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1.
This paper studied the mechanism of the alkene insertion elementary step in the asymmetric hydroformylation (AHF) catalyzed by RhH(CO)2[(R,S)-Yanphos] using four alkene substrates (CH2=CH- Ph, CH2=CH-Ph-(p)-Me, CH2=CH-C(==O)OCH3 and CH2=CH-OC(=O)-Ph, abbreviated as A1-A4). Interestingly, the equatorial vertical coordination mode (A mode) with respect to the Rh center was found for AI and A2 but not for A3 and A4, although the equatorial in-plane coordination mode (E mode) was found for A1 -A4. The relative energy of the E mode of the -q2-intermediates is lower than that of the A mode. In the alkene insertion step, Path 1 is more favorable than Path 2 for this system. As for AI and A2, there could be a transformation between 2eq and 2ax.  相似文献   

2.
A computational study at different levels of theory was performed for the not yet synthesized phosphastannaallenes >SnCP– in order to evaluate the strength of the SnC bond, the main postulated factor to stabilize such species, and the geometry in R2SnCPR derivatives. The influence of the substituents with various electronic effects (H, Me, Ph, F, Cl, OMe, SiMe3) at the Sn or P atoms of the SnCP unit on the SnC bond order was evaluated in the quest for a substituent that would stabilize the phosphastannaallenic unit. PC bond orders have also been calculated.  相似文献   

3.
《Vibrational Spectroscopy》2007,43(2):351-357
The FT-Raman and FTIR spectra of 12 generations of phosphorus-containing dendrimers:
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with terminal aldehyde and PCl groups have been recorded and analyzed. Their spectral pattern is determined by the ratio T/R (T, the number of terminal groups; R, the number of repeating units). The influence of the encirclement on the band frequencies and intensity was studied and due to the predictable, controlled and reproducible structure of dendrimers the information usually inaccessible was obtained. Bands assigned to the core, repeated units and terminal groups of dendrimers were separated by the differential spectroscopy method. The strong band at 1600 cm−1 show marked changes of optical density in dependence of the aldehyde (CHO) or azomethyne (CHN) substitution in aromatic ring. From the differential IR and Raman spectra of dendrimers it follows that for the generations higher than 6, the steric congestion disturbs the conformations of the terminal groups. The rather rigid repeated units with little conformational flexibility define the perfect microstructure of phosphorus-containing dendrimers up to 11 generation. FT-Raman and FTIR spectroscopy provides the unique detailed information about the structure of technologically relevant materials, which could not be obtained before with any other technique.  相似文献   

4.
Combined experimental and theoretical studies on molecular structure of the zero generation dendron, built from the hexafunctional cyclotriphosphazene core, with five OC6H4(CH2)2NHSO2C10H6N(CH3)2 terminal groups and one oxybenzaldehyde group G0 are reported. The Fourier transform Raman and IR spectra of G0 have been recorded. Conformations of low energy isomers of G0 have been studied at quantum-chemical level. The optimized geometry has been calculated by density functional (DFT) method at the PBE/TZ2P level of theory. The theoretical geometrical parameters, harmonic vibrational frequencies, IR intensities and Raman scattering activities are predicted in a good agreement with the experimental data. It was found that dendron molecule G0 has a concave lens structure with planar OC6H4CHO fragments and slightly non-planar cyclotriphosphazene core. Relying on DFT calculations the bands of the core and terminal groups were assigned. The frequencies of ν(NH) bands in the IR spectrum reveal the presence of the H-bonds in the dendron.  相似文献   

5.
The curing dynamics and network formation of cyanate ester resin/graphene oxide (GO) nanocomposites were studied by means of Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FT-IR) and Raman spectroscopies. The incorporation of GO into the resin showed a strong catalytic effect on the cure of the resin, especially in the initial stages. Addition of 4 wt.% GO resulted in the decrease of curing temperature significantly about 97 °C. Activation energy of the nanocomposites also maintained at a low level till the end of the cure. The most effective catalytic behavior was observed with 1 wt.% GO. Both FT-IR and Raman spectra revealed that OH group in GO reacted with cyanate group OCN in the resin to form O(CNH)O bond in the early stages of the cure. These results could provide a low temperature curing route for cyanate ester resins with improved curing efficiency.  相似文献   

6.
A set of small radicals SiF, SiCl, F–CO, CN–O, O3H, NO3, CH2NC, CF3O, and O3 exhibit pronounced discrepancies between different experimental as well as experimental and calculated values of the respective enthalpies of formation ΔfHo(298.15). For stable molecules, this quantity is well established and reliable values are available. However, for free radicals and other short-lived intermediates, the situation is not nearly as favorable. Consequently, critical evaluation of thermodynamic properties of free radicals is necessary, both originating from experiment and computation. Calculated enthalpies of formation for the above systems are based on the ab initio methods G3MP2B3 and CCSD(T)–CBS (W1U) for which mean absolute deviations are known.  相似文献   

