排序方式: 共有31条查询结果,搜索用时 447 毫秒
1.
2.
Salvatore Caccamese Giovanni Battista BarranoMateo Alajarin Baltasar BonilloÁngel Vidal Giuseppe BrunoGiuseppe Mazzeo Carlo Rosini 《Tetrahedron: Asymmetry》2011,22(3):270-276
The enantiomers of racemic 3,4-dihydroquinolines with an acetal or thioacetal spiro ring and a quaternary stereogenic carbon have been isolated through semipreparative chiral chromatography using a polysaccharide-derived chiral stationary phase (Chiralpak AD) and n-hexane/ethanol as a mobile phase. The absolute configurations of the enantiomers of four compounds have been determined by a comparison of density functional theory (DFT) calculations of their electronic circular dichroism (ECD) spectra with the experimental ECD data. A detailed conformer population search to achieve a conformational average of these compounds was crucial, due to the flexibility of these molecules. The conformer distribution was evaluated by spartan 02 and the structure of each of the conformers found within 4 kcal/mol energy range was optimized with DFT. The final calculated ECD spectrum obtained after Boltzmann averaging was compared with the ECD spectrum of the less well retained enantiomer and the correlation (R)/(−) was established for all compounds. The monocrystals of both enantiomers of one compound were obtained from the HPLC eluates. Their absolute configurations were determined by X-ray crystallographic analysis and confirmed by ECD analysis. In all cases, the second-eluted enantiomer in chiral HPLC exhibits an (R)-configuration. 相似文献
3.
Alajarin M Bonillo B Ortin MM Orenes RA Vidal A 《Organic & biomolecular chemistry》2011,9(19):6741-6749
N-(2-azidomethyl)phenyl ketenimines and N-(2-azidomethyl)phenyl-N'-alkyl(aryl) carbodiimides undergo, under mild thermal conditions, intramolecular [3 + 2] cycloaddition reactions between the azido group and either the C=C or the distal C=N double bonds of the ketenimine and carbodiimide functions respectively. The reaction products are indolo[1,2-a]quinazolines and/or indolo[2,1-b]quinazolines in the case of azido-ketenimines, and tetrazolo[5,1-b]quinazolines in the case of azido-carbodiimides. The formation of the two classes of indoloquinazolines implies the ulterior dinitrogen extrusion from the non-isolated, putative [3 + 2] cycloadducts between the azide and ketenimine functions, whereas in the case of azido-carbodiimides the initial cycloadducts, tetrazoloquinazolines, were cleanly isolated and further converted into 2-aminoquinazolines by thermally induced dinitrogen extrusion. 相似文献
4.
Francisco L. Hernández Baltasar Rodriguez-Salinas 《Israel Journal of Mathematics》1998,104(1):191-220
We study the setP
X
of scalarsp such thatL
p
is lattice-isomorphically embedded into a given rearrangement invariant (r.i.) function spaceX[0, 1]. Given 0<α≤β<∞, we construct a family of Orlicz function spacesX=L
F
[0, 1], with Boyd indicesα andβ, whose associated setsP
X
are the closed intervals [γ, β], for everyγ withα≤γ≤β. In particular forα>2, this proves the existence of separable 2-convex r.i. function spaces on [0,1] containing isomorphically scales ofL
p
-spaces for different values ofp. We also show that, in general, the associated setP
X
is not closed. Similar questions in the setting of Banach spaces with uncountable symmetric basis are also considered. Thus,
we construct a family of Orlicz spaces ℓ
F
(I), with symmetric basis and indices fixed in advance, containing ℓ
p
(Γ-subspaces for differentp’s and uncountable Λ⊂I. In contrast with the behavior in the countable case (Lindenstrauss and Tzafriri [L-T1]), we show that the set of scalarsp for which ℓ
p
(Γ) is isomorphic to a subspace of a given Orlicz space ℓ
F
(I) is not in general closed.
Supported in part by DGICYT grant PB 94-0243. 相似文献
5.
6.
For anyp > 1, the existence is shown of Orlicz spacesL
F andl
F with indicesp containingsingular l
p-complemented copies, extending a result of N. Kalton ([6]). Also the following is proved:Let 1 <α ≦β < ∞and H be an arbitrary closed subset of the interval [α, β].There exist Orlicz sequence spaces l
F (resp. Orlicz function spaces LF)with indices α and β containing only singular l
p-complemented copies and such that the set of values p > 1for which l
p is complementably embedded into lF (resp. L
F)is exactly the set H (resp. H ∪ {2}). An explicitly defined class of minimal Orlicz spaces is given.
Supported in part by CAICYT grant 0338-84. 相似文献
7.
Let 1<α≦β<∞ andF be an arbitrary closed subset of the interval [α,β]. An Orlicz sequence spacel
φ (resp. an Orlicz function spaceL
φ(μ)) with associated indices α and β is found in such a way that the set of valuesp for which thel
p-space is isomorphic to a complemented subspace ofl
φ (resp.L
φ(μ)) is precisely the given setF (resp.F ∪ {2}). Also, a recent result of Hernández and Peirats [1] is extended showing that, even for the case in which the indices
satisfy αφ
∞<2<βφ
∞, there exist minimal Orlicz function spacesL
φ(μ) with no complemented copy ofl
p for anyp ≠ 2.
Supported in part by CAICYT grant 0338-84. 相似文献
8.
Baltasar Rodriguez-Salinas 《Rendiconti del Circolo Matematico di Palermo》1992,41(2):295-301
It is proved that, under the Continuum Hypotesis (CH), every complete, locally determined, Radon measures of type (H), on a topological space with countable basis, is strictly localizable. This result is useful in the theory of invariant measures on a topological group and, in particular, in the theory of Hausdorff measures. 相似文献
9.
10.
Baltasar R.-Salinas 《Annali di Matematica Pura ed Applicata》1959,48(1):147-159
Sunto Si danno disuguaglianze per i coefficienti e limiti dello sviluppo asintotico di una funzione iu un angolo e disuguaglianze
per i limiti delle derivate di una funzione analitica in un angolo.
A Giovanni Sansone nel suo 70mo compleanno 相似文献