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1.
Potential energy surfaces of the reaction of SiH 2 and C 2H 2 (and C 2D 2) have been calculated by means of ab initio molecular orbital theory at the QCISD/6-311G++(2df, 2p)//MP2/6-31G(d, p) level with corrections for the triple excitations to the QCISD energies. The barrier heights for the two reaction channels of the adduct, thus calculated, were further utilized for the dynamical calculation of the rate constants in the framework of quantum statistical Rice-Ramsperger-Kassel theory. Contributions of the rate constants of the various pathways to the total rate constant ( KT) for the disappearance of the reactants are critically examined and compared with experiment. The pressure dependence of KT(C 2H 2) is primarily due to the formation of silirene. KT(C 2D 2) is consistently higher than KT(C 2H 2). The standard heat of formation of silirene is predicted to be 72.1 ± 3 kcal/mol. Rearrangement of silirene to vinylsilylene requires an activation energy smaller than that to silylacetylene. 相似文献
2.
The structure and stability of endohedral X@Si 20H 20 complexes (X = Li 0/+, Na 0/+, K 0/+, Be 0/2+, Mg 0/2+, Ca 0/2+) have been studied at the B3LYP/6-31G* level of density functional theory. It is found that complexes with X = Na 0/+, K 0/+, Mg and Ca 0/2+ are energy minimum structures with X at the cage center in I h symmetry, while those with X = Li 0/+, Be 0/2+, Mg 2+ have off-centered structures with X towards one pentagon face in C 5v symmetry. Large electron or charge transfer between the Si 20H 20 cage and the encapsulated X has been observed. 相似文献
3.
Ab initio Hartree–Fock (HF) calculations were carried out to determine the structures and energies of the endohedral complexes of C 58 cage with H 2 or CO. It was demonstrated that the formation of these complexes is endothermic with destabilization energies of 3.3 kcal/mol for H 2 and 18.6 kcal/mol for CO. Furthermore, the H 2 and CO molecules have different orientations in the C 58 cage, namely, the orientation of the molecular axis of the former is normal to the face of the 7-member ring, while that of the latter is parallel to that face. In addition, the H–H bond of the H 2 molecule is shortened inside the cage, whereas the length of the C–O bond remains unchanged. 相似文献
4.
We study here the reactions between C 60 and planar C 5H 5+ cations that lead to the formation of [C 60C 5H 5] + adduct cations in the chemical ionization source of the mass spectrometer. The structures, stabilities and charge locations of some possible isomers of [C 60C 5H 5] +: σ-adduct, π-complex, [1,4]- and [l,2]-addition cations, are studied by AM1 semiempirical molecular orbital calculations. We find that the most stable is the σ-addition cation. Another interesting and stable structure is the π-complex cation which is bonded by the electrostatic interaction at the inter-ring distance of 1.589 Å with the C5v symmetry. The C 5H 5+ cyclopentadienium cation seems to be an “inverted umbrella” sitting on a five-membered ring of the C 60 cage. 相似文献
5.
Structures, energies, and vibrational frequencies have been calculated for two C 30H 20 isomers with a dodecahedrane cage and two pentaprismane cages at the B3LYP/6‐31G* level of theory. Thus, two C 30H 20 isomers have the form of coplanar tri‐cage molecules. The symmetry of one C 30H 20 isomer is of D5d and that of another is of C2V. The heat of formation for two C 30H 20 isomers have been estimated. Heats of formation of two C 30H 20 isomers as well as the vibrational analysis indicate that two C 30H 20 isomers enjoy sufficient stability to allow for its experimental preparation. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
6.
(C6H(14)N2)[NH4(ClO4)3] is a newly developed porous hybrid inorganic-organic framework material with easy access and excellent detonation performances,however,its thermal properties is still unclear and severely hampered further applications.In this study,thermal behaviors and non-isothermal decomposition reaction kinetics of(C6H(14)N2)[NH4(ClO4)3] were investigated systematically by the combination of differential scanning calorimetry(DSC) and simultaneous thermal analysis methods.In-situ FTIR spectroscopy technology was applied for investigation of the structure changes of(C6H(14)N2) NH4(ClO4)3]and some selected referents for better understanding of interactions between different components during the heating process.Experiment results indicated that the novel molecular perovskite structure renders(C6H(14)N2)[NH4(ClO4)3] better thermal stability than most of currently used energetic materials.Underhigh temperature s,the stability of the cage skeleton constructed by NH4^+and ClO4^-ions determined the decomposition process rather than organic moiety confined in the skeleton.The simple synthetic method,good detonation performances and excellent thermal properties make(C6H(14)N2)[NH4(ClO4)3] an ideal candidate for the preparation of advanced explosives and propellants. 相似文献
7.
