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1.
The equilibrium constants of the reaction of cis, trans-[Ru(CO) 2(PMe 3) 2(CH 3)I] (Mc) with carbon monoxide to give cis, trans[Ru(CO) 2(PMe 3) 2 (COMe)i] (Ac) and trans, trans[Ru(CO) 2(PMe 3) 2(COMe)I] (At) were measured at various temperatures in toluene. The thermodynamic parameters are compared with those obtained for the isoelectronic complexes of iron, and the trend is discussed. The kinetics of the carbonylation reaction of Mc, as well as those of the inverse decarbonylation reaction of At were measured. The kinetics of the carbonylation of the new complex trans, trans-[Ru(CO) 2(PMe 3) 2(CH 3)I] (Mt) were also investigated. All the results afford further support to the previously proposed CO insertion mechanism occurring via methyl migration. The comparison of these kinetic results with those of isoelectronic complexes of iron indicates that ruthenium is more reactive than iron, which is reflected by its greater aptitude to act as catalyst in many processes. 相似文献
2.
The Monsanto acetic acid process is one of the most effective ways to produce acetic acid industrially. This process has been studied experimentally but theoretical investigations are so far sparse. In the current work the active catalytic species [Rh(CO) 2I 2] − (1) and its isomerisation has been studied theoretically using the hybrid B3LYP exchange and correlation functional. Similar calculations has been performed for the iridium complex [Ir(CO) 2I 2] − (2) that also is catalytically active in the methanol carbonylation. Experimental work has confirmed the existence of the cis forms of the active catalytic species, but they do not rule out the possibility of the trans isomers. Our gas phase results show that cis-1 has 4.95 kcal/mol lower free energy than trans-1, and cis-2 has 10.39 kcal/mol lower free energy than trans-2. In the case of rhodium, trans-1 can take part to the catalytic cycle but in case of iridium this is not very likely. We have also investigated the possible mechanisms of the cis to trans conversions. The ligand association mechanism gave free energy barrier of 13.7 kcal/mol for the rhodium complex and 19.8 kcal/mol for iridium. Thus the conversion for the rhodium complex is feasible whereas for iridium it is unlikely. 相似文献
3.
The complexes [Ru(S,S) 2(PPh 3) 2] [S,S = EtCOCS 2−, (CH 2) 4NCS 2−] react with a variety of tertiary phosphines with the substitution of triphenylphosphine and the formation of [Ru(S,S) 2(PR 3) 2]. The reaction occurs with the formation ofthe cis isomer, except for the complex with PMe 2Ph that gives rise to the trans isomer as the crystal structure shows. The effect of the different phosphines on the ruthenium complex is analysed in terms of the spectroscopic and electrochemical properties of the isolated compounds. The cyclic voltammetric studies of the cis complexes show that isomerization to the trans isomer occurs on oxidation. This isomerization is not observed in the trans-[Ru(S,S) 2(PMe 2Ph) 2] complexes that give rise to stable trans-ruthenium(II)/ruthenium(III) couples. In a similar way the diphosphine complexes afford a quasi-reversible cis-ruthenium(II)/ruthenium(III) process. 相似文献
4.
The monosilylated acyclic phosphazene ligand Me 3SiNP(NMe 2) 2NP(NMe 2) 2 NH 2 (3) has been synthesized and characterized. The reaction of 3 with antimony triacetate, Sb(OOCMe 3), in refluxing toluene forms a cyclic phosphazene derivative, [N{P(NMe 2) 2NH} 2Sb(OOCMe) 2 (4), which is characterized by elemental analyses, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis. Complex 4 crystallizes in the form of a cis and trans isomeric chain in the solid state. 相似文献
5.
Gas and vapour permeability in both freshly cast and aged poly(1-trimethylsilyl-1-propyne) (PTMSP) membranes were investigated in terms of solubility and diffusion coefficients for two probe molecules, a permanent gas (nitrogen) and an organic vapour (dichloromethane). To get reliable data for this study, we set up a fast and reproducible ageing procedure consisting of thermal treatment of the polymer films (100 °C during 24 h under vacuum). As expected, measurements recorded from time-lag experiments and isothermal sorption showed strong variations of the PTMSP transport properties before and after the thermal ageing procedure. Freshly cast membranes exhibited high permeability, whereas after ageing a 40–45% decrease of the permeability was recorded for both probes. The results demonstrated that only the glassy physical microstructure of PTMSP was affected by the ageing procedure, while the chemical structure was unchanged. Based on a dual-mode model for sorption and a Long's model for diffusion, the analysis of the data showed that the solubility and diffusion coefficients of the gas and the vapour were not affected in the same way. For nitrogen, only the diffusion coefficient decreased, whereas for dichloromethane, the thermal treatment mainly influenced the sorption coefficient. The lower permeability due to the combination of sorption and diffusion parameters could be attributed to a change of the PTMSP hole geometry or the hole connections. 相似文献
6.
