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1.
Tricyclo[5.2.1.02,6]deca-2(6),8-dien-3-one contains a highly strained central double bond due to geometrical constraints imposed by the tricyclic skeleton which does not allow optimal sp2 hybridization at the C2 and C6 bridgehead positions. Michael addition of various nucleophiles (alkoxides, cyanide, and malonate) under protic conditions resulted in an exclusive exo-facial selectivity. This preference can be explained by steric and electronic factors. Michael additions using lithium dialkylcuprates resulted in predominant formation of endo-products, but also some exo-products were obtained. These exo-products arising from endo-approach may be the result of coordination of the cuprate with both the enone moiety and the olefinic C8-C9 bond. Michael additions to tricyclo[5.2.1.02,6]dec-2(6)-en-3-one, which lacks this C8-C9 double bond showed exclusive exo-facial selectivity to give exo-products. Besides these additions were all considerably slower than those to tricyclo[5.2.1.02,6]deca-2(6),8-dien-3-one proving significant electronic participation of the C8-C9 double bond in reactions with this substrate.  相似文献   

2.
Active carbon-and MgF2-supported ruthenium catalysts characterized by a comparable metal dispersion were investigated in CCl2F2 hydrodechlorination. Ruthenium, especially when supported on carbon, exhibits a considerable selectivity to CHClF2. This propensity and a noticeable activity towards C2-products differentiate ruthenium from palladium catalysts. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday  相似文献   

3.
Photocatalytic water splitting to obtain hydrogen energy can transform low-density solar to high density, new and clean energy in a clean way, which is one of the ideal ways to solve the energy crisis and environmental pollution. In this paper, The CoxP/hollow porous C3N4 composite photocatalytic material was synthesized by simple methods. The photocatalytic hydrogen production rate of CoxP/hollow porous C3N4 reaches 1602 μmol g−1 h−1, which is 151 times of that of pure C3N4. The reasons for the high photocatalytic H2 evolution activity of CoxP/hollow porous C3N4 could be summarized as follows: (1) the hollow and porous structure of C3N4 shows higher light capture efficiency, larger specific surface area and more surface active sites. (2) metalloid CoxP loaded forms the Schottky contact with C3N4, which improves the photogenerated charges separation efficiency of C3N4, prolongs the photogenerated charges lifetime and improves the photocatalytic H2 evolution activity of C3N4. (3) The higher conductivity of metalloid CoxP and the lower overpotential of hydrogen production are other reasons for the higher activity of photocatalytic hydrogen production of CoxP/hollow porous C3N4. This work provides an important role for the design of efficient, stable, and efficient construction of photocatalysts for solar energy conversion.  相似文献   

4.
Hydrogen energy is an abundant, clean, sustainable and environmentally friendly renewable energy source. Therefore, the production of hydrogen by photocatalytically splitting water on semiconductors has been considered in recent years as a promising and sustainable strategy for converting solar energy into chemical energy to replace conventional energy sources and to solve the growing problem of environmental pollution and the global energy crisis. However, highly efficient solar-driven photocatalytic hydrogen production remains a huge challenge due to the poor visible light response of available photocatalytic materials and the low efficiency of separation and transfer of photogenerated electron-hole pairs. In the present work, organic heterojunction structures based on bacteriochlorophyll (BChl) and chlorophyll (Chl) molecules were introduced and used for solar-driven photocatalytic hydrogen production from water under visible light. Also, noble metal-free photocatalyst was successfully constructed on Ti3C2Tx nanosheets by simple successive deposition of Chl and BChl, which was used for the photocatalytic splitting water to hydrogen evolution reaction (HER). The results show that the optimal BChl@Chl@Ti3C2Tx composite has a high HER performance with 114 μmol/h/gcat, which is much higher than the BChl@Ti3C2Tx and Chl@Ti3C2Tx composites.  相似文献   

5.
The fullerenes C60 and C70 can be ionized by desorption from a liquid matrix upon bombardment by Cs+ ions of 7 keV kinetic energy. The resulting radical cations, when activated in the ion trap by collisions with Xe target, in the presence of helium, undergo extensive dissociation by loss of multiple C2 units. Large internal energies are deposited into these molecular ions and the dissociation efficiency is in excess of 60%.  相似文献   

