Unusual stereoselectivity in the synthesis of 4-oxa-δ-valerothiolactones: structure proof of β-hydroxythioamide

Stereoselectivity in the formation of 4-oxa-δ-valerothiolactone 2 from β-hydroxythioamide 1 is discussed. The structure of 1 is deduced from the structure of 2.     

The chemistry of O-silylated ketene acetals; diastereoselective Aldol reaction of 2,3-O-isopropylidene-D (and L)-glyceraldehydes leading to 2-deoxy-D (and L)-riboses

Diastereoselective carbon-carbon bond forming reaction of 2,3-O-isopropylidene-D (and L)-glyceraldehydes (D and L-2) with ketene silyl acetals (1a,b) occurred in acetonitrile under mild conditions to give the corresponding $\text{anti}$-β-siloxyesters (D and L-3a) as major products, which could be converted through a few additional steps to 2-deoxy-D(and L)-riboses.     

Laser Flash Photolysis of 2,2'-Dithiobls(pyridine N-oxide): Reactivity of N-Oxypyridyl-2-thio Radical

Abstract— Reaction kinetics of radicals produced by the nanosecond laser flash photolysis of 2,2'-dithiobis(pyridine N -oxide) and related compounds have been studied. The transient absorption band at 360 nm was attributed to the radical in which the unpaired electron mainly localizes on the S atom ( N -oxypyridyl-2-thio radical). The reactivities of the radical for conjugated dienes are lower than those of the pyridyl-2-thio radical, suggesting that a considerable unpaired electron density on the S atom delocalizes onto the N -oxypyridine moiety. The addition reaction rate of the radical to the conjugating diene was accelerated with hydrogen-bonding solvents and with addition of the cation, which may stabilize the N+-O^- canonical structure, increasing the unpaired electron density on the S atom. By the photolysis of N -hydroxypyridine-2-thione, the N-O bond was predominantly dissociated producing a pyr-idyl-2-thio radical. By the photolysis of its anion, photoejection took place followed by the N-O bond fission, yielding pyridine-2-thione.     

Intermediate resonance of inelastic 12C + 12C scattering

The intermediate resonances observed in the inelastic ¹²C + ¹²C cross sections to the single and mutual 2₁⁺(4.43 MeV) excitations and the single 3₁^? (9.64 MeV) excitation are studied by the coupled-channel method with the use of the coupling interaction derived by the folding procedure between ¹²C and ¹²C. It is shown that the model is successful in reproducing the gross structures of the inelastic cross sections and especially the correlated resonance energies of the inelastic channels. The inelastic resonances are shown to be due to the molecular resonances in an adiabatic potential between two ¹²C, which reproduces correctly the coupled channel resonances.     

Thermodynamics of aqueous mixtures of nonelectrolytes II. Isobaric heat capacities of water-n-alcohol mixtures at 25°C

Excess isobaric heat capacities of binary mixtures of water with methanol, ethanol, and 1-propanol were obtained from flow microcalorimetric measurements at 25°C over the entire composition range. The results are compared with those of previous investigations.     

Electrons and holes in HgTe and Hg0.82Cd0.18Te with controlled deviations from stoichiometry

The deviations from the stoichiometric composition of HgTe and Hg_0.82Cd_0.18Te crystals have been controlled by heat treatment under Hg vapor pressure. The magnetic field dependence of the Hall coefficient always shows the presence of two different sets of electrons and one set of holes. A low mobility electron is shown to belong to the conduction band. Vapor pressure dependence of hole concentration in HgTe shows that the concentration of nonstoichiometric defects decreases with increasing Hg vapor pressure, but the hole concentration is always higher than the electron concentration. In the case of Hg_0.82Cd_0.18Te, the electron concentration exceeds the hole concentration at high Hg vapor pressures. The dependence of the conduction band electron mobility in HgTe upon carrier density shows that the scattering by holes and impurities is predominant. In Hg_0.82Cd_0.18Te, however, optical phonon scattering is dominant when the deviation from stoichiometry is small and the effect of residual impurities can be neglected, and scattering by holes is dominant when the hole concentration is over $\text{10}{}^{17}\text{cm}{}^3$.     

Band broadening evaluation by back-and-forth capillary electrophoresis

The purpose of this study is to develop a method for precise evaluation of band broadening in capillary electrophoresis. A capillary electrophoresis system with on-column twin detectors is constructed. Back-and-forth electrophoresis permits zones to make a round trip between the twin detectors placed at distant positions on the capillary. The system is capable of eliminating extra-column effects and discriminating between reversible and irreversible band-broadening mechanisms.