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Ab initio molecular orbital calculations using an 8 s , 3 p ; 3 s Gaussian basis set, with contraction, have been used to study a series of primary amines XNH2, where X = H, CH3, OH, F, CN, CHO, and NO2. The geometries of the corresponding ammonium ions have been optimised and the energy differences have been used to estimate relative proton affinities. The 1 s orbital energies for both the amines and ammonium ions, when corrected for the effects of charges on the other atoms in the molecule by use of an ESCA equation, give a good correlation with the computed charge on the nitrogen atom. 相似文献
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The heat of immersion in water was measured at 25°C for three iron(III) oxides using a twin-type microcalorimeter. One of the samples was commercial α-Fe2O3 (sample C) and the other two (samples M and F) were prepared by calcining magnetite and iron(III) hydroxide in air at various temperatures, Tp, from 300 to 700°C. The samples were evacuated at outgassing temperature, To, between room temperature and 500°C at a pressure of 1 × 10?2?2.7 × 10?2N m?2 for 6 h. The heat of immersion, hi(J m?2), of samples C and M increased with an increase in To and showed the maximum hi at To =400°C, while sample F did not show the maximum up to To =500°C. The systematic correlation was not observed between hi and Tp of sample F. The heat of reproduction of the surface hydroxyl group on sample F was approximately estimated as 6.6 × 104 J mole?1 H2O. 相似文献
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In order to test the effect of a removal of an “equivalence” restriction, some excited states of B, C+ and C arising from the configuration 1s22s2pn (n = 2, 3) are calculated by the use of a one-diffuse-electron model with the optimal spin coupling (DO), in which the freedom of the spin coupling is fully used. The configuration employed is 1s22s2pn–12p′ (n = 2, 3). The DO method gives a good agreement with the term energies especially for boron (4P → 2P) and carbon (5S° → 3S°). A diffuse 3p natural orbital with a large occupation number is found for boron 2P and carbon 3S° by DO . This result is confirmed by configuration interaction calculations. Using the same configuration as above, we also examine a one-diffuse-electron model with a fixed spin coupling for boron. This method almost reproduces the results of restricted Hartree–Fock and the effect of a removal of an “equivalence” restriction is not found. The importance of utilizing the freedom of the spin coupling in a one-diffuse-electron model is strongly indicated in this article. 相似文献
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Charles W. Bauschlicher Jr 《Theoretical chemistry accounts》1995,92(3):183-198
Large atomic natural orbital (ANO) basis sets are tabulated for the Sc to Cu atoms. The primitive sets are taken from the large sets optimized by Partridge, namely (21s13p8d) for Sc and Ti and (20s12p9d) for V to Cu. These primitive sets are supplemented with threep, oned, sixf, and fourg functions. The ANO sets are derived from configuration interaction density matrices constructed as the average of the lowest states derived from the 3d n 4s 2 and 3d n+14s 1 occupations. For Ni, the1 S(3d 10) state is included in the averaging. The choice of basis sets for molecular calculations is discussed. 相似文献
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Combined Hartree‐Fock‐Roothaan calculations have been performed using noninteger n Slater type orbitals for the ground states of the lowest electron configurations 1s22s22pn (2 ≤ n ≤ 6) for negative ions of B, C, N, O and F. These results are compared with the corresponding results obtained from the use of integer n Slater type orbitals. All of the nonlinear parameters are fully optimized. The results of calculation of coupling‐projection coefficients, orbital and total energies and virial ratios are presented. It is shown that the noninteger n Slater type orbitals, in general, improve the orbital energies. 相似文献
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The hydrogen bond index (HBI) is the global invariant of a molecular graph and equals the number of vertices representing hydrogen and nitrogen atoms. This index was considered a measure of the capability of a complex to form hydrogen bonds. Optimization of the correlation weights of the HBI and local graph invariants was used for the QSPR modeling of the stability of 110 biometal M2+ complexes with -amino acids and phosphate derivatives of adenosine. The statistical parameters of the best model are n = 55, r = 0.9921, s = 0.279, and F = 3328 (learning sample) and n = 55, r = 99.35, s = 0.248, and F = 4027 (control sample). 相似文献
