New Peptide Lactones of the Streptogramin Family (Group B). Structures of Virginiamycin S5 and Viridogrisein II

Virginiamycin S₅ and viridogrisein II were isolated by liquid chromatography from the crude antibiotics virginiamycin and viridogrisein, respectively. Their structures were elucidated by amino-acid analysis and mass spectrometry.     

Reversible Photochemistry,Absorption- and 1H-NMR.-spectra,and oxidation of the [2,2]metacyclophane-1-ene ⇄ 4,5,15,16-tetrahydropyrene system

The reversible photointerconversion in the above system was investigated in a wide range of temperatures and wavelengths of irradiation. The tetrahydropyrenes are obtainable only photochemically. The unmethylated and the mono-methylated compound are oxidized with iodine quantitatively to 4,5-dihydropyrene, even at ?30°. This makes it possible to estimate the absolute concentration of the tetrahydropyrenes, and thereby their molar extinction coefficients and complete electronic absorption spectra. The quantum yields in both directions do not vary appreciably with the temperature, down to ?190°. This is the first case in which the photocyclization yield of a cis-stilbenelike compound is not attenuated on cooling, and reflects the special character of highly constrained structures. No emission was observed in solution. ¹H-NMR.-spectra of both modifications of the dimethylated compound were taken. They support the structures assumed for both modifications, and also allow an estimate of their relative concentrations.     

Study of the mechanism of hydroformylation at industrial reaction conditions

With a newly developed analytical technique, i.e. high temperature/pressure IR cell coupled to the reactor, it was possible to study the mechanism of hydroformylation at reaction conditions. It has been conclusively found that the hydrogenolysis of the acyl cobalt complex is performed by HCo(CO)₄ and not by molecular H₂, as proposed byHeck andBreslow.Therefore the formation of HCo(CO)₄ from Co₂(CO)₈ is an intermediate step in the sequence of hydroformylation reaction steps. The rate of hydroformylation of any of the olefins is smaller than the rate of formation of HCo(CO)₄ from Co₂(CO)₈. The IR spectra reveal that always more than 30% of the cobalt is in the form of HCo(CO)₄ under the reaction conditions.It is found that the formation of HCo(CO)₄ from Co₂(CO)₈ is the slowest and most temperature-dependent step of the hydroformylation reaction. Also the reaction between olefin and HCo(CO)₄ is slower than the hydrogenolysis of the acyl complex.The experiments were carried out under industrial oxo conditions. The diffusional effects were eliminated.With 6 FiguresPart of the Ph.D. dissertation 1974. N. H. Alemdarolu, J. M. L. Penninger, andE. Oltay, Mechanism of Hydroformylation, Part II. Mh. Chem.107, 1043 (1976).     

Specific isotopic labeling of sugars: Applications in mass-spectral analysis. The mass spectrum of 1,6-anhydro-2,3-O-iso-Propylidene-β-D-talopyranose

Derivatives of 1,6-anhydro-2,3-O-isopropylidene-β-D -talopyranose (I) specifically deuterated at C-3 (II), at C-4 (III), at C-3 and C-4 (IV), and in the isopropylidene group (V) have been examined by high-resolution, electron-impact mass spectrometry. From the elemental compositions of the fragment ions, the mass-number shifts upon deuterium incorporation, and analysis of metastable transitions, it was possible to identify the origin of the hydrogen atoms in all fragments formed from I and to present a complete scheme of fragmentation pathways undergone by this molecule.     

Das Kastenmodell als Grundlage für ein ab initio-Verfahren

Zusammenfassung Es werden die Resultate des in [1] entwickelten Verfahrens für den Fall des Wasserstoff- und des Heliumatoms mitgeteilt und diskutiert. Mit diesen Daten lassen sich Rückschlüsse auf die Anwendbarkeit des Verfahrens allgemein ziehen.

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The box model as a basis for an ab initio procedureIII. Results for the hydrogen and the helium atom

The results of the procedure developped in [1] are given in the case of the hydrogen and the helium atom. On the basis of these results conclusions can be drawn on the applicability of the whole method.