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本文对C_6H_6Cl_6不同的三氢正电集团、独立双氢正电集团与溶媒的耦合适应性进行了研究,讨论了这些正电性集团对溶媒化程度的影响,并预测了一些物质的相对溶解度,阐述了C_6H_6Cl_6异构体间熔点差异的原因. 相似文献
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甲醇在催化剂MgO(100)面上吸附的量子化学研究 总被引:3,自引:0,他引:3
本文用CNDO/2半经验最子化学计算方法对CH3OH分子在(MgO)4(100)面上的28种可能的吸附态进行了优化计算,得到以CH3OH分子中-CH3取向吸附在(MgO)4(100)面的O^-原子上,且为重叠式构型最稳态。此构型中由于-CH3上的三个氢原子形成结构适应的三氢正电集团与氧的静电作用的结果。从吸附态的能量及Mulliken集居数上分析得甲醇在MgO催化剂上有利于形成CH4和CO,这一结 相似文献
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辽河和孤岛渣油供氢与生焦趋势 总被引:2,自引:2,他引:0
首先以蒽为化学探针对孤岛,辽河和胜利减压渣油及其四组分的氢转移能力进行表征,原理是,蒽与渣油在350-400℃热反应,渣油向蒽供氢,使蒽率成9,10-二氢蒽,用气相色谱分析定量测定热反应产物中的9,10-二氢蒽,并计算出单位重量油样供氢量;然后在400℃下热处理测定三种渣油的生焦诱导期。 相似文献
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分别用MNDO,AM1和PM3三种半经验方法对C59HN所有1-2,1-4和1-6氢加成物C59H3N的异构体进行几何构型全优化,结合频率分析及HF/6-31G单点能计算,确定了各异构体的基态结构及其相对稳定性,计算结果表明,C59HN氢加成物的立体选择性规律与C60和C60H2的不同,最稳定异构体不是1-2加成物,而是1-4加成的6,18-或12,15-异构体,次稳定异构体为1-2加成物,三种半经验方法计算得到的两者能量差为13~15kJ/mol,N原子取代碳笼骨架C原子后,改变了碳笼氢加成物的立体选择性规律. 相似文献
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辽河和孤岛渣油供氢能力与生焦趋势 总被引:5,自引:1,他引:4
首先以蒽为化学探针对孤岛、辽河和胜利减压渣油及其四组分的氢转移能力进行表征,原理是,蒽与渣油在350~400℃热反应,渣油向蒽供氢,使蒽转化成9,10-二氢蒽,用气相色谱分析定量测定热反应产物中的9,10-二氢蒽,并计算出单位重量油样供氢量;然后在400℃下热处理测定三种渣油的生焦诱导期(定义为生焦01%时所用时间)。结果发现:虽然它们四组分相近,但氢转移潜力相差较大,特别是它们的沥青质的氢转移能力相差悬殊;渣油热生焦诱导期长短与它们氢转移能力趋势一致 相似文献
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复分解-配位反应与三硫化二铋的溶解性 总被引:1,自引:0,他引:1
通过实验和理论计算论证了三硫化二铋在无氧化性强酸中的溶解性.结果表明,三硫化二铋不能溶于稀硫酸中.三硫化二铋能溶于氢卤酸(除HF外)、稀硫酸与碱金属卤化物的混合液中,应是其溶解过程发生了复分解-配位两步反应的缘故.明确指出并修正了教科书中有失精当之处. 相似文献
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通过实验和理论计算论证了三硫化二铋在无氧化性强酸中的溶解性.结果表明,三硫化二铋不能溶于稀硫酸中.三硫化二铋能溶于氢卤酸(除HF外)、稀硫酸与碱金属卤化物的混合液中,应是其溶解过程发生了复分解-配位两步反应的缘故.明确指出并修正了教科书中有失精当之处. 相似文献
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对多原子体系的量子动力学计算非常重要, 然而, 对含六原子以上的分子体系进行精确量子动力学计算仍具挑战性. 面向过程的基函数定制(PBFC)-并行迭代(PI)方法是一种高效的量子动力学方法, 已应用于对含九原子的丙二醛异构体系的氢迁移速率的精确量子计算. 本综述首先阐明了PBFC的基本思想, 之后重点回顾了PBFC-PI方法的具体内容、 该方法与其它方法的结合及其应用方面的新进展. 应用这些方法实现了对单氢迁移、 协同双氢迁移和分步双氢迁移3种类型基准体系的大规模并行计算, 有助于获得对氢迁移过程的新认识. 相似文献
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Twenty one conformationally fixed amines and their N,N-dimethyl derivatives were obtained commercially or synthesized. These included cis and trans 4-t-butyl cyclohexylamine, 2-exo and 2-endo norbornylamine, 2-adamantylamine, 4-phenylpiperidine, 1-napthylamine and tetrahydro-1-napthylamine. The (1)H NMR spectra of these amines were measured in CDCl(3) solution, assigned and the (1)H chemical shifts given. This data was used to investigate the effect of the amino group on the (1)H chemical shifts in these molecules. These effects were analyzed using the CHARGE model. This calculates the electric field and steric effects of the amino group for protons more than three bonds removed, together with functions for the calculation of two-bond and three-bond effects. The rotational isomerism about the C--N bond of the amino group was investigated by ab initio calculations of the potential energy surface (PES) about this bond at the HF/3-21G level. The resulting conformers were then minimized at the B3LYP/6-311 + + G (d,p) level. These geometries were then used to calculate the (1)H chemical shifts in the above compounds by CHARGE and the ab initio gauge-invariant atomic orbital (GIAO) method at the B3LYP/6-311 + + G(d,p) level and the shifts were compared with those observed. The compounds investigated gave 170 (1)H chemical shifts ranging from 0.60 to 8.2 ppm. The rms errors (obs.-calc.) were ca 0.1 ppm (CHARGE) and ca 0.2 ppm (GIAO). Large deviations of ca 1.0 ppm were observed for the NH protons in the GIAO calculations. The complex spectra of alkyl and aryl amines can thus be successfully predicted by both ab initio and semiempirical methods except for the NH protons, for which the ab initio calculations are not sufficiently accurate. 相似文献
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Ebata T Hashimoto T Ito T Inokuchi Y Altunsu F Brutschy B Tarakeshwar P 《Physical chemistry chemical physics : PCCP》2006,8(41):4783-4791
