Pentadienylsilanes as new reagents of the siteselective dienylmethylation of electrophiles promoted by a Lewis acid

(2,4-Pentadienyl)- and (2,4-hexadienyl)trimethylsilanes, prepared from the corresponding pentadienylpotassiums and trimethylchlorosilane, react smoothly with various electrophiles such as acetals, aldehydes and acid halides to give pentadienylation products, with regiospecific transposition of the pentadienyl group.     

Evaluation of mass discrimination effects in the quantitative analysis of polydisperse polymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using uniform oligostyrenes

Mass discrimination effects in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) were quantitatively investigated using equiweight and equimolar mixtures of uniform polystyrene (PS) oligomers. Uniform PS oligomers were separated by preparative super-critical fluid chromatography (SFC) from commercial standard PS samples. The separated PS oligomers, with degrees of polymerization n = 2–25, have absolutely no molecular weight distributions. Equiweight and equimolar mixtures of uniform PS oligomers were accurately prepared by weighing by microbalance, and their spectra were recorded using a MALDI-TOF mass spectrometer. In the lower molecular weight region (less than about 10³) the oligomers with lower molecular weights give lower mass spectral intensities, with no correlation with laser power. In contrast, higher laser powers yield a decrease of mass spectral intensities in the higher molecular weight region. These results clearly show that mass discrimination effects occur at lower and higher molecular weights depending on the laser power, and provide quantitative information about the discrimination. Using the data on equiweight and equimolar mixtures of PS oligomers, it was possible to calibrate the MALDI-TOF mass spectral data for an analysis of molecular weight distribution of a standard monodisperse PS sample with number-averaged molecular weight of 10³, and to compare it with the molecular weight distribution measured by analytical SFC. The result from the calibrated MALDI-TOF mass spectrum, however, does not agree perfectly with that from the SFC results, because undetectable peaks in MALDI-TOF mass spectra at lower and higher molecular weights could not be included in the calibration of peak intensities. Copyright © 2001 John Wiley & Sons, Ltd.     

Thermoplastic photographic material for vibration measurements by speckle photography

In order to measure vibration amplitudes by speckle photography in quasi real-time, the feasibility of using thermoplastic photographic material for recording a speckle pattern image is studied experimentally to be proved true. An optimum recording condition of the material is also obtained.     

A phenomenological analysis on γp → π+n, πOp below 1.2 GeV

A phenomenological partial-wave analysis on γp → π⁺n and π^Op reactions has been performed in the energy range 0.25–1.2 GeV with available data, laying special emphasis on the polarization and asymmetry data. A good fit has been obtained.