共查询到20条相似文献,搜索用时 421 毫秒
1.
Both ab initio 6-31G, 3-21G and STO-3G basis sets and semiempirical PM3 and AM1 molecular orbital calculations are carried out on the C 24N 4 molecule of the Td symmetry group. Results on the fully optimized structure which constrained Td symmetry, molecular orbitals and vibrational frequency were obtained by both ab initio and semiempirical methods. The binding energy and various thermodynamic properties were also calculated via the PM3 and AM1 semiempirical methods. All the evidence of this work proves that the C 24N 4 molecule is stable and that its four six-membered rings with a remarkable delocalized C…C bond are similar to the related rings in the C 60 buckminsterfullerene structure. 相似文献
2.
CaRg n+ (Rg=He, Ne, Ar) complexes with n=1–4, are investigated by performing using the B3LYP/6-311+G (3df) density functional theory calculations. The CaHe n+ ( n=1–4) complexes are found to be stable. In the case of CaNe n+ and CaAr n+, stable structures and stationary point were found only for n=1 and 2. For n=3 in the C3V and the D3h point group as well as for n=4 in the Td (tetrahedral) point group a saddle point (imaginary frequency) is observed and global minimum could be obtained along the potential energy surface. 相似文献
3.
The mechanism of the H 2NO( 2B 1)→NO( 2Π)+H 2 reaction has been examined using ab initio molecular orbital methods. Ground-state and first-excited-state potential surfaces were plotted at the FOCI/cc-pVTZ level of theory as functions of two appropriate internal degrees of freedom. A conical intersection was found on the Cs pathway that is symmetric with respect to the plane perpendicular to the molecular plane of C2v H 2NO( 2B 1). It is therefore considered that trajectories that start from H 2NO( 2B 1) towards the product region detour around the conical intersection, pass through the neighborhood of the transition state that is located at the saddle point on the Cs pathway, and finally reach the products, NO( 2Π)+H 2. Thus we can explain the mechanism of the H 2NO( 2B 1)→NO( 2Π)+H 2 reaction, which has remained unclear to date. 相似文献
4.
This work uses ab initio calculations to obtain harmonic frequencies and anharmonic constants for the O–H symmetric and asymmetric stretches of H 2SO 4 in its C2, Cs, C1a, and C1b configurations. In addition, a high-resolution potential energy surface is calculated as a function of both O=S–O–H dihedral angles in order to accurately obtain minimum and saddle point energies. The resulting peak positions and Boltzmann populations are compared to experimental frequencies and intensities and provide evidence for the assignment of rotamers in H 2SO 4 as suggested in recent work. 相似文献
5.
At present C 94 is one of the highest sets of isomeric fullerenes that has been characterized by 13C NMR spectra. This contribution reports quantum-chemical computations on the C 94 system. The complete set of 134 isolated-pentagon-rule isomers of C 94 is described by four semiempirical quantum-chemical methods (MNDO, AM1, PM3, and SAM1). The C 94 energetics is also checked with Hartree–Fock SCF calculations in the standard 4-31G basis set (HF/4-31G). The calculations point out a C2 structure as the system ground state. As energetics itself cannot produce reliable relative stabilities at high temperatures, entropy terms are also computed and the relative-stability problem is entirely treated in terms of the Gibbs function. The lowest-energy structure remains the most populated isomer at higher temperatures. However, several other structures show significant populations at higher temperatures. The six most populated species at the AM1 computational level read: C2, C2, C1, C1, Cs, and C2. This selected six-membered isomeric set indeed contains the four symmetries observed in the available experiment ( C2, Cs, C2, and C2). This incidence represents a good agreement with the experiment and can be viewed as another evidence that the supposed inter-isomeric thermodynamic equilibrium does exist in experiments. 相似文献
6.
