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191.
Fernández I Duvall M I-Chia Wu J Schleyer Pv Frenking G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(7):2215-2224
The nature of the bonding and the aromaticity of the heavy Group 14 homologues of cyclopropenylium cations E3H3+ and E2H2E′H+ (E, E′=C–Pb) have been investigated systematically at the BP86/TZ2P DFT level by using several methods. Aromatic stabilization energies (ASE) were evaluated from the values obtained from energy decomposition analysis (EDA) of charged acyclic reference molecules. The EDA‐ASE results compare well with the extra cyclic resonance energy (ECRE) values given by the block localized wavefunction (BLW) method. Although all compounds investigated are Hückel 4n+2 π electron species, their ASEs indicate that the inclusion of Group 14 elements heavier than carbon reduces the aromaticity; the parent C3H3+ ion and Si2H2CH+ are the most aromatic, and Pb3H3+ is the least so. The higher energies for the cyclopropenium analogues reported in 1995 employed an isodesmic scheme, and are reinterpreted by using the BLW method. The decrease in the strength of both the π cyclic conjugation and the aromaticity in the order C?Si>Ge>Sn>Pb agrees reasonably well with the trends given by the refined nucleus‐independent chemical shift NICS(0)πzz index. 相似文献
192.
Alcaide B Almendros P Martínez del Campo T Redondo MC Fernández I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(52):15005-15013
An efficient chemodivergent metal-controlled methodology for the generation of different highly functionalized oxygen heterocycles from common enallenol substrates has been developed. Chemoselectivity control in the O-C functionalization of an enallenol can be achieved through the choice of catalyst: AuCl(3), PdCl(2), and [PtCl(2)(CH(2)=CH(2))](2) exclusively afford dihydrofurans through selective activation of the allenol moiety, whereas FeCl(3) solely gives tetrahydrofurans or tetrahydropyrans through selective activation of the alkenol moiety. We have also shown that a combination of metal-mediated hydroalkoxylation and allenic aminocyclization reactions can lead to a useful preparation of the tetrahydrofuro[3,2-b]piperidine core of the antimalarial alkaloid isofebrifugine. These divergent heterocyclization reactions have been developed experimentally and additionally, their mechanisms have been investigated by a theoretical study. 相似文献
193.
Suarez E Nguyen HP Ortiz IP Lee KJ Kim SB Krzywinski J Schug KA 《Analytica chimica acta》2011,706(1):157-163
Malaria is a devastating mosquito-borne disease, which affects hundreds of millions of people each year. It is transmitted predominantly by Anopheles gambiae, whose females must be >10 days old to become infective. In this study, cuticular lipids from a laboratory strain of this mosquito species were analyzed using a mass spectrometry method to evaluate their utility for age, sex and mating status differentiation. Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS), in conjunction with an acenaphthene/silver nitrate matrix preparation, was shown to be 100% effective in classifying A. gambiae females into 1, 7–10, and 14 days of age. MALDI-MS analysis, supported by multivariate statistical methods, was also effective in detecting cuticular lipid differences between the sexes and between virgin and mated females. The technique requires further testing, but the obtained results suggest that MALDI-MS cuticular lipid spectra could be used for age grading of A. gambiae females with precision greater than with other available methods. 相似文献
194.
E. V. Orlova A. E. Goldberg M. A. Kiskin P. S. Koroteev A. L. Emelina M. A. Bykov G. G. Aleksandrov Zh. V. Dobrokhotova V. M. Novotortsev I. L. Eremenko 《Russian Chemical Bulletin》2011,60(11):2236-2250
Binuclear heterometallic complexes (??2-bpy)CoLn(Piv)5(H2O), (??2-bpy)NiLn(Piv)5(H2O), and (??2-bpy)CuLn(Piv)5(HPiv) (Ln = Sm or Gd, Piv- is the pivalate anion) were synthesized. A comparative study of the structural characteristics and the thermolysis of the resulting compounds was performed. 相似文献
195.
Felix Goldberg 《Linear algebra and its applications》2011,434(7):1656-1662
Let μ(G) and ω(G) be the Colin de Verdière and clique numbers of a graph G, respectively. It is well-known that μ(G)?ω(G)-1 for all graphs. Our main results include μ(G)?ω(G) for all chordal graphs; μ(G)?tw(G)+1 for all graphs (where tw is the tree-width), and a characterization of those split (⊆ chordal) graphs for which μ(G)=ω(G). The bound μ(G)?tw(G)+1 improves a result of Colin de Verdière by a factor of 2. 相似文献
196.
In an attempt to perform a simple anion-exchange reaction on a pincer-carbene-ligated nickel complex using AgNO(3), we instead obtained an unexpected three-dimensional (3D) Ag(7) cluster containing a [Ag(6)] core in a twisted-bowtie geometry. The reverse-transmetalation reaction by which the carbene is transferred from nickel to silver is virtually unprecedented. The CNC pincer-carbene ligands exhibit unusual bridging modes of ligand bonding for all three donor atoms. Another unique feature is that the final structure exhibits a 3D structure brought about by the connection of two-dimensional layers of the [Ag(6)] core via a seventh Ag ion. 相似文献
197.
198.
A. Tschirsch Elmar Goldberg und A. B. Stevens 《Fresenius' Journal of Analytical Chemistry》1907,46(5):347-349
Ohne Zusammenfassung 相似文献
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