Acyclic Tetraethynylethene Molecular Scaffolding: Multinanometer-sized linearly conjugated rods with the poly(triacetylene) backbone and cross-conjugated expanded dendralenes

Derivatives of fully cross-conjugated tetraethynylethene (3,4-diethynylhex-3-ene-1,5-diyne) 1 are versatile precursors to multinanometer-sized molecular rods with all-C-backbones. Oxidative polymerization (CuCl, N,N,N′,N′-tetramethylethylenthylenediamine (TMEDA), O₂) of the trans-bis-deprotected trans-bis(triisopropylsilyl)-protected tetraethynylethene 2 yielded, after end-capping with phenylacetylene, the remarkably stable, soluble oligomers 3 – 7 with a persilylethynylated poly(triacetylene) (PTA) backbone [? (C?C? CR?CR? C?C)_n? ] and a length of 19.4 ( 3 ), 26.8 ( 4 ), 34.3 ( 5 ), 41.8 ( 6 ), and 49.2 ( 7 ) Å (Scheme 1). These compounds underwent facile one-electron reductions with the number of reversible reduction steps being equal to the number of tetraethynylethene moieties in each molecular rod. Oxidative Eglinton-Glaser homo-coupling of tetraethynylethenes 8 – 10 with a single free ethynyl group provided the fully silyl-protected 3,4,9,10-tetraethynyl-substituted dodeca-3,9-diene-1,5,7,11-tetraynes 11 – 13 (Scheme 2) and, after alkyne deprotection, the novel hydrocarbon 14 , a C₂₀H₆ isomer, and its partially silyl-protected derivative 15 . Oxidative hetero-coupling between two different tetraethynylethene derivatives, one with a single and the other with two free terminal ethynyl groups, yielded the extended chromophores 16 – 21 composed of 3 or 4 tetraethynylethene moieties (Scheme 3). The linearly conjugated oligomers 16 and 17 with the PTA backbone are isomeric to 19 and 20 , respectively, which are members of the cross-conjugated expanded dendralenes, i.e., dendralenes with butadiynediyl fragments inserted between each pair of double bonds [? (C?C? C(?CR₂)? C?C)_n? ]. The electronic absorption spectra of these compounds were compared and analyzed in terms of the competition between linear and cross-conjugation in determining the extent of π-electron delocalization. Although steric factors on π-electron conjugation remain to be clarified, this analysis strongly suggests that cross-conjugation is not an efficient mechanism for π-electron delocalization. All extended acetylenic-olefinic chromophores considered in this study exhibited remarkably high stability and did not decompose when exposed to laboratory air and light for months. In agreement with this observation, electrochemical studies demonstrated that the compounds are difficult to oxidize with the oxidation potentials in THF (0.1M (Bu₄N)PF₆) being higher than 1.0 V (vs. the ferrocene/ferrocenium couple).     

Raman scattering of silver chlorate single crystal

The room temperature Raman spectrum of silver chlorate single crystal have been investigated. We make an assignment of all the optical phonon and separate out the internal and external modes. The observed ClO^-₃ internal modes frequencies closely agree with the values obtained by other authors in different materials.     

Kinetic detection method for thin-layer chromatography

The feasibility of using kinetic detection and simultaneous kinetic methods for the determination of species separated on thin-layer chromatographic plates has been explored. The proposed method was tested by monitoring the reaction of ninhydrin with leucine, isoleucine, and phenylalanine. The results obtained using three instruments (two scanning instruments and an imaging instrument) were compared. Although none of the instruments provided ideal results, the premise of the kinetic approach for the in situ quantification of analytes was shown to be valid. The possibility of using kinetic methods to resolve responses from overlapped species was also investigated, and shows promise for improving the overall resolution of thin-layer chromatographic methods. A discussion of the instrumental requirements for successful utilization of the kinetic detection method is also given.     

Tetraethynylethenes: Fully cross-conjugated π-electron chromophores and molecular scaffolds for all-carbon networks and carbon-rich nanomaterials

The preparation of tetraethynylethene (3,4-diethynylhex-3-ene-1,5-diyne) 1 as well as of a great diversity of differentially mono-, di-, and triprotected derivatives by newly developed synthetic routes is described. These fully cross-conjugated molecules are versatile building blocks and precursors to two-dimensional all-C networks and novel C-rich nanoarchitecture with unusual structural and electronic properties, such as perethynylated expanded radialenes, or molecular wires and polymers with the novel polytriacetylene backbone. A key step in all of these routes was the Corey-Fuchs dibromoolefination of aldehydes and ketones. Dibromoolefination of silyl-protected penta-1,4-diyn-3-ones yielded the corresponding dibromomethylidene derivatives which, by twofold Pd-catalyzed alkyne coupling, were transformed into tetraethynylethene derivatives. In routes to tetraethynylethenes with free cis-or trans-enediyne moieties, dibromoolefination of aldehyde groups produced geminal dibromoethenes which, upon elimination/metallation with LDA followed by quenching with H⁺ or other electrophiles, yielded free or substituted ethynyl groups in high yields. Tetra- and triprotected tetraethynylethenes are rather stable compounds that could be isolated in pure form, whereas derivatives with two or more free ?C? H termini were only stable in dilute solution and polymerized rapidly in pure form. A trans-bis(triisopropylsilyl)-protected derivative represented an exception and could be isolated as stable crystals. X-Ray analysis revealed that the two bulky (i-Pr)₃Si groups isolate the reactive chromophores from one another in the crystal and prevent intermolecular reactions. The structures of several tetraethynylethenes were revealed in high-quality X-ray crystal structures.     

The anodic dissolution of chalcopyrite in water + acetonitrile solutions

The characteristics of chalcopyrite anodic electrodissolution in aqueous acetonitrile solutions have been studied. Experiments with a high-grade sample, of massive chalcopyrite have been carried out at 25°C in solutions containing 50 g l^?1 NaCl and different concentrations of sulphuric acid and acetonitrile. Galvanostatic and potentiostatic conditions were employed and the results obtained in solutions with and without acetonitrile compared.The characteristics of the mechanism involved in the chalcopyrite electrodissolution precluded acetonitrile having an influence at low potentials. However its influence is more noticeable at higher potentials where solvent decomposition reactions are involved. Chronopotentiometric experiments in acetonitrile aqueous solutions indicate the existence of diffusional (in the solid) and coulombic phenomena in originating the potential jump.