Quantum chemical calculations on thioridazine

Quantum chemical CNDO /2 calculations for the conformational preference of the side chain of thioridazine as a function of angle indicated the crystallographically determined structure gave the lowest energy. There is also a small region of conformational flexibility within the first 90° of rotation of the side chain. This is commensurate with the results which we had obtained previously for our similar calculations for promazine and its Cl and CF₃ derivatives, perazine and its Cl and CF₃ derivatives, and for the hypothetical hitherto unknown N-piperidinopromazine and its Cl and CF₃ derivatives. The conformational profile of thioridazine resembles that of the perazines. The calculated gross atomic populations on the alkyl nitrogen in thioridazine was within the range we had previously found necessary for neuroleptic activity.     

Quantum chemical calculations of hydration electrostatics and electrochemical oxidation potential of cyclic nitroxide radicals

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Direct first-principles chemical potential calculations of liquids

We propose a scheme that drastically improves the efficiency of Widom's particle insertion method by efficiently sampling cavities while calculating the integrals providing the chemical potentials of a physical system. This idea enables us to calculate chemical potentials of liquids directly from first-principles without the help of any reference system, which is necessary in the commonly used thermodynamic integration method. As an example, we apply our scheme, combined with the density functional formalism, to the calculation of the chemical potential of liquid copper. The calculated chemical potential is further used to locate the melting temperature. The calculated results closely agree with experiments.     

Quantum chemical calculations for polyvinylidene fluoride with substitution defects

The MNDO calculation method and molecular cluster model are used to study the influence of substitution defects formed by alkali metal (Li, Na, K) and halogen (Cl, I) atoms on the saturation polarization and forbidden gap of polyvinylidene fluoride (CH₂2CF₂) a pyroelectric with pronounced photoelectric properties. Densities of state are calculated for both the defectless pyroelectric and for the sample with substitution defects. The calculated energy characteristics are in good agreement with the available experimental data. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 3, pp. 468-473, May–June, 2000.     

H+NH3反应势能面的量子化学研究

本文采用UCCSD(T)/aug-cc-pVTZ方法研究了H NH3反应势能面,获得了夺氢反应和交换反应过渡态的的几何结构和振动频率。夺氢反应的过渡态具有Cs对称性,其能垒为61.92 kJ/mol。交换反应的过渡态具有C3v对称性,其能垒为39.69 kJ/mol。H NH3发生形成Td对称性的反应中间体NH4里德堡自由基。与夺氢反应相比,交换反应具有更低的反应能垒,并且NH4自由基在反应中可形成长寿命的共振态,和夺氢反应形成竞争关系,因此在H NH3反应的量子动力学研究中必须同时考虑这两类反应。本文还采用更大的基组aug-cc-pVQZ和aug-cc-pV5Z研究了势能面对基组的收敛行为。     

Quantum chemical CD calculations of dioncophylline A in the solid state

Although dioncophylline A (1) is the certainly best-investigated naphthylisoquinoline alkaloid, it still represents a challenging case for theoretical stereochemical investigations. Its biaryl axis, although being configurationally stable, still has a certain degree of rotational flexibility, rapidly twisting within certain margins, and thus, exerting a dramatic influence on the CD behavior of 1. Therefore, solid-state CD spectroscopy might provide a unique chance to study this flexible compound in a conformationally ‘frozen’ form, as fixed in the crystal. Based on the X-ray derived coordinates of the single conformer found in the crystalline state, CD calculations were performed by three different approaches, viz. by CNDO/S-CI, TD-B3LYP, and DFT/MRCI, each permitting the unambiguous attribution of the absolute axial configuration of dioncophylline A (1) as P, which is in full agreement with the previous assignments. Furthermore, to examine a possible influence of the neighboring molecules in the crystal on the CD behavior of 1, a set of dyads, each consisting of a given ‘central’ molecule and a second one from the nearest neighborhood, were considered at a semiempirical level, as well as a ‘one-piece’ cluster of 16 molecules from the crystal. The results were compared with those obtained by solution and solid-state CD spectroscopy, which confirmed the configurational assignment.     

