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841.
Mahandru GM Skauge AR Chowdhury SK Amarasinghe KK Heeg MJ Montgomery J 《Journal of the American Chemical Society》2003,125(44):13481-13485
A new strategy for effecting cascade cyclization processes using nickel enolates has been developed. Nickel enolates may be cleanly generated by the oxidative cyclization of an enal and alkyne with Ni(0), and the resulting enolate may be functionalized by a variety of alkylation processes. Partially and fully intramolecular versions of the process allow the rapid synthesis of complex polycyclics from simple achiral, acyclic precursors. 相似文献
842.
Premamoy Ghosh Dilip Kumar Chowdhury 《Journal of polymer science. Part A, Polymer chemistry》1985,23(5):1407-1419
Benzophenone (BP)-sensitized photopolymerization of methyl methacrylate (MMA) in near UV/visible light was studied at 40°C using dimethylaniline maleic acid (DMA—MA) combination as the photoinitiator. An instantaneous 1:1 complexation between DMA and MA takes place when they are mixed together in acetonitrile. Also, instantaneous complex formation occurs between DMA and MMA and between MA and MMA when they are dissolved in MMA in low concentrations, separately. Interestingly, when equimolar proportions of DMA and MA are mixed together in MMA, there is indication for further instantaneous complexation between (DMA—MMA) complex and (MA—MMA) complex forming the actual initiating species in the photopolymerization system. Initiator exponent was 0.28 and monomer exponent varied between 0.0 to 1.8 depending on the nature of the solvent and range of dilution used. Analysis of kinetic data indicates a free radical mechanism for the polymerization with initiator-dependent termination. Chain termination via degradative initiator transfer is quite significant; but the degradative effect becomes much less prominent in the higher range of initiator concentration indicating that the reinitiation reaction following the initiator transfer process assumes more proportionate significance as the initiator concentration is increased, probably as a result of higher reinitiation efficiency. Polymers obtained gave evidence for the incorporation of aromatic (amine) end groups in them. 相似文献
843.
The localised modes associated with interstitial hydrogen in the β-phases of Pd and Pd-Ag alloys have been studied by neutron energy loss at 295K, 80K and for Pd at 30K. Their energies vary little but their widths increase significantly with temperature and silver content, an effect which is ascribed to local disorder and anharmonic contributions. 相似文献
844.
I. Ahmad S.M. Austin B.B. Back R.R. Betts F.P. Calaprice K.C. Chan A. Chishti P. Chowdhury C. Conner R.W. Dunford J.D. Fox S.J. Freedman M. Freer S.B. Gazes A.L. Hallin T. Happ D. Henderson N.I. Kaloskamis E. Kashy W. Kutschera J. Last C.J. Lister M. Liu M.R. Maier D.J. Mercer D. Mikolas P.A.A. Perera M.D. Rhein E. Roa J.P. Schiffer T.A. Trainor P. Wilt J.S. Winfield M. Wolanski F.L.H. Wolfs A.H. Wuosmaa A. Young J.E. Yurkon 《Zeitschrift für Physik A Hadrons and Nuclei》1997,358(2):235-236
845.
We present results of what is to our knowledge the first experimental demonstration of simultaneous optical wavelength interchange by use of a two-dimensional second-order nonlinear photonic crystal. Fabrication and performance parameters of a 1535-1555-nm wavelength interchange nonlinear photonic crystal fabricated in lithium niobate are discussed. 相似文献
846.
Ameera Chowdhury 《Journal of Combinatorial Theory, Series A》2010,117(8):1095-1106
We prove a vector space analog of a version of the Kruskal-Katona theorem due to Lovász. We apply this result to extend Frankl's theorem on r-wise intersecting families to vector spaces. In particular, we obtain a short new proof of the Erd?s-Ko-Rado theorem for vector spaces. 相似文献
847.
The 4A2 → 2E transition of potassium chromicyanide has been studied under magnetic field. It has been found that the g-value is nearly isotropic, quite unlike the case of ruby. An attempt has been made to explain the zero-field splittings of 2E, 2T1 and 2T2 states and the g-value of the 2E state on the assumption that the distant ions are mainly responsible for lowering of symmetry of the crystal field from Oh. A reasonable choice of parameters can make the calculated values agree with the observed ones. 相似文献
848.
Tanmoy Chanda Sushobhan Chowdhury B. Janaki Ramulu Suvajit Koley Raymond C.F. Jones Maya Shankar Singh 《Tetrahedron》2014
An operationally simple and highly atom-economic anionic quadruple domino reaction sequence for the synthesis of hexacyclic indeno-fused naphthalene/quinoline molecules having structural resemblance with the C-nor-D-homo-steroid nucleus has been developed. Promoter and solvent specificity, regioselectivity and mechanistic details were experimentally established. Catalyst concentration and solvent dependent switching of domino steps creating four new C–C bonds are discussed. 相似文献
849.
Sushobhan Chowdhury Tanmoy Chanda Ganesh Chandra Nandi Suvajit Koley B. Janaki Ramulu S.K. Pandey Maya Shankar Singh 《Tetrahedron》2013
β-Allyl-β-hydroxydithioesters have been generated by the regioselective Grignard addition to the β-oxodithioesters. They have been successfully employed in selective C(sp3)–C(sp3) bond cleavage to construct α,β-unsaturated ketone residues by the treatment of an emerging catalyst yttrium(III)triflate for the first time. On the other hand, hetaryl substituted β-allyl-β-hydroxydithioesters led to the useful diene precursors through selective dehydration under the similar conditions. 相似文献
850.