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Garcia Ruano JL Alcudia A del Prado M Barros D Maestro MC Fernandez I 《The Journal of organic chemistry》2000,65(10):2856-2862
The addition of the lithium anions derived from (R)- and (S)-methyl and -ethyl p-tolyl sulfoxides to (S)-N-benzylidene-p-toluenesulfinamide provides an easy access route to enantiomerically pure beta-(N-sulfinyl)amino sulfoxides. Stereoselectivity can be achieved when the configurations at the sulfur atoms of the two reagents are opposite (matched pair), thus resulting in only one diastereoisomer, even for the case in which two new chiral centers are created. The N-sulfinyl group primarily controls the configuration of the carbon bonded to the nitrogen, whereas the configuration of the alpha-sulfinyl carbanion seems to be responsible for the level of asymmetric induction, as well as for the configuration of the new stereogenic C-SO carbon in the reactions with ethyl p-tolyl sulfoxides. An efficient method for transforming the obtained beta-(N-sulfinyl)amino sulfoxides into optically pure beta-amino alcohols, based on the stereoselective non-oxidative Pummerer reaction, is also reported. 相似文献
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Garcia Ruano JL Alemparte C Martin Castro AM Adams H Rodriguez Ramos JH 《The Journal of organic chemistry》2000,65(23):7938-7943
The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles. 相似文献
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The space group of alpha(')-NaV2O5 turns below T(c) = 34 K from Pmmn with all V sites equivalent, into Fmm2 with three independent vanadium sites per layer. This is incompatible with models of charge ordering into V4+ and V5+. Our structure determination indicates that the phase transition consists of a charge ordering with three distinct valence states, formally V4+, V4.5+, and V5+. The singlet formation is not associated with dimerization on the spin ladder, but with the formation of spin clusters. Finally, we ascribe the quadrupling of the c axis to the large polarizability of the V2O5 skeleton. 相似文献
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Acoustic performance in ultrasonic transmitters can be improved by means of a suitable electrical driving response and matching/tuning networks. It is important to predict this electrical response, but doing so is not easy because it departs notably from the nominal pattern with the loading probes. In practice, the analysis of HV pulser spikes in NDE applications requires fairly complex models in the transient regime and, in addition, non-linear problems could arise, especially in the case of tuned transmitters. In this paper, the most relevant influences of loading characteristics of NDT ultrasonic probes on the pulser electrical driving responses are evaluated in time and frequency domains. Conventional pulse generators and typical NDE pulsers are considered. Driving responses are analysed across commercial ultrasonic probes and, alternatively, across similar purely electrical loads. Distinct influences on pulser responses from electrical and motional sections of the probes are identified. All these aspects are studied on the basis of experimental and computer results. 相似文献
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Ascher P Audirac L Adimi N Blank B Borcea C Brown BA Companis I Delalee F Demonchy CE de Oliveira Santos F Giovinazzo J Grévy S Grigorenko LV Kurtukian-Nieto T Leblanc S Pedroza JL Perrot L Pibernat J Serani L Srivastava PC Thomas JC 《Physical review letters》2011,107(10):102502
The two protons emitted in the decay of 54Zn have been individually observed for the first time in a time projection chamber. The total decay energy and the half-life measured in this work agree with the results obtained in a previous experiment. Angular and energy correlations between the two protons are determined and compared to theoretical distributions of a three-body model. Within the shell model framework, the relative decay probabilities show a strong contribution of the p2 configuration for the two-proton emission. After 45Fe, the present result on 54Zn constitutes only the second case of a direct observation of the ground state two-proton decay of a long-lived isotope. 相似文献
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B. Blank A. Bey I. Matea J. Souin L. Audirac M. J. G. Borge G. Canchel P. Delahaye F. Delalee C. -E. Demonchy R. Domínguez-Reyes L. M. Fraile J. Giovinazzo Tran Trong Hui J. Huikari D. Lunney F. Munoz J. -L. Pedroza C. Plaisir L. Serani S. Sturm O. Tengblad F. Wenander 《The European Physical Journal A - Hadrons and Nuclei》2010,44(3):363-372
The half-lives of 38Ca and 39Ca have been measured at ISOLDE of CERN. The REXTRAP facility was used to prepare ultra-clean samples of radioactive nuclei for precision decay spectroscopy. 38Ca is one of the T z = - 1 , 0+ $ \rightarrow$ 0+ $ \beta$ -emitting nuclides used to determine the vector coupling constant of the weak interaction and the Vud quark-mixing matrix element. The result obtained, T 1/2 = 443.8(19) ms, is four times more precise than the average of previous measurements. For 39Ca , a half-life of T 1/2 = 860.7(10) ms is obtained, a result in agreement with the average value from the literature. 相似文献
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L. Audirac P. Ascher B. Blank C. Borcea B. A. Brown G. Canchel C. E. Demonchy F. de Oliveira Santos C. Dossat J. Giovinazzo S. Grévy L. Hay J. Huikari S. Leblanc I. Matea J. -L. Pedroza L. Perrot J. Pibernat L. Serani C. Stodel J. -C. Thomas 《The European Physical Journal A - Hadrons and Nuclei》2012,48(12):1-12
The two-proton radioactivity of 45Fe was studied experimentally with a time projection chamber. The aim of the experiment was the reconstruction of the proton tracks in three dimensions. Energy and angular correlations have been determined and the data are compared with theoretical models, in particular with a three-body model. Moreover, the decay of 43Cr was studied and ??-delayed one-, two- and three-proton emission could be established. The correlations observed for ??-delayed two-proton emission favour a sequential emission. Finally, ??-delayed two-proton emission was observed for the first time for 51Ni. 相似文献
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M. Lach P. Bednarczyk A. Bracco J. Grębosz M. Kadłuczka N. Kintz A. Maj J.C. Merdinger W. Męczyński J.L. Pedroza N. Schulz M.B. Smith K.M. Spohr J. Styczeń J.P. Vivien M. Ziębliński 《The European Physical Journal A - Hadrons and Nuclei》2001,12(4):381-382
High-spin states of the 44Ca nucleus populated in the 68 MeV 18O + 30Si reaction have been studied in a γ-γ-recoil coincidence experiment. The level scheme of 44Ca has been extended up to 12.2 MeV. In particular, the negative-parity band has been identified with the highest I = 13- level at 10.6 MeV. This state is interpreted as the band-terminating state for the ( d
3/2
-1
f
7/2
5) configuration.
Received: 7 November 2001 / Accepted: 3 December 2001 相似文献
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