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81.
82.
Jean‐Baptiste Arlin Alan R. Kennedy Kenneth Shankland 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(2):m29-m33
Three alkaline earth metal salts of phenylacetic acid were examined and all were found to have similar structural types to analogous salts of benzoic and halobenzoic acids. Thus, a synchrotron study shows that the cations in catena‐poly[[[tetraaquamagnesium(II)]‐μ‐phenylacetato‐κ2O:O′] phenylacetate], {[Mg(C8H7O2)(H2O)4](C8H7O2)}n, form a one‐dimensional coordination polymer that propagates through Mg—O—C—O—Mg interactions involving both crystallographically independent Mg centres (Z′ = 2) and through translation along the a axis. The polymeric chains pack to give alternate inorganic layers and organic bilayers. The Ca and Sr species catena‐poly[[[diaqua(phenylacetato‐κ2O,O′)calcium(II)]‐μ3‐phenylacetato‐1′:1:1′′κ4O:O,O′:O′] monohydrate], {[Ca(C8H7O2)2(H2O)2]·H2O}n, and catena‐poly[[[diaqua(phenylacetato‐κ2O,O′)strontium(II)]‐μ3‐phenylacetato‐1′:1:1′′κ4O:O,O′:O′] monohydrate], {[Sr(C8H7O2)2(H2O)2]·H2O}n, are essentially isostructural. Both form one‐dimensional coordination polymers through a carboxylate group that forms four M—O bonds. The polymeric chains propagate via 21 screw axes parallel to the b axis and are further linked in the bc plane by hydrogen bonding involving the non‐metal‐bound water molecule. Similarly to the Mg salt, both have inorganic layers that alternate with organic bilayers. 相似文献
83.
Moine B Réhault J Aloïse S Micheau JC Moustrou C Samat A Poizat O Buntinx G 《The journal of physical chemistry. A》2008,112(21):4719-4726
The photophysical and photochemical properties of four 3,3-diphenyl-3H-naphtho[2,1- b]pyrans substituted, via an acetylenic junction, to (thiophene) n oligomers (n = 0-3 units) were investigated by transient absorption in the femtosecond to microsecond time domain and by stationary absorption and fluorescence. The decay of the initially produced excited S1(pi pi*) state is found to occur via three competing processes: fluorescence, intersystem crossing, and a ring-opening reaction leading to a colored merocyanine product, with relative yields varying drastically with n. Whereas ultrafast (sub-picosecond) reaction dynamics and high product quantum yield are observed for n = 0 and 1, the reaction is considerably slowed down on going to the n = 2 (105 ps) compound and does not occur for n = 3. A reaction scheme that accounts for this behavior is proposed and the effect of the oligothiophenic chain length on the photoinduced properties is discussed. It is suggested that increasing the chain length from 1 to 3 thiophene units stabilizes the S1(pi pi*) state by pi conjugation and induces an excited-state potential barrier along the reaction pathway. 相似文献
84.
Summary Cross-linked polystyrene-bound and poly(ethylene glycol)-bound phase-transfer catalysts as well as homopolymers of cinchona
alkaloid derivatives have been synthesised. Both soluble and insoluble polymers have been investigated. The enantioselective
alkylation of N-diphenyl methylene glycine t-butyl ester has been successfully carried out in heterogeneous and homogeneous systems. High enantioselectivities (up to
96%) have been obtained. The polymer-bound catalysts have been easily recovered and conditions for efficient recycling have
been studied. 相似文献
85.
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87.
Konstantin Artiouchine Philippe Baptiste Christoph Dürr 《European Journal of Operational Research》2008
We study a scheduling problem, motivated by air-traffic control. When aircraft reach the final descent in the “Terminal Radar Approach CONontrol” area (tracon), a set of disjoint time windows in which the landing is possible, can be automatically assigned to each aircraft. The objective is then to determine landing times, within these time windows, which maximize the minimum time elapsed between consecutive landings. We study the complexity of the problem and describe several special cases that can be solved in polynomial time. We also provide a compact Mixed Integer Programming formulation that allows us to solve large instances of the general problem when all time windows have the same size. Finally, we introduce a general hybrid branch and cut framework to solve the problem with arbitrary time windows. Experimental results show that our approach outperforms earlier formulation of the problem. 相似文献
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90.
Fluorine, the most electronegative element plays nowadays a key role in pharmaceutical, agrochemical and material sciences. About 20% of all pharmaceuticals and about 30% of agrochemicals under development or recently introduced on the market contain fluorine. However, when one examines the relevant structures more closely, one quickly recognizes a structural monotony. The same fluorine bearing aromatic or heterocyclic “cores” appear over and over again. The search for novel molecules having “emergent” fluorinated groups and the development of an efficient access toward them is a challenging task for industrial as well as academic laboratories. For example, the trifluoromethoxy group finds increased utility as a substituent in bioactives, but it is still perhaps the least well understood fluorine substituent in currency. The present review will give an updated overview on the synthesis of α-fluorinated ethers, thioethers, amines and phosphines. 相似文献