Relationship between the configurations of 2-phenyltetrahydrothiophenium 1-methylides and their rearrangement products

trans-2-Phenyltetrahydrothiophenium 1-methylide (trans-3), which is generated by fluoride ion-induced desilylation of trans-2-phenyl-1-[(trimethylsilyl)methyl]tetrahydrothiophenium salt (trans-2), gave a mixture of 1,4,5,10a-tetrahydro-3H-2-benzothiocine (4) ([2,3]sigmatropic rearrangement product) and 4-methylsulfanyl-1-phenyl-1-butene (5) (Hofmann elimination product). Ylide trans-3 cannot undergo [2,3]sigmatropic rearrangement because the ylide-carbon is too far from the phenyl group, and trans-3 would instead isomerize to cis-3. In this paper, we discuss the mechanism of the isomerization of trans-3 to cis-3.     

Optimal control of ultrafast selection

Optimal laser control for ultrafast selection of closely lying excited states whose energy separation is smaller than the laser bandwidth is reported on the two-photon transition of atomic cesium; Cs(6S-->7D(J), J=5/2 and 3/2). Selective excitation was carried out by pulse shaping of ultrashort laser pulses which were adaptively modulated in a closed-loop learning system handling eight parameters representing the electric field. Two-color fluorescence from the respective excited states was monitored to measure the selectivity. The fitness used in the learning algorithm was evaluated from the ratio of the fluorescence yields. After fifty generations, a pair of nearly transform-limited pulses were obtained as an optimal pulse shape, proving the effectiveness of the "Ramsey fringes" mechanism. The contrast of the selection ratio was improved by approximately 30% from the simple "Ramsey fringes" experiment.     

Utilization of42Ar−42K generator for isotope dilution analysis of potassium in ultra-pure water

Carrier- and salt-free⁴²K milked from an⁴²Ar–⁴²K generator was utilized for isotope dilution analysis of potassium in ultra-pure water. Potassium in the sample marked with the⁴²K was shown to be concentrated easily 60 times by crown-ether extraction and acid back-extraction to be determined by atomic absorption spectrophotometry. The same extractions proved to be effective for removing the reagent blank. Cerenkov radiation counting was often suitable for⁴²K measurement. The⁴²K was used also for studying the interaction of ultra-low concentrations of potassium with vessel walls.     

New lignan glycosides from Chinese medicinal plant,Sinopodophillum emodi

Two new podophillotoxin glucosides, L-picropodophillotpxin 7'-O-(beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside) (2) and L-picropodophillotpxin 7'-O-beta-D-glucopyranoside (3), were isolated from Chinese medicinal plant, Sinopodophillum emodi, together with 4 known compounds, podophillotoxin (1), podorhizol 4'-O-beta-D-glucopyranoside (4), deoxypodophillotoxin (5), and dehydropodophillotoxin (6). The structures of 2 and 3 were finally determined by the extensive decouping and nuclear Overhauser effect (NOE) experiments in NMR spectra and circular dichroism (CD) spectra. Compound 2 is the second example of podophillotoxin diglucoside, and both the first one and 2 were isolated from S. emodi. X-ray crystal structure analysis of 1, 5, and 6 was carried out. Compounds 1 and 5 showed the different conformations from those reported.     

Photon angular distribution of Radiative Electron Capture into the M shell of He-like uranium ions at 110–140 MeV/u

Measurements of the photon angular distribution of Radiative Electron Capture into the M shell have been performed with He-like uranium ions in the range 110–140 MeV/u. In addition, L REC was studied at a projectile energy of 140 MeV/u. In both cases, the experimental data show an asymmetry around 90° and agree well with a fully relativistic theory.     

Influence of electronic state and dispersion of platinum particles on the conversion and selectivity of hydrogenation of an α,β-unsaturated aldehyde in supercritical carbon dioxide

The selective hydrogenation of cinnamaldehyde (CAL) was investigated using silica supported platinum catalysts in supercritical carbon dioxide. Selectivity to cinnamyl alcohol (COL) is enhanced as Pt⁰/Pt²⁺ ratio increases; namely, zero-valent metallic surface is beneficial to the formation of COL compared with less reduced surface. The influence of Pt⁰/Pt²⁺ ratio is more significant on the selectivity than on the total conversion. For the catalyst with small Pt⁰/Pt²⁺ value, the selectivity also depends on the degree of platinum dispersion. The selectivity to COL is higher for higher degree of platinum dispersion. The CO₂ pressure did not affect the conversion and selectivity so much.     

57Fe Mössbauer and 31P NMR Spectroscopic Characterisation of Fe(CO)3L2 Complexes (L=Phosphite and Phosphine)

Abstract

A series of mixed ligand complexes of the type [Fe(CO)₃L¹L²] (L¹=tri-phenylphosphite and L²=phosphine or phosphite) have been prepared to study the Fe-P bond. The ⁵⁷Fe Mössbauer spectra of trans-[Fe(CO)₃L¹L²] showed a quadrupole splitting doublet characteristic of the disubstituted iron carbonyls in trigonal bipyramidal symmetry. The linear dependence of the quadrupole splittings on the isomer shifts with a positive slope has revealed that the iron-to-phosphorus σ-donation is offset by the phosphorus-to-iron π-back donation. The ³¹P{¹H} NMR spectra showed a couple of doublets assigned to the coordinated phosphite and the coordinated phosphine. The doublet of the phosphite site was generally observed at the down field compared with that of the phosphine site. The coordination shifts increase with the Mössbauer isomer shifts, suggesting that the iron-to-phosphorus π-back donation plays an important role in the Fe-P bond of trans-[Fe(CO)₃L¹L²]. The relatively large coupling constants due to ²J(P,P) have demonstrated that there exists a strong interaction between trans phosphorus ligands through the d_π orbitals of the central iron. The coupling constant is a measure of the bond strength between Fe-P, while the Mössbauer isomer shift reflects the electron density at the iron nucleus. Thus, a linear correlation has been established between these two spectroscopic parameters.     

Novel high birefringence dibenzothiophenylacetylene liquid crystals

We have designed, synthesized and evaluated dibenzothiophenylacetylene homologues as new heterocyclic molecules which were expected to have high δα values and short wavelength UV absorption spectra. The dibenzothiophenyl acetylene homologues exhibited wide nematic phase ranges and had very high extrapolated δn of over 0.6 and directly measured values of 0.5. The compounds with two dibenzothiophenyl rings were colourless, so that we have succeeded in obtaining colourless super-high δn liquid crystals. We have also analysed the contribution of the transition band to the refractive indices and the birefringence. From the analysis, the main origins of δn for compounds 1 and 2 are lower MOs than the HOMO and this results in the compatibility of large δn and lack of colour. The dibenzothiophenylacetylene compounds behaved according to our design expectations.     

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