The effects of cyclopentadienyl ring size on the geometry of bimetallic organosamarium complexes have been studied by comparing the X-ray crystal structure of [(C 5H 4Me) 2(THF)Sm(μ-Cl)] 2, prepared from KC 5H 4Me and SmCl 3 in THF, with C 5Me 5 analogs. The complex crystallizes from THF at −30°C in space group Pbcn with a = 20.312(5), b = 9.626(2), c = 16.225(3) Å, V = 3172.5(12) Å 3 and Dcalc = 1.74 g cm −3 for Z = 4. Least-squares refinement of the model based on 1759 reflections [| Fo| > 2.0σ(| Fo|)] converged to a final RF = 5.0%. The complex adopts a geometry which has a molecular two-fold rotation axis perpendicular to the Sm 2Cl 2 plane and a crystallographic inversion center. Hence, both methyl groups of each (C 5H 4Me) 2Sm unit are located on the side opposite of the THF ligands, which are trans to each other, and the four C 5H 4Me ring centroids define a square plane. The Sm---Cl distances are 2.759(3) and 2.819(3) Å. 相似文献
8.
LnCl 3 (Ln=Nd, Gd) reacts with C 5H 9C 5H 4Na (or K 2C 8H 8) in THF (C 5H 9C 5H 4 = cyclopentylcyclopentadienyl) in the ratio of 1 : to give (C 5H 9C 5H 4)LnCl 2(THF) n (orC 8H 8)LnCl 2(THF) n], which further reacts with K 2C 8H 8 (or C 5H 9C 5H 4Na) in THF to form the litle complexes. If Ln=Nd the complex (C 8H 8)Nd(C 5H 9C 5H 4)(THF) 2 (a) was obtained: when Ln=Gd the 1 : 1 complex [(C 8H 8)Gd(C %H 9)(THF)][(C 8H 8)Gd(C 5H 9H 4)(THF) 2] (b) was obtained in crystalline form. The crystal structure analysis shows that in (C8H8)Ln(C5H9C5H4)(THF)2 (Ln=Nd or Gd), the Cyclopentylcyclopentadieny (η5), cyclooctatetraenyl (η8) and two oxygen atoms from THF are coordinated to Nd3+ (or Gd3+) with coordination number 10. The centroid of the cyclopentadienyl ring (Cp′) in C5H9C5H4 group, cyclooctatetraenyl centroid (COTL) and two oxygens (THF) form a twisted tetrahedron around Nd3+ (or Gd3+). In (C8H8)Gd(C5H9C5H4)(THF), the cyclopentyl-cyclopentadienyl (η5), cyclooctatetraenyl (η8) and one oxygen atom are coordinated to Gd3+ with the coordination number of 9 and Cp′, COT and oxygen atom form a triangular plane around Gd3+, which is almost in the plane (dev. -0.0144 Å). 相似文献
9.
In the present theoretical work we have explored mechanisms of dissociation reactions of the vinyl radical in the A 2A″ state (C 2H 3 (A 2A″)) and examined possible pathways for nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+). In the calculations we used the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with the cc-pVDZ and cc-pVTZ basis sets. Mechanisms for the following three dissociation channels of C 2H 3 in the A 2A″ state were explored: (1) C 2H 3 (A 2A″) → C 2H 2 ( trans, 3A u) + H, (2) C 2H 3 (A 2A″) → C 2H 2 ( cis, 3A 2) + H, and (3) C 2H 3 (A 2A″) → H 2CC ( 3A 2) + H. The CASSCF and CASPT2 potential energy curve calculations for the C 2H 3 (A 2A″) dissociation channels (1)–(3) indicate that there is neither transition state nor intermediate for each of the channels. At the CASPT2//CASSCF/cc-pVTZ level, the dissociation energies for channels (1)–(3) are predicted to be 84.3, 91.1, and 86.9 kcal/mol, respectively. For a recently observed nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+) + H [J. Chem. Phys. 111 (1999) 3783], two previously suggested internal conversion (IC) pathways were examined based on our CASSCF and CASPT2 calculations. Our preliminary CASSCF and CASPT2 calculations indicate that the assumed IC pathway via the twisted C 2H 3 (A 2A ′) structure might be feasible. The CASSCF/cc-pVTZ geometry optimization and frequency analysis calculations were performed for the four C 2v bridge structures in the 2B 2, 2A 2, 2B 1, and 2A 1 states along the pathways of the 1 2A ′ (X 2A ′), 1 2A″ (A 2A″), 2 2A″, and 2 2A ′ states of C 2H 3, respectively, and the CASPT2//CASSCF/cc-pVTZ energetic results indicate that the assumed IC pathway, via a C 2v ( 2A 2) structure and then 2A 2/ 2A 1 surface crossing, be not feasible since at their excitation wavelengths (327.4 and 366.2 nm) the C 2v ( 2A 2) structure could not be accessed. 相似文献
10.
