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91.
OUH体系的结构和分析势能函数 总被引:3,自引:0,他引:3
采用密度泛涵B3LYP方法优化出了OUH分子的各种结构,确定了最稳定构型和离解能,以及它们的谐性力常数,并导出双原子分子UH,UO的Murrell-Sorbie势能函数及其光谱数据。采用多体项展式方法,导出OUH(X^4A')基态分子的分析势能函数,获得OUH(X^4A')体系的势能面,考察了这个势能函数的基本性质,正确地复现出OUH分子的平衡结构特征,结果表明:U+OH,O+UH,H+UO的反应均为无阈能的放热能反应。为进一步探讨OUH体系的反应动力学过程打下了基础。 相似文献
92.
R.K.B GoverN.D. Withers S. AllenR.L. Withers J.S.O. Evans 《Journal of solid state chemistry》2002,166(1):42-48
SnP2O7 is a member of the ZrP2O7 family of materials, several of which show unusual thermal expansion behavior over certain temperature ranges and which show a number of displacive phase transitions on cooling from high temperature. Here we describe the structural properties of SnP2O7 from 100 to 1243 K as determined by X-ray and neutron powder diffraction. These studies reveal that SnP2O7 shows two phase transitions in this temperature range. At room temperature the material has a pseudo-cubic 3×3×3× superstructure. Electron diffraction studies show that the symmetry of this structure is P213 or lower. On warming to ∼560 K it undergoes a phase transition to a structure in which the subcell reflections show a triclinic distortion; above 830 K the subcell reflections show a rhombohedral distortion. Significant hysteresis in cell parameters is observed between heating and cooling. The structure of SnP2O7 is discussed with references to other members of the AM2O7 family of materials. 相似文献
93.
Diego Ardura 《Tetrahedron letters》2004,45(47):8691-8694
UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the effect of benzene solvent through the PCM-UAHF method render a concerted mechanism without fragmentation as the most favourable one for the Dowd-Beckwith radical ring expansion of the bromomethyl adduct of methyl cyclopentanone-2-carboxylate to yield methyl cyclohexanone-3-carboxylate. The corresponding concerted TS is a bicyclic alcoxy radical. 相似文献
94.
The reaction of 1-alkynylcyclobutanols with aryl iodides in the presence of Pd(OAc)2 and Et3N in acetonitrile at 80°C for 24 h gives 2-disubstituted methylenecyclopentan-1-ones in modest to good yields. The tandem insertion-ring expansion process proceeds via the formation of an alkynyl π-complex, followed by migration of a carbon-carbon bond of the tert-alkanol to form the cyclopentanones stereoselectively. 相似文献
95.
A de novo asymmetric synthesis of the octahydroisobenzofuran skeleton contained within the eunicellin family of natural products has been completed. The key transformations involve the convergent assembly of a tetrasubstituted tetrahydrofuran by condensation of a functionalised allylsiloxane with an aldehyde; controlled epimerisation of a C4 aldehyde by intramolecular trapping; installation of the isopropyl substituent by stereoselective Michael addition to a 5,5-bicyclic enone; and ring expansion of the 5,5-system to the target structure by radical-mediated cyclopropane fragmentation. 相似文献
96.
97.
Ksenia Shilyaeva Nils Elander Evgeny Yarevsky 《International journal of quantum chemistry》2007,107(6):1301-1315
Peaks in collision cross sections are often interpreted as resonances. The complex dilation method, as well as other methods relying on analytic continuation of the scattering formalism, can be used to clarify whether these structures are true resonances in the sense that they are poles of the S‐matrix and the associated Green function. The performance of the Mittag–Leffler expansion and T‐matrix Green function expansion methods are formally and computationally compared. The two methods are applied to two model potentials. Eigenenergies, s‐wave residues, and cross sections are computed with both methods. The resonance contributions to the cross sections are further analyzed by removing the residue contributions from the Mittag–Leffler and Green function expansion sums, respectively. It is suggested that the contribution of a resonance to a cross section should be defined through its S‐matrix residue. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
98.
There have been many experimental and theoretical studies on molecular conduction, as it is a fundamental parameter in the study of molecular‐scale electronics. We have investigated the features of molecular conduction using a Green's function method, which has often been used to solve problems in quantum transport and is also effective in elucidating electron transport in molecules. We have obtained the novel effective Green's functions, including the first‐order energy corrections, by accommodating the self‐energy of the electrodes as perturbation terms. Although these approximate Green's functions only provide information on the first‐order energy corrections, they can involve the elementary properties of molecular conduction. We propose a scheme for the analysis of the relations between molecular orbitals and their roles in molecular conduction and present analytical calculations for normal and cyclic polyenes. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
99.
The electrophilic iodocyclization reaction of (Z)- and (E)-5-n-alkylsubstituted 4-alken-1-ols followed by base-induced hydrodeiodination reaction stereoselectively gave, respectively, (Z)- and (E)-alkylidentetrahydrofurans in high yield. Completely different outcomes were observed with (Z)- and (E)-6,6-dimethylhept-4-en-1-ol: their iodocyclization furnished, respectively, threo- and erythro-2-(1-iodo-2,2-dimetylpropyl)tetrahydrofuran with high stereoselectivity. The threo isomer gave clean formation of 6-tert-butyl-3,4-dihydro-2H-pyran by base-induced ring expansion, while erythro isomer underwent a base-induced ring contraction to 1-cyclopropyl-3,3-dimethylbutan-1-one. Moreover, (Z)- and (E)-5-cyclopropylpent-4-en-1-ol underwent a 6-endo-iodocyclization to threo- and erythro-2-cyclopropyl-3-iodotetrahydro-2H-pyran, respectively, that under the same basic treatment, gave two isomeric 6-cyclopropyldihydro-2H-pyrans in a stereoselective fashion. 相似文献
100.
Gallardo J. Duran A. Garcia I. Celis J.P. Arenas M.A. Conde A. 《Journal of Sol-Gel Science and Technology》2003,27(2):175-183
Sol-gel hybrid organic-inorganic and inorganic SiO2-based protective coatings with and without added 3 m glass particles were developed and tested for their corrosion and wear behavior of an stainless steel substrate (AISI316L). The corrosion resistance greatly increases by incorporating glass particles in the sols. The incorporation of particles in the coatings allows the synthesis of thicker crack-free coatings. On the other hand, the corrosion resistance increases for coatings with a higher organic content obtained at lower sintering temperature. These coatings are also highly stable in saline aqueous solutions. However, the wear resistance is badly affected by the hybrid character of the SiO2 matrix. The optimum coating process in terms of corrosion and wear resistance, appears to be a hybrid system with a dense SiO2 network achieved at intermediate sintering temperatures. 相似文献