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1.
MNDO has been parametrized for bromine. Since d atomic orbitals (AOS) are not included, the calculations are restricted to BrI. Heats of formation, molecular geometries, ionization energies, and dioole moments are reproduced with useful accuracy. 相似文献
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We analyze the general features of the formation and interaction of transverse traveling waves and the appearance of filamentation in broad area semiconductor lasers with current profiling. For small apertures, the emitted profile is symmetric consisting of two counterpropagating transverse traveling waves, both emanating from the center of the device. For larger apertures, the emission becomes asymmetric as one of the traveling waves expands to occupy an increased area while the other occupies the remaining, smaller spatial region. In both devices, the pattern becomes unstable at higher injection currents due to optical filamentation, although an intermediate state is present in the wider device whereby the dominant wave undergoes a Hopf bifurcation before filamentation occurs. 相似文献
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Szabó T Bakandritsos A Tzitzios V Devlin E Petridis D Dékány I 《The journal of physical chemistry. B》2008,112(46):14461-14469
Loading of graphite oxide (GO) with tris(2,2'-bipyridyl) iron(II) ions and subsequent calcination affords a novel graphene-based composite with magnetic and electrically conductive properties. The pH of the starting aqueous suspension and the washing procedure play a crucial role in the successful immobilization of the iron precursor, which is mainly governed by ion exchange. The complex is intercalated between the graphene oxide layers, where it adopts a distorted conformation. Rapid heating of this solid results in the deflagration of GO and the formation of ultrafine ( d = 2-14 nm) Fe2O3 particles with maghemite as the dominant phase. The superparamagnetic maghemite crystals are dispersed uniformly in the high-surface-area diamagnetic matrix built up from single or turbostratic stacked graphenes. 相似文献
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Dugal-Tessier J Serin SC Castillo-Contreras EB Conrad ED Dake GR Gates DP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(20):6349-6359
The design of a synthetic route to a class of enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha-Peterson reaction) was used as the P=C bond-forming step. Attempted condensation of PhC(=O)Ox (Ox = CNOCH(iPr)CH(2)) and MesP(SiMe(3))Li gave the unusual heterocycle (MesP)(2)C(Ph)=CN-(S)-CH(iPr)CH(2)O (3). However, PhAk-Ox (S,E)-MesP=C(Ph)CMe(2)Ox (1?a) was successfully prepared by treating MesP(SiMe(3))Li with PhC(=O)CMe(2)Ox (52?%). To demonstrate the modularity and tunability of the phospha-Peterson synthesis several other phosphaalkene-oxazolines were prepared in an analogous manner to 1?a: TripP=C(Ph)CMe(2)Ox (1?b; Trip = 2,4,6-triisopropylphenyl), 2-iPrC(6)H(4)P=C(Ph)CMe(2)Ox (1?c), 2-tBuC(6)H(4)P=C(Ph)CMe(2)Ox (1?d), MesP=C(4-MeOC(6)H(4))CMe(2)Ox (1?e), MesP=C(Ph)C(CH(2))(4)Ox (1?f), and MesP=C(3,5-(CF(3))(2)C(6)H(3))C(CH(2))(4)Ox (1?g). To evaluate the PhAk-Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1?a and styrene were subjected to radical-initiated copolymerization conditions to afford [{MesPC(Ph)(CMe(2)Ox)}(x){CH(2)CHPh}(y)](n) (9?a: x = 0.13n, y = 0.87n; GPC: M(w) = 7400?g mol(-1) , PDI = 1.15). 相似文献
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Julien Dugal‐Tessier Spencer C. Serin Emmanuel B. Castillo‐Contreras Dr. Eamonn D. Conrad Prof. Dr. Gregory R. Dake Prof. Dr. Derek P. Gates 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(20):6349-6359
