/ and /l/ reliably demonstrated a trading relation similar to that of Americans. Discrimination results reflected the perceptual equivalence of temporal and spectral parameters. Discrimination by the 11 Japanese subjects who were unable to identify the /r/-/l/ series differed significantly from the skilled Japanese subjects and native English speakers. However, their performance could not be predicted on the basis of acoustic dissimilarity alone. These results provide evidence that the trading relation between temporal and spectral cues for the /r/-/l/ contrast is not solely attributable to general auditory or language-universal phonetic processing constraints, but rather is also a function of phonemic processes that can be modified in the course of learning a second language.     

Synthese des Flechtenmakrolids (+)-Aspicilin mit Photolactonisierung als Schlüsselreaktion

Synthesis of the Lichen Macrolide (+)-Aspicilin Using Photolactonization as a Key Reaction (+)-Aspicilin, obtained from a lichen source of the Black Forest, has been proven to have the absolute configuration depicted by formula la . It is easily built up from phenol ( 14a ), 1,9-nonanediol ( 13a ), and (?)-(S-) methyloxiarane ( 6 ) (cf. Scheme 2). The latter building block provides the first stereogenic center C(17). The heterocycle is produced by photolactonization, fairly early during the course of the synthesis. The second stereogenic center is generated diastereoselectively at C(6) in compound 8 , conveniently available from photolactone 9a or 9b / 9c . Its absolute configuration depends on the kind of reducing agent and is controlled by long-range conformational transmission of chiral information. To explore the cause of stereoselection, 2D-NMR spectroscopy, X-ray structural analysis, and/or computer-aided conformational search followed by energy minimization have been used extensively, revealing the importance of the local conformation of the lactone moiety. Compound 8 , on treatment with Yamamoto's reagent, affords pre-target compound 7a almost exclusively. The latter compound, on pyridine-accelerated dihydroxylation with OsO₄, gives preferentially (+)-Aspicilin.     

Zur Ultrarotdurchlässigkeit von BeO,BeS, MgO,MgS und Li2O

The compounds BeO, BeS, MgO, MgS and Li₂O are evaporated by electron bombardment and condensed onto substrates at low temperatures. Their infrared lattice vibration is measured between 10 and 42μ at different temperatures. Also Debye-Scherrer-diagrams are sketched for investigating the structure of the layers. All substances without MgS are crystalline after condensation. They have a high degree of disorder which does not disappear during heating up to 293°K. Only MgS shows an amorphous phase. The crystallization of MgS-layers occurs at 293°K. Besides the normal cubic modification a new hexagonal phase can be found. The infrared spectra of all three phases are discussed. Furthermore MgO- and Li₂O-layers are prepared by burning metal flakes and precipitating the oxyde smoke onto substrates. The characteristic infrared absorption of such layers is interpreted by a theory ofFröhlich.