The equilibrium geometry and the potential energy and dipole moment surfaces have been determined for the cis and trans isomers of the HONO molecule by an ab initio Moller–Plesset (MP2) calculation with a wide set of atomic orbitals. The multidimensional anharmonic vibrational Schrodinger equations are solved using the variational method with the Hamiltonian and wave functions written in the normal coordinates of cis and trans isomers. All one- and two-dimensional and a number of three-dimensional vibrational problems are solved to obtain the energy levels and vibrational eigenfunctions. The frequencies and intensities for the fundamental, overtone and some combination bands are determined in good agreement with the available experimental results. The calculation shows the strength of coupling between different vibrational modes and reveals the presence of strong resonances between the ( v1, v3, v6) and ( v1, v3−1, v6+2) states of cis-HONO. This fact may be important for understanding the energy redistribution between the intermolecular degrees of freedom. The magnitude and direction of vibrationally averaged ground-state dipole moment of both isomers, as well as the direction of transition dipole moments, are in good agreement with the experimental findings. The changes in the values of dipole moment and some geometrical parameters of cis- and trans-HONO on vibrational excitation are also computed. 相似文献
7.
Rhodococcus opacus PW4 cells were found to produce trans- and cis-carveol and/or carvone as result of limonene metabolism, depending on the type and concentration of the carbon source used for cell growth. In aqueous systems, cells grown on ethanol and toluene only produced trans-carveol, whilst cells grown on limonene and on toluene with a larger head-space available produced both trans-carveol and carvone. In biphasic systems, limonene was converted to trans- and cis-carveol as well as to carvone, regardless of the carbon source used, although carveol and carvone production rates were higher in toluene and limonene grown cells, respectively. A good and stable emulsion was obtained in a magnetically stirred two-phase reactor but both trans-carveol and carvone were produced at low rates: 0.08 and 0.02 nmol/min mg prot, respectively. No cis-carveol was formed. When (−)-carveol was added, carvone production increased 4.7 fold to 0.12 nmol/min mg prot. Using an aerated two-phase reactor, carvone production was enhanced even with cells grown on toluene. The highest trans- and cis-carveol and carvone production rates were attained with cells grown on limonene by continuously supplying limonene to the reactor through the air stream, carvone production reaching 0.58 nmol/min mg prot. The best trans-/ cis-carveol ratio (2.26) was observed with cells grown on toluene when limonene was supplied in the gas phase. When 50 mM limonene was added initially, carvone was produced 27.9 and 141.4 times faster than trans-carveol with cells grown on toluene and limonene, respectively. 相似文献
8.
The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C2 and Cs) of cis-3-hexene and of the three lowest energy rotamers (symmetry Ci, C2, and C1) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the Δ H of conversion between the rotamers C2 and Cs of cis-3-hexene and between the rotamers Ci, C2, and C1 of trans-3-hexene. 相似文献
9.
The IR and Raman spectra of ethyl trichloroacetate (E-TCA) and its deuterate (E-TCA- d5) have been measured in the liquid, glassy and crystalline states. Vibrational assignment was made by referring to isotopic wavenumber-shift, characteristic group frequencies of related esters and with the aid of a normal coordinate calculation on E-TCA and E-TCA- d5. It is suggested that in the liquid and glassy states there exist two molecular forms ( trans— trans— trans and trans— trans— gauche) with regard to the internal rotations about the ClC---C---O---CH 2CH 3 axis, and that the former persists in the crystalline state. The band pairs of E-TCA and the other ethyl esters are discussed in relation to the nature and number of rotational axes, effect of the heavy trichloromethyl group, and enhancement of band intensity by vibrational coupling. 相似文献
10.
The synthesis and characterization of a number of new coordination compounds of Pd II with the nitrogen donor 1-tert-butylpyrazole ( tBuPzH) are described. Compounds are trans-[Pd( tBuPzH) 2Cl 2] and the cyclometallated structures [Pd 2( tBuPz) 2(AcO) 2] and [Pd 3( tBuPz) 2(AcO) 4]. All these complexes are mixtures of syn and anti isomers. Also, the chloro-bridged complex [Pd 2( tBuPz) 2Cl 2] has been isolated as an equilibrium mixture of cis and trans isomers. The compounds have been studied by variable temperature 1H- and 13C-NMR spectroscopy. 相似文献
11.
