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排序方式: 共有59条查询结果,搜索用时 31 毫秒
1.
将取代色满酮(1)与芳肼反应生成的腙与HNCO发生[3+2]环加成反应,加成产物(2)经氧化得到偕偶氮异氰酸酯(3).化合物3在HBF4的催化下发生环化-重排反应,得到新颖的三环系2-氧代-1,2,4-三唑并[3,2-d][1,5]苯并氧氮杂化合物5a~5g. 相似文献
2.
Zur Synthese von fungizid wirksamen Isocamphanderivaten: Synthesen in der Isocamphanreihe, 34. Mitt.
Gerhard Buchbauer Helmut Spreitzer Margarete Kneidinger 《Monatshefte für Chemie / Chemical Monthly》1990,121(6-7):549-554
Summary Some esters of isocamphenilanic acid (4) have been prepared and tested for their fungicidal and insecticidal activity. Esters of various acids with isocamphanyl ethylalcohol (5) have also been synthesized and included in the fungicidal/acaricidal/insecticidal screening programme. All esters bear a geminal dimethyl group at C-3 of the bicyclus which is important because of its shielding effect. 相似文献
3.
Klaus Rakus Sergej P. Verevkin Hans-Dieter Beckhaus Christoph Rüchardt 《欧洲无机化学杂志》1994,127(11):2225-2234
The thermolysis reactions of the tricyanomethyl compounds 10a-c were studied in solution. 2,2-Dicyano-3-methyl-3-phenylbutyronitrile ( 10a ) and 2,2-dicyano-3-methyl-3-(4-nitrophenyl)butyronitrile ( 10b ) decomposed heterolytically into carbenium ions and (CN)3C− anions, while 9-methyl-9-(tricyanomethyl)fluorene ( 10c ) underwent about 11% homolytic C-C bond cleavage into 9-methyl-9-fluorenyl- and tricyanomethyl radicals. The rates of the homolysis were determined by a radical scavenger procedure under conditions of pseudozero order kinetics. From the temperature effect on the rate constants the activation parameters were determined [ΔH ( 10c ) = 155· 2 kJ mol−1, ΔS ( 10c ) = 58· 5 J mol−1 K−1]. Standard enthalpies of formation ΔH (g) were determined for 2,2-dicyanopropionitrile ( 2 ) (422.45 kJ mol−1), 2,2-dicyanohexanenitrile ( 3 ) (349.74 kJ mol−1), 2,2-dicyano-3-phenylpropionitrile ( 4 ) (540.75 kJ mol−1), 2-butyl-2-methylhexanentrile ( 5 ) (-133.20 kJ mol−1), 2,2-dimethylpentanenitrile ( 6 ) (-45.78 kJ mol−1), and 2-methylbutyronitrile ( 7 ) (2.44 kJ mol−1) from the enthalpies of combustion and enthalpies of sublimation/vaporization. From these data and known Δ (g) values for alkanenitriles and -dinitriles, thermochemical increments for ΔH (g) were derived for alkyl groups with one, two, or three cyano groups attached. The comparison of these increments with those of alkanes reveals a strong geminal destabilization, which is interpreted by dipolar repulsions between the cyano groups. - From ΔH (g) of 10c and ΔH of its homolytic decomposition the radical stabilization enthalpy for the tricyanomethyl radical 1 RSE ( 1 ) = -18 kJ mol−1 was determined. Thus, 1 is destabilized, in comparison with the RSEs of tertiary α-cyanalkyl (23 kJ mol−1) and α,α-dicyanoalkyl (27 kJ mol−1) radicals, which were recalculated from bond homolysis measurements[4] and the new thermochemical data. This change of RSE on increasing the number of α-cyano groups is discussed as the result of the additive contributions by resonance stabilization and increasing destabilization by dipolar repulsion. The amount of the dipolar energies was estimated by molecular mechanics (MM2). 相似文献
4.
Maxime Boudjelel Richard Declercq Sonia Mallet-Ladeira Ghenwa Bouhadir Didier Bourissou 《无机化学与普通化学杂志》2020,646(13):561-564
The vinyl carbenoid H2C=CBr(Li) has been used as key precursor to prepare a geminal C(sp2)-bridged phosphine-borane. Starting from bromoethene, two sequences of lithiation/electrophilic trapping, with ClPiPr2 and FBMes2 respectively, affords iPr2P–C(=CH2)–BMes2 3 [Mes = 2,4,6-(H3C)3C6H2]. This new phosphine-borane 3 was characterized by multi-nuclear NMR and mass spectroscopy. It adopts a monomeric open structure without P→B interaction. A few crystals of a secondary product 4 were analyzed by X-ray diffraction, revealing an unusual dimeric structure. 相似文献
5.