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New synthetic pathways and the infrared spectrum of bis(fluorosulfonyl)difluoromethane, (SO2F)2CF2, are reported. The geometric structure and conformational properties of the title compound have been studied by gas electron diffraction. Depending on the rotational position of the two SO2F groups, four conformers with different symmetries can occur in this compound: C2v symmetry, if both S? F bonds stagger the CF2 group. C2 or Cs symmetry, if one S?O bond of each group staggers the CF2 group. The experimental electron diffraction intensities can be fitted equally well with a C1 conformer or with a mixture of C2v, C2 and Cs conformers, in a ratio of 3:2:5. The following geometric parameters (ra distances, ∠α angles with 3σ uncertainties) were derived: C? F = 1.340(6) Å, S?O = 1.412(2) Å, S? F = 1.550(3) Å, C? S = 1.848(4) Å, S? C? S = 113.6(7)°, F? C? F = 110.0(10)°, O?S?O = 124.6(18)°, C? S? F = 96.5(16)° and C? S?O = 108.4(14)°. 相似文献
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The reactivity of phenylnitroso oxide, (p-methylphenyl)nitroso oxide, (p-nitrophenyl)nitroso oxide, (m-nitrophenyl)nitroso oxide, and (p-bromophenyl)nitroso oxide toward a number of olefins in acetonitrile at room temperature was studied using flash photolysis. It was found that the reaction rate constant decreased with decreasing energy of a molecular orbital with a maximum contribution from the atomic orbitals of carbon atoms in the C=C bond of olefins. This, along with a positive slope of the Hammett function for the reactions of substituted phenylnitroso oxides with 1-hexene and styrene, suggest an electrophilic character of these species. The temperature dependence of the rate constant of the reaction of phenylnitroso oxide with 1-hexene was studied: log A = 7.9 ± 0.4 [l mol-1 s-1]; Ea = 38 ± 2 kJ/mol.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 842–847.Original Russian Text Copyright © 2004 by Chainikova, Khursan, Safiullin. 相似文献
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Minimal basis set (STO) molecular orbital and valence-bond calculations are reported for the3 B 1 and1 A 1 states of CH2. The open-shell molecular orbital calculations used the Roothaan formulation. The valence-bond calculations used the Prosser-Hagstrom biorthogonalisation technique to evaluate the cofactors required in using Löwdin's formulae. Optimisation of geometry and orbital exponents in the molecular orbital calculation on the3 B 1 state gave a geometry of RC-H=2.11 a.u. and H-C-H=123.2 °. The energy obtained was ?38.8355 a.u. The molecular orbital and valencebond calculations are compared. In the valence-bond calculations the variation with bond-length and bond-angle of the configuration energies was studied. Valence bond “build-up” studies are also reported. Valence-bond calculations using hybrid orbitals instead of natural atomic orbitals showed that the perfect-pairing approximation is not as good for CH2 as BeH2. The nature of the lone-pair and bonding orbitals is found to be significantly different between the3 B 1 and1 A 1 states. In the3 B 1 state the 2s and 2p orbitals are fairly equally mixed between both types of orbital. However in the1 A 1 state the bonding orbitals have mainly 2p character and the lone pair orbitals have mainly 2s character. As was found for H2O, the bonding hybrid orbitals do not follow the hydrogen nuclei as the bond angle varies but continue to point approximately in their equilibrium directions. 相似文献
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The thermodynamic second dissociation constants of the protonated form of N-(2-acetamido)iminodiacetic acid were determined at 12 temperatures from 5–55°C by measurement of the electromotive force using a cell without liquid junction, with hydrogen and silver—silver bromide electrodes. At 25°C, pK2is 6.844. The standard changes in Gibbs energy, enthalpy, entropy and heat capacity were derived from the change of the pK2 values with temperature. At 25°C, ΔG° = 9335 cal mol-1, ΔH° = 2928 cal mol-1, ΔSo = -21.5 cal K-1 mol-1, and ΔC°p = -34 cal K-1 mol-1. The results are interpreted and compared with those of structurally related compounds. 相似文献
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Synthesis and Crystal Structure of the Nitrido Complex [Na-15-crown-5]2[MoNF4]2 · 2 CH3CN The title compound is synthesized by the reaction of [MoCl4(NSCl)]2 with excess NaF in boiling acetonitrile in the presence of the crown ether 15-crown-5. [Na-15-crown-5]2[MoNF4]2 · 2 CH3CN forms yellow crystals, which were characterized by an X-ray structure determination. Space group P1 , Z = 1. Lattice dimensions at ?90°C: a = 855.5, b = 1 069.9, C = 1 143.5 pm, α = 105.71°, β = 95.29°, γ = 102.25° (4 096 independent observed reflexions, R = 0.039). Short Na…?F contacts of 234 pm with the four axial fluoro ligands of the dimeric anion [MoNF4]22? allow formulation of a triple ion. The centrosymmetric anion is dimerized by bent fluoro bridges with Mo? F distances of 198 and 245 pm. The long Mo? F distances of the MoF2Mo ring are in transposition to the nitrido ligands, the bond lengths of which (165 pm) correspond to triple bonds. 相似文献
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K. Hegemann V. Staemmler R. Fink 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,27(3):211-217