利用实验观测与密度泛函理论(DFT)计算方法考察了新化合物 N, N'-二-[3-羟基-4-(2-苯并噻唑)苯基]脲(4-DHBTU)的红外、核磁与紫外吸收光谱性质.与单体2-(4-氨基-2-羟苯基)苯并噻唑(4-AHBT)相比, 4-DHBTU的实验紫外吸收强度显著增强,最大吸收峰发生了明显红移,并呈现出双吸收峰特征.结合实验光谱数据与密度泛函理论计算分析表明, 4-DHBTU分子最稳定的基态异构体为 cis-C 11和 trans-C 11,而导致上述紫外光谱差异的主要原因是4-DHBTU样品中 cis-C 11, trans-C 11, cis-C 22, trans-C 22等多种异构体共存.此外, 4-DHBTU与溶剂二甲基亚砜(DMSO)间氢键作用使得核磁实验中4-DHBTU的15H、16H氢谱化学位移显著增大. 相似文献
12.
A limited selection of ring modified diphenyldiacetylenes of the type where A=, Y=C nH 2n+1, CF 3, F, COMe, NH 2, and NMe 2, and A=, trans and cis with Y=F and trans with Y=C 3H 7, were synthesized. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These properties were generally poorer than those found in the parent benzene compounds. This was also true of some pyrimidine analogues reported earlier. Birefringence values also decreased as expected. 相似文献
13.
Reaction of cis-[Ptph 2(SMe 2) 2] with Me 2PCH 2PMe 2 (dmpm) gave cis-[PtPh 2(dmpm-P) 2] (1) or cis,cis-[Pt 2Ph 4(μ-dmpm) 2] (2) and reaction of 1 with [Pt 2Me 4(μ-SMe 2) 2] gave cis,cis-[Ph 2Pt(μ-dmpm) 2PtMe 2] (3). Reaction of 1 with trans-[PtClR(SMe 2) 2] gave cis, trans-[Ph 2Pt(μ-dmpm) 2PtClR], R = Me (5) or Ph (6), and in polar solvents, these isomerized to give [Ph 2Pt(μ-dmpm) 2PtR] +Cl −. When R = Me, further isomerization via the phenyl group transfer gave [PhMePt(μ-dmpm) 2PtPh] +Cl −. Oxidative addition of methyl iodide occurred reversibly at the cis-[PtMe 2P 2 unit of 3 to give cis, fac-[Ph 2Pt(μ-dmpm) 2PtIMe 3] but complex 2 failed to react with MeI. A comparison with similar known complexes of Ph 2PCH 2PPh 2 (dppm) is made and differences are attributed primarily to the lower steric hindrance of dmpm. 相似文献
14.
Both (2 S, 5 R)- and (2 R, 5 R)-2-hydroxy-5-alkyl-δ-valerolactone derivatives, cis and trans, respectively, show almost the same magnitude of spontaneous polarization ( Ps) when added to a non-chiral smectic C mixture. The stereochemistry of these chiral dopants was studied using 1H NMR. Trans derivatives seem to have a half-chair conformation with the 2, 5-diequatorial substituents and the cis derivatives have rather a flat conformation in solution. However in the liquid-crystalline phase, the cis and trans derivatives appear to change their conformation or the distribution of their conformations as the alkyl chain length is varied. The difference in the effect as a chiral dopant depends upon lateral interactions between chiral molecules through the solvent liquid crystal phase. 相似文献
15.
The adducts of O 2 and SO 2 with trans-MeOIr(CO)(PPh 3) 2 are formed in equilibria and have been characterized. Reaction of the SO 2 adduct, Ir(OMe)(SO 2)(CO)(PPh 3) 2 with dioxygen leads to the sulfato complex, Ir(Ome)(CO)(PPh 3) 2(SO 4), the structure of which has been determined. Ir(Ome)(CO)(PPh 3) 2(SO 4) crystallizes in the monoclinic system with a 11.958(2), b 14.163(3), c 12.231(2) Å, β 118.365(12)°, V 1822.7(6) Å 3 and Z = 2. Diffraction data for 2θ = 4.5–45.0° (Mo- K) were collected with a Syntex P2 1 diffractometer and the structure was solved (assuming space group P2 1/ m and an unpleasant 2-fold disordered model) and refined to R = 4.8% for all 2512 independent data ( R = 3.5% for those 2042 data with ¦F O¦ > 6σ(¦ F¦)). The iridium(III) atom has a distorted octahedral coordination sphere with trans PPh 3 ligands and a cis-chelating bidentate O, O′-SO 4 group; the structure is completed by mutually cis OMe and CO ligands. 相似文献
16.
