Synthesis,Properties, and Crystal Structure of Silyl Nitronates (Silyl Esters of aci-Nitroalkanes): Towards the SN2 Reaction Path with Retention of Configuration at Silicon

An efficient and flexible method for the preparation of silyl nitronates is described (see 1–10 ). NMR. spectral investigations indicate a rapid 1,3-silyl migration process, with an activation energy of about 10 kcal mol^?1. X-ray crystallographic studies on the silyl nitronates 3 and 8 show structures that lean towards an S_N2 retention pathway at silicon.     

Structure of poly(ethylene oxide) complexes. II. Poly(ethylene oxide)–mercuric chloride complex

The structure of the crystalline complex of poly(ethylene oxide) with mercuric chloride, whose composition is (CH₂CH₂O)₄ · HgCl₂, has been determined by x-ray diffraction. The unit cell is orthorhombic with the dimensions of a = 13.55 Å, b = 8.58 Å, and c (fiber axis) = 11.75 Å, and the unit cell contains 4 HgCl₂ molecules and 16 CH₂CH₂O units. Four chains pass through the lattice and four monomeric units are contained in the fiber identity period. The space group is Ccmm–D_2h¹⁷, Ccm2¹–C_2v¹², Cc2m–C_2v¹⁶ or C222₁–D₂⁵. The positions of Hg and Cl atoms have been determined by the Patterson function synthesized by the use of intensity data of the fiber sample, and the molecular conformation of poly(ethylene oxide) has been determined by examining the space not occupied by mercuric chloride molecules in the crystal lattice. The conformation of polyethylene oxide in the complex has been found to be the form of T₅GT₅G ; that is, where G and G mean the right- and left-handed gauche forms, respectively. This molecular structure has been confirmed further by the results of the Fourier syntheses by using the more accurate data refined by the intensity measurements with a diffractometer on the powder sample. The bond length between Hg and Cl in the complex (2.30 Å) is a little longer than that of HgCl₂ in the crystal (2.25 Å). This is consistent with the fact that the infrared absorption band associated with the antisymmetric stretching vibration of HgCl₂ shifts to 353 cm^?1 in the complex from 367 cm^?1 in the crystal. It was also found that another type of complex, giving a different infrared spectrum and x-ray diffraction pattern, was obtained when the original complex was soaked much longer in a saturated ether solution of HgCl₂.     

Agelasine-A, -B, -C and -D,novel bicyclic diterpenoids with a 9-methyladeninium unit possessing inhibitory effects on na,K-atpase from the okinawa sea sponge Agelas sp.1)

Agelasine-A, -B, -C and -D, novel bicyclic diterpenoids having inhibitory effects on enzymic reactions of Na,K-ATPase, have been isolated from the orange colored Okinawan sea sponge $\text{Agelas}$ sp. and the structures have been determined on the basis of their spectral data and chemical conversions.     

On the convergence of optimum stratifications for empiric distribution function in univariate case

Summary Let {X _n },n=1,2,..., be a sequence of independent random variables distributed according to a distribution functionF(x) with finite variance,F _n (x) be the empiric distribution function ofX ₁,...,X _n for eachn, andφ _(n) ^* andφ ^* be optimum stratifications corresponding toF _n (x) andF(x) respectively. It is shown in this paper thatφ _(a) ^* tends almost surely toφ ^* under a suitable criterion. Institute of Statistical Mathematics     

Recent advances in the synthesis of N-alkenyl carbazoles

N-Alkenyl carbazoles are important building blocks of poly(vinylcarbazole), which is used in photosensitive materials, semiconductors, electroluminescent devices, and non-linear optical materials. Recently, a CN bond formation reaction using transition-metal-catalyzed amination and transition-metal-catalyzed vinylation was successfully extended to the synthesis of N-alkenyl carbazoles. In this paper, I discuss recent examples of the synthesis of N-alkenyl carbazoles, including palladium and copper-catalyzed cross-coupling reactions of carbazoles with alkenes/alkenyl halides, and iridium-catalyzed vinylation of carbazole using vinyl acetate.     

Post‐Modification of the Ethene Bridge in the Rational Design of Photochromic Diarylethenes

Fine‐tuning of the molecular structure of organic bistable compounds to improve their photochromic performance or to introduce additional functions remains an important issue in the development of photoresponsive materials. Diarylethenes bearing heterocyclic moieties belong to the most intensively studied class of organic photochromes due to their excellent photochemical properties. A huge number of diarylethenes have been synthesized so far. Analysis of the literature data shows that there are very worthy examples of diarylethenes developed by the Irie and Feringa groups, which can be the common starting material for a number of diarylethenes functionalized in hetaryl moieties. We refer to these structures as photochromic diarylethene precursors. These diarylethenes have proved to be very useful in the construction of functional molecules with desired properties. On the other hand, in our groups, we have elaborated on diarylethene precursors with modifiable ethene bridges. In this review, we have collected examples of such structures and their chemical modifications, leading to the improvement or fine‐tuning of photochromic switching.     

Homogeneous nanosize palladium catalysts

Expanding the catalytic environment to a nanosize must be one of the most promising ways to improve the performance of homogeneous catalysts. In this Forum Article, recent developments in homogeneous nanosize palladium catalysts are reviewed. It contains solubilized palladium nanoparticles, metalated dendrimers, and complexes with well-defined nanosized ligands. These systems realize efficient catalyst recycling, unique selectivity, suppression of metal aggregation, and remarkable enhancement of the catalytic activity.     

Molecular simulation of pressure-driven fluid flow in nanoporous membranes

An extended nonequilibrium molecular dynamics technique has been developed to investigate the transport properties of pressure-driven fluid flow in thin nanoporous membranes. Our simulation technique allows the simulation of the pressure-driven permeation of liquids through membranes while keeping a constant driving pressure using fluctuating walls. The flow of argon in the liquid state was simulated on applying an external pressure difference of 2.4x10(6) Pa through the slitlike and cylindrical pores. The volume flux and velocity distribution in the membrane pores were examined as a function of pore size, along with the interaction with the pore walls, and these were compared with values estimated using the Hagen-Poiseuille flow. The calculated velocity strongly depends on the strength of the interaction between the fluid and the atoms in the wall when the pore size is approximately<20sigma. The calculated volume flux also shows a dependence on the interaction between the fluid and the atoms in the wall. The Hagen-Poiseuille law overestimates or underestimates the flux depending on the interaction. From the analysis of calculated results, a good linear correlation between the density of the fluid in the membrane pores and the deviation of the flux estimated from the Hagen-Poiseuille flow was found. This suggests that the flux deviation in nanopore from the Hagen-Poiseuille flow can be predicted based on the fluid density in the pores.