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991.
The conformers of the monohalocyclohexasilanes, Si6H11X (X=F, Cl, Br or I) and the haloundecamethylcyclohexasilanes, Si6Me11X (X=F, Cl, Br or I) are investigated by DFT calculations employing the B3LYP density functional and 6‐31+G* basis sets for elements up to the third row, and SDD basis sets for heavier elements. Five minima are found for Si6H11X—the axial and equatorial chair conformers, with the substituent X either in an axial or equatorial position—and another three twisted structures. The equatorial chair conformer is the global minimum for the X=Cl, Br and I, the axial chair for X=F. The barrier for the ring inversion is ~13 kJ mol?1 for all four compounds. Five minima closely related to those of Si6H11X are found for Si6Me11X. Again, the equatorial chair is the global minimum for X=Cl, Br and I, and the axial chair for X=F. Additionally, two symmetrical boat conformers are found as local minima on the potential energy surfaces for X=F, Cl and Br, but not for X=I. The barrier for the ring inversion is ~14–16 kJ mol?1 for all compounds. The conformational equilibria for Si6Me11X in toluene solution are investigated using temperature dependent Raman spectroscopy. The wavenumber range of the stretching vibrations of the heavy atoms X and Si from 270–370 cm?1 is analyzed. Using the van′t Hoff relationship, the enthalpy differences between axial and equatorial chair conformers (Hax?Heq.) are 1.1 kJ mol?1 for X=F, and 1.8 to 2.8 kJ mol?1 for X=Cl, Br and I. Due to rapid interconversion, only a single Raman band originating from the “averaged” twist and boat conformers could be observed. Generally, reasonable agreement between the calculated relative energies and the experimentally determined values is found. 相似文献
992.
The annealing induced morphological changes in isotropic block copoly(etherester)s are investigated by small angle X-ray scattering methods. The observed results are consistent with a lamellar model which is comprised of a crystalline core of thickness 35 to 45 Å, a diffuse boundary zone of width 9 Å, and an amorphous layer which is varying strongly in thickness. The enhanced crystallinity of the samples annealed at higher temperatures is mainly due the lateral growth of the lamellae; the long period increases by not more than 20%. The scattering power of the samples is explained by means of an equivalent two-phase model in which the crystalline phase has the same structure as theα-form of poly(butylene terephthalate), whereas the amorphous phase is a mixture of the uncrystallized ester segments and the ether segments. The crystallinity determined from the scattering power is very much higher than that determined from thermoanalytical investigations. 相似文献
993.
The CO_2 laser induced room temperature reactions of CH_3CF_2H or another protium-donorCH_3CHClCH_3 with chlorine-atom donors (Z--Cl) CFCl_2CF_2Cl, CF_3CCl_3, CFCl_3 or CF_2Cl_2, havebeen investigated. Some of these reactions can yield two important monomers (CF_2=CH_2 andCF_2=CFCl) for fluoropolymers simultaneously. The yield dependence of these two alkenes on experi-mental conditions has been studied. A laser-initiated chain process is supported by identifica-tion of Z--H intermediates in these reactions. 相似文献
994.
Tomoya Kitazume Zaiju Jiang Kana Kasai Yuma Mihara Mamie Suzuki 《Journal of fluorine chemistry》2003,121(2):205-212
The utility of reusable ionic liquid-proline (or aldolase antibody 38C2) reaction system, proceeding the aldol reactions, is described. Further, obtained α-chloro-β-hydroxy compounds were transformed to the optically active α,β-epoxy carbonyl compounds. The aldolase antibody 38C2-ionic liquid system was able to reuse in Michael additions and the reaction of fluoromethylated imines. 相似文献
995.
Xu J Mojet BL van Ommen JG Lefferts L 《The journal of physical chemistry. B》2005,109(39):18361-18368
The adsorption of oxygen and d2-propane (CH3CD2CH3) on a series of alkaline-earth-exchanged Y zeolite at room temperature was studied with in situ infrared spectroscopy. Surprisingly at room temperature, oxygen adsorption led to the formation of supercage M2+(O2) species. Further, at low propane coverage, propane was found to adsorb linearly on Mg2+ cations, but a ring-adsorption structure was observed for propane adsorbing on Ca2+, Sr2+, and Ba2+ cations. It is demonstrated that O2 and propane can simultaneously attach to one active center (M2+) to form a M2+(O2)(C3H8) species, which is proposed to be the precursor in thermal propane selective oxidation. Selectivity to acetone in the propane oxidation reaction decreases with increasing temperature and cation size due to the formation of 2-propanol and carboxylate ions. An extended reaction scheme for the selective oxidation of propane over alkaline earth exchanged Y zeolites is proposed. 相似文献
996.
The reactions of transition metal salts with taurine 5‐chlorosalicylaldelyde Schiff base gave two complexes [Ni(TCSSB)(H2O)3].H2O (1) and [Cu(TCSSB)(H2O)2]2[Cu(TCSSB)2].6H2O (2) (TCSSB=taurine‐5‐chlorosalicylaldelyde Schiff base), which were characterized by elemental analysis and X‐ray diffraction analysis. The complex 1 crystallized in monoclinic system with space group P2 1/c, and a=1.4816(2) nm, b=1.3953(2) nm, c= 0.7466(1) nm, β= 100.499(3)°, V=1.5176(4) nm3, Z=4, and an infinite 3‐D network structure was formed by hydrogen bonds among sulfo group, crystal water and coordinated water. Complex 2 crystallized in triclinic system with space group P1 , with the cell parameters: a = 0.6413(2) nm, b= 1.4596(3) nm, c= 1.6188(4) nm, a= 102.473(5)°, β= 98.979(4)°, γ=101.739°, V=1.4165(6) nm3, Z=1. The coordination environment between Cu(1) and Cu(2) is different. Cu(1) is slightly distorted square pyramidal while Cu(2) is distorted square‐plane. The complex 1 is mononuclear while the complex 2 is made up of two coordinated subunits, namely [Cu(TCSSB)2] and [CU(TCSSB)(H2O)2]2. Besides that the TG‐DTG of the complex 1 was analyzed, the thermal decomposition reaction of the complex was studied under a non‐isothermal condition by TG‐DTG. The TG and DTG curves indicate that the complex was decomposed in three stages: . 相似文献
997.
