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1.
David Zhigang Wang 《Tetrahedron》2005,61(30):7134-7143
In the framework of a helix theory recently developed for molecular chiralities and chiral interactions, it is further proposed that for an asymmetric reaction to be highly enantioselective, the helical characters, that is, the local energies of electrons on the helices, of the catalyst and the substrate complexed with it in the corresponding enantioselection-determining step must be matched. These helical characters can be analyzed on the basis of molecular polarizability and structure properties under a given reaction mechanism. This proposal highlights the importance of polarizability matching in three-dimension chiral space and in essence is a chiral version of the classical hard and soft acid-base theory. It also from an electronic effect angle sheds light on the nature of the conventional lock-and-key origin of high enantioselection and carries the message that, to design a good catalyst (the key), rather than focusing on the rigidity, bulkiness or C2-symmetry of the catalyst, one should focus more on the helical character of the substrate (the lock) with which the catalyst will interact. It is generally easier to discover a highly enantioselective catalyst for a substrate of a large helical character than for a substrate of a small helical character. The proposal is supported by theoretical modeling as well as numerous experiments and is used to understanding various aspects of current asymmetric catalysis. 相似文献
2.
根据化合物形成过程中价电子能量变化与生成焓之间的关系, 推导出烷烃的生成焓和电离能之间的关系. 以21个烷烃化合物为模型将实验测定的电离能与标准生成焓进行直接关联, 证实了模型方程的适用性, 所得回归方程的相关系数达到0.9999, 估算值与实验值之间的标准偏差仅为0.03 eV. 同时还利用实验测定的标准生成焓对一系列烷烃的电离能作了预测. 相似文献
3.
A polarizable molecular dynamics model for adiabatic electron transfer across the electrode|electrolyte interface is presented. The electronic polarizability of the water and of the metal electrode is accounted for by a dynamical fluctuating charge algorithm, image charges, and the Ewald summation adapted for a conducting interface. The effects of the solvent electronic polarizability are studied by computing the diabatic and adiabatic free energy curves for both polarizable and non-polarizable water models. This represents the first effort to compute the adiabatic free energy curves from simulation for a fully polarizable electrochemical system. 相似文献
4.
A Pluta polarizing interference microscope with a fibre stretching device attached was used to detect the changes in molecular structure that occur during the fibre cold drawing process. Fibres drawn with low draw ratios show different types of deformation mechanisms. The interference patterns recorded at different draw ratios are used to relate the deformation mechanisms with the measured structural parameters. Some optical parameters are measured such as; refractive indices nand n birefringence n, the polarizability per unit volume , the orientation distribution function f(θ), the angle θ between the stretching direction and the chain axis, and the angle θm which the transition dipole moment of the molecular species makes with the molecular axis (chain axis). Three polymeric fibres (Polyethylene terephthalate PET, Polypropylene PP and Polyamide PA) were used in this study and their interferograms are illustrated. 相似文献
5.
6.
M. Häser R. Ahlrichs H. P. Baron P. Weis H. Horn 《Theoretical chemistry accounts》1992,83(5-6):455-470
Summary The ab initio SCF computation of second-order properties of large molecules (with 50 atoms or more) on workstation computers is demonstrated for static dipole polarizabilities and nuclear magneting shieldings. The magnetic shieldings are calculated on the basis of gauge including atomic orbitals (GIAO). Algorithmic advances (semi-direct algorithms with efficient integral pre-screening, and use of a quadratically convergent functional for the polarizabilities) are presented together with an illustrative application to the fullerenes C60 and C70. 相似文献
7.
研究了微扰电场中 BeH~+的基函数的优化.使用 LCAO-SCF-MO 方法计算出 BeH~+分子轨道波函数和多极矩,进而计算出 BeH~+的极化率和超极化率. 相似文献
8.
Alexey N. Egorochkin Nadiya M. Khamaletdinova 《Journal of organometallic chemistry》2011,696(10):2199-2205
The literature data on substituent influence on the CS, CN, NC, NN, and NO stretching frequencies (ν) in the IR spectra and in specific cases on their respective stretching force constants (k) have been analyzed for 28 series of the transition metal complexes. The ν and k values were first established to depend not only on the inductive and resonance effects but on the polarizability of substituents as well. The contribution of the polarizability effect varies from 0 to 57% with the type of series. 相似文献
9.
E. TangarifeC.A. Duque 《Physica B: Condensed Matter》2011,406(4):952-956
This work is concerned with the theoretical study of the combined effects of applied electric field and hydrostatic pressure on the binding energy and impurity polarizability of a donor impurity in laterally coupled double InAs/GaAs quantum-well wires. Calculations have been made in the effective mass and parabolic band approximations and using a variational method. The results are reported for different configurations of wire and barriers widths, impurity position, and electric field and hydrostatic pressure strengths. Our results show that for symmetrical structures the binding energy is an even function of the impurity position along the growth direction of the structure. Also, we found that for hydrostatic pressure strength up to 38 kbar, the binding energy increases linearly with hydrostatic pressure, while for larger values of hydrostatic pressure the binding energy has a non-linear behavior. Finally, we found that the hydrostatic pressure can increase the coupling between the two parallel quantum-well wires. 相似文献
10.