Quantum chemical calculations on the catalytic dehydration of 2-propanol

The charge on atoms and the bond strengths in CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– and CH₃ CH₃...O(H)CH(CH₃)₂ have been calculated by the CNDO/2 method. The results are in agreement with published experimental observations on catalytic dehydration. A modified mechanism of anti-elimination on solid catalysts is proposed.

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CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– CH₃ CH₃...O(H)CH(CH₃)₂, CNDO/2. . .

     

Quantum chemical calculations of the redox potential of the Pu(VII)/Pu(VIII) couple

The redox potential of the Pu(VII)/Pu(VIII) couple was studied by density functional theory calculations. The spin-orbit effect was corrected at the CASSCF level. The redox potential (relative to the standard hydrogen potential) of the Pu(VII)/Pu(VIII) couple in alkaline solution was found to vary from 4.36 to 1.06 V depending on the number of Pu-O oxo bonds, coordination numbers, and coordination modes. The redox potential drops substantially as the number of Pu-O oxo bonds increases. Pu(VIII) may be synthesized in strong alkaline solution assuming that both Pu(VII) and Pu(VIII) exist in penta-oxo form, Pu (VII)O 5OH (4-) and Pu (VIII)O 5OH (3-), respectively. The Mulliken population of Pu in Pu(VII) and Pu(VIII) complexes are very similar, suggesting that the spin-orbit effect is rather small in Pu(VII) complexes and that when Pu(VII) is oxidized to Pu(VIII) the electron is stripped mainly from the ligand. Consequently, Pu(VIII) is in an unstable oxidation state and easily reduced back to Pu(VII) by the solvent water molecules. In acidic medium, the Pu(VII)/Pu(VIII) redox potential is too high to get the Pu(VIII) valence state.     

Quantum chemical calculations of the structure of hydrogen-bonded sulfuric acid-dimethylformamide complexes

The most characteristic structures of hydrogen-bonded (H₂SO₄)₂, H₂SO₄-dimethylformamide (DMF) and (H₂SO₄)₂-DMF complexes are obtained by means of B3LYP/cc-pVQZ. The changes in the geometric parameters of the complexes are analyzed and the energy values of the intermolecular interaction are estimated. The electronic mechanism for the formation of hydrogen bonds between molecules is considered. It is shown that complexes of (H₂SO₄)₂-DMF composition are more energy-stable than complex with one H₂SO₄ molecule. It is established that molecular complexes with very strong hydrogen bonds and complexes with proton transfer can be formed between an acid dimer and N,N-dimethylformamide. It is concluded that protons can be transferred in the gas phase in (H₂SO)₂-DMF, where the molecules in (H₂SO₄)₂ are bound by three hydrogen bonds.     

Quantum chemical calculations of N@Cn endofullerenes (n ≤ 60)

The geometric parameters and energy characteristics of small endofullerenes N@C_n (n = 20, 24, 30, 32, 40, 50) and N@C₆₀ in the quartet ground state were calculated by the B3LYP/6-31G* method. The N atom is located at the center of the carbon cage in all molecules except N@C₃₀, where it is bound to the cage wall. Encapsulation of nitrogen atom has little effect on the fullerene cage geometry for n = 40, 50, and 60. No significant charge transfer from the N endo-atom to the cage was revealed for all the N@C_n endofullerenes studied. The calculated spin density on the nitrogen endo-atom increases as the size (n) of the carbon cage increases. The relative stabilities of C_n fullerenes and corresponding endofullerenes N@C_n are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 15–20, January, 2006.     

Quantum chemical calculations on the interaction of diazomethane with proton acids

Diazoalkanes may form H-bonded associates with weak proton acids, whereas with strong acids proton transfer leads to the diazonium ion. In order to get information about protonation and association at and N, the corresponding energy balances, electron charge distributions and bond strengths have been calculated by means of quantum chemical ab initio methods with diazomethane as substrate and HF,NH₄⁺, OH₃⁺ as acids.     

