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991.
L. M. Khalilov E. A. Paramonov A. Z. Khalilova V. N. Odinokov A. A. Muldashev U. A. Baltaev U. M. Dzhemilev 《Chemistry of Natural Compounds》2001,37(4):339-342
The components of fragrance from four wormwood species of theArtemisiaL. genus were analyzed by GC-MS. The major and minor components of volatile essential oils typical of the studied plant species were determined. 相似文献
992.
The structure of the conformationally flexible 2-fluoroethanal molecule (CH2FCHO, FE) in the ground (S0) and lowest excited triplet (T1) and singlet (S1) electronic states was investigated by ab initio quantum-chemical methods. The FE molecule in the S0 state was found to exist as two conformers, viz., as cis (the F—C—C—O angle is 0°) and trans (the F—C—C—O angle is 180°) conformers. On going both to the T1 and S1 states, the FE molecule undergoes substantial structural changes, in particular, the CH2F top is rotated with respect to the core and the carbonyl CCHO fragment becomes nonplanar. The potential energy surfaces for the T1 and S1 states are qualitatively similar, viz., six minima in each of the excited states of FE correspond to three pairs of mirror-symmetrical conformers. Based on the potential energy surfaces calculated for the FE molecule in the T1 and S1 states, the one-dimensional problems on the torsion and inversion nuclear motions as well as the two-dimensional torsion-inversion problems were solved. 相似文献
993.
L. Stievano S. Calogero R. Psaro M. Guidotti R. Della Pergola F. E. Wagner 《Journal of Cluster Science》2001,12(1):123-137
193Ir and 57Fe Mössbauer spectroscopy was used to investigate the structure of the [Fe2Ir2(CO)12]2- cluster compound and the adsorption of this cluster on hydrated MgO. Supported samples were prepared by impregnation of the magnesia with solutions of [Et4N]2[Fe2Ir2(CO)12] in acetone. The Mössbauer and FT-IR spectra of the MgO-supported cluster confirm that the bimetallic carbonyl is molecularly physisorbed onto MgO without undergoing any transformation or decomposition. The easy solvent extraction of the intact cluster from the oxide surface excludes ion pairing between the cluster anion and the Mg2+ surface sites. Mössbauer spectra are in agreement with the refined structure of the molecular cluster and the temperature dependence of the 57Fe Mössbauer spectra above 80 K is consistent with the low degree of interaction of the cluster with the support. This technique, therefore, appears to be promising in order to infer structural information when X-ray determination fails. 相似文献
994.
超临界流体色谱在金属络合物和金属有机化合物中的分析应用 总被引:10,自引:0,他引:10
超临界流体色谱(SFC)在色谱分离过程中能在较低的温度下分析对热不稳定性的化合物,包括金属络合物和金属有机化合物。本文总结了近来文献报道的各种过渡金属、重金属、镧系和锕系以及铅、汞和锡的金属有机化合物的SFC分离,还讨论了SFC检测系统和金属有机化合物的溶解度的测定。 相似文献
995.
996.
Ewig CS Berry R Dinur U Hill JR Hwang MJ Li H Liang C Maple J Peng Z Stockfisch TP Thacher TS Yan L Ni X Hagler AT 《Journal of computational chemistry》2001,22(15):1782-1800
A class II valence force field covering a broad range of organic molecules has been derived employing ab initio quantum mechanical "observables." The procedure includes selecting representative molecules and molecular structures, and systematically sampling their energy surfaces as described by energies and energy first and second derivatives with respect to molecular deformations. In this article the procedure for fitting the force field parameters to these energies and energy derivatives is briefly reviewed. The application of the methodology to the derivation of a class II quantum mechanical force field (QMFF) for 32 organic functional groups is then described. A training set of 400 molecules spanning the 32 functional groups was used to parameterize the force field. The molecular families comprising the functional groups and, within each family, the torsional angles used to sample different conformers, are described. The number of stationary points (equilibria and transition states) for these molecules is given for each functional group. This set contains 1324 stationary structures, with 718 minimum energy structures and 606 transition states. The quality of the fit to the quantum data is gauged based on the deviations between the ab initio and force field energies and energy derivatives. The accuracy with which the QMFF reproduces the ab initio molecular bond lengths, bond angles, torsional angles, vibrational frequencies, and conformational energies is then given for each functional group. Consistently good accuracy is found for these computed properties for the various types of molecules. This demonstrates that the methodology is broadly applicable for the derivation of force field parameters across widely differing types of molecular structures. Copyright 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1782-1800, 2001 相似文献
997.
