New three-step domino reaction, "thiophilic addition-beta-elimination of fluoride-[3,3] sigmatropic rearrangement": Synthesis of alpha-allylic and alpha,alpha-bis(allylic) alpha-trifluoromethyl dithioesters

The three-step domino reaction, "thiophilic addition of an organomagnesium reagent onto dithioester-beta-elimination of fluoride-[3,3] sigmatropic rearrangement", provides the product of formal regiospecific substitution of a fluorine atom by an allyl group. This mild and versatile methodology was applied to the synthesis of various alpha-allylic and alpha,alpha-bis(allylic) alpha-trifluoromethyl dithioesters.     

Surface self-diffusion of organic molecules adsorbed in porous silicon

The pulsed field gradient nuclear magnetic resonance method has been employed to probe self-diffusion of organic guest molecules adsorbed in porous silicon with a 3.6 nm pore size. The molecular self-diffusion coefficient and intrapore adsorption were simultaneously measured as a function of the external vapor pressure. The latter was varied in a broad range to provide pore loading from less than monolayer surface coverage to full pore saturation. The measured diffusivities are found to be well-correlated with the adsorption isotherms. At low molecular concentrations in the pores, corresponding to surface coverages of less than one monolayer, the self-diffusion coefficient strongly increases with increasing concentration. This observation is attributed to the occurrence of activated diffusion on a heterogeneous surface. Additional experiments in a broad temperature range and using binary mixtures confirm this hypothesis.     

Universal equivalence of partially commutative nilpotent groups

We prove some necessary and sufficient conditions of the universal equivalence of the nilpotent R-groups of class 2 defined by trees, with R a binomial Euclidean ring.     

Differential games with random noise

A differential game is considered in which an opponent is a random noise. An ally uses ε-strategies, defined in the classical theory of differential games. The mathematical expectation of possible harm caused by the opponent's actions is minimized. Bibliography: 5 titles. Translated fromObchyslyuval'na ta Prykladna Matematyka, No. 80, 1996, pp. 78–89.     

Mobility of charge carriers in porous silicon layers

The (conduction) mobility of majority charge carriers in porous silicon layers of the n and p types is estimated by joint measurements of electrical conductivity and free charge carrier concentration, which is determined from IR absorption spectra. Adsorption of donor and acceptor molecules leading to a change in local electric fields in the structure is used to identify the processes controlling the mobility in porous silicon. It is found that adsorption of acceptor and donor molecules at porous silicon of the p and n types, respectively, leads to a strong increase in electrical conductivity, which is associated with an increase in the concentration of free carrier as well as in their mobility. The increase in the mobility of charge carriers as a result of adsorption indicates the key role of potential barriers at the boundaries of silicon nanocrystals and may be due to a decrease in the barrier height as a result of adsorption.     

4-Aryl(benzyl)sulfonyl-2-chloro-5-polyfluoroalkyl-1,2,3-triazoles. The first monocyclic N-chloro-1,2,3-triazoles

Treatment of 4-aryl(benzyl)sulfonyl-5-polyfluoroalkyl-v-triazoles with NaOCl gave the 4-aryl(benzyl)-sulfonyl-2-chloro-5-polyfluoroalkyl-v-triazole derivatives which contain a chlorine atom only on the N₍₂₎ atom of the heterocycle. The structure of 2-chloro-5-(1,1,2,2,3,3-hexafluoropropyl)-4-(p-tolyl-sulfonyl)-2H-[1,2,3]triazole has been established by X-ray structural investigation. The presence of a highly polarized N—Cl bond with a positive halogen atom causes the N-chlorotriazoles to react with KCN and KF as strong acids to form the potassium salts of the triazoles and to form 4-arylsulfonyl-2-(2-chloro-1-ethoxyethyl)-5-polyfluoroalkyl-2H-[1,2,3]triazoles with vinyl ethyl ether. It was found that chlorination of 4-arylsulfonyl-5-polyfluoroalkyl-v-triazoles in the presence of KF gives 4-chloro-5-polyfluoroalkyl-2H-[1,2,3]triazoles. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1342–1352, September, 2007.