LDA-catalyzed cycloisomerization of 2-(2-propynyloxy)ethyl iodides leading to 3-(iodomethylene)tetrahydrofurans

LDA catalyzes cycloisomerization of 2-(2-propynyloxy)ethyl iodides to give 3-(iodomethylene)tetrahydrofurans. The reaction is proposed to proceed through a mechanism involving exo-cyclization of an alkynyllithium intermediate and protonation of the resulting alkylidene carbenoid by the starting iodide. [reaction: see text]     

High-pressure synthesis and transport properties of a new binary germanide, SrGe6-delta (delta congruent with 0.5), with a cagelike structure

A new germanide, SrGe6-delta (delta congruent with 0.5), was synthesized by the reaction of Sr and Ge mixtures under a pressure of 5 GPa at 1200 degrees C. It crystallized in the orthorhombic space group Cmcm (No. 63) with a = 4.0981(6) A, b = 11.159(1) A, c = 12.6825(8) A, V = 580.0(1) A3, and Z = 4. SrGe6-delta is composed of a Ge covalent network having a cagelike structure and Sr atoms situated in the cages. Each Ge atom is coordinated by four neighboring Ge atoms. The coordination polyhedra are fairly distorted from an ideal tetrahedron, and the Ge network contains vacancies and disordering. The resistivity shows metallic behavior down to 2 K, and the positive thermoelectric power indicates the dominant carriers to be holes.     

Interface Microstructures of Si3N4/Fe and Fe-Cr Alloys Joints

Interfaces of solid state bonded Si₃N₄ceramics with Fe and Fe-(5, 10, 15 wt%)Cr alloy interlayers inArgon for 1 h at 1100°, 1200° and 1300°C have beencharacterized by electron probe microanalysis (EPMA) and transmissionelectron microscopy (TEM). Smooth interfaces with no evidence ofreactions products resulted when bonding at 1100°C. However, theinteraction between the ceramic and the metal increased at higherbonding temperatures and Cr-contents. In all samples Si and N fromthe ceramic dissolve and diffuse in the metal interlayer, whereas thesintering additives of the ceramic remain inactive.Low Cr-content (5%) interlayers resulted in the formationof an interfacial zone composed of two sublayer structures; adjacentto the ceramic was a thin one containing the sintering aids ofSi₃N₄ and fine precipitates of Fe₃Si and -Fe₄N in a bcc-Fe matrix. The second was thicker and includedfine Fe₃Si,-Fe₄N and-Fe₂N precipitates in abcc-Fe matrix. The bond region with high Cr-content interlayersincluded three sublayer structures. The first one next to the ceramicwas a bcc-Fe matrix containing sintering aids, fine dispersedFe₃Si and-Fe₄N, and CrN. The secondsublayer was similar but without any segregants from the ceramic. Thethird one, finally had a lamellae structure of Cr₂N/bcc-Fe and the Fe matrix contained also-Fe₄N.The interactionbetween the ceramic and the metal interlayer is believed to becontrolled by the solution rate of N in the alloy foils.     

Effect of 3,5-dichlorophenol on the extraction of technetium complexes with tetraphenylarsonium chloride

A radiometric method that permits to follow, in real time, the kinetics of crystals growth:¹³⁴CsClO₄;¹³⁴CsHC₄H₄O₆;¹³⁴Cs₂CrO₄;¹³⁴Cs₂[PtCl₆] and¹³⁴Cs[AgI₂], in gelatin medium is presented. Constants of the diffusion of¹³⁴Cs⁺ radioactive ions through gel and of the reaction between this cation and anions under study, leading to the formation of crystals were calculated. An approximately invesely proportional ratio was found between the rate of nucleation and the solubility of the crystal.     

The network structure of amorphous silicon-carbon alloy

The network structure of amorphous silicon-carbon alloy (a-Si_1−xC_x) has been studied over a wide range of x. The a-Si_1−xC_x thin films were prepared by sputtering silicon and carbon target with argon in radio-frequency magnetron sputtering equipment. The films were characterized by X-ray photoelectron spectroscopy, optical absorption, infrared absorption, and mechanical measurements. The results showed that the network structure could be classified neither as the random covalent network nor as the chemically ordered covalent network. The structure as a whole was close to the random covalent network, but the Si-Si combination at x>0.5 showed a feature of the chemically ordered covalent network. The film at 0.6<x<0.8 was hard and showed a high energy gap, due to the sp³ configuration in Si-C combinations.     

Plasma Processing Based Synthesis of Functional Nanocarbons

Our recent research has shown that plasma processing techniques, which allow versatile control of both chemical and physical aspects, have considerable potential for the innovative synthesis and functionalization of three varieties of low-dimensional nanocarbons, which show great promise in the development of nanoscience and its applications. In the case of 0-D fullerenes, the mission is the high-yield production of atom (X) encapsulated fullerenes (X@C₆₀). The formation of macro-quantities of charge-exploited Li@C₆₀ and overwhelmingly-high purity spin-exploited N@C₆₀ are realized for the first time by the control of alkali-fullerene and nitrogen double plasmas, respectively. In the case of 1-D carbon nanotubes the challenge is precise structure control, i.e., chirality control of single-walled carbon nanotubes (SWNTs). The extremely narrow-chirality distributed growth of SWNTs is realized with time-programmed and nonmagnetic-catalyzed plasma CVD. As for functionalization of SWNTs, the enhanced p-type C₆₀@SWNTs created under the substrate-bias control in collisionless plasmas are found to be effective for harvesting solar energy in the infrared wavelength range and adapted to the use for multiple exciton generation in solar cells. Concerning 2-D graphene, our aim is to overcome two serious issues for electronics applications. One is the realization of the direct growth of graphene on an insulating (SiO₂) substrate by adjusting the growth parameters using non-equilibrium diffusion plasma CVD. The other is the direct fabrication of field-effect transistor device of a narrow-width (≥20 nm) graphene nanoribbon using a new, simple, and scalable method based on rapid heating plasma CVD, which shows a clear transport gap and a high on/off ratio. Finally the prospects for the above-mentioned results are discussed together with ripple effects of the nanocarbon research on the progress of nanoscience and its applications.     

1,2,4-Triazoles. V. Nuclear magnetic resonance study of N-Methyl derivatives of 1,2,4-triazoles

The chemical shifts of the N-methyl protons of a number of N-methylated-1,2,4-triazoles were studied. Substitution of methyl and methylthio groups in position 3 causes upfield shifts of the N-methyl signals, while substitution of α-pyridyl, γ-pyridyl, and phenyl groups causes downfield shifts. In 3,5-disubstituted 1,2,4-triazoles, substituents in positions 3 and 5 have additive effects on the chemical shifts of N-methyl groups, so that the chemical shifts of the N-methyl groups of such compounds can be calculated. In this way, it was possible to assign the peaks of mixtures of N-monomethylated derivatives obtained by methylation of 1,2,4-triazoles.