The ring-opening metathesis polymerization (ROMP) of norbornene catalyzed by bis(acetonitrile) molybdenum and tungsten complexes, [M(η 3-C 3H 5)Cl(CO) 2(NCMe) 2] (1-Mo: M = Mo, 1-W: M = W), which have two labile acetonitrile ligands, has been investigated. These complexes catalyzed the ROMP of norbornene as a single-component initiator. The highly cis-selective polymerization proceeded in a THF solution (95% for 1-Mo and 96% for 1-W), whereas polymerization in CH 2Cl 2 or toluene resulted in lower cis selectivity. The polymerization of terminal acetylenes using these complexes was also examined. The tungsten complex 1-W showed a high catalytic activity for the polymerization of terminal acetylenes, such as phenyl- and tert-butylacetylene. A highly active catalytic system for the ROMP of norbornene was achieved by the activation of the tungsten complex, 1-W, with one equivalent of phenylacetylene, giving poly(norbornene) with a high molecular weight ( Mn = 391 × 10 4) and a high cis selectivity ( cis 89%). 相似文献
17.
For-
-Pro-
-Pro-NH 2 is an ab initio model of the prolyl-proline sequence unit present in numerous peptides and proteins. Cis– trans isomerization of the peptide linkage is a crucial step in accessing the active conformation of several proline containing macromolecules. The present study focuses on the flexibility of the five-membered pyrrolidine ring, which is considered to help other conformational changes as well as cis–trans isomerization. Ring flexibility is characterized by the pseudorotational amplitude, A, and the phase angle, P. Calculations are carried out at the RHF/6-31+G(d) level of theory. The choice of method and level of theory is further supported by single point DFT calculations. In the course of NMR structure determination of peptides or proteins, proline residues present in the sequences need special attention. Because of the lack of an amide hydrogen, sequential assignment of proline is rather complicated. Furthermore, in solution state, peptide cis–trans isomers are almost always present. Ab initio study on the For-
-Pro-
-Pro-NH2 model is a useful tool to discover the structural characteristics of the prolyl-proline sequence unit. 相似文献
18.
Poly(1-trimethylsilyl-1-propyne) [PTMSP], a high-free-volume glassy polymer, has the highest gas permeability of any known synthetic polymer. In contrast to conventional, low-free-volume, glassy polymers, PTMSP is more permeable to large, condensable organic vapors than to permanent gases. The organic-vapor/permanent-gas selectivity of PTMSP based on pure gas measurements is low. In organic-vapor/permanent-gas mixtures, however, the selectivity of PTMSP is much higher because the permeability of the permanent gas is reduced dramatically by the presence of the organic vapor. For example, in n-butane/methane mixtures, as little as 2 mol% n-butane (relative n-butane pressure 0.16) lowers the methane permeability 10-fold from the pure methane permeability. The result is that PTMSP shows a mixed-gas n-butane/methane selectivity of 30. This selectivity is the highest ever observed for this mixture and is completely unexpected for a glassy polymer. In addition, the gas mixture n-butane permeability of PTMSP is considerably higher than that of any known polymer, including polydimethylsiloxane, the most vapor-permeable rubber known. PTMSP also shows high mixed-gas selectivities and vapor permeabilities for the separation of chlorofluorocarbons from nitrogen. The unusual vapor permeation properties of PTMSP result from its very high free volume - more than 20% of the total volume of the material. The free volume elements appear to be connected, forming the equivalent of a finely microporous material. The large amount of condensable organic vapor sorbed into this finely porous structure causes partial blocking of the small free-volume elements, reducing the permeabilities of the noncondensable permanent gases from their pure gas values. 相似文献
19.
The magnetic coupling interaction for Cu(II) binuclear systems with bridging groups C 2O 42−, C 2O 2(NH) 22− ( cis), C 2O 2(NH) 22− ( trans) and C 2S 2(NH) 22− ( trans) was studied by the broken symmetry (BS) approach within the framework of the density functional theory (DFT). The influence of different coordination atoms and geometry on magnetic coupling interaction was theoretically analyzed. Both of the calculated and experimental results were compared. The variation trends of coupling interaction calculated are in agreement with experimental ones. 相似文献
20.
Ab initio optimizations of the complete acrolein molecular geometry accomplished using analytical gradient methods at the 6-31G* SCF level at ten points during rotation from the planar trans- to the planar cis-form (rotation about the single C---C bond) are used to calculate the values of the Pitzer function F(φ), the coefficients of its Fourier expansion, and the coefficients in the potential energy expansion. The theoretical potential expansion coefficients are then adjusted using the experimental torsional frequencies and their overtones for the trans- and cis-forms of CH 2=CH---CH=O and CH 2=CH---CD=O. For the cis-conformer two different sets of experimental frequencies are employed. The dependence of the slope of the acrolein potential energy curve on the experimental frequency set used for the cis-rotamer is discussed. 相似文献
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