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61.
Alejandra Salemo Graciela Buldain Isabel A. Perillo 《Journal of heterocyclic chemistry》2001,38(4):849-852
1H NMR spectra of a series of 1,2 and 1,3‐diarylimidazolidines are analyzed and correlated with their conformational features. Results were interpreted on the basis of chemical shifts and coupling constants of hydrogen atoms and confirmed by ID nOe difference experiments. 1,3‐Diarylimidazolidines ( 1–7 ) show a fast inversion of the N‐aryl nitrogen in all studied cases. 1,2‐Diaryl‐3‐methyl (or benzyl) imidazolidines ( 8–13 ) display a preferential conformation with a transoid orientation of N3 and C2 substituents. 相似文献
62.
Dediazoniation of 1-naphthalenediazonium tetrafluoroborate in aqueous acid and in micellar solutions
Carlos Bravo-Diaz Maria Jose Pastoriza-Gallego Sonia Losada-Barreiro Veronica Sanchez-Paz Alejandra Fernandez-Alonso 《国际化学动力学杂志》2008,40(6):301-309
We have measured the rates and product yields of dediazoniation of 1-naphthalenediazonium (1ND) tetrafluoroborate in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by employing a combination of UV–vis spectroscopy and high-performance liquid chromatography (HPLC) measurements. Kinetic data were obtained by a derivatization procedure with product yields were determined by HPLC. HPLC chromatograms show that in aqueous acid and in micellar solutions only one dediazoniation product is formed in significant quantities, 1-naphthol (NOH), and the observed rate constants (kobs) are the same when 1ND loss is monitored spectrometrically and when NOH formation is monitored by HPLC. Activation parameters were obtained both in the presence and absence of SDS micellar aggregates. In both the systems, the enthalpies of activation are high and the entropies of activation are positive. The enthalpy of activation in the absence of SDS is very similar to that in the presence of SDS micelles, but the entropy of activation is lower by a factor of 4. As a consequence, SDS micelles speed up the thermal decomposition of 1ND and increase kobs by a factor of 1.5 when [SDS] = 0.02 M. In contrast, results obtained in the presence of complexing systems such as crown ethers and polyethers show significant stabilization of the parent arenediazonium ions. Kinetic and HPLC data are consistent with the heterolytic DN + AN mechanism that involves the rate-determining fragmentation of the arenediazonium ion into a very reactive phenyl cation that reacts competitively with available nucleophiles. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 301–309, 2008 相似文献
63.
We report an experimental study of group-velocity dispersion effect on an entangled two-photon wave packet, generated via spontaneous parametric down-conversion and propagating through a dispersive medium. Even in the case of using cw laser beam for pump, the biphoton wave packet and the second-order correlation function spread significantly. The study and understanding of this phenomenon is of great importance for quantum information applications, such as quantum communication and distant clock synchronization. 相似文献
64.
Emilie Barriau Alejandra García Marcos Holger Kautz Holger Frey 《Macromolecular rapid communications》2005,26(11):862-867
Summary: A convenient three‐step strategy has been developed for the preparation of well‐defined amphiphilic, linear‐hyperbranched block copolymers by hypergrafting. The synthetic procedure is based on a combination of carbanionic polymerization with the alkoxide‐based, controlled ring‐opening multibranching polymerization of glycidol. A linear AB diblock copolymer polystyrene‐block‐polybutadiene (PS‐b‐PB) with narrow polydispersity was obtained by anionic copolymerization. Subsequent hydroxylation by hydroboration led to PS508‐b‐(PB‐OH)56, used as macroinitiator for the polymerization of glycidol under slow monomer addition conditions.
65.
66.
Mónica Alejandra Herrera María Rosende Marco Aurélio Zezzi Arruda Manuel Miró 《Analytica chimica acta》2016
In-vitro physiologically relevant gastrointestinal extraction based on the validated Unified BARGE Method (UBM) is in this work hyphenated to inductively coupled plasma optical emission spectrometry in a batch-flow configuration for real-time monitoring of oral bioaccessibility assays with high temporal resolution. A fully automated flow analyzer is designed to foster in-line filtration of gastrointestinal extracts at predefined times (≤15 min) followed by on-line multi-elemental analysis of bioaccessible micro-nutrients, viz., Cu, Fe and Mn, in well-defined volumes of extracts (300 μL) of transgenic and non-transgenic soybean seeds taken as model samples. 相似文献
67.
A convenient two-step procedure for the synthesis of primary (Z)-allyl amines, (Z)-homoallyl amines [(Z)-but-3-enylamines], and (Z)-pent-4-enylamines using the Wittig reaction was achieved. The use of nonstabilized ylides from triphenylphosphonium salt, potassium salt, and apolar solvent produced (Z/E)-geometric isomer ratios generally greater than 1.6. The amine moiety was masked using a phtalimide group that was removed successfully in the last step of the process in two different conditions, NH2NH2/EtOH/rt or CH3NH2/EtOH/rt. However, in some cases, reduction of the C = C double bond in the deprotection with hydrazine was concomitantly observed. 相似文献
68.
Carmen S. Renamayor Alejandra Pastoriza Cesar L. Usma Ines F. Pierola 《Colloid and polymer science》2013,291(10):2439-2446
Ionic liquids extend the Hofmeister series and create a wide range of new possibilities for processes involving salt effects on both soluble and crosslinked systems. This work reports on some mixtures of water with NaCl or an ionic liquid, either 1-ethyl-3-methylimidazolium tosylate or 1-hexyl-3-methylimidazolium chloride, which are better solvents for linear poly(N-vinylimidazole) (L-PVI) than water, i.e., that exhibit a salting-in effect. The intensity of the salt effects was measured on the basis of the polymer solubility, the decrease in polymer–solvent interaction parameter (measured by light scattering), and the increase of coil size (measured through the intrinsic viscosity). It was thus found that the intensity of the salting-in effect of either NaCl or 1-hexyl-3-methylimidazolium chloride on L-PVI is different (larger for the ionic liquid), which denotes that salt effects are not under anion control, and the mechanisms operating in the linear and crosslinked polymers are different. These results are discussed after accounting for the role of ion–polymer interactions. 相似文献
69.
We report the synthesis of new prochiral imines by the reaction of nonsymmetric benzophenone derivates, bencylamines, and anilines in good yields. All the products were characterized by 1H and 13C NMR as an isomeric E/Z mixture. Also, the molecular structures for five derivatives determined by single-crystal x-ray experiments are presented. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
70.
We propose a generalisation of the congruence subgroup problem for groups acting on rooted trees. Instead of only comparing the profinite completion to that given by level stabilizers, we also compare pro-
$$\mathcal {C}$$
completions of the group, where
$$\mathcal {C}$$
is a pseudo-variety of finite groups. A group acting on a rooted, locally finite tree has the
$$\mathcal {C}$$
-congruence subgroup property (
$$\mathcal {C}$$
-CSP) if its pro-
$$\mathcal {C}$$
completion coincides with the completion with respect to level stabilizers. We give a sufficient condition for a weakly regular branch group to have the
$$\mathcal {C}$$
-CSP. In the case where
$$\mathcal {C}$$
is also closed under extensions (for instance the class of all finite p-groups for some prime p), our sufficient condition is also necessary. We apply the criterion to show that the Basilica group and the GGS-groups with constant defining vector (odd prime relatives of the Basilica group) have the p-CSP. 相似文献