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71.
72.
We give a new proof of Bartholdi's theorem for the Bartholdi zeta function of a graph.
Supported by Grant-in-Aid for Science Research (C) 相似文献
73.
74.
Electronic spectra of tris[2.2.2]paraxylylene (3°-PX) and some related compounds were measured in order to investigate the electronic interaction (pπ-pπ and pσ-pσ type) between “normal” (undistorted) benzene rings. 3°-PX showed a large hypochromic effect, i.e., its oscillator strength was observed to be 0·61 times of that of the corresponding linear polyparaxylylene. Charge-transfer (CT) spectra between these compounds and some electron acceptors were also studied. MO calculations (the VI/1, CNDO/2 and CI methods) were carried out in order to elucidate the electronic structure of 3°-PX and also the CT interactions between tetracyanoethylene and 3°-PX, benzene, toluene or p-xylene. 相似文献
75.
Asymmetric synthesis of β-lactams by means of the reaction of dimethylketene silyl acetal with (S)-alkylidene(1-arylethyl)amines in the presence of titanium tetrachloride was studied. The extent of the asymmetric induction was in the range of 44–78% (diastereomeric purity 72–89%) and the (S)-configuration was turned to be preferentially induced at the 4C position of the resulting β-lactams. 相似文献
76.
Six chiral selectors of S-(-)-t-Leu-cyclopropylamide, S-(-)-t-Leu-cyclopentylamide, S-(-)-t-Leu-cyclohexylamide, S-(-)-t-Leu-cycloheptylamide, S-(-)-t-Leu-cyclooctylamide, S-(-)-t-Leu-cyclododecylamide have been prepared and anchored individually through amide bonding to a polydimethylsiloxane functionalized with 2,2,2-trifluoroethyl ester groups by way of nucleophilic displacement reaction. The resulting chiral polysiloxanes have been provided as stationary phases for the separation of amino acid enantiomers by capillary GC. Amino acids were derivatized into N(O)-trifluoroacetyl isopropyl esters. Especially, polydimethylsiloxane anchored with S-(-)-t-Leu-cyclooctylamide was found to be efficient for the separation of aspartic acid (Asp) enantiomers. The method was applied to the estimation of ages from the extent of Asp racemization in human dentines. 相似文献
77.
78.
Ai Ito Takamasa Amaki Ayako Ishii Kazuo Fukuda Ryu Yamasaki Iwao Okamoto 《Tetrahedron letters》2018,59(45):3994-3998
Aromatic amides bearing 2-azulenyl group on the amide nitrogen were synthesized and their structures were investigated. The π-electron density of the N-aryl group was found to influence the cis-trans conformational preferences of these compounds in solution. X-ray crystallography revealed that the plane of the 2-azulenyl ring has a strong tendency to lie coplanar with the amide plane when the azulene group is located on the same side as the amide oxygen atom. 相似文献
79.
A concise synthesis of maremycins A and D1 has been accomplished via cycloaddition of a chiral cyclic nitrone with ( E)-3-ethylidene-1-methylindolin-2-one as a key step. This synthesis clarifies the stereochemistry of the maremycins and is suitable for large-scale synthesis for biological screening. 相似文献
80.
A novel oxidative cyclization of quinone-arenols 5 leading to products 6 with a dibenzofuran-1,4-dione structure, which forms the core of several natural products, has been developed and applied to the synthesis of violet-quinone (4). 相似文献