Cyclopolymerisation. 3. Mitt. ESR-Untersuchungen von Diallylaminen mit Redox-Systemen

Ohne Zusammenfassung     

Regio- and stereo-selectivity of alkenyl radical ring closure: A theoretical study

A theoretical study has been undertaken of the relative rates and the regio- and stereo-chemistry of ring closure of a variety of alkenyl, alkenylaryl, alkenylvinyl and similar radicals. The method involves the application of MM2 force-field calculations to model transition structures for which the dimensions of the arrays of reactive centres have been obtained by MNDO-UHF techniques. The results, which generally accord with guidelines based on stereochemical considerations, show excellent qualitative and satisfactory quantitative agreement with experimental data. The method has been successfully applied to complex systems including ring closure of alkylperoxy radicals, and formation of the triquinane system by three consecutive cyclisations.     

New strategic reactions for organic synthesis: catalytic asymmetric C-H activation alpha to oxygen as a surrogate to the aldol reaction

The C-H activation of silyl ethers by means of rhodium carbenoid-induced C-H insertion represents a very direct method for the stereoselective synthesis of silyl-protected beta-hydroxy esters. The reaction can proceed with very high regio-, diastereo-, and enantioselectivity and represents a surrogate to the aldol reaction. The reaction is catalyzed by the rhodium prolinate complex Rh(2)(S-DOSP)(4). A critical requirement for the high chemoselectivity is the use of donor/acceptor-substituted carbenoids such as those derived from methyl aryldiazoacetates. A range of silyl ethers may be used such as allyl silyl ethers, tetraalkoxysilanes, and even simple trimethylsilyl alkyl ethers. In general, C-H activation preferentially occurs at methylene sites, as the reactivity is controlled by a delicate balance between steric and electronic effects.     

Three-dimensional blow-up solutions of the Navier-Stokes equations

In this paper we extend the plane blow-up results of Grundy& McLaughlin (1997) to the three-dimensional Navier-Stokes equations.Using a solution structure originally due to Lin we first providenumerical evidence for the existence of blow-up solutions on- < x, z < , 0 y 1 with boundary conditions on y = 0and y = 1 involving derivatives of the velocity components.The formulation enables us to consider plane and radial flowas special cases. Various features of the computations are isolatedand are used to construct a formal asymptotic solution closeto blow-up. We show that the numerical and asymptotic analysesprovide a mutually consistent global picture which supportsthe conclusion that, for the family of problems we considerhere, blow-up in fact can take place in three dimensions butat an inverse linear rate rather than the faster inverse squareof the plane case.     

Long-term retention of ice-nucleating active Pseudomonas fluorescens by overwintering colorado potato beetles

Ice nucleating-active Pseudomonas fluorescens F264C was fed to Colorado potato beetles to determine bacterial retentioin in the beetle gut and its effect on the cold hardiness of this insect pest. The bacrterium was present in beetles recovered after overwintering in the field, seven months after their exposure to P. fluorescens. Retention was evident not only in the detection of the P. fluorescens ice nucleating gene, inaW, in bacterial cultures from beetle guts but also in the elevated supercooling points of some treated beetles.     

Low-lying (K π = 0+) states of gadolinium isotopes

The sd-interacting boson approximation (sd-IBA) and the df-interacting boson approximation (df-IBA) can be related to each other and the states of the interacting boson approximation model can be identified with the fully symmetric states in the sdf interacting boson approximation model. A systematic study of the sdf-IBA model showed that the constructed Hamiltonian can successfully describe the strong octupole correlations in the deformed nuclei. We showed that the interacting boson approximation may account for many of these K ^π ?=?0⁺ states. It was found that the calculated energy spectra of the gadolinium isotopes agree quite well with the experimental data. The observed B(E2) values were also calculated and compared with the experimental data.