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381.
Ethyl 3-halo-2-propynoates undergo facile (no heating, no base, no solvent) palladium- and copper-free cross-coupling with 4,5,6,7-tetrahydroindoles on alumina to afford the corresponding 4,5,6,7-tetrahydroindole-2-propynoates in 46% and 71% yields. The yield of the by-products [ethyl 3,3-di(4,5,6,7-tetrahydro-1H-indol-2-yl)acrylates] under appropriate conditions can reach 79%. 相似文献
382.
Ushakov I. A. Afonin A. V. Voronov V. K. Stepanova Z. V. Sobenina L. N. Mikhaleva A. I. Trofimov B. A. 《Russian Journal of Organic Chemistry》2002,38(12):1775-1781
According to the 1H and 13C NMR data, the molecule of 2-(2-benzoylethenyl)-1-vinylpyrrole has a nearly planar structure with trans arrangement of the vinyl and oxovinyl groups. The unsaturated fragments give rise to effective conjugation. The vinyl group in 5-substituted 2-(2-acylethenyl)-1-vinylpyrroles strongly deviates from the heteroring plane because of steric effect of the substituent; however, this effect does not change the arrangement of the other unsaturated fragments. 相似文献
383.
T. P. Stepanova A. N. Pogrebnaya V. M. Kapralova S. S. Skorokhodov 《Polymer Science Series A》2007,49(2):205-210
A comparative study of dipole polarization relaxation in the absence and in the presence of an external orienting electric field was performed for linear segmented polyesters with alternating rigid (oxyfumaroylbis-4-oxybenzoates) and flexible (methylene-CH2-, ethylene oxide-CH2CH2-O-, and dimethylsiloxane-Si(CH3)2-O-Si(CH3)2-) fragments in dilute solutions. Polyesters that do not display mesomorphic properties in the bulk show several regions of dielectric absorption with relaxation character. These regions are associated with the motions via the local mobility mechanisms of different polar fragments of the macromolecule. In solutions of polyesters that possess LC properties in the bulk, large-scale dipole polarization relaxation with long relaxation times and high activation energies was revealed along with local dielectric relaxation transitions. This process is associated with the cooperative motion of mesogenic fragments in their associates. In an external orienting electric field, the intensity of dielectric absorption usually increases for all types of dielectric transition; relaxation times and activation energies experience changes only for large-scale processes. 相似文献
384.
Yu. Yu. Samitov A. S. Yavorskii A. I. Gren' A. V. Bogat-skii O. S. Stepanova 《Chemistry of Heterocyclic Compounds》1975,11(8):904-908
2-Methyl-and 2,5-dialkyl-5-phenoxy-1,3-dioxanes were synthesized and separated into their geometrical isomers by precision rectification. The configuration and conformations of these isomers were determined by PMR spectroscopy. It is shown that the low-boiling trans isomers exist primarily in the chair conformation with an equatorial phenoxy group, whereas the high-boiling cis isomers exist primarily in the chair conformation with an axial phenoxy group. 相似文献
385.
G. I. Goryashina A. V. Bogatskii Yu. Yu. Samitov O. S. Stepanova N. I. Karelina 《Chemistry of Heterocyclic Compounds》1968,4(3):288-294
Twenty-six previously unreported 5-alkoxymethyl-2,5-dialkyl-1,3-dioxanes have been synthesized by the condensation of 2-alkoxymethyl-2-alkylpropane-1,3-diols with aldehydes. It has been shown by an analysis of the PMR spectra of these dioxanes that the 1,3-dioxanes considered are mixtures of two stereoisomers. In some cases these mixtures have been resolved into the individual isomers by vacuum fractionation in efficient columns. The configurations and conformations of the stereoisomeric 5-alkoxymethyl-2,5-dialkyl-1,3-dioxanes have been established by the NMR method; it has been shown that the lower-boiling isomers have the trans configuration and predominantly the chair conformation and the higherboiling isomers the cis configuration and predominantly an unsymmetrical boat conformation.For part XX, see [7]. 相似文献
386.
387.
Turchaninov V. K. Chipanina N. N. Stepanova Z. V. Kanitskaya L. V. Fedorov C. V. Gavrilova G. A. Murzina N. M. Aksamentova T. N. Sobenina L. N. Mikhaleva A. I. 《Russian Journal of General Chemistry》2003,73(3):440-449
Theoretical (B3LYP/6-31G*) and experimental (NMR, UV, and IR spectroscopy) data on the electronic and steric structure of 2-(2-benzoyl-1-phenylethenyl)-5-phenylpyrrole have been analyzed in the context of the hypothesis of the zwitter ionic nature of its ground state. The molecule involves a strong NH···O bond, and its ground state can be described as a hybrid of the neutral and zwitter ionic canonical forms; this conclusion was confirmed by the observation of a reversible medium effect on the electronic absorption spectrum of the substrate. 相似文献
388.
Abstract Several series of liquid crystalline polyaroyl-bis-oxyarylates containing 1,4-phenylene, 4,4′-biphenylene and 2,6-naphthylene units have been synthesized with the use of aroyl-bis-oxyaroyl dichlorides. Melting and clearing temperatures of every polymer under investigation were compared with those of corresponding polyterephthaloyl-bis-4-oxybenzoates. 相似文献
389.
L. I. Stepanova L. S. Ivashkevich G. A. Branitskii 《Russian Journal of Inorganic Chemistry》2009,54(10):1553-1558
The phase composition, particle size, and morphology of ultrafine products recovered as a result of hydrothermal treatment
of precursor solutions were studied. The precursor solutions were prepared by ion exchange and contained various proportions
of tungsten and molybdenum. When tungsten percentages in the precursor solution were 20–95 mol %, the major synthesis product
was a mixed oxide (substitutional solid solution (W, Mo)O3 · 1/3H2O based on the structure of crystal hydrate WO3 · 1/3H2O). When the tungsten percentage was 5 mol %, the product was (W, Mo)O3 solid solution with the structure of orthorhombic MoO3. Particle shapes and sizes (ranging from 20 to 8 000 nm) were dictated by the proportion between tungsten and molybdenum
compounds in the precursor solution and by the method used to prepare the precursor. 相似文献
390.