An Isolable Silicon Analogue of a Ketone that Contains an Unperturbed Si=O Double Bond

Despite tremendous efforts to synthesize isolable compounds with an Si=O bond, silicon analogues of ketones that contain an unperturbed Si=O bond have remained elusive for more than 100 years. Herein, we report the synthesis of an isolable silicon analogue of a ketone that exhibits a three‐coordinate silicon center and an unperturbed Si=O bond, thus representing the first example of a genuine silanone. Most importantly, this silanone does not require coordination by Lewis bases and acids and/or the introduction of electron‐donating groups to stabilize the Si=O bond. The structure and properties of this unperturbed Si=O bond were examined by a single‐crystal X‐ray diffraction analysis, NMR spectroscopy, and theoretical calculations. Bimolecular reactions revealed high electrophilicity on the Si atom and high nucleophilicity on the O atom of this genuine Si=O bond.     

Synchronism of an incompressible non-free Seifert surface for a knot and an algebraically split closed incompressible surface in the knot complement

We give a necessary and sufficient condition for knots to bound incompressible non-free Seifert surfaces.

     

Study of chiral property of nuclear matter through measurements of Φ meson decays

The experiment E325 being performed at KEK 12GeV-PS is to investigate the chiral property of QCD in dense matter through the measurements of vector mesons which decay inside nucleus. The status of the experiment and the preliminary mass distribution of Φ → K⁺K⁻ decays are presented.     

High-resolution gamma-ray spectroscopy of ΛLi

We report on the first observation of hypernuclear γ transitions using germanium detectors. Using a large-acceptance Ge detector system, we observed two γ transitions in _Λ⁷Li, the spin-flip transition at 689±4keV and the transition at 2050±2 keV (preliminary). The strength of the ΛN spin-spin interaction is derived from the energy of the former transition. As for the latter transition, B(E2) was measured to be 3.9±0.6±0.4 e²fm⁴ (preliminary), which indicates a shrinkage of the nuclear size of _Λ⁷Li from ⁶Li and confirms “glue-like role” of Λ.     

Synthesis, properties, and reactions of a series of stable dialkyl-substituted silicon-chalcogen doubly bonded compounds

The first dialkyl-substituted silicon-chalcogen doubly bonded compounds [R2Si=X; R2=1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl, X = S (4), Se (5), and Te (6)]were synthesized by the reactions of an isolable dialkylsilylene R2Si: (3) with phosphine sulfide, elemental selenium, and elemental tellurium, respectively. Systematic changes of characteristics of silicon-chalcogen double bonds are elucidated by X-ray analysis, UV-vis spectroscopy, and DFT calculations. In the solid state, the unsaturated silicon atom in 4-6 adopts planar geometry and the extent of the shortening of Si=X double bonds from the corresponding Si-X single bonds decreases in the order 4 > 5 > 6. In the absorption spectra of 4-6, pi -->pi* transition bands are observed distinctly in addition to n -->pi* transition bands. Both the n -->pi* and pi -->pi* transitions are red-shifted in the order 4 < 5 < 6, and the difference between the energies of the two transitions is kept almost constant among 4-6. The tendency is explained using the qualitative perturbation theory and is reproduced by the DFT calculations for model silanechalcogenones. Addition reactions of water, methanol, and isoprene to 4-6 are reported.     

Electromagnetic moments of short lived β emitters 21F, 23Mg, 27Si and 39Ca

The β-NMR spectra of ²¹F, ²³Mg, ²⁷Si and ³⁹Ca which were produced in heavy ion collisions and implanted in various crystals have been observed. The magnetic moments of ²¹F and ²⁷Si were determined to be |μ(²¹F)| = 3.9194 ± 0.0012 μ_N and |μ(²⁷Si)| = 0.8653 ± 0.0003 μ_N, respectively. The electric quadrupole coupling constants were determined for the first time to be |eqQ(²¹F in MgF₂)/h|= 9.94 ± 0.09 MHz, |eqQ(²³Mg in MgF₂)/h|= 1.96 ± 0.06 MHz, |eqQ(²⁷Si in Al₂O₃)/h|= 1.90 ± 0.12 MHz, |eqQ(³⁹Ca in CaCO₃)/h|= 0.60 ± 0.04 MHz. From the present eqQ/h, the Q moments were deduced as |Q(²¹F)|= 110 ± 22 mb, |Q(²³Mg)|= 114 ± 3 mb, |Q(²⁷Si)|= 60 ± 13 mb and |Q(³⁹Ca)|= 36± 7 mb. The present data were compared with the theoretical values obtained by the OXBASH shell model code. This revised version was published online in August 2006 with corrections to the Cover Date.     

Excited-state reactions of an isolable silylene with aromatic compounds

The first intermolecular reactions of the excited state of a silicon divalent compound (silylene) with benzene derivatives were discovered. Typically, when a benzene solution of an isolable silylene is irradiated with light of wavelengths longer than 420 nm at room temperature, the corresponding silacyclohepta-2,4,6-triene (silepin) is yielded quantitatively. The photochemical insertion of the silylene toward substituted benzenes occurs in general to give the corresponding substituted silepins. The insertion reaction is highly sensitive to the steric hindrance at a reacting C-C double bond in benzene; during the reactions of the silylene with substituted benzenes, only unsubstituted C-C double bonds in the benzene ring reacted selectively. The irradiation of the silylene in the presence of mesitylene afforded the insertion product to a benzylic C-H bond, indicative of the biradical nature of the excited-state silylene.     

Sila-metalation route to hydrido(trialkylsilyl)silyllithiums

The proton abstraction (sila-metalation) of trialkylsilyl-substituted dihydridosilanes with t-BuLi or LDA in THF was found to be a convenient route to the corresponding silyllithiums (RR'SiHLi; 1a, R, R' = t-BuMe(2)Si; 1b, R, R' = Me(3)Si; 1c, R, R' = i-Pr(2)MeSi; 1d, R = t-BuMe(2)Si, R' = 4-methylphenyl). Hydridosilylithium 1a was isolated as air- and moisture-sensitive, but thermally stable, colorless crystals. X-ray analysis has shown that 1a is dimeric in the solid state, where two lithium atoms bridge between anionic silicon atoms forming a parallelogram, each lithium atom is coordinated by one THF molecule, and the Si-H hydrogen atoms are in the plane of the parallelogram. X-ray analysis has shown that (t-BuMe(2)Si)(2)GeHLi (5) has a dimeric structure similar to that of 1a.     

Optimal measurements for general quantum systems

We give a general formulation of the theory of optimal quantum measurements, based on Gudder's [8] convex structure approaches to axiomatic quantum mechanics, which includes the case of Holevo's formulation [14] and operational quantum mechanics [3]. Simple and general conditions for existence of Bayes optimal measurements are obtained by a method without operator valued measure techniques. For this purpose, a representation of convex prestructures and a characterization of a class of loss functions are obtained. Finally, an application of the results to Wald's theory of statistical decision functions is shown.