An anomalous charge density distribution of La atom encapsulated in a C 82 cage has been revealed for La@C 82 by the maximum entropy method (MEM)/Rietveld analysis using synchrotron powder diffraction data. The obtained La atom charge density shows a feature almost like a bowl or a hemisphere, suggesting that the La atom has a giant motion (large amplitude motion) inside the C 82 cage at room temperature. From the obtained MEM charge density, the main results are (1) the cage structure of La@C 82 (I) has C 2V symmetry; (2) La atom locates at an off-centered position adjacent to a six-membered ring of the carbon cage; (3) the nearest La–C distance is 2.55(8)
and (4) the amount of charge transfer from the La atom to the carbon cage is about 3.2 e, which corresponds to the nominal electronic structure, La 3+@C 823−. 相似文献
11.
The thermolysis of C 60H 2 to yield C 60 and H 2 was studied by hybrid density functional theory (B3LYP/6-311G**//B3LYP/3-21G). The concerted loss of dihydrogen requires an activation energy of 92 kcalmol −1 at T=452 K. An alternative radical mechanism, which is first order in the C 60H 2 concentration, has an activation energy at 452 K of only 61 kcalmol −1. Monitoring of the C 60H 2 decomposition in 1,2-dichloro-[D 4]-benzene solution by NMR spectroscopy indicates a pseudo first-order reaction with an activation energy of 61.38±2.35 kcalmol −1. 相似文献
12.
C 60 is the most important fullerene cage and glycine is the simplest representative of a backbone unit of a protein. In this paper, the structures and the energies of glycine–C 60 complexes were calculated at the B3LYP/6-31G(d) level DFT. It was found that the binding of glycine to C 60 generated a slightly unstable complex via its amino nitrogen, a moderately unstable complex via its hydroxyl oxygen, and a very unstable complex via its carbonyl oxygen. This indicates that fullerene cages might be unable to form stable bindings to proteins via their amino nitrogen, hydroxyl oxygen and carbonyl oxygen active sites. 相似文献
13.
运用密度泛函(DFT)理论,采用Materials Studio 8.0,用GGA/BP方法研究了C_6H_2(OH)_3CH_3氧化成羟基苯甲酸的反应路径。结果表明,甲基上的氢原子被氧化成羟基以及羟基被氧化为醛基及醛基被氧化成羧基均为放热过程。分子C_6H_2(OH)_3CH_3中甲基氧化成羧基的主路径为三个氢原子氧化反应路径,其路径为C_6H_2(OH)_3CH_3+3O→C6H2(OH)3C(OH)3→C6H2(OH)3COOH+H2O,该路径受限于羟基直接被氧化成羧基过程,需克服130 k J/mol的反应势垒,反应速率常数对数ln(k)为-22.96 s-1;醛基、羟基优先被氧化成羧基的顺序为:-CHO-C(OH)3-HC(OH)2-H2C(OH);提高反应温度、氧气浓度均有利于羟基苯甲酸的生成,适当的催化剂有利于促进整个反应的进行。 相似文献
14.
Fourteen structures of C 20 are studied at DFT/B3LYP/6-31G* theoretical level. Except ring, bowl, cage and isomer 1 which have been studied before, other isomers have not been reported so far. Calculated results show that the ring has the lowest energy at this level and isomers 1, 2, 3 and 4 have lower energies than that of cage. Analyses of optimized bond lengths, electronic structure indicate that some carbon atoms express super-valence property. In addition, NICS value is consistent with molecular orbital character in denoting aromaticity of C 20 molecule. Delocalization character averts influence of curvature strain, which can well explain the stability of the cage. 相似文献
15.
The title compound 2,3-dicyclopentadiene-2,3-dimethylbutane (C 5H 5CMe 2CMe 2C 5H 5) 1 shows the typical staggered conformation of a highly substituted ethane derivative with the two largest substituents (C 5H 5) adopting a trans position. The molecule shows C 2 symmetry about the central C–C bond. Due to the high substitution, the central bond of the ethane is elongated to 160.0 pm (X-ray structure analysis) while the DFT calculation finds a value of 159.2 pm. 相似文献
16.
