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181.
Compounds that undergo Au(I)-catalyzed cycloisomerizations affording tetracyclic products that can be converted into compounds with the skeleton of bruceantin are described. The Au(I)-catalyzed cycloisomerizations reported herein are hindered by a 1,3-diaxial interaction between the substituent and the methyl group in the transition state. The use of small substituents was found to increase the yield of the desired product, while the reaction of substrates with large substituents afford undesired constitutional isomers. 相似文献
182.
A. Breakstone R. Campanini H. B. Crawley M. Cuffiani G. M. Dallavalle M. M. Deninno K. Doroba D. Drijard F. Fabbri A. Firestone H. G. Fischer H. Flöge H. Frehse W. Geist L. Gesswein G. Giacomelli R. Gokieli M. Gorbics M. Gorski P. Hanke M. Heiden W. Herr D. Isenhower E. E. Kluge J. W. Lamsa T. Lohse R. Mankel W. T. Meyer T. Nakada M. Panter A. Putzer K. Rauschnabel B. Rensch F. Rimondi M. Schmelling G. P. Siroli J. Skeens R. Sosnowski M. Szczekowski O. Ullaland D. Wegener R. Yeung 《Zeitschrift fur Physik C Particles and Fields》1989,43(2):185-192
The production of ρ(770)0,K *(892)0, \(\bar K^* (892)^0 \) andf 2(1270) mesons as leading particles in hadron jets (<z>~0.7) has been measured in deep inelasticpp interactions at the CERN ISR at \(\sqrt s = 62\) GeV. The comparison of vector and pseudoscalar meson production at the same transverse momentum provides a rather model independent way to determine the fragmentation parameterV/P. We determine(V/P) u,d =1.66±0.18±0.63 from the ρ/π ratio and(V/P) s =0.90±0.13±0.27 from theK */K ratio. For thef 2(1270) production we findf 2/ρ0=0.30±0.08. 相似文献
183.
W. Bell K. Braune G. Claesson D. Drijard M. A. Faessler H. G. Fischer H. Frehse R. W. Frey S. Garpman W. Geist C. Gruhn P. Hanke M. Heiden W. Herr P. G. Innocenti T. J. Ketel E. E. Kluge I. Lund G. Mornacchi T. Nakada I. Otterlund M. Panter B. Povh A. Putzer E. Stenlund T. J. M. Symons R. Szwed O. Ullaland 《Zeitschrift für Physik A Hadrons and Nuclei》1986,324(1):67-73
We have investigated kinematical correlations between the outgoing beam proton and the proton emerging from the fragmentingα-particle inpα collisions at \(\sqrt {s_{p\alpha } } = 88GeV\) . Strong correlations are seen, indicating the dominance of quasi-elasticpp scattering in the fragmentation channelp+α→p+pX, for the ¦t¦ range 0.05–1.00 (GeV/c)2. A Monte Carlo simulation of this process can explain the observed correlation spectra assuming an admixture of about 16% spectator protons. 相似文献
184.
A. Breakstone R. Campanini H. B. Crawley M. Cuffiani G. M. Dallavalle K. Doroba D. Drijard F. Fabbri A. Firestone H. G. Fischer H. Frehse W. M. Geist L. Gesswein G. Giacomelli R. Gokieli M. S. Gorbics P. Hanke M. Heiden W. Herr E. E. Kluge L. D. Isenhower J. W. Lamsa T. Lohse R. Mankel W. T. Meyer T. Nakada M. Panter A. Putzer K. Rauschnabel B. Rensch F. Rimondi M. Schmelling G. P. Siroli R. Sosnowski M. Szczekowski O. Ullaland D. Wegener Ames-Bologna-CERN-Dortmund-Heidelberg-Warsaw Collaboration 《Zeitschrift fur Physik C Particles and Fields》1986,31(2):185-190
Data are presented for the exclusive reaction pp → pp π+ π? at \(\sqrt s = 62GeV\) with two leading protons at large Feynman-x and a centrally produced π+;π? system. In this kinematical configuration one expects a substantial contribution from Double Pomeron Exchange, which is a potential source of glueballs. The experiment was performed at the CERN ISR using the Split Field Magnet spectrometer. In the mass range between 1,000 and 1,700 MeV/c2 the invariant mass distribution for the central π+;π? system exhibits a very significant signal for thef 0(1270) and no other obvious resonant states. 相似文献
185.
