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R. W. Lourie 《Zeitschrift fur Physik C Particles and Fields》1991,50(2):345-351
We calculate the recoil polarization observables for neutral pion electroproduction on the proton. In particular, for theN(938)→N *(1440) transition, we study these observables for several quark models of the resonant amplitudes. We find that the polarization response functions, unlike the unpolarized cross section, have encouragingly large sensitivity to the presence of the Roper. Furthermore, these observables can clearly reveal the presence of a longitudinal coupling. 相似文献
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Yurii A. Serguchev Maxim V. Ponomarenko Lyudmila F. Lourie Andrey A. Fokin 《Journal of Physical Organic Chemistry》2011,24(5):407-413
The addition of 1‐chloromethyl‐4‐fluoro‐1,4‐diazoniabicyclo[2.2.2]octane bis‐tetrafluoroborate (F‐TEDA) to unsaturated systems was modelled computationally at the ab initio levels and studied experimentally. The reaction of olefins with F‐TEDA is driven exclusively by charge transfer and displays the antibonding orbital picture in the transition structure for F‐transfer, similarly to that for the reactions of olefins with F‐radical. In contrast, the electrophilic and concerted fluorinations, respectively with H2O???F+ complex and with F2, show strong bonding interactions between the fluorine and olefin moieties in the transition structures. The reaction with F‐TEDA involves an initial formation of highly delocalized charge‐transfer complexes in the first step with further low‐barrier (ca 4 kcal) migration of fluorine and is best described as an inner‐sphere electron transfer. This nonelectrophilic mechanism is operative for the transannular addition of F‐TEDA to 3‐methylene‐7‐ethylidenebicyclo[3.3.1]nonane studied experimentally. The addition mode is determined by the formation of a more stable complex via the ethylidene fragment and demonstrates selectivities that differ from conventional electrophilic additions. This mechanistic scenario may be extended to the fluorination with xenon difluoride where similar products are formed in high yields. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Lyudmila F. Lourie Galina V. Shevchenko Alexander N. Chernega Eduard B. Rusanov Judith A.K. Howard 《Journal of fluorine chemistry》2006,127(3):377-385
The selective fluorolactonization was achieved by treatment of cis-5-norbornene-2,3-endo-dicarboxylic acid or its monomethyl and dimethyl esters with F-TEDA-BF4 or XeF2. The reactions of 5-norbornene-endo-2-carboxylic acid and its monomethyl ester with F-TEDA-BF4 or XeF2 proceed in a non-selective manner to give fluorolactonization, addition and rearrangement products. The basic factor responsible for selectivity of the fluorolactonization is the presence of two endo-oriented carboxyl groups in the substrate molecule. The electrophilicity and type of the fluorinating agent is of secondary importance in this regard. It is postulated that the fluorolactonization of norbornenecarboxylic acids and their methyl esters with F-TEDA-BF4 or XeF2 is realized mainly via “open” fluoronorbornyl carbocation intermediates which in the reaction with XeF2 are postulated as the tight ion pairs. 相似文献
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