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91.
Koki Yamaguchi Masashi Eto Yasuyuki Yoshitake Kazunobu Harano 《Journal of Physical Organic Chemistry》2013,26(1):64-69
The reaction of 3,5‐bis(methoxycarbonyl)‐4‐oxo‐4H‐pyrazole 1,2‐dioxide (1a) with 1,3,5‐cycloheptatriene (2b) gave a mixture of the novel endo‐[4 + 6]‐cycloadduct (4ab), anti‐exo‐[4 + 2]‐cycloadduct (5ab), and the heterocage (6ab) derived from the intramolecular 1,3‐dipolar cycloaddition reaction of the syn‐endo‐[4 + 2]‐cycloadduct. Analogous endo‐[4 + 6] selectivity in 1,3‐dipolar cycloadditions has not been reported previously. The X‐ray analysis indicates that 6ab has a very long Nsp3–Nsp3 bond distance of 1.617(4) Å. The cycloaddition behaviour is discussed on the basis of transition‐state structures optimized at the B3LYP/6‐31G(d) level of theory, from which predictions of the peri‐, regio‐, and stereoselectivities agreed well with the experimental results. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
92.
Koki YamguchiMasashi Eto Kenta HigashiYasuyuki Yoshitake Kazunobu Harano 《Tetrahedron letters》2011,52(46):6082-6085
2,5-Bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone (1) reacts with 4-phenylbut-3-yn-2-one (2b) in the presence of DABCO to give the bicyclic carbocycles (6b) and the tetracyclic carbocycle (7b) under extremely mild reaction conditions. 相似文献
93.
Yanying Zhang Koichi Mitsudo Shunzo Suematsu Daisuke Horii Kenji Tamamitsu 《Tetrahedron letters》2009,50(44):6057-6059
Novel long-chain dialkyl fluorene-9,9-dicarboxylates were synthesized by treating fluorene with lithium diisopropylamide followed by alkyl chloroformates. The fluorene derivatives were readily electro-oxidized to form electroactive films on the surface of a glassy carbon electrode. From the viewpoint of suitable potential window (from −2.5 to 1.5 V vs Ag/Ag+), cyclic voltammograms of the films indicated the electroactive properties of the fluorene derivatives that make them good candidates for electrochemical capacitor materials. 相似文献
94.
95.
Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive vibrational technique to obtain the structural information of chemical species on their surface and interface. In this short article, we briefly review the current research regarding the reaction mechanism and kinetics on the cathode surface of the Li–O2 battery by in situ SERS observations, including reaction intermediates and products, influence of solvent, discharge/charge mechanisms, and mediation mechanism of redox mediators. 相似文献
96.
We report a successful attempt to derive a closed-form expression for the relaxation function of a complex system by solving a set of coupled kinetic equations connecting the excitation/de-excitation rates to the number of particles (such as electrical charges, dipoles, etc.) in excited states. Our approach, originating from developments in dielectric and mechanical relaxation studies, allows the use of a unified treatment for a wide array of natural processes which often pose challenges to theoretical modeling. We use the notions that (i) a dipole represents any pair formed by a particle in an excited state (such as an energy level in optically excited molecules, or an electrode in dielectric spectroscopy) and its image in the ground state (or reference electrode), that (ii) coupling between such dipoles may be described as particle transfer from one excited state to another with lower energy, and that (iii) the relaxation function for such a system of dipoles is mathematically equivalent to the cumulative distribution function of particles, i.e., the total number of particles that are still in an excited state at a time t following excitation. Taken together, these ideas naturally lead to the identification of two types of relaxation – parallel and serial relaxation – and allow one to tackle systems with either geometrical or physical self-similarity within a unified mathematical scheme. 相似文献
97.
Morphology and properties of globular polymeric materials in the solid state: A composite material of DNA with a cationic surfactant 下载免费PDF全文
Emmanuel C. Ossai Yuka Tomimori Shota Ohki Koki Okada Takeshi Yonekura Kazuya Furusawa Naoki Sasaki 《Journal of Polymer Science.Polymer Physics》2016,54(7):730-738
The aim of the present study was to control entanglements in order to regulate the properties of polymeric solids. Initially, fabrication of polymeric solids with few entanglements was attempted. Films of the DNA–cationic surfactant, cetyltrimethylammonium bromide (CTAB) (DNA–CTA), were cast from ethanol solution at room temperature. Morphological examination of DNA–CTA complex films using atomic force microscopy (AFM) revealed that these films were constructed by particle‐like substances. Geometrical analysis of AFM images showed that the particle‐like substances were the aggregates of several DNA–CTA globules. Mechanical characterization suggested that there were fewer entanglements than with normal plastic films. Small angle X‐ray scattering experiments during annealing indicated that molecular motions were highly excited in the surface region of each particle. In conclusion, a globular polymeric film with fewer entanglements was fabricated. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 730–738 相似文献
98.
Broad-line 1H NMR spectra of linear polyethylene at temperatures in the α-transition range can be analyzed in terms of contributions from the crystalline and noncrystalline components provided molecular motion in the crystalline region is adequately considered. The spectrum of solid n-C32H66 or n-C44H90 prior to melting is used to take account of the contribution of the crystalline region of the polymer to molecular motions. The temperature dependence of the component distribution in the polymer is briefly discussed for a wide range of temperatures, together with previously reported results at low temperatures. The noncrystalline component is in a rigid glassy state at very low temperatures but with rising temperature it transforms to a mobile glassy state with restricted molecular motion, and transforms partially to the rubbery state at high temperature. The crystalline component remains rigid at low temperature, but some molecular motion is associated with it at higher temperatures in the α-transition range. 相似文献
99.
We studied the far-infrared emission spectrum resulting from recombination of an electron with an ionized impurity of As and
Sb in germanium under impact ionization at liquid, helium temperatures. The emission peaks at the position corresponding to
the transition from the 2p
± excited state to the ground state. This observation indicates that recombination occurs through the capture by the excited
states of the donor impurity, which is consistent with the cascade trap model. The intensity of emission radiation is of the
order of 10−7 watts for the excitation power of about one watt, which implies a dominant process of recombination to be accompanied by
phonon emission. 相似文献
100.