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101.
Jozef Noga Miroslav Urban Vladimír Kellö Ivan Hubač 《Theoretical chemistry accounts》1981,59(3):309-317
The efficiency of the MB-RSPT in the calculations of the correlation contributions to the interaction energies was investigated, using He2 as a model Van der Waals system. The attention has been focused on the convergency of the perturbation expansion in the calculations of the interaction energy and on the analysis of the fourth-order terms of MB-RSPT. The rôle of the renormalization term in the correct long-range behaviour of the interaction potential has been emphasized. 相似文献
102.
Rong-Bin Huang Nan-Feng Zheng Su-Yuan Xie Lan-Sun Zheng 《Journal of inclusion phenomena and macrocyclic chemistry》2001,40(1-2):121-124
Crystal structure analysis shows that the p-tert-butylcalix[8]arene host and its four pyridine guests sit around an inversion center in the P21/c crystal lattice. The monoclinic cell parameters and its volume are: a = 19.617(4), b = 9.912(2), c = 25.178(5) , = 101.03(3)°, V =4805.27(17) 3. For Z = 2 and Mw = 1614.18, the calculated density Dcalc = 1.116 g/cm3. A host calixarene molecule includes four pyridine guests in two different ways: by hydrogen bonding and by possible C–H· interaction between the molecules. The hydrogen bonding drives the host macrocycle into a chair-like conformation. 相似文献
103.
John D. Watts Miroslav Urban Rodney J. Bartlett 《Theoretical chemistry accounts》1995,90(5-6):341-355
Summary This paper reports a series of coupled-cluster (CC) calculations through CCSDT on the theoretically challenging ground state of the BeO molecule. Along with CC methods, quadratic configuration interaction (QCI) approximations to CC theory have been used (QCISD and QCISD(T)), which show several dramatic failings. Equilibrium electrical properties (,
xx
, and
zz
) and basic spectroscopic properties (r
e, e,D
e, and infrared intensity (I)) have been computed. Basis set and electron correlation effects are analyzed in order to arrive at accurate values of the dipole moment and polarizability, which are not known experimentally. For the dipole moment, we obtain a value of 6.25 D, with an uncertainty of about 0.1 D. For
xx
and
zz
, we suggest respective values of 32 and 36 atomic units (a.u.) and error bars of about 1 and 2 a.u. With extended basis sets, the spectroscopic propertiesr
e, e, andD
e are reproduced to high accuracy, which is the first time this has been achieved for this species byab initio methods. At the highest calculation levels,I is predicted to be very small. AlthoughI has not been measured, some support for this prediction comes from a recent infrared study of BeO-rare gas complexes. The QCI methods are shown to be much more sensitive to basis set, and even with large basis sets yield values of
zz
andI which differ from CC results by an order of magnitude and three orders of magnitude, respectively. These differences doubtless arise from the importance of single excitations (T
1) for this molecule, as several terms involvingT
1 are neglected in the QCISD approximation compared with CCSD. We also report CC calculations with Brueckner orbitals, which yield results similar to those obtained with restricted Hartree-Fock orbitals. 相似文献
104.
The effects of adding millimolar quantities of a series of compounds containing the carbonyl function on the conductances of solutions (0.2 mM) of tri-n-butylammonium picrate ino-dichlorobenzene solvent at 25°C have been measured. Values of the complex formation constants K
1
+
for 1:1 cation-ligand complexes are derived from these data. The corresponding values of –G
1
0
at 25°C are (in kcal-mole
–1
): 4-butyrolactone, 4.29; propylene carbonate, 3.87; ethylene carbonate, 3.59; cyclopentanone, 3.42; ethyl acetate, 2.84; and diethyl carbonate, 2.78. These results together with earlier results from this laboratory are discussed in terms of the effects of structure on cation-ligand affinity. 相似文献
105.
Xiaoling Bao Jianhong Liu Qingshu Zheng Wei Pei Yimei Yang Yanyun Dai Tao Tu 《中国化学快报》1990,30(12):2266-2270
A novel protocol allowing convenient and highly selective visual recognition of melamine in raw milk via selective metallo-hydrogel formation at a concentration as low as 10 ppm without any tedious pretreatment has been developed. 相似文献
106.