Quantum chemical ab initio calculations for excited states of F IV

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.     

Quantum calculations of vibrational energies of H3O2- on an ab initio potential

We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initio electronic energies. A major feature of this potential is a barrier of roughly 200 cm-1 to internal rotation of the two hydroxyl groups about a line connecting the two oxygen atoms and the bridging hydrogen atom. The potential is used in calculations of vibrational energies, performed with the "Reaction Path" version of the code "MULTIMODE". The results are compared to recent infrared messenger experiments and are used to propose interpretations of the experimental results.     

Quantum chemical calculations of silicon clusters in silicon dioxide and point defects in β-cristobalite

A local electronic-state density in β-cristobalite in the empirical tight-binding approximation has been calculated by the recursion method. In particular, silicon clusters have been considered in β-cristobalite containing up to three coordination spheres of silicon atoms.     

Quantum chemical calculations on the Peterson olefination with alpha-silyl ester enolates

The reaction of stabilized Peterson reagents (alpha-silyl ester enolates) with ketones has been studied theoretically and experimentally. Enolate geometry was studied by trapping experiments and NMR spectroscopy and was found to differ markedly with the nature of the base (LiHMDS vs LDA vs KHMDS). The chelating effect of the lithium counterion was found to be critical for the reaction. For the two ketones studied, the combined weight of experimental and computational data assigns geometrical selectivity to the initial addition transition state, though in general there appears to be a fine balance between three possible choices for the rate-determining step.     

Quantum mechanical calculations of vibrational transition probabilities in collinear atom–triatom collisions

Quantum mechanical calculations have been made of vibrational transition probabilities in the collinear collision of an inert gas atom with either CO₂ or OCS. The dependence of the transition probability on the relative translational energy and the reduced mass is similar to that found for atom–diatom collisions. The transition P_{00 → 10} (excitation of the first stretching mode) is much greater than P_{00 → 01} (the second stretching mode). This is largely due to the difference in frequencies but it has been shown that there is an independent mass factor responsible for this difference.     

甲烷水合物分子间势能的量子化学研究

用Hartree-Fock SCF和密度泛函(BLYP,B3LYP,MPW1PW91)方法对以结构-Ⅰ为单元的甲烷水合物进行了分子间势能的理论研究.该结构单元为正十二面体,其中包括20个水分子,甲烷分子在其中心.采用从头算HF/6-31G(d,p)对甲烷分子进行几何优化,采用ST2模型对水分子作几何优化.水-水间氢键势能Ehb(l)和水-甲烷间范德华势能Evdw(l)作为边长l的函数进行计算,计算时固定水和甲烷分子的几何形状.所有计算中均使用6-31G(d,p)基组.基组重叠误差(BSSE)经校正其上限和下限为水-水氢键能加以确定.由B3LYP经基组重叠误差(BSSE)校正得到的O—O距离为RO—O=0.280 nm,C—O距离RC—O=0.392 nm,比其他方法更接近实验值的0.282和0.395 nm.结果表明,在天然气水合物结构-Ⅰ中水-水分子对的氢键能(30~36 kJ/mol)大于水的二聚体(H2O)2氢键能(-22.6±2.9)kJ/mol,亦大于六角形冰的(-21.7±0.5)kJ/mol,十二面体结构为一稳定单元.以上分子间相互作用势能的结果为得出Lennard-Jones和Kihara势能参数提供了坚实的基础,此参数对分子动力学模拟天然气水合物是非常有用的.     

Quantum chemical calculations of fluoroethylene molecules by the CNDO and INDO methods

Conclusions A quantum chemical calculation of seven fluoroethylene molecules and two fluorochloroethylene molecules and two fluorochloroethylene molecules by the CNDO and INDO methods has made it possible to explain the experimentally observed change in reactivity and direction of addition reactions at the double bond. The data of a calculation of the relative stability of various isomers also agree with the experimental results.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2199–2202, October, 1973.