6.
《Tetrahedron: Asymmetry》2003,14(7):787-790
A series of racemic dirhodium(II) compounds with two ortho-metalated aryl phosphine ligands in a head-to-tail arrangement Rh2(O2CR)2(pc)2 (pc=ortho-metalated aryl phosphine) (1ak) were tested in the regio- and stereoselective cyclopropanation of racemic 1-diazo-6-methyl-3-(2-propenyl)-5-hepten-2-one 2, which possesses two different reactive CC double bonds for a five-membered-ring formation. The complexes Rh2(O2CCH3)2(pc)2 {pc=[(C6H4)P(C6H5)2], [(p-CH3C6H3)P(p-CH3C6H4)2], and [(C6H4)P(C6H5)(C6F5)]} (1ad) successfully enhanced the cyclopropanation of trisubstituted versus monosubstituted CC bonds to give an 80:20 selectivity ratio. The reaction occurred with excellent diastereoselectivity; the syn-products were the only stereoisomers observed in the whole series of the catalysts. Enantioenriched products were obtained when enantiomerically pure dirhodium(II) complexes were used.  相似文献   

7.
A formal carbene insertion into CO double bonds of 2-hydroxycinnamaldehydes catalyzed by Rh2(esp)2 with Na2CO3 as additive has been disclosed by using aryldiazoacetates as carbene precursors. 2H-chromenes with a quaternary carbon at C-2 position were readily obtained from simple starting materials in good yields with excellent diastereoselectivity under mild reaction conditions in one pot. The reaction mechanism was investigated and proposed as the formation of epoxide intermediate from Rh(II)-associated carbene and (E)-2-hydroxycinnamaldehyde and followed by a cascade epoxide ring-opening procedure in which the (E)-intermediate was converted into the (Z)-intermediate to give (Z)-products.  相似文献   

8.
Butadiene cation radicals are produced symmetrically from the ring and side-chain of the vinylcyclohexene cation radical near the onset of the fragmentation. The appearance energies of C4H6+? and C4H2D4+? from (3,3,6,6-D4)vinylcyclohex ene were measured as 11.07 ± 0.05 and 11.06 ± 0.06 eV, respectively. This sets the barrier to retro-Diels-Alder decomposition at 1140 kJ mol?1 above the energy of 1 and 44 kJ mol?1 above the thermochemical threshold corresponding to C4H6+? + C4H6. Topological molecular orbital calculations indicate that this lowest-energy path involves a sequential rupture of the C3C4 and C5C6 bonds, with a calculated barrier of 211 kJ mol?1. The second, two-step reaction channel proceeds by subsequent fission of the C5C6 and C3C4 bonds with a barrier of 299 kJ mol?1. This channel is found experimentally as a break on the ionization efficiency curve at 12.1 eV. Both the supra-supra and the supra-antara pericyclic reactions go through energy maxima and are therefore forbidden. The supra-supra process is the most favorable route for decomposition from the first excited state, the activation energy being 333 kJ mol?1. The preference for the two-step mechanism is due to hyperconjugative stabilization of intermediate molecular configurations.  相似文献   

9.
We examined the influence of the gas flow-rate, microwave power and trichloroethylene concentration on the destruction of trichloroethylene with a system based on a microwave helium plasma operating at atmospheric pressure. Based on the experimental results obtained, the proposed system allows input concentrations of C2HCl3 in the ppmv range to be reduced to output concentrations in the ppbv range (i.e. virtually quantitative destruction) by using a microwave plasma power below 1000 W. High helium flow-rates and C2HCl3 concentrations allow energy efficiency values above 600 g/kW h to be obtained. Analyses of the output gases by gas chromatography and species present in the plasma by optical emission spectroscopy confirmed the negligible presence of halogen compounds resulting from the destruction of C2HCl3, and that of CCl4 and C2Cl4 as the sole chlorine species exceeding levels of 30 ppbv. Gaseous by-products consisted mainly of CO2, NO and N2O in addition to Cl2 traces.  相似文献   