An analytical method was utilized to detect ppt levels of VOCs in air. The method was based on the US-EPA method TO-14, consisting of canister sampling, three module enrichment and GC/MS analysis. Target compounds included chlorofluorocarbons (four kinds), benzene and its derivatives (14), halogenated hydrocarbons (20), and others (three). The minimum detection limits of the method for the target compounds ranged from 0.016 to 0.040 ppb (0.06–0.23 μg/m3). The recoveries of the target compounds ranged from 77 to 113% and relative coefficients of variation (n=4) were 3.0–9.0%. The sampled air was stable for at least 14 days after pressurizing with humidified nitrogen gas at 200 kPa (absolute pressure). The method was applied to analyze the VOCs in the air of Yakushima, a remote island of south-west Japan where no distinct local pollution source is considered. 相似文献
998.
Vasyl I. Zaremba Ihor R. Muts Yaroslav M. Kalychak Rolf-Dieter Hoffmann Rainer Pttgen 《Journal of solid state chemistry》2001,160(2):415
The title compound was synthesized by reacting the elements in an arc-melting apparatus under purified argon and subsequent annealing at 870 K. Ca3Ni8In4 was investigated using X-ray diffraction on both powders and single crystals: P63mc, a=898.9(1) pm, c=752.2(2) pm, wR2=0.0591, 327 F2 values, and 35 parameters. This structure is an ordered, noncentrosymmetric variant of the BaLi4 type. The nickel and indium atoms build a complex three-dimensional [Ni8In4] polyanion in which the calcium atoms fill distorted hexagonal channels. To a first approximation the formula may be written as (3 Ca2+)6+ [Ni8In4]6−. Within the polyanion the Ni1, Ni3, and Ni4 atoms form one-dimensional cluster units which extend in the c direction while the Ni2 atoms have only indium neighbors in a distorted tetrahedral coordination. The Ni–Ni distances in the cluster range from 241 to 266 pm. The cluster units are surrounded and interconnected by indium atoms. The group– subgroup relation from centrosymmetric BaLi4 to noncentrosymmetric Ca3Ni8In4 is presented. Chemical bonding in Ca3Ni8In4 and the structural relation with Lu3Co7.77Sn4, Ca3Au6.61Ga4.39, and Co2Al5 is briefly discussed. 相似文献
999.
Charles H. Langley Jenn‐Huei Lii Norman L. Allinger 《Journal of computational chemistry》2001,22(13):1426-1450
Open‐chain aliphatic ketones were studied with the molecular mechanics (MM4) force field. A total of seven compounds were examined. Structures were well fit, including moments of inertia. Rotational barriers, vibrational spectra, and dipole moments were also well fit. The overall root mean square errors for MM3 and MM4 were 0.27 and 0.18%, respectively, for the six moments of inertia (known experimentally for two compounds) and 31 and 20 cm?1, respectively, for the vibrational frequencies (over 99 weighted modes). © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1426–1450, 2001 相似文献
1000.
Charles H. Langley Jenn‐Huei Lii Norman L. Allinger 《Journal of computational chemistry》2001,22(13):1451-1475
Molecular mechanics (MM4) calculations were carried out on cycloketones for ring sizes ranging from 4 to 11 carbon atoms. The MM4 relative energies for the various conformations of the cycloketones were compared to density functional theory (DFT) calculations (B3LYP/6‐31G*), which were also carried out in this work. For small ring sizes (n=4–6), calculated molecular geometries, dipole moments, moments of inertia, and vibrational spectra were compared to experimental data. The axial–equatorial energy differences in methyl‐substituted cyclohexanones were also calculated by MM4 and compared to ab initio, DFT, and experimental results. The results of the MM4 studies on cycloketones showed significant improvement from those of MM3 calculations performed in parallel with the MM4 calculations. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1451–1475, 2001 相似文献