Photochemical cyclization of compound 1, a homoenediyne (-CCC=CCH2CC-) bearing two ethynylanthracene chromophores, yields two isomeric dihydrocyclopent[a]indene ring systems, spiro-fused to the 9-position of a 9,10-dihydroanthracene moiety. Evidence of a photochemically initiated diradical cyclization pathway is proposed on the basis of (i) hydrogen abstraction from reaction with 1,4-cyclohexadiene (1,4-CHD) and (ii) the observation of 1,4-addition of benzene (solvent). The reaction was further analyzed by a complete density functional theory (DFT) study, using an unrestricted approach (UBLYP) with a 6-31G* basis set for the open-shell triplet states of the reactants, products, and diradical intermediates to model the photochemical nature of observed transformation. A mechanism detailing the observed cyclization/addition reaction is proposed. 相似文献
Polarography, cyclic voltammetry and coulometry reveal that a catalytic reduction of the tetraalkylammonium cation, R4N+, of the supporting electrolyte is involved in the electrochemical reduction of triphenylphosphine (TPP) and its oxide (TPPO) in aprotic solvents such as acetonitrile, dimethylformamide and hexamethylphosphoramide. There is however progressive consumption of TPP and TPPO resulting in the final formation of phenyl substitution products (RPØ2 and ROPØ2). Comparison with the reduction of the BuPØ3+ cation allows to propose the following mechanism which involves a chemical type catalytic process:
Redox type catalytic mechanisms are discussed and shown to be unlikely. Values of the alkylation rate constant are derived from the polarographic or the coulometric data or from cyclic voltammetry according to its magnitude which varies with the solvent. TPP anion radical appears as more readily alkylable than TPPO anion radical. 相似文献
Grignard reactions with alkoxysilanes or carbonyl compounds produce alkoxymagnesium halides as by-products. Kinetic measurements for reactions of silanes and of a ketone were performed with Grignard reagents, enriched in alkoxymagnesium halides and taken in a great excess.The alkoxide-type reaction products complex tightly with Grignard reagents and enhance in this way their nucleophilicity, thus accelerating the reaction. However, alkoxides branched at α-C atom exert an unfavorable steric hindrance to reaction resulting in a decrease in the reaction rate. 相似文献
The synthesis of model long-chain hydrocarbons (C13 and C19) carrying a vinyl group and a trichloro- or a triethoxysilyl group at each end is reported. These compounds are suitable for linkage to a hydroxylated silicon surface and at the other end with vinyl group for further functionalization and multilayer formation. 相似文献
Kinetics of the reactions of butylmagnesium chloride and phenylmagnesium bromide with tetraethoxysilane and methyltrichlorosilane was investigated in diethyl ether and diethyl ether-toluene mixtures. Replacement of ether by toluene significantly accelerates the reaction with alkoxysilanes, while no effect was found for the reaction with chlorosilanes. We established that the reaction with alkoxysilanes consists of replacement of a donor molecule at the magnesium center by the silane followed by subsequent rearrangement of the complex to products through a four-center transition state. Chlorosilanes react differently without solvent molecule replacement but also via a four-center transition state. Large negative activation entropies are consistent with formation of cyclic transition states. Small activation enthalpy values together with remarkable exothermicity point to early transition states of the reactions. 相似文献
The disproportionation of elemental sulfur at moderate temperatures is investigated in the redox condensation involving o‐halonitrobenzenes 1 and benzylamines 2 . As a redox moderator, elemental sulfur plays the dual role of both electron donor and acceptor, generating its lowest and highest oxidation states: S?2 (sulfide equivalent) in benzothiazole 3 and S+6 (sulfate equivalent) in sulfamate 4 , and filling the electron gap of the global redox condensation process. Along with this process, a cascade of reactions of reduction of the nitro group of 1 , oxidation of the aminomethyl group of 2 , metal‐free aromatic halogen substitution, and condensation finally led to 2‐arylbenzothiazoles 3 . 相似文献
Journal of Radioanalytical and Nuclear Chemistry - The aim of this study was to find trace elements that increase risk of breast cancer based on the deviation of the concentration of trace elements... 相似文献