10.
IrH(CO)(PH3)2(C60), IrCl(CO)(PH3)2(C60), and RhH(CO)(PH3)2(C60) were theoretically investigated with DFT and MP2 to MP4(SDQ) methods.  Because the DFT method considerably underestimates the binding energy compared to the MP2 method, their binding energies were evaluated by the ONIOM(MP4(SDQ):UFF) method.  The binding energy decreases in the order IrH(CO)(PH3)2(C60) (59.4) > RhH(CO)(PH3)2(C60) (48.2) > Pt(PH3)2(C60) (47.2) > IrCl(CO)(PH3)2(C60) (43.0), where in parentheses are the binding energy (in kcal/mol) calculated with the ONIOM(MP4(SDQ):UFF) method and that of Pt(PH3)2(C60) was calculated with the same method and the same basis sets in our previous work.  This decreasing order is interpreted in terms of the dπ orbital energy, the d orbital expansion, the presence of the empty dσ orbital, and the distortion energy of the metal fragment induced by the complexation; for instance, the dπ orbital is at higher energy and more expands in IrH(CO)(PH3)2 than in the Rh analogue, which leads to the larger binding energy of IrH(CO)(PH3)2(C60) than that of the Rh analogue. IrCl(CO)(PH3)2 is less favorable than IrH(CO)(PH3)2 because of the lower energy of dπ orbital.  Although the π-back donation is stronger in IrCl(CO)(PH3)2(C60) than in RhH(CO)(PH3)2(C60), the binding energy of IrCl(CO)(PH3)2(C60) is smaller than that of RhH(CO)(PH3)2(C60) due to the larger distortion energy of the IrCl-(CO)(PH3)2 moiety.  Although the dπ orbital of Pt(PH3)2 is at higher energy than that of IrH-(CO)(PH3)2, the binding energy of IrH(CO)(PH3)2(C60) is larger than that of Pt(PH3)2(C60) because the distortion energy is large and the dσ orbital is doubly occupied in Pt(PH3)2(C60).  It is also noted that these binding energies are much larger than those of the ethylene analogues like those of the Pt(0) complexes, which is reasonably interpreted in terms that the LUMO of C60 is at much lower energy than those of ethylene.  相似文献   

11.
At normal temperature and pressure, pulse corona plasma was used as a new method for the dehydrogenative coupling of methane in the absence of oxygen. The effects of voltage polarity and input energy on the dehydrogenative coupling of methane were investigated. The parameter “energy efficiency” was introduced to examine the coupling of the input energy and the dehydrogenative coupling of methane. The experimental results show that positive corona gives higher energy efficiency than negative corona. When the positive corona was chosen, C2 yield per pass was 31.6% and acetylene yield per pass was 30.1% with 44.6% methane conversion at an input energy density of 1788kJ/mol and a pulse repetition frequency of 66Hz. The function of input energy density towards methane conversion may be expressed as a formula of-In(1-X) =k (PIF). In the range of input energy employed, C2 yield is proportional to input energy density, but energy efficiency drops off with increasing input energy density.  相似文献   

12.
Production of multicarbon products (C2+) from CO2 electroreduction reaction (CO2RR) is highly desirable for storing renewable energy and reducing carbon emission. The electrochemical synthesis of CO2RR catalysts that are highly selective for C2+ products via electrolyte‐driven nanostructuring is presented. Nanostructured Cu catalysts synthesized in the presence of specific anions selectively convert CO2 into ethylene and multicarbon alcohols in aqueous 0.1 m KHCO3 solution, with the iodine‐modified catalyst displaying the highest Faradaic efficiency of 80 % and a partial geometric current density of ca. 31.2 mA cm?2 for C2+ products at ?0.9 V vs. RHE. Operando X‐ray absorption spectroscopy and quasi in situ X‐ray photoelectron spectroscopy measurements revealed that the high C2+ selectivity of these nanostructured Cu catalysts can be attributed to the highly roughened surface morphology induced by the synthesis, presence of subsurface oxygen and Cu+ species, and the adsorbed halides.  相似文献   

