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排序方式: 共有620条查询结果,搜索用时 15 毫秒
1.
Vattoly J. MajoJaya Prabhakaran J.John MannJ.S. Dileep Kumar 《Tetrahedron letters》2003,44(47):8535-8537
A novel and convergent palladium catalyzed synthesis of 2-arylbenzothiazoles has been investigated. The key step in the synthesis is a Suzuki biaryl coupling of 2-bromobenzothiazole with aryl boronic acids to provide a variety of 2-arylbenzothiazole derivatives in good yield. The synthetic utility of this methodology is demonstrated by the synthesis of 2-(4-aminophenyl)-6-methoxybenzothiazole, a PET probe precursor for the in vivo imaging of Alzheimer's disease. 相似文献
2.
B. Sanjeeva Rao M. Ramakrishna Murthy 《Journal of Polymer Science.Polymer Physics》1989,27(6):1187-1194
Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ-irradiated in air at room temperature and recorded at room temperature and at liquid-nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least-squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10-line spectra are assigned to the chain radicals CH3? CH? CH2 ~ and/or ~ CH2? CH? CH2 ~. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the Cα? Cβ bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption. 相似文献
3.
J.S. Yadav B.V. Subba Reddy V. Sunitha K. Srinivasa Reddy K.V.S. Ramakrishna 《Tetrahedron letters》2004,45(42):7947-7950
Aryl amines react with endocyclic ene-carbamates such as tert-butyl 2,3-dihydro-1H-1-pyrrolecarboxylate and tert-butyl 1,2,3,4-tetrahydro-1-pyridinecarboxylate, on the surface of montmorillonite KSF clay under mild conditions to afford the corresponding 3-aminopropylhexahydropyrrolo[3,2-c]quinoline or 4-aminobutyloctahydrobenzo[h][1,6]naphthyridine derivatives in excellent yields with moderate diastereoselectivity. 相似文献
4.
The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm,
Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of 137Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the
photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other
measured values. 相似文献
5.
Excess enthalpies (H
E
) for mixtures of cyclohexanone with propan-1-ol. propan-2-ol, butan-1-ol, butan-2-ol and 2-methyl propan-1-ol at 298.15 K
have been measured over the entire composition range. All mixed endothermically with the maximum values ofH
E
occurring at equimole fraction. Comments about the molecular interactions contributing to the excess enthalpies of a cyclic
ketone + an alcohol are made on the basis of these results. 相似文献
6.
Charles L. Watkins Larry K. Krannich Colacot J. Thomas Dileep Srivastava 《Polyhedron》1994,13(24):3299-3307
The reactions of (Me2AlH)3 with Me2AsNMe2, MeAs(NMe2)2, and As(NMe2)3 were investigated as a function of time at room temperature and over the temperature range −90 to 24°C by use of 1H and 13C NMR spectroscopy. (Me2AlH)3 was found to be very reactive toward the aminoarsines, even at −90°C, and no stable Me2AlH-aminoarsine adducts were observed. Instead, the initial stages of the reactions involved AS---N bond cleavage with the generation of highly reactive AlN- and AsH-bonded species. The subsequent course of each reaction and the final arsenic-containing product distribution depended upon the original AL:N stoichiometric ratio and the respective aminoarsine. When the Al:N ratio was 1:1, the reactions were straightforward for each aminoarsine. However, in every case, [Me2AlNMe2]2 was the final AlN-containing product. Independent reactions were carried out to verify many of the proposed decomposition pathways that lead to thermodynamically stable products. The results of this study are compared with those of the analogous, previously reported (Me3Al)2-aminoarsine systems. Additionally, a new synthetic route to [Me2AlAsMe2]3 has been established from the reaction of (Me2AlH)3 with Me2AsH. 相似文献
7.
A highly sensitive and selective spectrofluorimetric method for the determination of 0.05-2.00 mug germanium is described. Germanium is treated with chromotropic acid at pH 2.5 and the resultant anionic complex is extracted as an ion pair with rhodamine into toluene. Addition of butanol to the organic extract releases the fluorescent dye and facilitates its measurement at 570 nm after exciting at 540 nm. The method provides a detection limit of 0.003 mug ml(-1) and is virtually free from interference from extraneous ions. The relative standard deviaiton is 2.9% for ten determinations of 1.0 mug germanium. The method has been applied to the determination of germanium in various ores, minerals and rock samples. 相似文献
8.
A total synthesis of d-(+)-biotin is described starting from d-(+)-glucosamine using acyliminium chemistry. 相似文献
9.
Studies on chemical modification of demineralized bone matrix (DBM) have opened new arenas in the field of clinical orthopedics owing to its potential osteoinductivity with desired chemical functionality. To widen its usage to biomolecular delivery, graft polymerization of glycidylmethacrylate onto DBM was carried out by a free-radical initiating process using ceric ammonium nitrate as an initiator. The evidence of the grafting reaction was examined by chemical analysis using Fourier transform IR spectroscopy. The grafting condition was standardized by regulating the reaction parameters such as the concentrations of the backbone, the monomer and the initiator, the polymerization temperature and time. The optimum polymerization temperature and time to have the maximum grafting yield were 40 °C and 3 h, respectively. The percentage of grafting and the percentage of grafting efficiency were determined as a function of the reaction parameters, and both were found to increasing initially and thereafter decrease in most of the cases. The grafting results are discussed in a detailed fashion and a reaction mechanism is proposed. 相似文献
10.
The changes in free energy, enthalpy and entropy for the extraction of thorium by solutions of thenoyltrifluoroacetone (HTTA) and mixtures of solutions of HTTA and tri-n-butylphosphate (TBP), in three diluents, viz. cyclohexane, benzene and chloroform, were determined using the solvent extraction data obtained at different temperatures. From these data the thermodynamic parameters associated with the formation of Th(TTA)4 · TBP in the respective organic diluents were evaluated. Trends in the enthalpy changes were attributed to different degrees of association of the diluents with themselves and with the solutes present in them. 相似文献