Application de la RMN du 13C a la determination de la configuration de centres quaternaires en serie alicyclique et hydrate de carbone a chaine ramifiee

Configurational assignments to quaternary centres of 2-(l,3-dithianyl) branched-chain carbohydrates, important intermediates for the synthesis of carbohydrate-containing antibiotics, have been made through natural abundance ¹³C NMR spectroscopy. Configurations of quaternary carbons in 21, 24 and 26 were assigned by comparison with ¹³C spectra of structurally-related alicyclic derivatives 1–16.     

C60 in intense short pulse laser fields down to 9 fs: excitation on time scales below e-e and e-phonon coupling

The interaction of C60 fullerenes with 765-797 nm laser pulses as short as 9 fs at intensities of up to 3.7 x 10(14) W cm(-2) is investigated with photoion spectroscopy. The excitation time thus addressed lies well below the characteristic time scales for electron-electron and electron-phonon couplings. Thus, energy deposition into the system is separated from energy redistribution among the various electronic and nuclear degrees of freedom. Insight into fundamental photoinduced processes such as ionization and fragmentation is obtained from the analysis of the resulting mass spectra as a function of pulse duration, laser intensity, and time delay between pump and probe pulses, the latter revealing a memory effect for storing electronic energy in the system with a relaxation time of about 50 fs. Saturation intensities and relative abundances of (multiply charged) parent and fragment ions (C60(q+), q=1-6) are fingerprints for the ionization and fragmentation mechanisms. The observations indicate that for final charge states q>1 the well known C60 giant plasmon resonance is involved in creating ions and a significant amount of large fragments even with 9 fs pulses through a nonadiabatic multielectron dynamics. In contrast, for energetic reasons singly charged ions are generated by an essentially adiabatic single active electron mechanism and negligible fragmentation is found when 9 fs pulses are used. These findings promise to unravel a long standing puzzle in understanding C60 mass spectra generated by intense femtosecond laser pulses.     

Symmetry of Weighted L1-Algebras and the GRS-Condition

Let G be a compactly generated, locally compact group of polynomialgrowth. Removing a restrictive technical condition from a previouswork, we show that the weighted group algebra is a symmetric Banach *-algebra if and only if theweight function satisfies the GRS-condition. This conditionexpresses in a precise technical sense that grows subexponentially.2000 Mathematics Subject Classification 43A20, 22D15, 22D12.     

Copper-catalyzed coupling of aryl iodides with aliphatic alcohols

[reaction: see text] A simple and mild method for the coupling of aryl iodides and aliphatic alcohols that does not require the use of alkoxide bases is described. The reactions can be performed in neat alcohol. For more precious alcohols, the etherification was carried out in toluene as solvent using 2 equiv of alcohol. Additionally, the cross-coupling of an optically active benzylic alcohol with an unactivated aryl halide was demonstrated to proceed with complete retention of configuration.     

Sobolev- und Sobolev-Hardy-Räume aufS 1: Dualitätstheorie und Funktionalkalküle

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