Cascade radical reactions catalyzed by a Pd/light system: cyclizative multiple carbonylation of 4-alkenyl iodides

Cascade reactions of 4-alkenyl iodides, involving a carbonylation-cyclization-carbonylation sequence, were accomplished by a hnu/Pd system. The stereochemical outcomes suggest that radical carbonylation and subsequent acyl radical cyclization may be involved in this reaction.     

Vapor quenched Fe-Ti alloys: Formation of amorphous phase,and metastable Ti2Fe phase by aging

Mössbauer spectra were observed for amorphous Fe-Ti alloys produced by vapor quenching. The average values of the hyperfine field, the quadrupole splitting and the isomer shift vary gradually with increase in Ti concentration. After being annealed at 400°C for few hours, the amorphous phase is maintained around 33 at % Ti, while an intermediate phase, Ti₂Fe, appears around 67 at % Ti.     

A matroid generalization of theorems of Lewin and Gallai

This paper presents a theorem concerning a matroid with the parity condition. The theorem provides matroid generalizations of graph-theoretic results of Lewin and Gallai.     

DTA and x-ray studies on extended-chain crystals of polyethylene under high pressure

The relation between the thermal behavior of extended-chain crystals (ECCs) of polyethylene and the phase transitions, i.e., orthorhombic ? hexagonal ? melt, of polyethylene at high pressures above about 400 MPa has been studied by high-pressure differential thermal analysis (DTA), and with a high-pressure and high-temperature x-ray diffraction apparatus equipped with a position-sensitive proportional counter measuring system. The original sample used in this study consists mainly of two kinds of ECC, which we designate as “ordinary extended-chain” crystals (OECCs) and “highly-extended-chain” crystals (HECCs). Experimental results at pressures below 300 MPa substantiate the results previously reported: i.e., the phase diagram indicating the relation between the melting temperatures and pressure for the OECCs and HECCs can be determined for pressures up to 500 MPa. In heating at pressures above about 500 MPa, the peak intensity of the (100) reflection of the hexagonal structure decreases in two stages with increasing temperature. The phenomenon corresponds to the thermal behavior determined by high-pressure DTA in which two small endothermic peaks can be observed at temperatures above that of the crystal transition evidenced by the strong peak. This phenomenon suggests melting in two stages of hexagonal structures with different thermal stabilities, and that the change at higher temperature may be due to fusion of the hexagonal phase annealed either below or above the transition temperature.     

Experimental investigation of bubbling in particle beds with high solid holdup

A series of experiments on bubbling behavior in particle beds was performed to clarify three-phase flow dynamics in debris beds formed after core-disruptive accident (CDA) in sodium-cooled fast breeder reactors (FBRs). Although in the past, several experiments have been performed in packed beds to investigate flow patterns, most of these were under comparatively higher gas flow rate, which may be not expected during an early sodium boiling period in debris beds. The current experiments were conducted under two dimensional (2D) and three dimensional (3D) conditions separately, in which water was used as liquid phase, and bubbles were generated by injecting nitrogen gas from the bottom of the viewing tank. Various particle-bed parameters were varied, including particle-bed height (from 30 mm to 200 mm), particle diameter (from 0.4 mm to 6 mm) and particle type (beads made of acrylic, glass, alumina and zirconia). Under these experimental conditions, three kinds of bubbling behavior were observed for the first time using digital image analysis methods that were further verified by quantitative detailed analysis of bubbling properties including surface bubbling frequency and surface bubble size under both 2D and 3D conditions. This investigation, which hopefully provides fundamental data for a better understanding and an improved estimation of CDAs in FBRs, is expected to benefit future analysis and verification of computer models developed in advanced fast reactor safety analysis codes.     

Phase behaviour of a thermotropic cubic mesogen of 1,2-bis(4′-n-hexyloxybenzoyl)hydrazine under pressure

The phase behaviour of the thermotropic cubic mesogen 1,2-bis(4′-n-hexyloxybenzoyl)hydrazine [BABH(6)] was investigated under pressure up to about 55 MPa using a polarising optical microscope equipped with a high-pressure optical cell. BABH(6) shows the crystal (Cr)–cubic (Cub)–isotropic liquid (I) phase transition at ambient pressure on heating. The smectic C (SmC) phase was induced above 32 MPa, showing the unusual phase sequence of Cr–Cub–SmC–I, similar to those in BABH(n) (n = 8–10). The boundary between the Cub and SmC phases exhibited a negative slope dT/dP of about –1.0 ºC MPa^?1.     

