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排序方式: 共有221条查询结果,搜索用时 234 毫秒
1.
Density functional calculations have been carried out on a series of linearly annelated acenes and their BN analogues. Even though borazine shows aromatic and reactivity behavior parallel with that of benzene, its condensed derivatives show patterns different from those of their hydrocarbon analogues. Nucleus independent chemical shift (NICS) values in acenes suggest that the aromaticity of the inner rings is more than that of benzene, whereas in BN-acenes there is no substantial change in the aromaticity of the individual rings. Molecular electrostatic potential (MESP) is employed to obtain further insights into the bonding and reactivity trends for these systems. The MESP topography patterns of acenes and BN-acenes are substantially different, with BN-acenes showing more localized pi electron features compared to those of acenes. The MESP values at the critical points (CPs) indicate overall lowering of aromaticity in these annelated systems. However, this change is gradual among the BN-acenes. 相似文献
2.
Singha K Roy A Dutta PK Tripathi S Sahabuddin S Achari B Mandal SB 《The Journal of organic chemistry》2004,69(19):6507-6510
A simple synthesis of chiral spironucleosides and spirobisnucleosides is described. Intramolecular 1,3-dipolar nitrone cycloaddition reaction of d-glucose-derived precursors having olefin at C-3 and nitrone at C-5, C-1, or C-2 (in nor-series) furnished bisisoxazolidinospirocycles 4-7, 11, and 12 in good yields. Reductive ring opening of the isoxazolidine moieties in 4-6 followed by construction of a nucleoside base upon the generated amino groups smoothly yielded spirobisnucleosides 17 and 18 and spironucleosides 20 and 21. 相似文献
3.
Polycondensation of the diacid chloride of 2-(3-carboxy vinyl)phenyl-1,3-dioxoisoindoline-5-carboxylic acid with m-phenylenediamine and the diacid chloride of 2-(4-carboxy phenyl)-1,3-dioxoisoindoline-5-carboxylic acid with 1,5-bis(3-aminophenyl)1,4-pentadien-3-one was carried out in polar solvents to produce new unsaturated polyamide–imides. The solution and the thermal, electrical, and a few other properties of the polymers were studies. The polymers were soluble in highly polar solvents. The solubility parameter of the polymers was calculated from the Small's group contribution. The polymers were fairly thermostable and underwent crosslinking creaction when heated, preferably in the presence of a suitable catalyst. The crosslinked polymers were in soluble even in highly polar solvents and possessed higher thermal stability. The swelling behavior of the polymers was studied and the molecular weight between two consecutive crosslinks was determined. X-ray diffraction and the dielectric properties of the polymers and their crosslinked products were also studied. 相似文献
4.
Carsten Lenczyk Dr. Dipak Kumar Roy Bijoy Ghosh Johannes Schwarzmann Prof. Ashwini K. Phukan Prof. Dr. Holger Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(36):8585-8589
A series of bis(σ)-borane complexes of Group 6 transition metals were prepared by direct dihydroborane coordination to the metal center. Reaction of [M(CO)3(PCy3)2] and two dihydroboranes [DurBH2] and [(Me3Si)2NBH2] (Dur=2,3,5,6-Me4C6H) yielded bis(σ)-borane complexes fac-[M(CO)3(PCy3){η2-(H2BR)}] (R=Dur; 1 : M=Cr, 2 : M=W; R=N(SiMe3)2; 3 : M=Cr, 4 : M=W). In the case of molybdenum, we have isolated an arene complex ( 5 ) with [DurBH2] in which the Dur group acts as a η6-bound ligand, and with [(Me3Si)2NBH2] a similar bis(σ)-borane complex was isolated, cis,trans-[Mo(CO)2(PCy3)2{η2-(H2BN(SiMe3)2}] ( 6 ), with a different pattern of auxiliary ligands. The complexes were investigated by multinuclear NMR spectroscopy, mass spectrometry, X-ray diffraction analysis, and computational methods. Quantum theory of atoms in molecules (QTAIM) calculations demonstrated that the borane complexes may be described as pure bis(σ)-borane complexes rather than elongated or stretched examples given that the calculations do not show the presence of a ring-critical point (RCP) at the ring formed by the interactions of the B−H with metal center. 相似文献
5.
Organic halides absorbed without solvent onto sodium phenylsulfinate on alumina (1) gave phenylsulfones (2) under microwave or ultrasound activation. 相似文献
6.
7.
An expeditious protocol for amidation arylboronic acid has been developed using TsNBr2 as the nitrogen source in presence of a CuI as catalyst. Various arylboronic acids could be transformed into corresponding N-arylsulfonamide derivatives within a very short time using CuI as catalyst in presence of DBU at room temperature. 相似文献
8.
The graft copolymerization of methyl methacrylate onto poly-(ethylene terephthalate) using metal complexes of Mn3+, Co3+, and Fe3+ as initiators was studied. The rate of polymerization, Rp, increased with increasing complex concentrations. The rate of polymerization was also studied by varying monomer concentrations. Increasing monomer concentrations, the rate of polymerization increases significantly. The graft yield increases with increasing temperature within the range 60–75°C. The graft yield is medium dependent. A suitable kinetic scheme has been pictured and rate equations have been derived. 相似文献
9.
Subramanya Hegde Jayadevan Jayashankaran Atanu Ghosal T.S.R Prasanna Y. Shivaraj K. Mohana Raju 《Journal of heterocyclic chemistry》2013,50(2):442-449
A straightforward and general approach for the stereoselective synthesis of fused pyrrolo[1,2‐a] indoles frameworks from>intramolecular 1,3‐dipolar cycloaddition using N‐alkylated Baylis–Hillman derivatives is presented. It was found that the cycloaddition proceeded efficiently under microwave irradiation in solvent‐free condition to afford highly stereoselective cycloadducts in good yield. 相似文献
10.
A new hybrid catalyst has been developed by incorporating nicotinic acid onto an organomodified silica. The catalyst was applied as a heterogeneous catalyst for the synthesis of benzoyl fumarate. The reactions work well in the presence of 20 wt % of the catalyst at room temperature to produce the desired products in high yield. The catalyst could be recovered and reused without appreciable change in activity. 相似文献