Charge-density-wave phase of 1T-TiSe2: the influence of conduction band population

The charge-density-wave phase of TiSe(2) was studied by angle-resolved photoelectron spectroscopy and resistivity measurements investigating the influence of the band gap size and of a varying population of the conduction band. A gradual suppression of the charge-density-wave-induced electronic superstructure is observed for a variation of the band gap in the ternary compounds TiC(x)Se(2-x) with C=(S,Te) as well as for an occupation of only the conduction band by H(2)O adsorption-induced band bending. These observations point to an optimum band gap and support an excitonic driving force for the charge-density wave.     

Phosphorbestimmungsmethoden

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Cycloadditions of Bifunctional Vinyl Ethers with Electrophilic Alkenes through Tetramethylene Zwitterion Intermediates

Bifunctional vinyl ethers react with electron‐poor alkenes to cyclobutanes in good yields. The second C?C bond reacted with neither the cyclobutane nor its zwitterion intermediate, even on heating. Cyclobutanes formed from ‘tetracyanoethylene’ ( 8 ) were transformed into tetrahydropyridines by reaction of the corresponding zwitterion with MeCN as the solvent. In contrast, cyclobutanes formed from dimethyl (dicyanomethylidene)propanedioate ( 9 ) did not react with MeCN, which is ascribed to diminished stabilization of the zwitterion intermediate, and increased steric effects. These results extend the classical studies of Huisgen and his co‐workers.     

Stable Algebraic Topology and Stable Topological Algebra

Algebraic topology is a young subject, and its foundations arenot yet firmly in place. I shall give some history, examplesand modern developments in that part of the subject called stablealgebraic topology, or stable homotopy theory. This is by farthe most calculationally accessible part of algebraic topology,although it is also the least intuitively grounded in visualizablegeometric objects. It has a great many applications to othersubjects such as algebraic geometry and geometric topology.Time will not allow me to say as much as I would like aboutthat. Rather, I shall emphasize some foundational issues thathave been central to this part of algebraic topology since theearly 1960s, but that have been satisfactorily resolved onlyin the last few years. 1991 Mathematics Subject Classification55P42, 55N20.     

205T1-NMR and UV-Visible spectroscopic determination of the formation constants of aqueous thallium(I) hydroxo-complexes

The hydrolysis of T1(I) has been studied at 25°C using²⁰⁵T1-NMR spectroscopy and UV-Vis spectrophotometry in aqueous solutions with ionic strengths maintained by NaC10₄ at 2, 4, 6, and 8M. The formation constant and the spectral characteristics for the hydroxo complex, T10Hℴ have been determined. At high hydroxide ion concentrations there is clear evidence from the UV-Vis data for the formation of a T1(OH)₂-species. The spectrum and an estimated formation constant for this second hydroxo complex are also reported.     

Eine Vollanalyse von Hypoehlorit

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Organocatalyzed Asymmetric Conjugate Addition of Heteroaryl and Aryl Trifluoroborates: a Synthetic Strategy for Discoipyrrole D

Bis‐heteroaryl or bis‐aryl stereocenters were formed by an organocatalytic enantioselective conjugate addition using the respective trifluoroborate salts as nucleophiles. Control studies suggested that fluoride dissociation is necessary in the anhydrous conditions. This strategy is applicable to the synthesis of discoipyrrole D, an inhibitor of BR5 fibroblast migration.