Refractory Metal-Containing Polymers and Nanocomposites: Preparation and Properties

Summary: Novel polymers containing refractory metal in the main chain or side chains can be prepared. An attractive approach is polymerization of the Hf (Ta, Nb)-monomers with (meth)acrylate, fumarate or monomethylmethacrylate ethyleneglycol groups, synthesized for the first time in this study. New types of hafnium (tantalum, niobium)-containing nanocomposites are prepared by combining polymer synthesis and controlled thermolysis. The composition and structure of the synthesized metal-containing precursors and thermolysis products are determined by elemental analysis, IR and ¹H-NMR spectroscopies, X-ray diffraction and TEM analysis.     

Aspects of structural thiohydroxamate chemistry—on a systematic in the 5-(p-methoxyphenyl)-4-methylthiazole-2(3H)-thione series

Bond angles at thiohydroxamate oxygen in crystal structures of 3-alkoxy-5-(p-methoxyphenyl)-4-methylthiazole-2(3H)-thiones gradually increased with the size of the 3-alkoxy substituent. This effect was attributed to strain on the basis of (i) a linear free energy relationship (Taft-Dubois correlation) and (ii) signal coalescence from resonances of diastereotopic CH₃ groups in solution (O-cumyl substituent; DNMR). Substitution at oxygen along the sequence OR (R=prim-, sec-, and tert-alkyl), OH, and OLi was reflected in a gradual decrease of N,O distances and lengthening of associated C,S bonds. The responsivity for these changes was more pronounced in the thiazole-2(3H)-thione than in the pyridine-2(1H)-thione series.     

Alkylation of schleyer's lithiocarbon C4Li4 by methyl iodide

Alkylation of lithiocarbon C₄Li₄ gives the hydrocarbon C₈H₁₂ to which the structure of tetramethyltetrahedrane has been ascribed.     

A simple and fast procedure for efficient synthesis of β- and γ-azidoarylketones

A simple and efficient method for preparing β- and γ-azido substituted arylketones has been achieved by short microwave irradiation of the corresponding halo arylketones and sodium azide in DMSO.     

Ion-exchange resins in non-aqueous solvents-II Sorption of P-nitroaniline and other weak bases in water-organic solvent mixtures

Sorption of p-nitroaniline and several weak organic bases on macro- and microreticular hydrogen-form resins is reported. The solvents used in the study are mixtures of water and fourteen watermiscible organic solvents. The distribution coefficients change from a large value at pure organic solvent to a minimum value at 80% organic solvent-20% water, then increase again except for the basic solvents where no sorption takes place at high organic solvent concentration. It is suggested that in the vicinity of the minimum D a transition in sorption mechanism takes place. A similar behaviour is observed for several other weak organic bases. The sorption of p-nitroaniline in 80% organic solvent-20% water as a function of time is reported. Mesh size and percentage cross-linking are other variables considered.     

Absolute stereochemistry of allylic alcohols,amines, and other ene moieties: a microscale cross metathesis/exciton chirality protocol

A microscale chemical/chiroptical protocol for the determination of absolute configurations of allylic alcohols, amines, and related systems has been developed. The method is based on the conversion of the double bonds into a styrene, lambdamax 248 nm (epsilon 15 000), or other styrenoid chromophores by cross olefin metathesis. The obtained styrenoid chromophore then couples with the allylic acylate to yield a distinct couplet. The proposed method allows one to determine the absolute configuration of both moieties flanking the double bond. It also overcomes the restriction of the conventional allylic benzoate method that gives rise to weak CD couplet, for which in many cases only one wing of the couplet is observable.