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951.
The biomimetic synthesis of the bisesquiterpene lactones (+/-)-biatractylolide 1 and (+/-)-biepiasterolide 2 via dimerization of the captodative stabilized radical 8 is reported. Atractylon 7 has also been shown to be a possible intermediate during the biosynthesis of biatractylolide 1, biepiasterolide 2, atractylolide 3, and hydroxyatractylolide 4. 相似文献
952.
Brian F.G. Johnson Jack Lewis Paul R. Raithby George M. Sheldrick Georg Süss 《Journal of organometallic chemistry》1978,162(2):179-187
The reduction of Os3(CO)12 by NaBH4 in tetrahydrofuran has been studied, and the formation of the anionic clusters [HOs3(CO)11]?, [H3Os4(CO)12]? and [H2Os4(CO)12]2? observed. The previously unreported dianion [H2Os4(CO)12]2? was prepared in satisfactory yield, and characterised as the bis(triphenylphosphine)iminium salt. This compound crystallizes in the space group P, with Z = 1, and cell dimensions of a 11.014(2), b 14.751(3), c 15.168(3) Å, α 123.95(2)°, β 95.77(2)°, γ 98.73(2)°. The structure was solved by a combination of multisolution sign expansion and Fourier methods, and final residuals were R 0.067 and RW 0.066 for 5972 observed intensity data. The dianion comprises a distorted tetrahedron of osmium atoms, each metal also bonding to three terminal carbonyl ligands, which as staggered with respect to the metalmetal bonds. Unlike the cation, the cluster anion is statistically disordered between two centrosymmetrically related sites. 相似文献
953.
We propose a modification of Hazi and Taylor's stabilization method for calculating resonance energies by adding a positive definite operator to the hamiltonian. The purpose of this operator is to raise the energies of scattering states while not significantly affecting the bound or resonance states. The method has advantages over the ordinary stabilization techniques. We treat two model problems and discuss possible applications to atomic and molecular systems. 相似文献
954.
Ajit Banerjee John W. Kenney Jack Simons 《International journal of quantum chemistry》1979,16(6):1209-1237
The polarization Green's-function formalism in the superoperator notation of Goscinski and Lukman is re-derived using a multiconfiguration self-consistent-field (MC -SCF ) reference state to establish the superoperator metric. The potential advantages of employing this more general reference state in Green's-function theories and certain inherent weaknesses associated with the traditional Hartree–Fock or Rayleigh–Schrödinger perturbation theory reference state choices are briefly discussed. The Hermiticity of the superoperators is analyzed within the framework of the MC –SCF reference state. Using a concept of order appropriate for this reference state choice, explicit formulas and computational procedures for the implementation of this Green's-function theory are presented and specialized to include terms consistent through second order. 相似文献
955.
Clifford C. Leznoff Polina I. Svirskaya Varda Yedidia Jack M. Miller 《Journal of heterocyclic chemistry》1985,22(1):145-147
The uracil analog, 4-fluoro-2-pyridone was synthesized by ether cleavage of 4-fluoro-2-methoxypyridine with trimethylsilyl iodide. Improved procedures for the preparations of 2-methoxypyridine N-oxide hydrochloride and 2-methoxy-4-nitropyridine N-oxide are described. 相似文献
956.
B-Tris(alkylamino)-N-trialkyl-borazines and B-tris(arylamino)-N-triaryl-borazines may be prepared almost quantitatively by employing the appropriate stoichiometry in the reaction between boron trichloride and an alkyl- or aryl-amine. The borazines so formed react with boron trifluoride or boron trifluoride etherate to give good yields of the B-trifluoro-N-trialkyl- and B-trifluoro-N-triaryl-borazines. Using this methods, (CH3NBF)3, (p-ClC6H4NBF)3 and (C6F5NBF)3 have been prepared. The analogous reaction using (C6F5)3B as a route to B-tris(pentafluorophenyl)borazines was unsuccesful. 相似文献
957.
Reactions of lactim ethers with α-cyanoacetone dianion gave bicyclic 2-amino-4(1H)-pyridones. 相似文献
958.
In the crystal structure of the title compound at 98 K the dimethylamino group has pyramidal geometry. The nitrogenlone pair is not directed towards the triple bond; instead, one N? CH3 bond lies almost in the plane of the disubstituted ring, directed away from the triple bond, while the other N? CH3 bond and the lone pair are directed to opposite sides of the plane, nearer to the acetylene. There is a remarkably short intramolecular contact (2.39 Å) between a methyl H- and an acetylenic C-atom. The Taft σI parameter of the arylethynyl substituent appears to be similar to that of a carboxylic ester, judging from the bond-angle deformation at the ipso-C-atom. 相似文献
959.
Jack Simons 《Chemical physics letters》1973,22(3):619-621
We discuss the calculation of local concentration fluctuations, at constant volume and temperature, for an open, non-interacting, chemically-reactive fluid. One conclusion is that even for ideal mixtures, fluctuations cannot be calculated using a grand-canonical theory if the open volume element constitutes a non-negligible part of the total system. It is also shown that the calculation of equilibrium fluctuation for interacting molecules is, in general, not given by the ordinary grand-canonical result. There does exist a coupling between reaction progress fluctuations and concentration fluctuations due to migration. 相似文献
960.
Thomas Hübert Jack Schwarz Bernd Oertel 《Journal of Sol-Gel Science and Technology》2006,38(2):179-184
The aluminium oxide films on austenitic steel are prepared from sols of re-dispersed boehmite nano powders in water. After
dip-coating of the sol, a heat treatment including drying, calcination and annealing in vacuum at temperatures up to 1100°C
is performed to obtain crack-free coatings of a thickness up to 6 μm. XRD measurements detect α- and γ-alumina, a TiOx-phase at the metal/coating interface and a gradient of phase formation in the coating. The strong adhesion on the substrates
is due to the layered assembly and gradient composition of the coating caused by an inter-diffusion of metal cations and oxygen
in the metal/oxide interface during heat treatment. Residual stress measurements by X-rays result in compressive stresses
of 2–4 GPa in the alumina coatings. The pin-on-disc test shows a remarkable improvement of wear resistance obtained by sol-gel
coatings. The α-alumina content and the compressive stress of the coatings correlate with wear resistance of the coatings. 相似文献