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71.
Yvette Mettey Jean-Michel Vierfond Claude Thai Marcel Miocque 《Journal of heterocyclic chemistry》1983,20(1):133-137
The action of organolithium reagents such as phenyllithium or n-bulyllithium on 2-methylquinoxaline gave lithiation of the methyl group which upon reaction with electtropholesphiles produce side chain alkenyl derivatives. On the other hand organolithium reagents react with the quinoxaline azomethine bond to give I-lithio-2-alkyl)or ary-1)-3 methylquinoxalines which can be further loithiated on the methyl group to give 2-alkyl(or aryl)-3-alkenylquinoxaline derivatives. The adducts can be condensed with clectrophiles such as benzonitrile or methlyl benzoate but only methyl benzoate leads to N condensed derivatives. Furthermore substituted 1,2,3,4-terahydroqinoxalines are available via the above lithio intermediates. 相似文献
72.
Claude Peker Michel Herlem et Janine Badoz-Lambling 《Fresenius' Journal of Analytical Chemistry》1966,224(1):302-309
Résumé L'évolution de la rapidité de la réduction électrochimique des ions Co2+, Ni2+, Pb2+, In3+ et Zn2+ dans plusieurs milieux complexants a d'abord été étudiée: l'élongation et l'étalement des pics obtenus sont donnés pour une concentration 10–5 M pour chaque ion. Ensuite la résolution des couples Zn2+/Co2+, Zn2+/Ni2+, In3+/Cd2+ et Pb2+/Tl+ a été considérée dans les mêmes milieux complexants. Pour chaque couple on donne la différence E entre les potentiels de demi-vague des éléments et l'allure des polarogrammes.
En hommage au Prof. Dr. M. von Stackelberg à l'occasion de son 70ème anniversaire.
Associé au Centre National de la Recherche Scientifique. 相似文献
Summary The electrochemical reduction rate of the ions Co2+, Ni2+, Pb2+, In3+ and Zn2+ is studied in solutions of various complexing agents. The width and the shape of the peaks for each ion in 10–5 M concentration are given. The resolution of the couples Zn2+/Co2+, Zn2+/Ni2+, In3+/Cd2+ and Pb2+/Tl+ in the same electrolytes is shown hereafter. The difference E of the half-wave potentials and the behaviour of the polarograms for each couple is given.
Zusammenfassung Die Abhängigkeit der elektrochemischen Reduktionsgeschwindigkeit von verschiedenen Komplexbildnern wird am Beispiel der Ionen Co2+, Ni2+, Pb2+, In3+ und Zn2+ untersucht. Ausdehnung und Form der Polarogramme werden für jedes Element in 10–5 m Lösung angegeben. In den gleichen komplexbildenden Elektrolyten wird sodann die Trennung der Ionen Zn2+/Co2+, Zn2+/Ni2+, In3+/Cd2+ und Pb2+/Tl+ untersucht. Für jede Ionenkombination wird die Halbstufenpotentialdifferenz E angegeben und das Polarogramm erläutert.
En hommage au Prof. Dr. M. von Stackelberg à l'occasion de son 70ème anniversaire.
Associé au Centre National de la Recherche Scientifique. 相似文献
73.
The kinetics of the copolymerization of methyl methacrylate and maleic anhydride was investigated in benzenic solutions at 60 and 70° C and in bulk at 60°C. The microstructure of the copolymers was determined by 1H-NMR and IR spectrophotometry. In benzene solutions the mechanism of copolymerization involves the participation of an associative species between both comonomers. In bulk a terminal model is sufficient to explain all the results. 相似文献
74.
75.
76.
Alain C Schuler BM McDonald KL 《The Journal of the Acoustical Society of America》2002,111(2):990-995
The neural processes underlying concurrent sound segregation were examined by using event-related brain potentials. Participants were presented with complex sounds comprised of multiple harmonics, one of which could be mistuned so that it was no longer an integer multiple of the fundamental. In separate blocks of trials, short-, middle-, and long-duration sounds were presented and participants indicated whether they heard one sound (i.e., buzz) or two sounds (i.e., buzz plus another sound with a pure-tone quality). The auditory stimuli were also presented while participants watched a silent movie in order to evaluate the extent to which the mistuned harmonic could be automatically detected. The perception of the mistuned harmonic as a separate sound was associated with a biphasic negative-positive potential that peaked at about 150 and 350 ms after sound onset, respectively. Long duration sounds also elicited a sustained potential that was greater in amplitude when the mistuned harmonic was perceptually segregated from the complex sound. The early negative wave, referred to as the object-related negativity (ORN), was present during both active and passive listening, whereas the positive wave and the mistuning-related changes in sustained potentials were present only when participants attended to the stimuli. These results are consistent with a two-stage model of auditory scene analysis in which the acoustic wave is automatically decomposed into perceptual groups that can be identified by higher executive functions. The ORN and the positive waves were little affected by sound duration, indicating that concurrent sound segregation depends on transient neural responses elicited by the discrepancy between the mistuned harmonic and the harmonic frequency expected based on the fundamental frequency of the incoming stimulus. 相似文献
77.
Acousto-optic (AO) imaging is a promising technique that is able to reveal optical properties in the millimeter range inside scattering media by tagging the photon paths with an ultrasonic beam. To increase both the contrast and the resolution of the AO images, we have explored the possibility of using the nonlinear response of the speckle modulation. Variation of the second-harmonic signal as the square of the ultrasonic amplitude has been found, and strong reduction of the tagged zone size has been demonstrated. 相似文献
78.
We build an irreducible unitary representation of SO( ) from the usual one of SO( n ) in the space of harmonic homogeneous polynomials of degree m of
n
. We give a characterization of these new representations which extends in a natural way the finite dimensional characterization. In the particular case of SO( ), we thus get some results of Olshanskii (cf. [12]). This leads to a new proof of McKean conjecture about irreducible representations of ( infin ) (cf. [10]). 相似文献
79.
Claude LeBrun 《Mathematische Annalen》1991,289(1):383-392
Work supported in part by NSF Grant #DMS-8704401 相似文献
80.