7.
Treatment of the complex [Ru{C(CCPh)CHPh}Cl(CO)(PPh3)2] (1) with one equivalent of CNR(R =tBu, C6H3Me2-2,6) gives [Ru{C(CCPh)CHPh}Cl(CNR)(CO)(PPh3)2]. Addition of a further equivalent of isonitrile and [NH4]PF6 leads to the salts [Ru{C(CCPh)CHPh}Cl(CNR)2(CO)(PPh3)2]PF6 and the mixed species [Ru{C(CCPh) CHPh}(CO)(CNtBu)(CNC6H3Me2-2,6)(PPh3)2]PF6. The related [Ru{C(CCPh)CHPh}(CNt(CO)2  相似文献   

8.
The FT Raman spectra of the zero and first generations of phosphorus-containing dendrimers built from thiophosphoryl, cyclotriphosphazene and phthalocyanine core with terminal oxybenzaldehyde groups have been recorded and analyzed. The structural optimization and normal mode analysis were performed for dendrimers on the basis of the density functional theory (DFT). The calculated geometrical parameters, harmonic vibrational frequencies and Raman scattering activities are predicted in a good agreement with the experimental data. The experimental Raman spectra of dendrimers were interpreted by means of potential energy distribution. Relying on DFT calculations the lines of the cores, repeating units and terminal groups of dendrimers were assigned.The influence of the encirclement on the line frequencies and intensities was studied and due to the predictable, controlled and reproducible structure of dendrimers the information, usually inaccessible is obtained. The strong line at 1600 cm−1 show marked changes of intensity in dependence of aldehyde (CHO) or azomethyne (CHN) substituents in the aromatic ring. The polarizabilities and lipophilicity of dendrimers were estimated.  相似文献   

9.
The reaction of RuTp(COD)Cl (1) with PR3 (PR3 = PPh2iPr, PiPr3, PPh3) and propargylic alcohols HCCCPh2OH, HCCCFc2OH (Fc = ferrocenyl), and HCCC(Ph)MeOH has been studied.In the case of PR3 = PPh2iPr, PiPr3 and HCCCPh2OH, the 3-hydroxyvinylidene complexes RuTp(PPh2iPr)(CCHC(Ph)2OH)Cl (2a) and RuTp(PiPr3)(CCHC(Ph2)OH)Cl (2b) were isolated.With PR3 = PPh2iPr and HCCCFc2OH as well as with PR3 = PPh3 and HCCCPh2OH dehydration takes place affording the allenylidene complexes RuTp(PPh2iPr)(CCCFc2)Cl (3b) and RuTp(PPh3)(CCCPh2)Cl (3c).Similarly, with PPh2iPr and HCCC(Ph)MeOH rapid elimination of water results in the formation of the vinylvinylidene complex RuTp(PPh2iPr)(CCHC(Ph)CH2)Cl (4).In contrast to the reactions of the RuTp(PR3)Cl fragment with propargylic alcohols, with HCC(CH2)nOH (n = 2, 3, 4, 5) six-, and seven-membered cyclic oxycarbene complexes RuTp(PR3)(C4H6O)Cl (5), RuTp(PR3)(C5H8O)Cl (6), and RuTp(PR3)(C6H10O)Cl (7) are obtained. On the other hand, with 1-ethynylcyclohexanol the vinylvinylidene complex RuTp(PPh2iPr)(CCHC6H9)Cl (8) is formed. The reaction of the allenylidene complexes 3ac with acid has been investigated. Addition of CF3COOH to a solution of 3ac resulted in the reversible formation of the novel RuTp vinylcarbyne complexes [RuTp(PPh2iPr)(C–CHCPh2)Cl]+ (9a), [RuTp(PPh2iPr)(C–CHCFc2)Cl]+ (9b), and [RuTp(PPh3)(C–CHCPh2)Cl]+ (9c). The structures of 3a, 3b, and 5b have been determined by X-ray crystallography.  相似文献   

10.
Levoglucosan (1,6-anhydro-β-d-glucopyranose) decomposition is an important step during cellulose pyrolysis and for secondary tar reactions. The mechanism of levoglucosan thermal decomposition was studied in this paper using density functional theory methods. The decomposition included direct CO bond breaking, direct CC bond breaking, and dehydration. In total, 9 different pathways, including 16 elementary reactions, were studied, in which levoglucosan serves as a reactant. The properties of the reactants, transition states, intermediates, and products for every elementary reaction were obtained. It was found that 1-pentene-3,4-dione, acetaldehyde, 2,3-dihydroxypropanal, and propanedialdehyde can be formed from the CO bond breaking decomposition reactions. 1,2-Dihydroxyethene and hydroxyacetic acid vinyl ester can be formed from the CC bond breaking decomposition reactions. It was concluded that CO bond breaking is easier than CC bond breaking due to a lower activation energy and a higher released energy. During the 6 levoglucosan dehydration pathways, one water molecule which composed of a hydrogen atom from C3 and a hydroxyl group from C2 is the preferred pathway due to a lower activation energy and higher product stability.  相似文献   

