Quantum chemical study of interactions of ketones with zeolites

The CNDO/2 method is employed to study the interactions of acetone, methyl ethyl ketone and diethyl ketone with OH groups in zeolites modelled by the Si₃AlO₄(OH)₈ H clusters. It is demonstrated that this interaction, accompanied by the formation of the H-complexes of ketones, leads to the transfer of electron density from the ketone to the zeolite and polarization of the molecule. Both these effects then cause weakening of the CO, C-H and O-H bonds and strengthening of the C-C bonds. Similar perturbation of the acetone molecule is indicated by the results of model electrostatic calculations on the interactions of acetone with the Na cationic sites in zeolites. The calculated changes in the strengths of the individual bonds of the ketones interacting with the zeolite active sites correlate well with the shifts in the corresponding vibrational bands observed for ketones interacting with these centres.     

Quantum chemical study of cyclic dipeptides

The preferred conformations of cyclic dipeptides were first studied systemically using the density functional theory (DFT) B3LYP method at the 6‐31G(d) level. The structural characteristics of cyclic dipeptides were revealed, most of which have not been confirmed until now. Our studies showed that the six‐member main circles of cyclic dipeptides composed of natural L ‐amino acid residues appeared as boat conformations. The important factors that influence conformations of cyclic dipeptides, such as molecular total energy, nuclear repulsion energy, molecular orbit, spatial effects, and reactive mechanism, are discussed in detail. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

斑蝥素衍生物的量子化学研究

在112种合成的斑蝥素衍生物中,N-羟基斑蝥胺(2)、N-甲基斑蝥胺(3)、N-乙基斑蝥胺(4)、N-烯丙基斑蝥胺(5)具有抗肝癌活性,且毒副作用很小。其中N-羟基斑蝥胺和N-甲基斑蝥胺已用于临床试验,疗效较好。关于斑蝥素衍生物化学结构与抗肝癌活性之间的关系,已有报道,但尚未从电子结构方面系统考察构效因素。本文用CNDO/2法对五个活性和三个非活性斑蝥素衍生物分子,进行了量子化学计算,以探讨药物的构效关系。     

Quantum chemical study of allyl halides

Using the MNDO method we have shown that the bathochromic shift of the longwavelength region of absorption in the electronic spectrum of allyl bromide and allyl iodide on going to nonplanar conformers is due to the fact that, in this case, the transition ^* to the low-lying ^* orbital appears, which is forbidden in planar forms. In allyl fluoride and allyl chloride, , and the transition ^*, which depends little on conformation, is long-wavelength. In the gauche conformers of allyl halides, the frontier MOs are appreciably delocalized as a result of - interaction; in the s-trans conformer, the unshared pair of the heteroatom makes an insignificant contribution to the orbital only in allyl iodide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2552–2557, November, 1989.     

平面五元水分子簇的量子化学研究

选用Gaussian03的B3LYP/6-31G(d,p)、DMol3的BLYP/DNP和deMon的BLYP/TZVP等方法计算了甲烷水合物(结构-1)中平面五元水分子簇的结合能和氢键能,作了基组重叠误差(BSSE)和色散能(dispersion)的修正,估算了次级相互作用的贡献.在DMol3程序中使用了大型数值基组DNP,将基组重叠误差降至最低.在Gaussi-an03的B3LYP/6-31G(d,p)计算中,采用平衡法(Counterpoise)校正基组重叠误差.两种计算方法给出了一致的结果,证实了在使用6-31G(d,p)基组时,一对水分子在平衡距离的基组重叠误差高达8 kJ/mol.为估算色散能的贡献,使用了新近发展的包含色散能的密度泛函的DFT程序deMon计算了五元水分子簇.用多种方法计算出了经基组重叠误差和色散能修正的五元水分子簇的分子间结合能和氢键能的较为精确的势能超曲面,为甲烷和其他气体水合物的分子动力学模拟提供了依据.     

Quantum chemical study of model fluorozirconate clusters

A number of fluorozirconate clusters having the general formula {fx41-01} were investigated by the DV-X_α quantum chemical method. The results of calculations are used to explain the existence of polyhedm with coordination numbers of the central atom 6, 7, and 8 in crystalline fluomzirconates. In the title series of clusters, the [ZrF₆]^2- octahedron and the dimer of edge-sharing seven-vertex polyhedm [Zr₂F₁₂]^4-s are highly stable. Translated from Zhumal Struktumoi Khimii, Vol. 41, No. 1, pp. 49-57, January–February, 2000.     

Quantum chemical study of allyl mercury compounds

Conclusions The appearance of a long-wavelength absorption band in nonplanar allyl mercury compounds is due to the , -conjugation effect. In planar compounds, this electronic transition lies in the far UV region.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2493–2496, November, 1987.     

Quantum chemical study of self-organized water fractals

The energetically possible ways of water condensation at the molecular level were considered. The quantum chemical calculations of the relative stability of elementary modules of the fractal structure without external fields using AM 1, CNDO /2, and MNDO methods were done. It was shown that CNDO /2 gives the most adequate results for simple water clusters. Condensation energy per molecule was chosen as a criterion of the cluster stability. It was shown that the twisted modules are the stable structures with respect to the water dissociation. In comparing the energies of the icelike and twisted structures, we conclude that the latter may exist under certain conditions. © 1996 John Wiley & Sons, Inc.     