Quantum chemical ab initio calculations have been performed for the ground state and for several excited states of the F3+ ion (F IV). Three levels of accuracy have been used: Frozen-core SCF calculations (FRC-SCF) to determine orbital energies ε nl and quantum defects δ l for excited Rydberg orbitalsnl; frozen-core SCF followed by CI calculations (FRC-CI) which account for multiplet splittings and configuration mixings, and multi-configuration coupled-electron-pair approximation (MC-CEPA) calculations which include dynamic correlation effects. The accuracy of the calculated excitation energies is in the order of 5000 cm?1 at the FRC-CI level and in the order of 500 cm?1 at the MC-CEPA level. This latter error amounts to about 0.1% for excitation energies in the range of 400000 to 600000 cm?1. The MC-CEPA calculations have been performed for 17 experimentally known states and for 14 experimentally unknown states, in particular for the configurations 2s2p 2 (2 D)3s, 2s 2p 2(2 S)3s, 2s 2 2p 4p, and 2s 2 2p 5p. 相似文献
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A new approach is presented for obtaining graph invariants which have very high discriminating ability for different vertices within a graph. These invariants are obtained as the solution set (local invariant set, LOIS) of a system of linear equationsQ · X = R, whereQ is a topological matrix derived from the adjacency matrix of the graph, andR is a column vector which encodes either a topological property (vertex degree, number of vertices in the graph, distance sum) or a chemical property (atomic number). Twenty examples of LOOIs are given and their degeneracy and ordering ability of vertices is discussed. Interestingly, in some cases the ordering of vertices obtained by means of these invariants parallels closely the ordering from an entirely different procedure based on Hierarchically Ordered Extended Connectivities which was recently reported. New topological indices are easily constructed from LOISs. Excellent correlations are obtained for the boiling points and vaporization enthalpies of alkanesversus the topological index representing the sum of local vertex invariants. Les spectacular correlations with NMR chemical shifts, liquid phase density, partial molal volumes, motor octane numbers of alkanes or cavity surface areas of alcohols emphasize, however, the potential of this approach, which remains to be developed in the near future. 相似文献
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H. X. Ma N. N. Zhao B. Yan Y. L. Guan J. F. Li J. R. Song 《Journal of Structural Chemistry》2012,53(3):534-541
Bis-(3,3-dinitroazetidinyl)-oxamide ((DNAZ-CO)2) is an acyl derivative of 3,3-dinitroazetidine (DNAZ). It is prepared and its crystal structure is determined. The crystal is orthorhombic, Fdd2 space group, a = 13.136(14) Å, b = 19.48(3) Å, c = 10.326(14) Å, V = 2642 (6) Å3, Z = 8. A density functional theory (DFT) method of the Amsterdam Density Functional (ADF) package is used to calculate the geometry, frequencies, and properties. The optimized geometry, frontier orbital energy, and main atomic orbital percentage are obtained. The thermal behavior is studied under a non-isothermal condition by DSC and TG/DTG methods. The apparent activation energy (E a) and pre-exponential factor (A) of the exothermic decomposition reaction of (DNAZ-CO)2 are 164.10 kJmol?1 and 1013.38 s?1 respectively. The critical temperature of thermal explosion is 272.20°C. The values of ΔS ≠, ΔH ≠, and ΔG ≠ of this reaction are 6.44 Jmol?1·K?1, 163.76 kJmol?1 and 160.34 kJmol?1 respectively. 相似文献
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Multi-ζ Slater-type orbitals are frequently used in molecular orbital calculations. Master formulae and numerical tables are available in literature for overlap integrals between s, p, and d atomic orbitals up to principal quantum number (n) = 3 and for some other selected quantum numbers. However, no master formula or numerical table is available for quantum numbers n = 5 and above and involving ? orbitals. In this article recursion formulae have been presented for the calculation of the overlap integral between any two s, p, d, and ? atomic orbitals formed by a linear combination of Slater-type orbitals. These formulae, when expanded, would give rise to all the master formulae reported in the literature as well as formulae hitherto unreported. 相似文献
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Hiroshi Tatewaki 《International journal of quantum chemistry》1973,7(5):971-984
The 1P and 3P states arising from the configuration (1s)2(2s)(2p) of the Be isoelectronic sequence are investigated. In the single configuration approximation, the energies of the two states are expressed as E0 + K2s2p and E0 - K2s2p, respectively. K2s2p is the exchange integral between the 2s and 2p electrons and E0 is the energy of a model in which K2s2p is deleted. First we calculate the 2s- and 2p-orbitals in this model. Second, by taking account of K2s2p in this model, effects of this term on the 2p-orbitals in the 1,3P states are investigated. In this manner, an explanation is given for the following facts which are obtained from a minimal Slater-type orbital set; (1) for Be and B+, the 2p-orbital of the 1P state is broader than that of the 3P state; (2) for C2+, the extension of the 2p-orbital in the two states is almost the same; (3) for O4+ and Ne6+, in contrast to Be and B+, the 2p-orbital of the 1P state is tighter than that of the 3P state. 相似文献