11.
DFT calculations with B3LYP and PBE1PBE functionals and 6–311++G(d,p) basis set have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the RCN?HF H-bonded complexes with R = NH2, CH3O, CH3, OH, SH, H, Cl, F, CF3, CN and NO2. As expected, it has been verified as a red-shift of the HF stretching frequency (νHF), in conformity with the elongation of the bond after complexation. On the other hand, the CN stretching frequency (νCN) is blue-shifted and corresponds to a shortening of the bond. The binding energies (ΔEc), including BSSE and ZPVE corrections, show a linear correlation with several structural, electronic and vibrational properties. In particular, an important linear dependence between the binding energy and the calculated dipole moment of the free RCN molecule (μRCN) has been found. This result suggests that μRCN can be a useful quantity in order to predict the ability of this fragment to form a hydrogen-bond. The IR intensities of stretching and bending modes of complexed HF acid fragment are adequately interpreted through the atomic polar tensor of the hydrogen atom in HF using the modified CCFO model for infrared intensities. The new vibrational modes arising from complexation show several interesting features.  相似文献   

12.
An overview is given on synthesis and structures of new bidentate phosphaalkene ligands [(RMe2Si)2CP]2E (E = O, NR, N?) and (RMe2Si)2CPN(R′)PR′′2. Exceptional properties of these ligands, extending beyond predictable properties of phosphaalkenes are: (i) the NSi bond cleavage of [(iPrMe2Si)2CP]2NSiMe3 with AuI and RhI chloro complexes under mild conditions leading to binuclear complexes of the 6π-delocalised imidobisphosphaalkene anion [(iPrMe2Si)2CP]2N?, and (ii) the chlorotropic formation of molecular 1:2 PdII and PtII metallochloroylid complexes with novel ylid-type ligands [(RMe2Si)2CP(Cl)N(R)PR2]?, and the transformation of a P-platina-P-chloroylid complex into a C-platina phosphaalkene by intramolecular chlorosilane elimination. Properties of the heavier congeners [(RMe2Si)2CP]2E (E = S, Se, Te, PR, P?, As?) and (RMe2Si)2CPEPR′′2 (E = S, Se, Te) are also described.  相似文献   

13.
Functionalized nanodiamond particles (NDs) represent carbon nanomaterial with unique properties for various applications. Here we report on a new approach to surface modification of NDs by their exposure to radio frequency (RF) plasma or laser irradiation (LI) plasma directly in aqueous solution. By using grazing angle reflectance Fourier transform infrared spectroscopy and supporting analysis by X-ray photoelectron spectroscopy, zeta-potential, and Kelvin force microscopy we show that surface chemistry of NDs produced by detonation process (DNDs) or high-pressure high-temperature process (HPHT NDs) works in different way. Moieties on as-received NDs are dominated by COOH and COC groups due to wet chemical cleaning procedures. On DNDs, both RF and LA treatment lead to removal of sp2 shell and additional oxidation of the surface to C OC groups. On HPHT NDs the RF treatment leads to reduction of COC groups that are transformed into COH and CH moieties. Thus at least partial hydrogenation of colloidal HPHT NDs seems feasible.  相似文献   

14.
Reaction of [WNAr(CH2tBu)2(CHtBu)] (Ar = 2,6-iPrC6H3) with silica partially dehydoxylated at 200 °C does not lead only to the expected bisgrafted [(SiO)2WNAr(CHtBu)] species, but also surface reaction intermediates such as [(SiO)2WNAr(CH2tBu)2]. All these species were characterized by infrared spectroscopy, 1D and 2D solid state NMR, elemental analysis and molecular models obtained by using silsesquioxanes. While a mixture of several surface species, the resulting material displays high activity in the olefin metathesis.  相似文献   

15.
The role of reactive intermediates of water radiolysis (eaq, H, HO, O2/HO2) in decoloration and mineralization of aqueous solutions of Acid Red 1 dye was investigated. The decoloration is highly effective in the reactions of eaq and H, and less effective in HO reactions. The O2/HO2 pair does not take part in decoloration. For mineralization, which is an oxidative degradation, HO radicals are needed: the efficiency increases with the dissolved oxygen concentration. The reactions of the O2/HO2 radical pair slightly increase the rate of mineralization. Iron and copper ions (possible constituents of waste waters) in low concentration do not influence the reactions.  相似文献   

