Stickstoff

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Kohlenwasserstoffe

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Revisiting the concept of the (a)synchronicity of diels‐alder reactions based on the dynamics of quasiclassical trajectories

A number of model Diels‐Alder (D‐A) cycloaddition reactions (H₂C?CH₂ + cyclopentadiene and H₂C?CHX + 1,3‐butadiene, with X = H, F, CH₃, OH, CN, NH₂, and NO) were studied by static (transition state ‐ TS and IRC) and dynamics (quasiclassical trajectories) approaches to establish the (a)synchronous character of the concerted mechanism. The use of static criteria, such as the asymmetry of the TS geometry, for classifying and quantifying the (a)synchronicity of the concerted D‐A reaction mechanism is shown to be severely limited and to provide contradictory results and conclusions when compared to the dynamics approach. The time elapsed between the events is shown to be a more reliable and unbiased criterion and all the studied D‐A reactions, except for the case of H₂C?CHNO, are classified as synchronous, despite the gradual and quite distinct degrees of (a)symmetry of the TS structures. © 2015 Wiley Periodicals, Inc.     

Dithiocarbamate complexes of cyclopentadienylcobalt(III), [Co(η-C5H5)(L)(S2CNR2)] (L = ligand)

The reactions of [Co(η-C₅H₅)(L)I₂] with Na[S₂CNR₂] (R = alkyl or phenyl) give [Co(η-C₅H₅)(I)(S₂CNR₂)] (I) when L = CO and [Co(η-C₅H₅)(L)(S₂CNR₂)]I (II) when L is a tertiary phosphine, phosphite or stibine, or organo-isocyanide ligand. In similar reactions [Co(η-C₅H₅)(CO)(C₃F₇)I] gives [Co(η-C₅H₅)(C₃F₇)(S₂CNMe₂)] and [Mn(η-MeC₅H₄)(CO)₂(NO)]PF₆ forms [Mn(η-MeC₅H₄)(NO)(S₂CNR₂)]. The iodide ligands in I may be displaced by L, to give II, or by other ligands such as [CN]^?, [NCS]^?, H₂O or pyridine whilst SnCl₂ converts it to SnCl₂I. The iodide counter-anion in II may be replaced by others to give [BPh₄]^?, [Co(CO)₄]^? or [NO₃]^? salts. However [CN]^? acts differently and displaces (PhO)₃P from [Co(η-C₅H₅){P(OPh)₃}(S₂CNMe)]I to give [Co(η-C₅H₅)(CN)(S₂CNMe₂)] which may be alkylated reversibly by MeI and irreversibly by MeSO₃F to [Co(η-C₅H₅)(CNMe)(S₂CNMe₂)]⁺ salts. Conductivity measurements suggest that solutions of I in donor solvents are partially ionized with the formation of [Co(η-C₅H₅)(solvent)(S₂CNR₂)]⁺ I^? species. The IR and ¹H NMR spectra of the various complexes are reported. They are consistent with pseudo-octahedral “pianostool” molecular structures in which the bidentate dithiocarbamate ligands are coordinated to the metal atoms through both sulphur atoms.     

Effect of epitaxial realignment on the leakage behavior of arsenic-implanted,as-deposited polycrystalline Si-on-single crystal Si diodes

When dopants are indiffused from a heavily implanted polycrystalline silicon film deposited on a silicon substrate, high thermal budget annealing can cause the interfacial “native” oxide at the polycrystalline silicon-single crystal silicon interface to break up into oxide clusters, causing epitaxial realignment of the polycrystalline silicon layer with respect to the silicon substrate. Anomalous transient enhanced diffusion occurs during epitaxial realignment and this has adverse effects on the leakage characteristics of the shallow junctions formed in the silicon substrate using this technique. The degradation in the leakage current is mainly due to increased generation-recombination in the depletion region because of defect injection from the interface.     

High-power InGaAsP edge-emitting LEDs for single-mode optical communication systems

The letter describes 1.3 ?m InGaAsP edge-emitting LEDs which couple 40 to 60 ?W into a single-mode fibre. The 1.0 ns rise times and 30 to 45 nm spectral widths of these LEDs make suitable for optical communication systems operating at data rates as high as 400 Mbit/s.     

How Not to Schedule a Stitching Room

This is a case study of a project to introduce computer-aided scheduling into the stitching room of a shoe factory, which led instead to an automated microcomputer-controlled work-handling system. The outcome has been an increase in productivity and wages earned, together with a large reduction in throughput time and work-in-progress.     

The use of SO2Cl2 in organometallic chemistry. Convenient high yield syntheses of [Fe(η-C5H5)(CO)3] [FeCl4] and [M(CO5Cl] (M = Mn or Re)

Depending on the substrate and the reaction conditions, SO₂Cl₂ is a useful reagent which brings about either chlorination or the formation of cationic species on reaction with transition metal carbonyl complexes.