The design of a synthetic route to a class of enantiomerically pure phosphaalkene–oxazolines (PhAk‐Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha‐Peterson reaction) was used as the P?C bond‐forming step. Attempted condensation of PhC(?O)Ox (Ox=CNOCH(iPr)C H2) and MesP(SiMe3)Li gave the unusual heterocycle (MesP)2C(Ph)?CN‐(S)‐CH(iPr)CH2O ( 3 ). However, PhAk‐Ox (S,E)‐MesP?C(Ph)CMe2Ox ( 1 a ) was successfully prepared by treating MesP(SiMe3)Li with PhC(?O)CMe2Ox (52 %). To demonstrate the modularity and tunability of the phospha‐Peterson synthesis several other phosphaalkene–oxazolines were prepared in an analogous manner to 1 a : TripP?C(Ph)CMe2Ox ( 1 b ; Trip=2,4,6‐triisopropylphenyl), 2‐iPrC6H4P?C(Ph)CMe2Ox ( 1 c ), 2‐tBuC6H4P?C(Ph)CMe2Ox ( 1 d ), MesP?C(4‐MeOC6H4)CMe2Ox ( 1 e ), MesP?C(Ph)C(CH2)4Ox ( 1 f ), and MesP?C(3,5‐(CF3)2C6H3)C(CH2)4Ox ( 1 g ). To evaluate the PhAk‐Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1 a and styrene were subjected to radical‐initiated copolymerization conditions to afford [{MesPC(Ph)(CMe2Ox)}x{CH2CHPh}y]n ( 9 a : x=0.13n, y=0.87n; GPC: Mw=7400 g mol?1, PDI=1.15). 相似文献
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Eamonn JoycePaul Kavanagh Dónal LeechJolanta Karpinska Patrick McArdleFawaz Aldabbagh 《Tetrahedron letters》2012,53(29):3788-3791
Acetic anhydride mediates a facile and rapid condensation of benzimidazole with aromatic o-diacid dichlorides to precipitate p-dione adducts in excellent yields. Condensation with pyridine-3,4-dicarbonyl dichloride produced a 1:1 mixture of isomeric p-diones. The X-ray crystal structure of one of the latter isomers revealed unusual high density, and inter-layer separation similar to graphite. Cyclic voltammetry demonstrated that p-dione is capable of two consecutive one-electron-reductions with formal potentials influenced by the fused (hetero)aromatic and substituent effects. 相似文献
8.
Enantioselective synthesis of non-natural amino acids using phenylalanine dehydrogenases modified by site-directed mutagenesis 总被引:2,自引:0,他引:2
Busca P Paradisi F Moynihan E Maguire AR Engel PC 《Organic & biomolecular chemistry》2004,2(18):2684-2691
The substrate scope of three mutants of phenylalanine dehydrogenase as biocatalysts for the transformation of a series of 2-oxo acids, structurally related to phenylpyruvic acid, to the analogous alpha-amino acids, non-natural analogues of phenylalanine, has been investigated. The mutant enzymes are more tolerant than the wild type enzyme of the non-natural substrates, especially those with substituents at the 4-position on the phenyl ring. Excellent enantiocontrol resulted in all cases. 相似文献
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Michael J. S. Dewar Eamonn F. Healy Andrew J. Holder Yate-Ching Yuan 《Journal of computational chemistry》1990,11(4):541-542
A reparameterized version (PM3) of AM1 has recently been reported and the results for several hundred molecules compared with those from AM1 itself. The comparison implied that PM3 represents a significant improvement over the earlier treatment. The apparently poor performance of AM1 is, however, due to the inclusion of “AM1 results” for elements (A1,P,S) for which AM1 parameters were unavailable. If these are omitted, PM3 is seen to be only marginally better than AM1. Since this conclusion refers only to a specific set of stable molecules, it is not clear whether even this small improvement will apply to other species or studies of reactions. It is in any case insufficient to justify the confusion caused by the release of the new treatment. 相似文献
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Vadavi R Conrad ED Arbuckle DI Cameron TS Essoun E Aquino MA 《Inorganic chemistry》2011,50(23):11862-11864
[Ru(2)(μ-O(2)CCH(3))(4)(MeOH)(2)](PF(6)) reacts with chiral diphosphines (R,R)- and (S,S)-chiraphos, leading to disassembly and production of the enantiomers Λ-[Ru(η(2)-O(2)CCH(3))(η(2)-(R,R)-chiraphos)(2)](PF(6)) and Δ-[Ru(η(2)-O(2)CCH(3))(η(2)-(S,S)-chiraphos)(2)](PF(6)) in high yield and purity. X-ray crystallography and solid-state circular dichroism (CD) show that only the indicated isomers are present in the solid state. Solution CD measurements also indicate their predominance in solution. 相似文献