IR-UV double resonance spectroscopy and ab initio calculations were employed to investigate the structures and vibrations of the aromatic amino acid, L-phenylalanine-(H(2)O)(n) clusters formed in a supersonic free jet. Our results indicate that up to three water molecules are preferentially bound to both the carbonyl oxygen and the carboxyl hydrogen of L-phenylalanine (L-Phe) in a bridged hydrogen-bonded conformation. As the number of water molecules is increased, the bridge becomes longer. Two isomers are found for L-Phe-(H(2)O)(1), and both of them form a cyclic hydrogen-bond between the carboxyl group and the water molecule. In L-Phe-(H(2)O)(2), only one isomer was identified, in which two water molecules form extended cyclic hydrogen bonds with the carboxyl group. In the calculated structure of L-Phe-(H(2)O)(3) the bridge of water molecules becomes larger and exhibits an extended hydrogen-bond to the pi-system. Finally, in isolated L-Phe, the D conformer was found to be the most stable conformer by the experiment and by the ab initio calculation. 相似文献
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A series of ab initio 1H and 13C NMR chemical shifts are presented for all molecules for which gas-phase experimental measurements exist. Quantitative agreement with this large set of data is achieved by the use of gauge-invariant atomic orbitals in an SCF perturbation theory approach. The effect of basis set completeness on these 1H and 13C chemical shifts is also examined. The 4-31G basis set is found to provide internally consistent results and give satisfactory agreement with gas-phase experimental data. Errors within 6% for 1H shifts and 3% for 13C shifts result. Increasing the basis set to the 6-31G* level does not significantly improve the agreement. For 1H shifts only, the 3-21G basis set is adequate. The validity of the particular computational approach employed here is further substantiated by comparison to another ab initio magnetic shielding method. 相似文献
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An ab initio centroid molecular dynamics (CMD) method is developed by combining the CMD method with the ab initio molecular orbital method. The ab initio CMD method is applied to vibrational dynamics of diatomic molecules, H2 and HF. For the H2 molecule, the temperature dependence of the peak frequency of the vibrational spectral density is investigated. The results are compared with those obtained by the ab initio classical molecular dynamics method and exact quantum mechanical treatment. It is shown that the vibrational frequency obtained from the ab initio CMD approaches the exact first excitation frequency as the temperature lowers. For the HF molecule, the position autocorrelation function is also analyzed in detail. The present CMD method is shown to well reproduce the exact quantum result for the information on the vibrational properties of the system. 相似文献
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The infrared spectrum of methyl tert-butyl ether (MTBE) in liquid water has been studied using both FTIR absorption and FTIR-ATR spectroscopy in conjunction with ab initio calculations. Compared to the liquid MTBE IR spectrum, the C-O and C-C stretching vibrational frequencies of MTBE in water are found to shift to the red and blue by up to 26 and 9 cm (-1), respectively. Ab initio calculations suggest that these shifts are caused by complexation of the MTBE molecule with water molecules through hydrogen bonding. Our observation of the vibrational frequency shifts in the IR spectrum of MTBE in water provides the IR spectroscopic evidence of organics-water complexes in the diluted aqueous solution. The implication of the effect of the hydrogen bond in organics-water complexation on solvation and reactivity of the organic compound in aqueous chemical processes is discussed. 相似文献
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Kondo M Mates TE Fischer DA Wudl F Kramer EJ 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):17000-17012
Interfaces between phenylacetylene (PA) monolayers and two silicon surfaces, Si(111) and Si(100), are probed by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and the results are analyzed using ab initio molecular orbital calculations. The monolayer systems are prepared via the surface hydrosilylation reaction between PA and hydrogen-terminated silicon surfaces. The following spectral features are obtained for both of the PA-Si(111) and PA-Si(100) systems: a broad π-π* shakeup peak at 292 eV (XPS), a broad first ionization peak at 3.8 eV (UPS), and a low-energy C 1s → π* resonance peak at 284.3 eV (NEXAFS). These findings are ascribed to a styrene-like π-conjugated molecular structure at the PA-Si interface by comparing the experimental data with theoretical analysis results. A conclusion is drawn that the vinyl group can keep its π-conjugation character on the hydrogen-terminated Si(100) [H:Si(100)] surface composed of the dihydride (SiH(2)) groups as well as on hydrogen-terminated Si(111) having the monohydride (SiH) group. The formation mechanism of the PA-Si(100) interface is investigated within cluster ab initio calculations, and the possible structure of the H:Si(100) surface is discussed based on available data. 相似文献
