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31.
Abbotto A Beverina L Bozio R Facchetti A Ferrante C Pagani GA Pedron D Signorini R 《Organic letters》2002,4(9):1495-1498
[structure: see text]. The synthesis and nonlinear optical characterization of two novel heteroaromatic-based chromophores is described. The new dyes present an A-pi-D-pi-A general framework, where A is a pi-deficient heteroaromatic ring (pyridine, quinoline, benzothiazole) and D a pi-excessive pyrrolyl moiety. Both systems exhibit large two-photon absorption (TPA) values in the femtoseconds regime (TPA cross section as high as 150 x 10(-50) cm(4) s photon(-1) molecule(-1) with 150 fs laser pulses). Their TPA-based optical limiting activity is also shown. 相似文献
32.
The hydrolysis reactions of several title esters in water at 60 degrees C follow the rate law k(obs) = (k(a) + k(b)[OH(-)])/(1 + a(H)/K(a)), where K(a) is the ionization constant of the hydroxy group of the ester and k(b) is the second-order rate constant for the S(N)2(S) attack of hydroxide ion on the ionized ester. Hammett and Br?nsted correlations are consistent with a previous proposal that the mechanism related to k(a) is dissociative. An unusual relationship between k(a) values and redox equilibrium constants for substituted quinones is found to hold: this finding further supports the dissociative nature of the pathway related to k(a). 相似文献
33.
The synthesis of two S-proline derivatives is described together with their use as chiral ligands for lithium in reactions of n-butyllithium with benzaldehyde to give 1-phenyl-1-pentanol with moderate optical purity. The presence of lithium salts in the reaction mixture causes a decrease in asymmetric induction. 相似文献
34.
Giorgio Malesani Maria Grazia Ferlin Sergio Masiero 《Journal of heterocyclic chemistry》1983,20(2):459-460
Dehydrogenation and contemporaneous demethylation of the parent 4,9-dimethoxy-5,6,7,8-tetrahydro-1H-benz[f]indole ( 2 ) yielded the expected aromatization products 4 and 5 (1H-benz[f]indole-4,9-dione and 4,9-di-hydroxy-1H-benz[f]indole, respectively). 相似文献
35.
Cesare Oliva Anatoli V. Vishniakov Ivan E. Mukovozov Giorgio Termignone Lucio Forni 《Radiation Physics and Chemistry》1995,45(6):945-948
Evidence of quantum spin fluid and of quantum spin glass behaviour has been detected by extended EPR analysis in some La-cuprate catalysts of general formula La2−xEuxCuO4 + δ. Some features of the EPR spectrum, appearing in a few cases, are also discussed and attributed to a pseudo Jahn-Teller effect due to a particular coordination of up to five oxygen ions around surface copper ions at low temperature. 相似文献
36.
The main problem on caps, posed originally by Segre in the fifties, is to determine the values of k for which there exists a complete k-cap. Very few results on this problem are known. The cardinality of the largest cap(s) and the smallest complete cap(s) are crucial. In this paper it is shown that there exist complete k-caps in PG(3, q), q an odd prime 5 or q = 9, such that k = (q2 + q + 6)/3 or k = (q2 + 2q + 6)/3. These complete caps are smaller than those currently known for q odd.In memoriam Giuseppe Tallini 相似文献
37.
38.
39.
Giorgio Abbiati Alessandro Cirrincione de CarvalhoElisabetta Rossi 《Tetrahedron》2003,59(37):7397-7402
The cycloaddition reactions of 1-p-tolyl and 1-benzyl- 2,4-diphenyl-1,3-diazabuta-1,3-dienes with a variety of aryl and alkyl isocyanate and isothiocyanate are described. The reaction mechanism is also discussed. 相似文献
40.
Giorgio Busetto 《Annali di Matematica Pura ed Applicata》1985,142(1):91-103
Sunto Siano G e
due gruppi, : GG una proiettività e N un sottogruppo normale di G. Vengono provati alcuni risultati sulle proprietà di immersions in
e G rispettivamente, del gruppi
, la chiusura normale di N in
modulo il nocciolo di N in
, e
.
Supported by a C.N.R. grant. 相似文献
Supported by a C.N.R. grant. 相似文献