Grant J. Sherborne Avetik G. Gevondian Ignacio Funes-Ardoiz Amit Dahiya Christoph Fricke Prof. Dr. Franziska Schoenebeck 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(36):15673-15678
Selective C –C couplings are powerful strategies for the rapid and programmable construction of bi- or multiaryls. To this end, the next frontier of synthetic modularity will likely arise from harnessing the coupling space that is orthogonal to the powerful Pd-catalyzed coupling regime. This report details the realization of this concept and presents the fully selective arylation of aryl germanes (which are inert under Pd0/PdII catalysis) in the presence of the valuable functionalities C−BPin, C−SiMe3, C−I, C−Br, C−Cl, which in turn offer versatile opportunities for diversification. The protocol makes use of visible light activation combined with gold catalysis, which facilitates the selective coupling of C−Ge with aryl diazonium salts. Contrary to previous light-/gold-catalyzed couplings of Ar–N2+, which were specialized in Ar–N2+ scope, we present conditions to efficiently couple electron-rich, electron-poor, heterocyclic and sterically hindered aryl diazonium salts. Our computational data suggest that while electron-poor Ar–N2+ salts are readily activated by gold under blue-light irradiation, there is a competing dissociative deactivation pathway for excited electron-rich Ar–N2+, which requires an alternative photo-redox approach to enable productive couplings. 相似文献
998.
D. Mihrin Dr. P. W. Jakobsen A. Voute Dr. L. Manceron Prof. R. Wugt Larsen 《Chemphyschem》2019,20(23):3238-3244
The high-resolution infrared absorption spectrum of the donor bending fundamental band ν of the homodimer (HCN)2 has been collected by long-path static gas-phase Fourier transform spectroscopy at 207 K employing the highly brilliant 2.75 GeV electron storage ring source at Synchrotron SOLEIL. The rovibrational structure of the ν transition has the typical appearance of a perpendicular type band associated with a Σ–Π transition for a linear polyatomic molecule. The total number of 100 assigned transitions are fitted employing a standard semi-rigid linear molecule Hamiltonian, providing the band origin ν0 of 779.05182(50) cm−1 together with spectroscopic parameters for the degenerate excited state. This band origin, blue-shifted by 67.15 cm−1 relative to the HCN monomer, provides the final significant contribution to the change of intra-molecular vibrational zero-point energy upon HCN dimerization. The combination with the vibrational zero-point energy contribution determined recently for the class of large-amplitude inter-molecular fundamental transitions then enables a complete determination of the total change of vibrational zero-point energy of 3.35±0.30 kJ mol−1. The new spectroscopic findings together with previously reported benchmark CCSDT(Q)/CBS electronic energies [Hoobler et al. ChemPhysChem. 19 , 3257–3265 (2018)] provide the best semi-experimental estimate of 16.48±0.30 kJ mol−1 for the dissociation energy D0 of this prototypical homodimer. 相似文献
999.
1000.
Summary The grafting of minerals by alkenylchlorosilanes leads to organomineral derivatives which are superficially covered by unsaturated organic groups. These groups may be of value when the grafted mineral is used as a reinforcing agent in a polymeric matrix. In this case, the unsaturated grafted groups copolymerize with an organic monomer to build up a composite material. It is therefore of importance to preserve the unsaturated character of the alkenyl-silane during the grafting reactions. It is shown that in certain synthesis conditions, the hydrochloric acid present in the reaction medium adds to the alkenyl-groups. For instance, in the grafting of methylvinyl-dichlorosilane, this reaction is of minor importance, whereas in the case of allyldimethylchlorosilane, no allyl groups are grafted as such on the mineral surface.
With 2 figures
Part 1: Nature and role of the hydrolysis products of the methylvinyldichlorosilane in the grafting of silicates in hydrochloric acid and isopropanolThis journal 256, 135 (1978). 相似文献
Zusammenfassung Die Pfropfung von silicatischen Mineralen mit Alkenylchlorosilanen führt zu organischen Derivaten, deren Oberfläche mit ungesättigten organischen Gruppen bedeckt ist. Diese Gruppen können Vorteile bieten, wenn die so behandelten Minerale als Fül-stoffe oder Verstärker in einer Polymermatrix eingesetzt werden. Die ungesättigten Gruppen können miteinem organischen Monomer kopolymerisieren und ein echtes Verbundmaterial bilden. Die Pfropfung muß allerdings so geführt werden, daß der ungesättigte Charakter der Alkenylsilane erhalten bleibt. In der Arbeit werden experimentelle Bedingungen dafür berichtet.
With 2 figures
Part 1: Nature and role of the hydrolysis products of the methylvinyldichlorosilane in the grafting of silicates in hydrochloric acid and isopropanolThis journal 256, 135 (1978). 相似文献