Susanne Bhr Sabine Brinkmann‐Chen Marc Garcia‐Borrs John M. Roberts Dimitris E. Katsoulis K. N. Houk Frances H. Arnold 《Angewandte Chemie (International ed. in English)》2020,59(36):15507-15511
Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild‐type cytochrome P450 monooxygenase (P450BM3 from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this non‐native activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves C?H bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native C?H hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire. 相似文献
6.
Irena Blute Martin Svensson Krister Holmberg Margareta Bergh Ann-Therese Karlberg 《Colloids and surfaces. A, Physicochemical and engineering aspects》1999,150(1-3):105-113
It has previously been shown that alcohol ethoxylates readily undergo autoxidation and that one of the major oxidation products is the surfactant aldehyde, i.e. an ethoxylate carrying a –CH2CHO group at the terminal end of the polyoxyethylene chain. In this work the cloud point, phase behavior and aggregation characteristics of the surfactant aldehyde produced by oxidation of C12H25(OCH2CH2)5OH (C12E5) are determined and compared with the values obtained with the parent surfactant. It was found that the physico–chemical behavior of the two species was very similar, which indicates that a considerable portion of the aldehyde group is in hydrated state, i.e. the surfactant aldehyde consists of a mixture of aldehyde in carbonyl form and the corresponding geminal diol. The cloud point of the surfactant aldehyde decreased rapidly with time, even when it was stored at low temperature. Also the parent surfactant and its homologue C12E6 exhibited a decrease in cloud point during storage. For instance, a 1% aqueous solution of C12E6 showed a cloud point decrease from 62 to 32°C after 4 months storage at 40°C. Such a change in solution behavior can have important practical implications. 相似文献
7.
Babasaheb P. Bandgar Sangita S. Makone Sulakshana R. Kulkarni 《Monatshefte für Chemie / Chemical Monthly》2000,131(4):417-420
Summary. A simple, efficient, and environmentally friendly synthesis of geminal diacetates using Envirocat EPZ10? under microwave activation and solvent-free conditions is described. Easy separation and recyclability of the catalyst, high
reaction rates, high yields, and easy work-up are important advantages of this method.
Received November 3, 1999. Accepted November 24, 1999 相似文献
8.
Cationic,Methylene‐Bridged,Intramolecular Donor‐Acceptor Systems Based on Zirconium and Hafnium and Phosphino‐methanides
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Martin Pieper Pauline Auer Sabrina Schwarzbich Franziska Kühn Beate Neumann Hans‐Georg Stammler Norbert W. Mitzel 《无机化学与普通化学杂志》2017,643(14):909-915
A new access to cationic zirconium and hafnium compounds [L2MCH2PR2][MeB(C6F5)3] (L = Cp, Ind; R = iso‐Pr, tert‐Bu; M = Zr, Hf) exhibiting an intramolecular donor‐acceptor system was established by treating the precursors L2M(Me)CH2PR2 with B(C6F5)3 (BCF). Precursors 1 – 6 [L2M(Me)CH2PR2 with L = Cp, Ind; R = iso‐Pr, tert‐Bu; M = Zr, Hf] were fully characterized. The crystal structures of these compounds revealed large M–CH2–P bond angles with values of about 134° indicating the absence of interactions between the Lewis‐acid and Lewis‐base. The cationic compounds [L2MCH2PR2][MeB(C6F5)3] ( 7 – 12 ) were obtained by treatment of 1 – 6 with BCF. They were characterized by NMR spectroscopy, mass spectrometry, and elemental analyses; in H/D‐scrambling experiments with H2/D2 mixtures 7 – 12 disclosed their reactivity towards cleavage of hydrogen. 相似文献
9.
Corrigendum: IR Spectrum and Structure of Protonated Monosilanol: Dative Bonding between Water and the Silylium Ion
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10.
IR Spectrum and Structure of Protonated Monosilanol: Dative Bonding between Water and the Silylium Ion
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M. Sc. Martin Andreas Robert George Dr. Nguyen Xuan Truong Dipl.‐Phys. Marco Savoca Prof. Dr. Otto Dopfer 《Angewandte Chemie (International ed. in English)》2018,57(11):2919-2923
We report the spectroscopic characterization of protonated monosilanol (SiH3OH2+) isolated in the gas phase, thus providing the first experimental determination of the structure and bonding of a member of the elusive silanol family. The SiH3OH2+ ion is generated in a silane/water plasma expansion, and its structure is derived from the IR photodissociation (IRPD) spectrum of its Ar cluster measured in a tandem mass spectrometer. The chemical bonding in SiH3OH2+ is analyzed by density functional theory (DFT) calculations, providing detailed insight into the nature of the dative H3Si+‐OH2 bond. Comparison with protonated methanol illustrates the differences in bonding between carbon and silicon, which are mainly related to their different electronegativity and the different energy of the vacant valence pz orbital of SiH3+ and CH3+. 相似文献