Pyrolysis of azidopyrazines

2,3-Dichloro- and 2,5-dichloropyrazines were treated with sodium azide. The former gave diazidopyrazines and the latter, monoazidomonochloropyrazines. Pyrolysis of 2,3-diazidopyrazines resulted the production of 1,2-dicyanoiminoethanes and that of 2-azido-5-chloropyrazines, chloroimidazoles.     

One-carbon extrusion from carbohydrates via C1-alkoxy radical fragmentation. An easy access to erythrose and threose

Generation and fragmentation of the C1-alkoxy radicals of pyranose derivatives are nicely promoted by (diacetoxyiodo)benzene or lead tetraacetate in the presence of iodine catalyst under mild conditions to give the corresponding mixed-acetal formates which are further converted to the furanose derivatives by acid-catalysed transacetalization.     

Ohmic Contacts for Compound Semiconductors

Although there has been strong demand for low -resistance, highly reliable Ohmic contacts for compound semiconductors to realize high-frequency transistors, high-power devices, and light-emitting (LED) and laser diodes (LD), development of the Ohmic contact technologies has been made on a trial-and-error basis. The primary reason is lack of fundamental data to design ideal metal/semiconductor interfaces due to complexity of elements involved at the interfacial reaction. In this article, we review recent systematic studies carried out for Ohmic contact materials to n-GaAs and then address critical issues to apply the methodology established in n-GaAs to develop low-resistance Ohmic contacts for p-ZnSe and p-GaN, which are desperate for blue-green LED and LD.     

Efficient planar-type butt coupling of a proton-exchanged waveguide on a Z-cut LiTaO3 substrate

A half-wave thin film was formed on the facet of a proton-exchanged waveguide by the oblique deposition of Ta₂O₅. Planar-type butt coupling of the waveguide on the z-cut LiTaO₃ substrate to the AlGaAs laser diode in transverse electric mode oscillation was realized with coupling efficiency as high as 53%.     

A carbon-carbon bond formation using endoperoxides of 1,2-dihydropyridines

A novel type of a nucleophilic substitution on the piperidine ring was achieved by a stannous chloride-effected reaction of endoperoxides of N-alkoxycarbonyl-1,2-dihydropyridines with various kinds of carbon nucleophiles.     

Viscoelastic behaviors and molecular motions of highly syndiotactic poly(vinyl alcohol) fibers

The viscoelastic behavior and molecular motion of highly syndiotactic poly(vinyl alcohol) (S‐PVA) fibers with a dyad syndiotacticity (r) of 69% were studied by dynamic mechanical thermal analysis and wide‐angle X‐ray diffraction and compared with those of atactic poly(vinyl alcohol) (A‐PVA) fibers with r = 54%. The β_c dispersion, based on the molecular motion of the chain molecules in the crystalline regions, was observed for A‐PVA around 120–140 °C, and the only primary (α_c) dispersion was observed for S‐PVA around 180 °C. The thermal expansion coefficients for the a and c axes of the A‐PVA crystal changed discontinuously around 120 °C, which corresponded to the β_c dispersion. For S‐PVA, the coefficient for the (002) plane changed discontinuously around 100 °C, similarly to A‐PVA, but that for the (100) plane remained unchanged between 20 and 220 °C. These results showed that the intermolecular hydrogen bonding of S‐PVA was stronger in the direction of the a axis than in the other directions, suppressing the β_c dispersion. The storage modulus and thermal expansion coefficient of the (020) plane (molecular axis) of S‐PVA decreased markedly around 180 °C, and this indicated that the α_c dispersion was due to the torsional motion of the molecular chains in the crystalline regions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 800–808, 2004