Towards the optimality of Feistel ciphers with substitution-permutation functions

We explore the optimality of balanced Feistel ciphers with SP-type F-functions with respect to their resistance against differential and linear cryptanalysis. Instantiations of Feistel ciphers with the wide class of (SP) \(^u\) and (SP) \(^u\) S F-functions are considered: one F-function can contain an arbitrary number of S-box layers interleaved with linear diffusion. For the matrices with maximum diffusion, it is proven that SPS and SPSP F-functions are optimal in terms of the proportion of active S-boxes in all S-boxes—a common efficiency metric for substitution-permutation ciphers. Interestingly, one SP-layer in the F-function is not enough to attain optimality whereas taking more than two S-box layers does not increase the efficiency either.     

The conformation of alkyl cyclohexanones and terpenic ketones. Interpretation for the ‘alkylketone effect’ based on the CH/π(CO) hydrogen bond

Ab initio MO calculations were carried out, at the MP2/6-311++G(d,p)//MP2/6-311G(d,p) level, to investigate the Gibbs free energy of the conformational isomers of 2-alkyl, 3-alkyl, and 4-alkyl cyclohexanones. The calculation gave results consistent with the general trend experimentally found. The genesis of stabilization of the axial conformers in 2- and 3-alkyl cyclohexanones, as compared to the structurally corresponding cyclohexane derivatives, was sought in the context of the attractive CH/π(CO) hydrogen bond. In support of this hypothesis, short nonbonded distances have been noted between CHs in the alkyl group and the carbonyl carbon in the relevant axial conformers. Calculations were also carried out to study the conformational energies of several terpenic ketones. For isomenthone, more than a half molecular fraction (ca. 55%) has been suggested to be in the isopropyl-axial conformation, while for isocarvomenthone ca. 77% has been suggested to be in the axial-isopropyl conformation; this is consistent with bibliographic experimental data. A crystallographic database search has provided results compatible with this conclusion. We suggest that the relative stability of the axial alkyl substituent, often observed in terpenic and steroidal ketones is rationalized in terms of an attractive molecular force, the CH/π(CO) hydrogen bond.     

Identification of two types of exchangeable sites for monovalent copper ions exchanged in MFI-type zeolite

Three different approaches have been used to characterize the state of exchanged copper ions in copper-ion-exchanged MFI (CuMFI) samples. (1) Two types of an ion-exchangeable site with different adsorption properties for N(2) or CO molecules were identified depending on the pre-treatment temperature (723 or 873 K) of a sample prepared by using an aqueous solution of CuCl(2). (2) The state of the active sites formed by the evacuation of a sample at 873 K that had been prepared using a mixture solution of aqueous NH(4)CH(3)COO and Cu(CH(3)COO)(2) was analysed utilizing both (13)C(18)O and (12)C(16)O to identify the two types of active adsorption sites for CO molecules. (3) CuMFI samples prepared by the ion-exchange method employing anhydrous CuCH(3)COO showed a surprising adsorption feature characterized by a single IR band occurring at 2159 cm(-1) due to the adsorbed CO molecules, but there was no corresponding IR band due to adsorbed N(2) molecules. A successful preparation of CuMFI, in which the monovalent copper ions exclusively occupied another one of the two types of ion-exchangeable sites, was also carried out utilizing the solid-ion exchange method using Cu(CH(3)COO)(2).H(2)O. This site exhibits an IR band occurring at 2151 cm(-1) for CO molecules and also acts as an active site for N(2) molecules. These experimental data correlate, and clearly indicate that there are at least two types of exchangeable sites for copper ions in MFI-type zeolites.     

1,6-Stannatropic strategy: effective generation and cyclization of 1,5-dipoles from o-stannylmethylated thioanilides or phenyl isothiocyanates

[reaction: see text] A new method for the generation of 1,5-dipoles from o-stannylmethylated thioanilides via 1,6-stannatropy under neutral conditions was developed. Cyclization of the 1,5-dipoles afforded indole derivatives effectively. The strategy has potential for application to the generation of alternative 1,5-dipoles from o-stannylmethylated aryl isothiocyanates leading to indole derivatives having a stannylthio group that was readily converted to other functional groups.