In the present paper, the behavior of a single polymer chain under various solvent conditions was modeled by self-avoiding walks (SAW) with nearest neighbors attraction Δε on a simple cubic lattice. Determination of the θ-condition wasbased on the numerical results of the mean square radius of gyration and end-to-end distance. It was found that at the θtemperatue Δε/kT equals -0.27. The exponents a in the Mark-Houwink equation with different interaction parameters areconsistent with the results of experiments: under θ-condition, a = 0.5, and for a good solvent α= 0.74-0.84, respectively. 相似文献
107.
由RhCl_3·xH_2O制备了不同Rh含量的Rh/SiO_2和Rh-V/SiO_2催化剂,采用化学吸附和原位TPD-IR方法考察钒助剂对Rh/SiO_2催化剂在常温和高温的H_2和CO化学吸附的影响。结果再次表明:1)不同Rh中心对H_2和CO的化学吸附性能不同,钒助剂对不同Rh中心的H_2和CO吸附的影响也不同。H_2主要吸附在Rh~Ⅱ和Rh~Ⅲ中心上,而在Rh~Ⅰ中心上的吸附弱。2)Rh-钒助剂的强相互作用主要是Rh~Ⅱ和Rh~Ⅲ与钒助剂之间的相互作用,H_2吸附受到比CO吸附更强烈的抑制。钒助剂对Rh/SiO_2的H_2和CO吸附性能的影响可用覆盖模型解释。 相似文献
108.
严继民 《中国科学B辑(英文版)》1990,(7)
An ab initio calculation of the hydrogen bond complex (HF)_2 is given with the 6-311 G~(**) basis set, according to which the potential surface around the balance point of the distancès and the orientations between two HF molecules is obtained. The atomic charges in the system are calculated with the PD/LSF method (potential-derived/least-square-fitting method) and then an analysis of the hydrogen bond interaction between two HF molecules is given with the (exp-6-1) potential function, by means of which it is shown that the main interaction between them is not an electro-static but a charge transfer one. The potential curve between two HF molecules is like a Morse function. 相似文献
109.
Klärner FG Lobert M Naatz U Bandmann H Boese R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(20):5036-5047
The novel trimethylene-bridged clips 3 and 4 have been synthesized by using repetitive stereoselective Diels-Alder reactions of the benzo- and naphthobismethylenenorbornenes 8 and 19 as dienes and norbornadiene 9 as bisdienophile, and subsequent dehydrogenation of the primary cyclobisadducts 10 and 20 by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Clips 3 and 4 serve as receptors for a variety of electron-deficient neutral and cationic aromatic substrates, comparable to the molecular tweezers 1 and 2. The thermodynamic parameters of the complex formation, K(a) and DeltaG, were determined by (1)H NMR titration experiments and, in the case of the highly stable complex TCNB 32@4, by the use of isothermal titration microcalorimetry. The finding that clip 4 forms more stable complexes than 3 can be explained by the larger van der Waals contact surfaces of the naphthalene sidewalls in 4 compared to the corresponding benzene systems in 3. In the complexes with 4 as receptor, the plane of each aromatic substrate molecule is calculated to be oriented almost parallel to the naphthalene sidewalls. However, in the complexes of tweezers 2, the substrate is usually oriented parallel to the central naphthalene spacer unit. Due to the more open topology of 4, most complexes were calculated to consist of two or more equilibrating noncovalent conformers. 相似文献
110.
Summary An HPLC reversed-phase ion interaction reagent method is presented, which makes use of chiral compounds as the interaction
reagents. By employing the optical isomeric forms of malic, tartaric and mandelic acids as the interaction reagents, a good
separation of D(−) and L(+) ascorbic acid has been achieved. The method has also been applied to the identification of vitamin
C in some medical formulations. The separation of te enantiomeric forms of DL malic acid has been attempted and a shor discussion
is presented about the elution sequence in chromatographic separation of D- and L-enantiomers. 相似文献