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排序方式: 共有435条查询结果,搜索用时 15 毫秒
431.
Flow chemistry approach for partial deuteration of alkynes: synthesis of deuterated taxol side chain
S. Chandrasekhar B.V.D. VijaykumarB. Mahesh Chandra Ch. Raji ReddyP. Naresh 《Tetrahedron letters》2011,52(30):3865-3867
The partial deuteration of alkynes proceeds via a flow chemistry approach under Lindlar’s heterogeneous catalysis to provide cis-dideuterated olefins in good yields. Further, dideuterated olefin has been successfully utilized for Sharpless asymmetric dihydroxylation followed by Mitsunobu reaction for the synthesis of deuterated taxol side chain. 相似文献
432.
Jingfang Wang Zhenxing Wang Ronald J. ClarkAndrew Ozarowski Johan van Tol Naresh S. Dalal 《Polyhedron》2011,30(18):3058-3061
We report the high frequency electron paramagnetic resonance (HF-EPR) study of Cr3(dpa)4Cl2, a linear tri-atomic (CrII)3 chain, that was reported to be EPR silent at the X-band (9.5 GHz). Higher frequencies yield well resolved spectra for this S = 2 system even at room temperature. At 30 K, our variable frequency (34-400 GHz) EPR spectra yield a large axial zero-field splitting (D) of −1.643(1) cm−1 as well as a small rhombic ZFS parameter E = 0.0339(4) cm−1; with gx = 1.9978(4), gy = 1.9972(4), and gz = 1.9808(4). The magnetic susceptibility measurements fully support the earlier magnetic susceptibility studies and the current EPR results. The observation of the EPR spectrum of only the S = 2 state at room temperature suggests that the ground state is well isolated from the excited states. 相似文献
433.
434.
Naresh Dadhich 《Pramana》2010,74(6):875-882
We prove the theorem: The second-order quasilinear differential operator as a second-rank divergence-free tensor in the equation
of motion for gravitation could always be derived from the trace of the Bianchi derivative of the fourth-rank tensor, which
is a homogeneous polynomial in curvatures. The existence of such a tensor for each term in the polynomial Lagrangian is a
new characterization of the Lovelock gravity. 相似文献
435.
Vivek K. Gupta Shaveta Mahajan Naresh K. Satti Krishan A. Suri G. N. Qazi 《Journal of chemical crystallography》2008,38(10):769-773
Abstract (20R,22R)-6α,7α-Epoxy-5α,27-dihydroxy-1-oxowitha-2,24-dienolide (27-hydroxy-withanolide B) was isolated from Withania somnifera. The structure of the withanolide was established by spectral analysis and X-ray diffraction studies. The compound crystallizes
in the orthorhombic space group P212121 with unit cell parameters: a = 9.2163(3), b = 11.1828(4), c = 23.6146(9) ?, Z = 4. The crystal structure was refined to R = 0.0495 for 3,284 observed reflections. All the rings of the steroid skeleton are trans connected. Rings A and B exist in
a half-chair conformation, ring C a chair, and five membered ring D is intermediate between a half-chair and an envelope.
The δ-lactone ring E adopts a distorted sofa conformation. The twist along the length of the steroid nucleus is −6.5°. The
characteristic pattern observed in the packing diagram is the appearance of twisted chains of molecules packed together to
form layers.
Index Abstract Isolation and crystal structure analysis of (20R,22R)-6α,7α-epoxy-5α,27-dihydroxy-1-oxowitha-2,24-dienolide.
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