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11.
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First examples of amphiphilic alkyl pentakis(phenylethynyl)benzene ethers containing functional groups at the terminal position of their alkoxy chains were synthesized by etherification of pentabromophenol with 11-bromoundecan-1-ol and 11-bromoundecanoic acid ethyl ester, respectively, and subsequent palladium catalyzed, fivefold coupling reactions with the substituted phenylacetylene. Two undecanoic acid derivatives with different pentakis(phenylethynyl)phenoxy substituents in the ω-position were prepared by ester cleavage from the corresponding ethyl esters. The thermal behaviours of five penta-alkynes in their pure states, as well as of their charge transfer complexes formed from mixtures with 2,4,7-tri-nitrofluorenone, were examined. 相似文献
13.
D. Sinha G.K. Sarker S. Ghosh A. Kulshreshtha K.K. Dwivedi D. Fink 《Radiation measurements》1998,29(6):599-604
Photon induced modifications in Triafol-TN and Triafol-BN polymers have been studied in the dose range of 101–106 Gy at room temperature using a 60Co source. To monitor the chemical and structural changes induced by gamma rays, UV, IR, and ESR studies were carried out. Thermal studies were also conducted for understanding the effects of gamma irradiations on these polymers. Variation of track etching characteristics and activation energy for bulk etching have been studied at different gamma rays doses. The experimental results are presented and discussed. 相似文献
14.
G. Mante R. Claessen T. Buslaps S. Harm R. Manzke M. Skibowski J. Fink 《Zeitschrift für Physik B Condensed Matter》1990,80(2):181-185
Applying angle-resolved photoemission spectroscopy of high angular and energy resolution we have measured the electronic structure of single crystals of Bi2Sr2CaCu2O8 near the Fermi energy. Along the high symmetry direction X a band is observed to disperse upwards and to cross the Fermi level, whose unoccupied part constitutes the hole-like carriers responsible for the superconductivity. From spectra along the M direction we find evidence for an electron pocket around the M point. The measured band widths appear to be drastically reduced compared with band structure calculations indicating strong electronic correlation effects. From the observation of Fermi-Dirac-like cut-offs in the spectra due to band crossings through the Fermi level we can confirm the existence and, in particular, the shape of the Fermi surface as calculated by band structure calculations. 相似文献
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Directional couplers in image guide technique for millimeter-wave circuits are discussed, and steps to improve their properties are demonstrated. The simple two-line-9 dB coupler with periodical coupling is compared to a design with an intermediate dielectric coupling element to reduce the frequency dependence. Radiation from the waveguide bends can be reduced significantly by inserting absorber materials at critical points. Experimental results for a-3 dB coupler are also given. 相似文献
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Two distinct proton exchange reactions occur in metastable gaseous benzylbenzenium ions, generated by isobutane chemical ionization of diphenylmethane and four deuterium-labelled analogues. Whereas the proton ring-walk at the benzenium moiety is fast giving rise to a completely random intraannular proton exchange, the interannular proton exchange is surprisingly slow and competes with the elimination of benzene. A kinetic isotope effect of kH/kD= 5 has been determined for the interannular proton transfer, and a particularly high energy barrier of 50–75 kJ mol?1 has been estimated. These observations are attributed to steric restrictions of the ring-to-ring proton transfer in benzylbenzenium ions and contrasted to the fast interannular proton exchange in the higher homologues. 相似文献
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20.
Dietmar Kuck 《Journal of mass spectrometry : JMS》1994,29(3):113-125
The electron impact-induced fragmentation of 2,2-dimethyl- and 2-ethyl-1,3-indandione, 1 and 2, and their isomers, 3-isopropylidene- and 3-propylidenephthalide, 3 and 4, respectively, was studied in detail by mass-analysed ion kinetic energy (MIKE) and collision-induced dissociation (CID-MIKE) spectrometry, including 2H and 13C. labelled analogues of 1 and 2. In all regimes of internal energy, the molecular ions 1+. ? 4+. interconvert by up to seven consecutive, reversible isomerization steps prior to the main fragmentation processes, viz. loss of CH3. and C2H4. 1,3-Indandione and 3-methylenephthalide ions with identical alkylidene moieties (i.e. 1+.?3+. and 2+.?4+.) equilibrate rapidly and completely prior to fragmentation, whereas these pairs of isomers interconvert only slowly via a five-step rearrangement of the indandione ions 1+.?2+.. Distinct from the behaviour of simpler ionized carbonyl species, a 1,2-C shift of a (formally) neutral carbonyl group is found to occur along with that of a protonated one. Also distinct from simpler cases, methyl loss does not take place from the ionized enol intermediates formed within the interconversion 1+.?2+. of the diketone ions but rather from the n-propylidenephthalide ions 4+.. This follows from CID-MIKE spectrometry of the [M ? CH3]+ ions of 1–4 and two reference C10H7O2+ (m/z 159) ions of authentic structures (protonated 2-methylene-1,3-indandione and protonated 1,4-naphthoquinone). The characteristic CID fragmentation of the C10H7O2+ ions is rationalized. Finally, the multistep isomerization of ionized 1,3-indandiones apparently also extends to higher homologues [e.g. 5+. from 2-ethyl-2-methyl-1,3-indandione (5) and 6+. from 2,2-diethyl-1,3-indandione (6)]: the ionized phthaloyl group of 1,3-indandione radical cations 1+., 2+., 5+. and 6+., originally attached with its two acyl functionalities to the same carbon of the aliphatic chain, performs, in fact, a ‘multi-step migration’. 相似文献