The symmetry unrestricted C 36F 2 isomers formed from fullerene C 36, the initial symmetry of which is C6v, C6h, or D2d, have been extensively studied with semi-empirical (AM1 and PM3) calculations. Based on the relationship between the isomer's stability and the adding positions, three patterns of the adding sites of F 2 moiety in the additive reactions have been deducted. The results of the π-orbital axis vector (POAV) analysis indicate that the chemical reactivity of C 36 is the result of the high strain in the C 36 cage. But, in order to form stable compounds, the effects, which guide the F 2 moiety to select carbon atoms in the C 36 cage, are dominated by the conjugate effect in C 36F 2 system rather than the strain release in the C 36 cage. 相似文献
7.
The macrocyclic compound, [1,2-C 2B 10H 10-1,4-C 6H 4-1,7-C 2B 10H 10-1,4-C 6H 4] 2 (5)—a novel cyclooctaphane, was prepared by condensation of the C,C′-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)- ortho-carborane. The X-ray crystal structure of 5·C 6H 6·6C 6H 12 was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic Cs and local C2v symmetry; the macrocycle adopts a butterfly (dihedral angle 143°) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D2h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal mol −1 higher in energy than the C2v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful. 相似文献
8.
The equilibrium structures and relative stabilities of BN-doped fullerenes C 70−2x(BN) x ( x=1–3) have been studied at the AM1 and MNDO level. The most stable isomers of C 70−2x(BN) x have been found out and their electronic properties have been predicted. The calculation results show that the BN substituted fullerenes C 70−2x(BN) x have considerable stabilities, though they are less stable than their all carbon analog. For C 68BN, the isomers whose BN is located in the most chemically active bonds of C 70 (namely B and A) are among the most stable species, of which B is predicted to be the ground state. The stabilities of C 68BN decrease and the dipole moments increase with increasing the distance between the heteroatoms. For C 66(BN) 2, the lowest energy species is the isomer in which the B–N–B–N bond is formed; For C 64(BN) 3, the most stable species should have three BN units located in the same hexagon to form B–N–B–N–B–N ring. The ionization potentials and the affinity energies of the most stable species of BN-doped C 70 are almost the same as those of C 70 because of the isoelectronic relationship. The ionization potentials and affinity energies depend on the relative position of the heteroatoms in C 68BN, the chemical reactivities of the isomers whose heteroatoms are well separated should differ significantly from their all carbon analog. 相似文献
9.
The temperature dependence of the rate constants, for the reactions of hydrated electrons with H atoms, OH radicals and H 2O 2 has been determined. The reaction with H atoms, studied in the temperature range 20–250°C gives k(20°C) = 2.4 × 10 10M -1s 1 and the activation energy EA = 14.0 kJ mol -1 (3.3 kcal mol -1). For reaction with OH radicals the corresponding values are, k(20° C) = 3.1 × 10 10M -1s -1 and EA = 14.7 kJ mol -1 (3.5 kcal mol -1) determined in the temperature range 5–175°C. For reaction with H 2O 2 the values are, k(20° C) = 1.2 × 10 10M -1s -1 and EA = 15.6 kJ mol -1 (3.7 kcal mol -1) measured from 5–150°C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction of hydrated electron with H 2PO 4- was determined to k(20° C) = 1.5 × 10 7M -1s -1 and EA = 7.4 kJ mol -1 (1.8 kcal mol -1) in the temperature range 20–200°C. 相似文献
10.
Reaction of YbI 2 with two equivalents of cyclopentylindenyl lithium (C 5H 9C 9H 6Li) affords ytterbium(II) substituted indenyl complex (C 5H 9C 9H 6) 2Yb(THF) 2 (1) which shows high activity to ring-opening polymerization (ROP) of lactones. The reaction between YbI 2 and cyclopentylcyclopentadienyl sodium (C 5H 9C 5H 4Na) gives complex [(C 5H 9C 5H 4) 2Yb(THF)] 2O 2 (2) in the presence of a trace amount of O 2, the molecular structure of which comprises two (C 5H 9C 5H 4) 2Yb(THF) bridged by an asymmetric O 2 unit. The O 2 unit and ytterbium atoms define a plane that contains a Ci symmetry center. 相似文献
11.
