Mechanochemical reduction of hematite by room temperature ball milling

Reduction of α-Fe₂O₃ with Al, B, Cr and Si by room temperature ball milling is presented. Complete reduction is achieved with the formation of α-Fe and frequently an iron-reducer agent alloy. The method is suitable for the synthesis of nanometer-sized oxide-metal composites.     

Molecular associations of [2.2]paracyclophanearylhydrazones with organic acceptors,VIII

Summary Molecular complexes of mono and disubstituted [2.2]paracyclophanehydrazones with organic acceptors have been studied by means of thermodynamic and spectroscopic properties. Furthermore, the enhancement of the donor strength, induced by the hydrazono group, is viewed in the light of substituent as well as transannular effects.

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Molekulare Assoziation von [2.2]Paracyclophanarylhydrazonen mit organischen Akzeptoren, 8. Mitt.

Zusammenfassung Es wurden Molekülkomplexe von mono- und disubstituierten [2.2]Paracyclophanarylhydrazonen mit organischen Akzeptoren mittels thermodynamischer und spektroskopischer Methoden untersucht. Zusätzlich wird der Anstieg in der Donorstärke, der von der Hydrazonogruppe induziert wird, im Hinblick auf Substituenten- und auch transannulare Effekte diskutiert.

     

On the oxidizability of 1-methyl-1,2,3,4-tetrahydropyrimido[1,2-a]indole-10-carboxaldehyde and its crystal structure

The study of the molecular geometry of 1-methyl-1,2,3,4-tetrahydropyrimido[1,2-a]indole-10-carboxaldehyde as determined by X-ray analysis and the electrochemical properties of that compound are reported. These are compared with those of a number of indole-3-carboxaldehyde, differently substituted at 1 and 2 position. This was done in order to understand the unsuccessful attempts to convert the title compound into the corresponding acid. The result indicate that this anomalous behaviour may be attributed to easy oxidizability of the pyrimido ring nitrogen.     

Light within small particles

We calculate the energy density distribution in the ultraviolet within small spheres containing concentric cavities, aimed at simulating interstellar dust grains. We explore the dependence on chemical composition by progressively changing, in an arbitrary way, the refractive index of the sphere material. We conclude that a significant fraction of the energy of the impinging radiation is trapped throughout the particle interior.     

Palladium-catalyzed C-C bond formation involving aromatic CH activation. X-ray structure of 5-nitro-8-(2[2.2.1]bicycloheptyl)-1,2,3,4,4a,8b-hexahydro-1,4-methanobiphenylene

A new CC bond formation reaction involving activation of two aromatic CH bonds is reported. The X-ray structure of the title methanobiphenylene derivative is described.     

Matrix algebras in Quasi-Newton methods for unconstrained minimization

Summary.  In this paper a new class of quasi-Newton methods, named ℒQN, is introduced in order to solve unconstrained minimization problems. The novel approach, which generalizes classical BFGS methods, is based on a Hessian updating formula involving an algebra ℒ of matrices simultaneously diagonalized by a fast unitary transform. The complexity per step of ℒQN methods is O(n log n), thereby improving considerably BFGS computational efficiency. Moreover, since ℒQN's iterative scheme utilizes single-indexed arrays, only O(n) memory allocations are required. Global convergence properties are investigated. In particular a global convergence result is obtained under suitable assumptions on f. Numerical experiences [7] confirm that ℒQN methods are particularly recommended for large scale problems. Received December 30, 2001 / Revised version received December 20, 2001 / Published online November 27, 2002 Mathematics Subject Classification (1991): 65K10 Correspondence to: P. Zellini     

Stereochemistry of decarbalkoxylation of arylmethylene-propanedioic acids dimethyl esters

Halide ions increase the rate of decarbalkoxylation of arylmethylene-propanedioic acids dimethyl esters.