13.
The electrochemical carbon dioxide reduction reaction (CO2RR) to C2 chemicals has received great attention. Here, we report the cuprous oxide (Cu2O) nanocubes cooperated with silver (Ag) nanoparticles via the replacement reaction for a synergetic CO2RR. The Cu2O-Ag tandem catalyst exhibits an impressive Faradaic efficiency (FE) of 72.85% for C2 products with a partial current density of 243.32 mA·cm−2. The electrochemical experiments and density functional theory (DFT) calculations reveal that the introduction of Ag improves the intermediate CO concentration on the catalyst surface and meanwhile reduces the C-C coupling reaction barrier energy, which is favorable for the synthesis of C2 products.  相似文献   

14.
Lead halide hybrids have shown great potentials in CO2 photoreduction, but challenging to afford C2+ reduced products, especially using H2O as the reductant. This is largely due to the trade-off problem between instability of the benchmark 3D structures and low carrier mobility of quasi-2D analogues. Herein, the lead halide dimensionality of robust coordination polymers (CP) was modulated by organic ligands differing in a single-atom change (NH vs. CH2), in which the NH groups coordinate with interlamellar [PbI2] clusters to achieve the important 2D→3D transition. This first CP based on 3D cationic lead iodide sublattice possesses both high aqueous stability and a low exciton binding energy of 25 meV that is on the level of ambient thermal energy, achieving artificial photosynthesis of C2H5OH. Photophysical studies combined with theoretical calculations suggest the bridging [PbI2] clusters in the 3D structure not only results in enhanced carrier transport, but also promotes the intrinsic charge polarization to facilitate the C−C coupling. With trace loading of Rh cocatalyst, the apparent quantum efficiency of the 3D CP reaches 1.4 % at 400 nm with a high C2H5OH selectivity of 89.4 % (product basis), which presents one of the best photocatalysts for C2 products to date.  相似文献   

15.
The effectiveness of applying a pulsed corona discharge to the destruction of olfactory pollution in air was investigated. This paper presents a comparative study of the decomposition of three representative sulfide compounds in diluted concentrations: hydrogen sulfide (H2S), dimethyl sulfide (DMS), and ethanethiol (C2H5SH), which could be completely removed when a sufficient but reasonable energy density was deposited in the gas. DMS showed the lowest energy cost (around 30 eV/molecules); C2H5SH and H2S had an EC of respectively 45 eV and 115 eV. The efficiency of the non-thermal plasma process increased with decreasing the initial concentration of sulfide compounds, while the energy yield remained almost unchanged. SO2 was the only identified byproduct of H2S decomposition, but the sulfur balance suggests the formation of undetected SO3. The byproducts analyzed during the degradation of DMS and C2H5SH enabled to propose a reaction mechanism, starting with radical attack and breaking of C–S bonds.  相似文献   

16.
Vacuum ultraviolet (VUV) dissociative photoionization of isoprene in the energy region 8.5–18 eV was investigated with photoionization mass spectroscopy (PIMS) using synchrotron radiation (SR). The ionization energy (IE) of isoprene as well as the appearance energies (AEs) of its fragment ions C5H7+, C5H5+, C4H5+, C3H6+, C3H5+, C3H4+, C3H3+ and C2H3+ were determined with photoionization efficiency (PIE) curves. The dissociation energies of some possible dissociation channels to produce those fragment ions were also determined experimentally. The total energies of C5H8 and its main fragments were calculated using the Gaussian 03 program and the Gaussian‐2 method. The IE of C5H8, the AEs for its fragment ions, and the dissociation energies to produce them were predicted using the high‐accuracy energy model. According to our results, the experimental dissociation energies were in reasonable agreement with the calculated values of the proposed photodissociation channels of C5H8. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