Photolyses of CF 3C(O)X and C 2F 5C(O)X (X=Cl, F) at 254 nm in the presence of O 2 yield the perfluorinated radicals C 2F 5O (C 2) and CF 3O (C 1), respectively. The C 2 radicals decompose to give CF 3 radicals: which, in turn, react with O 2 leading to the formation of C 1 radicals. When in addition to O 2, CO is present, the C 1 radicals react with it leading to its catalytic oxidation to CO 2. The trioxide CF 3OC(O)O 3C(O)OCF 3 was observed following the photolysis of all four halides in the presence of O 2 and CO. The other radical partners coming from the initial step in the photolysis (XC(O)) as well as the products of their reaction with O2 (XC(O)Oy, y=1, 2) do not react with CO but when X=F they lead to the formation of a new stable peroxy molecule with the formula CF3OC(O)O2C(O)F. Some of the properties of this new molecule, its stability and its IR features are presented in this work. 相似文献
12.
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
13.
Likely candidates for the lowest potential energy minima of (C 60) nCa 2+, (C 60) nF − and (C 60) nI − clusters are located using basin-hopping global optimisation. In each case, the potential energy surface is constructed using the Girifalco form for the C 60 intermolecular interaction, an averaged Lennard–Jones C 60–ion interaction, and a polarisation potential, which depends on the first few non-vanishing C 60 multipole polarisabilities. We find that the ions generally occupy the interstitial sites of a (C 60) n cluster, the coordination shell being tetrahedral for Ca 2+ and F −. The I − ion has an octahedral coordination shell in the global minimum for (C 60) 6I −, however for 12 n 8 the preferred coordination geometry is trigonal prismatic. 相似文献
14.
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
15.
Thermal displacement of coordinated nitriles RCN (R = CH 3, C 2H 5 or n-C 3H 7) in [C 5H 5Fe(L 2)(NCR)]X complexes (L 2 = P(OCH 3) 3) 2, (P(OC 6H 5) 3) 2 or (C 6H 5) 2PC 2H 4P(C 6H 5) 2 (DPPE)) by E(CH 3) 2 affords high yields of [C 5H 5Fe(L 2)(E(CH 3) 2)]X compounds (E = S, Se and Te; X = BF 4 or PF 6). Spectroscopic data and ligand displacement reactions are presented and discussed together with related observations on [C 5H 5Fe(CO) 2(E(CH 3) 2)]BF 4 compounds. The molecular structure of [C 5H 5Fe(P(OCH 3) 3) 2(S(CH 3) 2)]PF 6 was determined by a single-crystal X-ray diffraction study: monoclinic, space group P2 1/ n- C52h (No. 14) with a = 8.4064(12), b = 11.183(2), c = 50.726(8) Å, β = 90.672(13)° and Z = 8 molecules per unit cell. The coordination sphere of the iron atom is pseudo-tetrahedral with an Fe---S bond distance of 2.238 Å. 相似文献
16.
Four neutral bimetallic clusters X 2M 2 (X=Si, Ge, M=Al, Ga) are investigated using density functional theory (DFT) and post-HF methods. The calculated results show that each of four X 2M 2 species has two energetically close stable isomers with rhombic structure ( D2h symmetry) and trapezoidal structure ( C2v symmetry) respectively. For the Ge 2Al 2 species the rhombic ( D2h) isomer is the ground state, whereas for other three species Ge 2Ga 2, Si 2Al 2, and Si 2Ga 2, the trapezoidal ( C2v) isomers are the ground states. The calculated magnetic susceptibility anisotropy ( χanis) and nucleus-independent chemical shift (NICS) indicate that a strong diatropic ring current exists in the two heterocyclic planar isomers, suggesting they are highly aromatic. A detailed molecular orbital analysis further reveals that both heterocyclic isomers possess multiple aromaticity derived from one delocalized π MOs and two delocalized σ MOs. 相似文献
17.
The rate coefficients for the reactions of C 2H and C 2D with O 2 have been measured in the temperature range 295 K T 700 K. Both reactions show a slightly negative temperature dependence in this temperature range, with kC2H+O2 = (3.15 ± 0.04) × 10 −11 ( T/295 K) −(0.16 ± 0.02) cm 3 molecule −1 s −1. The kinetic isotope effect is kC2H/ kC2D = 1.04 ± 0.03 and is constant with temperature to within experimental error. The temperature dependence and the C 2H + O 2 kinetic isotope effect are consistent with a capture-limited metathesis reaction, and suggest that formation of the initial HCCOO adduct is rate-limiting. 相似文献
18.
