排序方式: 共有195条查询结果,搜索用时 78 毫秒
51.
Company A Lamata D Poater A Solà M Rybak-Akimova EV Que L Fontrodona X Parella T Llobet A Costas M 《Inorganic chemistry》2006,45(14):5239-5241
Two dicopper(I) complexes containing tertiary N-methylated hexaaza ligands which impose different steric constraints to the Cu ions have been synthesized, and their reactivity toward O2 has been compared with a mononuclear related system, highlighting the importance of cooperative effects between the metal centers in O2 activation. 相似文献
52.
[reaction: see text] A readily available chiral amino alcohol has been immobilized on silica by sol-gel synthesis and grafting. The solid prepared according to the latter method led to the best enantioselectivity (77% ee) described for the asymmetric addition of diethylzinc to benzaldehyde using inorganic solids. 相似文献
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54.
Atomic Fukui indices, which are obtained from the electron density, have been previously shown to be useful in predicting which atoms in a molecule are most likely to suffer nucleophilic, electrophilic, or radicalary attacks. Here, we present a second-order generalization of these indices based on the electron pair density. We show how second-order atomic Fukui indices can be used to analyze the effects of electron loss or gain in several molecules from an electron pair point of view. Further, these indices also highlight which atoms or pairs of atoms are more likely to suffer nucleophilic, electrophilic, or radical attacks. In conclusion, second-order indices can complement first-order ones by affording relevant information on molecular reactivity from an electron pair perspective. 相似文献
55.
Alvarez A Ochoa E Verdecia Y Suárez M Solá M Martín N 《The Journal of organic chemistry》2005,70(8):3256-3262
The 1,3-dipolar cycloaddition of azomethine ylides bearing the biologically active 1,4-dihydropiridine ring to C(60) was investigated by means of quantum mechanical calculations at the semiempirical AM1 and DFT (B3LYP/6-31G) methods. The presence of two chiral centers and one chiral axis in the resulting fulleropyrrolidines leads to four possible [6,6] cycloaddition products. Formation of atropoisomers has also been considered. The transition-state structures were computed for the four different cycloaddition pathways to find out the lowest activation energy stereoisomer. In all cases, a frequency analysis and an IRC calculation were carried out to fully characterize the located transition-state structures. AM1 results and single-point energy calculations at the B3LYP/6-31G//AM1 level for the four transition-state structures yield activation energies values below 5 kcal/mol. 相似文献
56.
The enzyme-catalysed reduction of nitrate was studied utilising Aspergillus niger nitrate reductase (NR) and phenosafranin in solution as the enzyme regenerator, working at lower potentials than that of the more common methyl viologen mediator. Cyclic voltammograms when enzyme, phenosafranin and substrate were together put in evidence the enzyme-catalysed reduction of nitrate, although with a relatively slow kinetics. From slope values not dependent on mediator concentration, the apparent Michaelis-Menten constant was evaluated. Analytical parameters for the enzyme-modified electrode in the presence of phenosafranin for the determination of nitrate content in water were assessed, including a recovery assay for nitrate added to a river water sample. The stability of the electrode was checked. 相似文献
57.
Fontes M Verdaguer X Solà L Vidal-Ferran A Reddy KS Riera A Pericàs MA 《Organic letters》2002,4(14):2381-2383
[reaction: see text] The addition of diethylzinc to dicobalt hexacarbonyl complexes of acetylenes mediated by (R)-2-piperidino-1,1,2-triphenylethanol takes place with very high enantioselectivity (96-99% ee) to afford the S enantiomers of dicobalt hexacarbonyl complexes of 1-alkynyl-1-propanols. The utility of this process is exemplified by the development of a short, highly enantioselective (99% ee) synthesis of unnatural incrustoporin. 相似文献
58.
In this work, we have analyzed the local aromaticity of the six-membered rings (6-MRs) of planar and pyramidalized pyracylene species through the structurally based harmonic oscillator model of aromaticity (HOMA), the electronically based para-delocalization index (PDI), and the magnetic-based nucleus independent chemical shift (NICS) measurements, as well as with maps of ring current density. According to ring currents and PDI and HOMA indicators of aromaticity, there is a small reduction of local aromaticity in the 6-MRs of pyracylene with a bending of the molecule. In the case of NICS, the results depend on whether the NICS value is calculated at the center of the ring (NICS(0)) or at 1 A above (NICS(1)(out)) or below (NICS(1)(in)) the ring plane. While NICS(1)(out) values also indicate a slight decrease of aromaticity with bending, NICS(0) and NICS(1)(in) wrongly point out a large increase of aromaticity upon distortion. We have demonstrated that the NICS(0) reduction in the 6-MRs of pyracylene upon bending is due to (a) a strong reduction of the paratropic currents in 5-MRs and (b) the fact that, due to the distortion, the paratropic currents point their effects in other directions. 相似文献
59.
Poater J Fradera X Duran M Solà M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(2):400-406
This work introduces a new local aromaticity measure, defined as the mean of Bader's electron delocalization index (DI) of para-related carbon atoms in six-membered rings. This new electronic criterion of aromaticity is based on the fact that aromaticity is related to the cyclic delocalized distribution of pi-electrons. We have found that this DI and the harmonic oscillator model of aromaticity (HOMA) index are strongly correlated for a series of six-membered rings in eleven planar polycyclic aromatic hydrocarbons. The correlation between the DI and the nucleus-independent chemical shift (NICS) values is less remarkable, although in general six-membered rings with larger DI values also have more negative NICS indices. We have shown that this index can also be applied, with some modifications, to study of the aromaticity in five-membered rings. 相似文献
60.
Diastereoselective synthesis of fulleropyrrolidines from suitably functionalized chiral cyclobutanes
Illescas BM Martín N Poater J Solà M Aguado GP Ortuño RM 《The Journal of organic chemistry》2005,70(17):6929-6932
The first diastereoselective synthesis of fulleropyrrolidines endowed with diastereomerically pure functionalized cyclobutanes is reported. The new C(60)-based cyclobutane derivatives 7a,b and 9 are suitably functionalized for further incorporation into peptide surrogates. 相似文献