17.
Electroreduction of CO2 to multi-carbon (C2+) products is a promising approach for utilization of renewable energy, in which the interfacial water quantity is critical for both the C2+ product selectivity and the stability of Cu-based electrocatalytic sites. Functionalization of long-chain alkyl molecules on a catalyst surface can help to increase its stability, while it also tends to block the transport of water, thus inhibiting the C2+ product formation. Herein, we demonstrate the fine tuning of interfacial water by surface assembly of toluene on Cu nanosheets, allowing for sustained and enriched CO2 supply but retarded water transfer to catalytic surface. Compared to bare Cu with fast cathodic corrosion and long-chain alkyl-modified Cu with main CO product, the toluene assembly on Cu nanosheet surface enabled a high Faradaic efficiency of 78 % for C2+ and a partial current density of 1.81 A cm−2. The toluene-modified Cu catalyst further exhibited highly stable CO2-to-C2H4 conversion of 400 h in a membrane-electrode-assembly electrolyzer, suggesting the attractive feature for both efficient C2+ selectivity and excellent stability.  相似文献   

18.
From previous reports, graphitic carbon nitride (g‐C3N4) can be used as a photocatalyst, although the low efficiency of solar energy utilization, small specific surface area and high recombination rate of photogenerated electron–hole pairs limit its practical application. For the purpose of increasing photocatalytic activity, especially under irradiation of visible light, we successfully synthesized a new composite, namely porous g‐C3N4/Ag/Cu2O, through chemical adsorption of Ag‐doped Cu2O on porous g‐C3N4, which has not been investigated carefully worldwide. The composition, morphology and optical properties of the composite were investigated through methods including X‐ray diffraction, energy‐dispersive X‐ray, Fourier transform infrared, UV–visible and photoluminescence spectroscopies and transmission electron microscopy. Using rhodamine B as organic pollutant to be degraded under the irradiation of visible light, different mass ratios of Ag/Cu2O doped on porous g‐C3N4 led to enhanced photocatalytic performance of the composite compared to pure porous g‐C3N4. When the mass ratio of Ag/Cu2O is 15%, porous g‐C3N4/Ag/Cu2O exhibits a degradation rate 2.015 times higher than that of pure porous g‐C3N4. The reasons for this phenomenon may be attributed to the increased utilization efficiency of visible light, high‐speed separation of photogenerated electron–hole pairs, accelerated interfacial transfer process of electrons and increased surface area of the composite. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
Quenching of electronically excited states of Ln3+* ions generated upon photoexcitation of toluene solutions of Ln(acac)3·H2O (Ln = Tb, Eu) complexes by C60 fullerene at 293 K was detected and investigated. The dependences of quenching efficiency on C60 concentration obtained from data on the decrease in the photoluminescence intensity and Ln3+* lifetimes obey the Stern-Volmer law. Quenching is due to inductive-resonant energy transfer from Ln3+* to C60 fullerene. The bimolecular rate constants for quenching, the overlap integrals of the Ln3+* photoluminescence spectra with the C60 absorption spectra, and the critical energy transfer distances were determined. No sensitized luminescence of C60 in the system studied was detected. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 921–925, June, 2006.  相似文献   

20.
We explored the interactions of gas molecules such as H2, CH4, C2H4, C2H6, CO2, and CS2 sandwiched by two pyrazine (Pz) molecules, which were employed as a model of organic linker in the Hofmann-type metal?Corganic framework (MOF). The MP2.5/aug-cc-pVTZ method was employed here, because this method presents almost the same binding energy as that calculated by the CCSD(T)/aug-cc-pVDZ with MP2.5-evaluated basis set extension effects to aug-cc-pVTZ basis set. The binding energy of the gas molecule increases in the order H2?<?CH4?<?CO2?<?C2H4????C2H6?<?CS2. The energy decomposition analysis of the interaction energy indicates that the electrostatic term presents the largest contribution to the interaction energy at the Hartree?CFock level. However, the dispersion interaction provides dominant contribution to the total binding energy at correlated level. We newly found a linear correlation between the z-component of polarizability of gas molecules and dispersion energy, where the z-axis was taken to be perpendicular to two Pz rings. These results are useful for understanding and predicting the binding energy of the gas molecule with the organic linkers of MOF.  相似文献   

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