Quantum chemical study of the autoxidation of ascorbate

Reactions involved in the autoxidation of ascorbate have been investigated with quantum chemical first‐principles and ab initio methods. Reaction energies and Gibbs energies of the reactions were calculated at the density functional theory level applying the gradient‐corrected BP86 and the hybrid B3LYP functionals together with def2‐TZVP basis sets. Results of single‐point CC2, CCSD, and CCSD(T) calculations were used for calibration of the density functional theory data and show excellent agreement with the B3LYP values. Based on the Gibbs energy ascorbic acid AscH₂ is found to be the energetically lowest species in aqueous solution, whereas the monoanion ascorbate AscH is the most abundant one near pH = 7. Asc was found to be the preferred reducing agent for autoxidation and oxidation processes. The results also support a metal‐catalyzed synthesis of the reactive oxygen species H₂O₂ according to a redox cycling mechanism proposed in literature. © 2016 Wiley Periodicals, Inc.     

Quantum chemical study of the reactivity of adamantanylidene

The specific features of inclusion of a carbenium center in the polycyclic system of adamantanylidene was investigated by the semiempirical MNDO method. The calculated characteristics of the adamantylcarbeneproton system are in agreement with the experimentally postulated nucleophilicity of singlet adamantanylidene.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 116–121, March–April, 1993.     

Quantum chemical study of oxidation processes in Cu-phthalocyanine

Quantum chemical calculations reproduced quite well the experimental infrared spectra of CuPc and CuNO₃Pc · HNO₃. The agreement in the changes of line intensities during the oxidation supports the idea of ligand oxidation. This result is in agreement with the Mulliken population analysis.     

Quantum chemical study of trivalent group 12 fluorides

In view of the recent experimental observation of the existence of tetravalent Hg (IV) in HgF 4, a quantum chemical study of various trivalent group 12 M(III) fluoride complexes has been carried out. The M-F bonds in neutral MF 3 are relatively weak, making these species unlikely targets. Some additional stability can be obtained by dimerizing HgF3 to Hg2F6, which has a doubly fluorine-bridged triplet ground state. Anionic [MF4]- and [MF5]2- species are found to be more stable toward F2 elimination and M-F bond breaking than neutral MF 3.     

Quantum chemical study of the structure of molybdenum pentafluoride

The geometrical and electronic structure of various configurations of molybdenum pentafluoride are studied in the nonrelativistic approximation of the DV-X_α method. It is shown in a cluster approximation that the presence of the MoF₅ monomer with a distorted trigonal bipyramid (C_2v symmetry) and cyclic trimer [MoF₅]₃(D_3h symmetry) configurations is most probable for the liquid and gaseous phases. High probability of the existence of cyclic tetramers [MoF_{5 4} of lower symmetry (D_2h) is confirmed for the crystalline state. The geometrical parameters calculated for the most stable clusters and the data on their stability agree well with the experimental data.     

Quantum chemical study of the rearrangement of phenoxyl-hydroxyphenyl radicals

The absorption spectra and decomposition kinetics of intermediates formed upon the photolysis of p-iodophenol are studied via flash photolysis. The extinction coefficient of the p-iodophenoxyl radical is calculated. It is found that p-iodophenol acts as an inhibitor of light-independent liquid-phase oxidation reactions.     

Quantum chemical study of the stabilization process of faujasites

The CNDO/2 method is employed in the study of the energetics of the zeolite stabilization process in which skeletal Al atoms are replaced by amorphous Si. It is shown that such a process results in the stabilization of the zeolitic skeleton and that the stabilizing effect increases with decreasing Si: Al ratio as well as with the degree of hydration of the Al-cation formed.

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/2 , Al Si. , Si:Al, Al.

     

Quantum chemical studies of non-covalent interactions between the ethyl cation and rare gases

By taking into consideration the facts that rare gases (Ar, He, Kr, and Ne) are practically inert and that the structure of the ethyl cation (C₂H₅⁺) is stabilized through the hyperconjugation effect, a theoretical study at the B3LYP/6-311 + +G(d,p) level of calculation was carried out here in order to investigate the formation of the C₂H₅⁺···Ar, C₂H₅⁺···He, C₂H₅⁺···Kr, and C₂H₅⁺···Ne complexes. The charge transfers among H and Ar, He, Kr or Ne prove that the loss of electronic density on the rare gases are clearly noticeable. Additionally, the synergism between the structural changes and the vibration shifts have been demonstrated and justified on the basis of the Bent rule and QTAIM calculations. In complement, the interaction strength in H⁺···Ar, H⁺···He, H⁺···Kr, and H⁺···Ne was examined, although the covalent character is completely null because these contacts are very weak.     

Quantum chemical study on the thermal rearrangements of HNCRCR''''CO

MINDO/3 molecular orbital theory has been used to study the thermal rearrangements of HNCRCR'CO.The results obtained show that the activation energy of this rearrangement depends on the migrating group R and the group R'.     

Quantum chemical study on asymmetric catalysis reduction of imine

The asymmetric catalysis reaction is considered to be an important way by which chiral compounds are generated. Chiral 1,3,2-oxazaborolidine, as an effective asymmetric catalyst, is used widely in the enantioselective reduction of prochiral ketones, imines, and carbon-carbon double bonds[1—3]. Up to now, a number of quantum chemical modeling investigations of the en-antioselective reduction of prochiral ketones with borane catalyzed by chiral oxazaborolidines have been carried out[4—7]. Howe…