A. Breakstone R. Campanini H. B. Crawley G. M. Dallavalle M. M. Deninno K. Doroba D. Drijard F. Fabbri A. Firestone H. G. Fischer H. Frehse W. Geist G. Giacomelli R. Gokieli M. Gorbics P. Hanke M. Heiden W. Herr L. D. Isenhower E. E. Kluge J. W. Lamsa R. A. Leacock T. Lohse R. Mankel W. T. Meyer G. Mornacchi T. Nakada M. Panter A. Putzer K. Rauschnabel B. Rensch F. Rimondi M. Schmelling G. P. Siroli J. D. Skeens R. Sosnowski M. Szczekowski O. Ullaland D. Wegener R. Yeung 《Zeitschrift fur Physik C Particles and Fields》1990,48(4):569-575
Data are presented on Pomeron-Pomeron interactions which produce a centralπ + π ? system in proton-proton collisions at \(\sqrt s = 62 GeV\) at the CERN Intersecting Storage Rings. This process may favor the production of gluonic bound states. A partial-wave analysis of theπ + π ? system shows evidence for the production of the statesf 0(975),f 0(1400), andf 2(1270). The fitted mass for thef 2(1270) is about 50 MeV below the world average. In addition, the production mechanism for thef 2(1270) is uniquely different from that for the other final states in that there is a correlation between the outgoing protons. this is consistent with a picture of two-gluon exchange with thef 2(1270) produced by gluon fusion, and could indicate that thef 2(1270) has a glueball component. 相似文献
186.
T. Mitani S. Suga Y. Tokura K. Koyama I. Nakada T. Koda 《International journal of quantum chemistry》1980,18(2):655-659
The optical reflectivity spectra of quasi-one-dimensional polymers (SN)x, trans-(CH)x, and polydiacetylene are investigated in an energy range from 1 to 25 eV by use of synchrotron radiation. Observed structures associated with π-electron states are interpreted in terms of the quasi-one-dimensional one-electron bands calculated by the LCAO -type model. 相似文献
187.
188.
[reaction: see text] The first total synthesis of (+)-phomopsidin has been achieved via a diastereoselective transannular Diels-Alder (TADA) reaction. Key steps in the synthesis include diastereoselective ynone reduction with (-)-alpha-pinene and 9-BBN, macrocyclization by E-selective intramolecular Horner-Wadsworth-Emmons (HWE) reaction, as well as carbometalation under Wipf's conditions, followed by HWE reaction at low temperature to selectively construct the (E)-1-methylpropenyl and (1E,2E)-4-carboxy-1,3-butadienyl substituents. 相似文献
189.
Highly enantioselective reduction of five-, six-, seven-, and eight-membered prochiral 1,3-cycloalkanediones possessing a methyl group and a protected hydroxymethyl group at their C2 position with baker's yeast or CBS catalyst and a new efficient and general method for preparing the 1,3-cycloalkanediones have been developed. These baker's yeast mediated reductions were found to produce corresponding ketols with high optical purity (>99% ee) and high yield. All of the prepared ketols and their derivatives, chiral building blocks, have been fully characterized, and their absolute configurations have been determined. These compounds would be useful for the convergent synthesis of complex natural products. 相似文献
190.
M. Nakada M. Saeki N. M. Masaki S. Tsutsui 《Journal of Radioanalytical and Nuclear Chemistry》1998,232(1-2):201-207
Preparation of source and sample holder is described for the Mössbauer studies of237Np and238U. For the Mössbauer measurement of237Np, a source assembly with small sources of241Am metal was developed taking account of the transport regulations for radioactive substances. The source assembly of241Am showed a sufficient activity enough to measure the Mössbauer spectra of237Np. In order to handle237Np compounds safely, trebly sealed holders were designed which could encapsulate237Np samples without the seepage of liquid helium. A source for238U Mössbauer measurement was also developed from a highly pure242PuO2. 相似文献