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Penta- and hexa-coordinated silicon is rare, occurring as a transient species in some glasses, nonaqueous organosilicon solutions and organosilicon gels such as silicone, and is stable at high pressures within the earth in dense phases such as stishovite. The stable form expected in aqueous solution is quadra-coordinated silicon. A recent study proposed the existence of hypercoordinated silicon-polyalcohol complexes in aqueous solution, based on (29)Si NMR shifts at -102 to -103 ppm and -145 to -147 ppm. Here, we report ab initio molecular orbital calculations of (29)Si NMR chemical shifts and relative stabilities of silicon-polyalcohol monocyclic and spirocyclic complexes, from ethylene glycol (C(2)H(6)O(2)) to arabitol (C(5)H(12)O(5)) with Si in quadra-, penta- and hexa-coordination ((Q)Si, (P)Si, (H)Si), calculated at the HF/6-311+G(2d,p)//HF/6-31G* level. Calculated shifts are accurate with a 1-8% error for (Q)Si and 2-9% for (P)Si. Shifts calculated for the hypercoordinated silicon complexes having structures proposed in the literature are much more negative (-128 and -180 ppm for (P)Si and (H)Si) than observed. We propose that cyclic trimers complexed by polyalcohols can explain the -102 ppm shift, where the Si atoms are all (Q)Si, or where two silicons are (Q)Si and one is (P)Si with rapid exchange between the Si sites. The -145 ppm resonance results from structures similar to those proposed in the experimental NMR study for the -102 ppm peak. Our relative stability calculations indicate that structures proposed in the literature for hypercoordinated silicon complexes are thermodynamically unstable in aqueous solution at acidic to neutral conditions but may exist in degrading silicone-gel breast-implants. Thus, aqueous hypercoordinated silicon-polyalcohol complexes are unlikely to play an important role in biological silicon uptake and hold little promise for novel silica synthesis routes from aqueous solutions under nonextreme conditions. 相似文献
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Jacek Wójcik Krystyna Kamienska-Trela Magdalena Pecul Elzbieta Bartoszak-Adamska Siergiej I Vdovienko Igor I Gerus 《Chemphyschem》2004,5(2):209-215
Concentration- and temperature-dependent IR, NMR and dipole-moment studies on 4-N,N-dimethylamino-1,1,1-trifluoro-3-buten-2-one and two of its higher homologues showed that these compounds undergo reversible dimerization in nonpolar solvents. Antiparallel "closed" dimers are formed with a network of improper intermolecular C-H...O hydrogen bonds. Quantitative analysis of the 1H NMR data yielded delta H0 = -17.6 kJ mol-1 and delta S0 = -46.9 J deg-1 mol-1. The interactions observed are the strongest among those involving a C-H group reported so far. The complex described here is the first example of a cyclic complex stabilized by two improper C-H...O hydrogen bonds. The conclusions drawn from the solution and solid-state data were confirmed by ab initio calculations. 相似文献
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A group additivity methodology for predicting the thermochemistry of oxygen-containing organosilanes
A combinatorial approach was applied to devise a set of reference Si–C–O–H species that is used to derive group-additivity values (GAVs) for this class of molecules. The reference species include 62 stable single-bonded, 19 cyclic, and nine double-bonded Si–C–O–H species. The thermochemistry of these reference species, that is, the standard enthalpy of formation, entropy, and heat capacities covering the temperature range from 298 to 2000 K was obtained from quantum chemical calculations using several composite methods, including G4, G4MP2, and CBSQB3, and the isodesmic reaction approach. To calculate the GAVs from the ab initio based thermochemistry of the compounds in the training set, a multivariable linear regression analysis is performed. The sensitivity of GAVs to the different composite methods is discussed, and thermodynamics properties calculated via group additivity are compared with available ab initio calculated values from the literature. 相似文献