The quasi-isothermal curing of a diepoxide resin with a triamine of polyoxypropylene was studied by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The complex heat capacity measurements allows to analyse the vitrification process at curing temperatures ( Tc) below the maximum glass transition of the fully cured epoxy ( Tg∞=85.8°C). Initially, the modulus of the complex heat capacity, | C*p|, increases until a maximum (conversion between 0.42 and 0.56) and then decreases. This step is followed by an abrupt decay of | C*p|, due to the vitrification of the system, which allows the determination of the vitrification time. This value agrees well with that determined by the partial curing method. The phase angle and out-of-phase heat capacity show an asymmetric wide peak during the vitrification process. The change in | C*p| at vitrification decreases with the increase of Tc becoming zero at temperature Tg∞. This epoxy-triamine system shows a delay of the vitrification process respect to other model epoxy systems probably due to the presence of polyoxypropylene chains in the network. The decay of |C*p| during vitrification may be normalised between unity and zero by defining a mobility factor. This mobility factor has been used to simulate the reaction rate during the stage where the reaction is controlled by diffusion. The observed reaction rate is simulated by the product of the kinetic reaction rate, determined by the autocatalytic model, and the mobility factor. 相似文献
19.
Using pseudopotentials and double zeta basis sets with s, p diffuse functions and two sets of d functions, MRD-CI calculations were performed on As 2(±), As 4(+), GaAs −, GaAs 2(±) and Ga 2As 2(±). This study complements previous theoretical investigations on Ga (±) to Ga 4(±) and GaAs (+). For As 4 tetrahedral symmetry was assumed, and Re of X 1A 1 determined as 4.73 a0. Vertical ionization potentials to several states of As 4+ were calculated. For GaAs 2, GaAs 2+ and GaAs 2−, ground and one low-lying state were geometry-optimized, both in C 2v (Ga-As-As), and linear symmetry (GaAsAs, C ∞h and AsGaAs, D ∞h). The lowest state of GaAs 2 is 2B 2 in C 2v. For Ga 2As 2, the lowest state and low-lying excited states were optimized in various geometries. The most stable state has rhombic structure ( 1A g in D 2h), but T-form and other forms (C 2v, C ∞v, D ∞h) are only 1–2 eV less stable. In D 2h symmetry, several low-lying excited states of Ga 2As 2 were studied. The ground states of Ga 2As 2+ and Ga 2As 2− were found to be 2B 2u, and 2B 2g, respectively. Trends in ionization potentials (IP), electron affinities (EA), atomization energies and fragmentation energies for the molecules Ga xAs y and the pure compounds Ga n and As n up to 4 atoms, were studied. Ga xAs y clusters, with x + y even, have higher IP's than odd-numbered clusters. An experimentally observed alternation of EA, whereby an odd number of atoms have higher EA than their even neighbors, is confirmed. The mixed compounds Ga xAs y have atomization energies between those of Ga n and As n ( x + y = n), usually closer to those of Ga n. Fragmentation of Ga xAs y occurs such that As----As bonds are retained, and if possible, also Ga----As bonds, since the dissociation energy of As 2 is higher than that of GaAs, which in turn is higher than that of Ga 2. Calculated fragmentation energies agree qualitatively with experimental observations about the composition of 3-atomic and 4-atomic clusters Ga xAs y. 相似文献
20.
A metal-organic complex, which has the potential property of absorbing gases, [LaCu 6(μ-OH) 3(Gly) 6im 6](ClO 4) 6 was synthesized through the self-assembly of La 3+, Cu 2+, glycine (Gly) and imidazole (Im) in aqueous solution and characterized by IR, element analysis and powder XRD. The molar heat capacity, Cp,m, was measured from T = 80 to 390 K with an automated adiabatic calorimeter. The thermodynamic functions [ HT − H298.15] and [ ST − S298.15] were derived from the heat capacity data with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimetry (DSC). 相似文献
|