用INDO系列方法对由(C 59N) 2和苯甲醚合成的衍生物C 59(C 6H 4OCH 3)N进行了理论研究,得到了分子的稳定构型.结果表明,C 59(C 6H 4OCH 3)N具有C s对称性.以优化构型为基础讨论了分子的UV-Vis光谱、NMR谱线数,结果与实验符合得很好.本文还计算了C 59(C 6H 4OCH 3)N的二阶非线性光学系数β μ,结果表明这种物质具有较大的二阶非线性光学系数. 相似文献
17.
Dissolution of Mo 2O 5((CH 3) 2NCH 2CH 2NHCH 2CH 2S) 2 in dimethylformamide results in the formation of a species without coordinated sulphur, as indicated by 95Mo NMR spectroscopy. Subsequent crystallization of this solution yielded the compound Mo 4O 12(C 12H 30N 4S 2) 2(C 3H 7ON) 2 which X-ray crystallography shows to consist of a novel Mo 4O 12 core, containing an eight-membered Mo 4O 4 ring with the two pairs of diagonal molybdenum atoms linked by disulphido-containing groups. 相似文献
18.
A new approach in the synthesis of water-soluble boron-rich compounds was proposed. The closo-dodecaborate cage is used as a hydrophilic substitutent providing for the water-solubility of the molecule whereas the carborane cage can be used for attachment to biomolecules using earlier developed methods. The double-cage molecules [ o-, m-, and p-CB 10H 10C(CH 2) 4OB 12H 11] 2− were prepared by the reaction of the tetramethylene oxonium derivative of the closo-dodecaborate anion, [B 12H 11O(CH 2) 4] −, with the corresponding lithiated carboranes. The compounds obtained have doubled the boron contents and could serve for the synthesis of agents for boron neutron capture therapy (BNCT). 相似文献
19.
The complex [MoW(μ-CC 6H 4Me-4)(CO) 2(η 7-C 7H 7)(η 5-C 2B 9H 10Me)] reacts with diazomethane in Et 2O containing EtOH to afford the dimetal compound [MoW(OEt)(μ-CH 2){μ-C(C 6H 4Me-4)C(Me)O}(η 7-C 7H 7)(η 5-C 2B 9H 10Me)]. The structure of this product was established by X-ray diffraction. The Mo---W bond [2.778(4) Å] is bridged by a CH 2 group [μ-C---Mo 2.14(3), μ-C---W 2.02(3) Å] and by a C(C 6H 4Me-4)C(Me)O fragment [Mo---O 2.11(3), W---O 2.18(2), Mo---C(C 6H 4Me-4) 2.41(3), W---C(C 6H 4Me-4) 2.09(3), Mo---C(Me) 2.26(3) Å]. The molybdenum atom is η 7-coordinated by the C 7H 7 ring and the tungsten atom is η 5-coordinated by the open pentagonal face of the nido-icosahedral C 2B 9H 10Me cage. The tungsten atom also carries a terminally bound OEt group [W---O 1.88(3) Å]. The 1H and 13C-{ 1H} NMR data for the dimetal compound are reported and discussed. 相似文献
20.
利用凝胶溶胶法和浸渍法制备了Ce-Fe/Al 2O 3/cordierite催化剂,实验研究了其催化丙烷选择性还原NO的特性。结果表明,当铈的负载量从1%增加至5%时,Ce-Fe/Al 2O 3/cordierite的C 3H 8-SCR性能先增强后减弱,3.5Ce-Fe/Al 2O 3/cordierite具有最佳的脱硝性能,在有氧条件下,600℃时可实现96.5%的脱硝效率。Ce的加入能够提升Fe/Al 2O 3/cordierite催化剂的抗硫性能。烟气中通入0.02%的SO 2后,3.5Ce-Fe/Al 2O 3/cordierite催化丙烷还原NO的转化率始终维持在93%,而没有经过Ce修饰的Fe/Al 2O 3/cordierite的NO转化率从88%下降为80%左右。利用XRD、N 2吸附-脱附、SEM、H 2-TPR、吡啶吸附红外光谱等手段研究了催化剂的物理化学性质。结果表明,加入助剂铈能与Fe形成了固溶体,增加催化剂表面Lewis酸浓度和氧化还原能力,从而提高了催化丙烷还原NO的性能。过多的铈引入会减少Fe 2O 3结晶体的形成,不利于在C 3H 8-SCR反应中形成NO 2/NO 3-物种,从而导致NO还原效率下降。 相似文献
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