16.
Intercalates 3RVS2NH3 and 3RTaS2NH3, isostructural with 3RTiS2NH3, are described for the first time. Magnetic properties of 3RTiS2NH3, 3RVS2NH3, and 2HTaS2NH3 respectively are interpreted in terms of a charge transfer (in agreement with an ionic model) from the intercalant to the lowest conduction band which consists mainly ofeg, a1g anda′1 transition metald states.  相似文献   

17.
The study reports the inter-molecular interactions and dynamics of CO and CH stretching modes of NN- Dibutyl Formamide (DBF) in DMSO solvent using Raman spectroscopic technique. The Raman band of CO and CH stretching modes have been deconvoluted into two distinct bands for neat as well as in DMSO solvent. Peak wavenumbers of CO stretching modes show red shift while CH stretching modes shows blue shift with the increase in solvent concentrations. The optimized geometric parameters, vibrational wavenumbers, Mulliken atomic charges and natural bond orbitals of the molecule has been computed using Density Functional Theory (DFT) method with basis set 6-31 +G (d, p). In addition, the same basis set has been carried out with counterpoise keyword accounting BSSE calculation on monomer and dimer states with DMSO solvent to present an appropriate interacting environment. IEF-PCM solvation model has also been computed using the same basis set and compares the geometrical parameters and vibrational wavenumbers of the molecules and in their complexes. In order to get a complete study of the DBF + DMSO complexes, explicit solvation model has also been calculated for Monomer DBF in two solvent molecules. Theoretical calculations of frequencies have been compared with the experimental findings and the results are found in good agreement.  相似文献   

18.
《Vibrational Spectroscopy》2007,43(1):104-110
The Raman spectra of serine [α-amino-β-hydroxypropionic acid; HOCH2CH(NH3)+COO] and 3,3-dideutero-serine [HOCD2CH(NH3)+COO] in aqueous solution were studied in the range 4000–300 cm−1. The data obtained for the deuterated compound are novel and provide compelling evidence that previously reported assignments for the undeuterated amino acid should be revised.  相似文献   

19.
Although 1,1-bis(trifluoromethyl)butadiene-1,3 (1) reacts with dimethylamine with selective formation of 1,4-adduct [trans-(CF3)2CHCHCHCH2N(CH3)2], halogenation of 1 proceeds with predominant formation (>92%) of 1,2-adducts (CF3)2CCHCHXCH2X (X = Cl or Br). Electrophilic conjugated addition of “ClF” or “BrF” to 1 proceeds exclusively with the formation of 1,2-adducts (CF3)2CCHCHFCH2X (major) and (CF3)2CCHCHXCH2F (X = Cl or Br). Difluorocarbene adds selectively to CHCH2 moiety of 1 forming thermally stable vinylcyclopropane. In Diels-Alder reaction with linear or cyclic dienes (butadienes, cyclopentadiene, cyclohexadiene-1,3) and quadricyclane compound 1 behaves as dienophile providing for the reaction electron-deficient CHCH2 bond. The relative rate of cycloaddition of 1 and other fluoroolefins to quadricyclane, measured by high temperature NMR, indicates that (CF3)2CCH acts as very strong electron-withdrawing substituent. Synthetic utility of products based on 1 was also demonstrated.  相似文献   

20.
Mid-Infrared spectra of pyrimidine (PM) and pyrazine (PZ) were recorded in the gas phase using a multi-pass long path gas cell. The IR band structure of these compounds above and below 3000 cm−1 is very broad and contains many humps and shoulders. These humps and shoulders are due to various higher quantum excitation of low-frequency vibrational modes, which participate in Fermi resonance with the nearby CH stretch fundamentals and appears in this region. We constructed an Effective Spectroscopic Hamiltonian (ESH) in a mixed local mode (LM) normal mode (NM) basis to assign the various overtone and combination bands in the CH stretching region of these compounds. The CH stretching vibrations of both PZ and PM were treated as symmetrized anharmonic Morse oscillators in local coordinates and the in-plane deformations down to 1000 cm−1 were treated as normal coordinates. The ESHs were diagonalized and the resulting eigenvalues were subsequently fitted in a given parameter space with the experimentally observed bands. The eigenvalues of the converged Hamiltonian are the anharmonic frequencies and the transition intensities were obtained by summing the squared eigenvector components. The overtone and combination transitions near 3000 cm−1 of both PM and PZ were identified and assigned from the eigenvector coefficients of the ESH matrix. The wavefunctions of a pure CH stretch, overtone of the HCC in-plane bend and due to Type 1 Fermi coupling (resonance between a fundamental with an overtones of a low frequency mode, in this case resonance between the CH strech and the overtone of HCC in-plane bending modes) has been demonstrated pictorially.  相似文献   

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