Reactivite du tetraallyletain et d'allyltrialkyletains vis a vis d'aldehydes,de cetones et d'epoxydes

Tetraallytin reacts readily with non activated ketones and exothermically with aldehydes contrary to other allylic organotins such as allytributyltin. Homoallylic alcohols are obtained after acidolysis of the adducts. Upon extended heating, allylic organotins and epoxides form products which correspond to additon products of isomeric carbonyl compounds. However, starting from cis- and trans-1-phenyl-1,2-epoxypropanes, direct regiospecific but non-stereospecific ring opening is observed with poor yields.     

Autodiffusion sous pression dans l'ytterbium-γ-cc

The pressure effect on the self-diffusion rate has been studied in b.c.c. γ-ytterbium. The experiments were performed at three different temperatures: 730, 760 and 800°C, and under hydrostatic pressure varying from 4.5 to 10 Kbar.The activation volume is determined to be 0.59 vol. mol. This value agrees with semi empirical models and suggests the vacancy mechanism for diffusion     

Comportement en photooxydation de quelques polymeres du chlorure de vinyle contenant des structures oxygenees

We have studied the photooxidation of PVC samples modified by introduction of oxygen, carbon monoxide or acetylenic diester (ADCE) in the polymerisation medium. The presence of O₂ and (or) CO results in photosensitization, principally due to the conjugated polyenes. These groups are formed in a zip elimination reaction initiated by thermolabile oxygenated groups such as α-chloro peroxide or β chloroketones. The fumarate structures, formed during the PVC-ADCE copolymerization, play a stabilizing role at a concentration near to 0.10%. The inhibition mechanism has not been elucidated.     

Optical Detection and Spectroscopy of Single Molecules

The optical study of single molecules opens new paths in molecular spectroscopy, solid state physics and quantum optics. And recent experiments at room temperature hold great promise for chemistry and biology as well     

Approaches toward the synthesis of 2,5-disubstituted-1,3-thiazolidines

Synthetic approaches for new 2,5-disubstituted-1,3-thiazolidines are described. Steric and electronic effects of the N-substituent of the thiazolidine ring represent the major parameter in the rearrangement process. The nmr studies demonstrate that N-unsubstituted 2,5-disubstituted-1,3-thiazolidines exist as epimeric mixture, while the corresponding N-acetylated analogues exist as a conformer mixture.     

Noncommutative homology of some three-dimensional quantum spaces

We compute the Hochschild and cyclic homology of certain three-dimensional quantum spaces (type A algebras), introduced by Artin and Schelter. We show that the Hochschild homology is determined by the quasi-classical limit.     

Diffusion Crosslinking Kinetics of Thermoset Polymers

The problem of the delayed crosslinking arising due to the diffusion of a crosslinker molecule from a vector particle within a thermoset polymer matrix is discussed. The crosslinker molecules, initially embedded in the vector particles, diffuse from the particle to the polymer matrix and react with the functional groups grafted to polymer chains. The two‐step diffusion crosslink kinetics is studied theoretically on the example of polyethylene functionalized with anhydride groups reacting with 1,4‐butanediol as a crosslinker molecule. This provides the independent of time limiting distribution functions of the concentration of crosslinks, unreacted and intermediate functional groups, which are shown to be rather sensitive to system parameters as rates of chemical reactions, ratio of diffusion coefficients of matrix to vector particles, stoichiometric composition of the reactive groups, etc. The nonmonotonic distribution of the crosslink concentration around the vector particles at certain range of the parameters is revealed.