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81.
Orthorhombic inclusion compounds of cyclohexaamylose with methanol,n-propanol, acetic acid and water as guest molecules were studied using13C and2H NMR techniques.13C chemical shifts were correlated with structural data, whereas2H NMR lineshapes were used to derive information on guest molecule motions.Issued as NRCC No. 25568. Presented in part at the 2nd International Symposium on Clathrate Compounds and Molecular Inclusion Phenomena, Parma, Italy, 30 Aug.–3 Sept. 1982 相似文献
82.
Both STO-3G ab initio and s-p separation-type-modified INDO semiempirical methods were applied to molecular-orbital calculation of the N20 molecule. From these two methods, the optimized bond distances between the nearest N atoms (dn-n) and the most calculated thermodynamic data are close to each other. The positive values of ΔHa° and ΔGa° for the atomization reaction in this work prove that N20 is stable. In contrast to conventional INDO and MINDO/3, but similar to former AMI and MNDO calculations, both ΔHr° and ΔGr° are positive in the formation reaction, which indicates that N20 belongs to the category of high-energy molecules. 相似文献
83.
New types of lower rim proximally bridged thiacalix[4]arenes have been prepared by direct aminolysis of starting tetraacetate derivative in the cone conformation using aliphatic α,ω-diamines. X-ray crystallography revealed the highly preorganized array of -C(O)NH- bonds resulting in strong intramolecular hydrogen bonding between amide groups of both bridges. The length of the corresponding diamine was found to have an essential influence on the yield of these bridged molecules. 相似文献
84.
Ion-molecule reactions between the O=P(OCH(3))(2) (+) phosphonium ions and five aliphatic esters (methyl acetate, methyl propionate, methyl 2-methylpropionate, methyl butyrate and ethyl acetate) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2) (+) phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with aliphatic esters to give an adduct ion [RR'CHCOOR", O=P(OCH(3))(2)](+), which loses spontaneously a molecule of ketene CH(2)=CO or substituted ketenes RR'C=CO. Isotope-labeled methyl acetate was used to elucidate fragmentation mechanisms. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2) (+) and methyl acetate is described. 相似文献
85.
Three-dimensional quantum mechanical calculations for vibrational predissociation of HeI2(B) van der Waals molecules are presented using the time-dependent wave packet technique within the golden rule approxima tion.The total and partial decay widths,lifetimes,rates and their dependence on initial vibrational states were obtained for HeI2 at low initial vibrational excited levels.Our calculations show that the calculated tota decay widths,lifetimes and rates agree well with those extrapolated from experimental data available The predicted total decay widths as a function of initial vibrational states exhibit highly nonlinear behavior.The very short propagation time (less.than 1 ps) required in the golden rule wave packet calculation is determined by the duration time of the final state inter-action between the fragments on the vibrationally deexcited adiabatic potential surface.The final state interaction between the fragments is shown to play an important role in determining the final rotational distri 相似文献
86.
Filippi A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(21):5396-5403
The model reaction between the (R)-1,3-dimethyl-1-cyclohexyl cation (I) and methanol has been investigated under gas-phase radiolytic conditions (750 Torr; 25-120 degrees C) with the aim of evaluating the intrinsic factors that govern the facial selectivity of biased carbocations. The peculiarity of the experimental approach allows the formation of different CH(3) (18)OH.I ionic adducts. Subsequent conversion of these adducts to give the corresponding E/Z covalent products follows different reaction coordinates, which are characterized by their own activation parameters. On the grounds of density functional theory (DFT) results, several [CH(3)OH.I] structures have been located on the relevant potential-energy surface (PES). The experimental results point to a gas-phase facial selectivity, which is mainly governed by entropic factors that arise as a result of the occurrence of different noncovalent ion-molecule "facial adducts" (FA). The formation of FAs may also play an important role in both the reaction dynamics and the positional selectivity. The present results cannot be interpreted by any of the models based on solution-phase experiments. 相似文献
87.
We discuss two possible approaches for extracting kinetic information from single-molecule experiments. The first approach is based on computing correlation functions from measured fluorescence signals, and the second on studying the statistics of on and off times of the same fluorescence signal. We show that in both cases it is possible to extract kinetic information about the nature of intramolecular fluctuations of the single molecule. We show that for single-molecule kinetics the intramolecular fluctuations produce stochastic memory effects which lead to new dynamic features that do not exist in traditional chemical kinetics. In particular, we investigate a new type of chemical oscillations in correlation functions observed experimentally by Edman and Rigler (Proc. Natl. Acad. Sci. USA 2000, 97, 8266). 相似文献
88.
Kenta Hongo Yoshiyuki Kawazoe Hiroshi Yasuhara 《International journal of quantum chemistry》2007,107(6):1459-1467
The diffusion Monte Carlo (DMC) method shows that correlation in H2 produces a set of three spatial changes: (i) an enhancement in the electron density distribution n( r ) in the left and right anti‐binding regions that include separately the immediate vicinity of each of the two nuclei, (ii) a reduction in n( r ) in the binding region intervening between the two nuclei as a counterbalance, and (iii) a concomitant increase in the equilibrium internuclear separation. It is stressed that the correlation energy Ec (= Tc + Vc) for diatomic molecules be defined by the difference in the total energy between the exact and the Hartree–Fock (HF) variational calculations that are performed at individually optimized internuclear separations. It is this definition that makes it possible to involve a significant contribution from a correlation‐induced change in the equilibrium internuclear separation as part of the correlation energy and to relate (i) and (ii) to (iii) in consistency with the electrostatic theorem. The present calculations fulfill the virial theorem to an accuracy of ?V/T = 2.00 for DMC and ?VHF/THF = 2.000 for HF. The present correlation energy Ec = ?0.0408 hartree is not only in good agreement with the most accurate value previously reported, but also can be analyzed into all its components in accordance with the correlational virial theorem 2Tc + Vc = 0. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
89.
90.
S. F. Ruzankin V. F. Anufrienko S. A. Yashnik Z. R. Ismagilov 《Journal of Structural Chemistry》2006,47(3):404-412
This paper reports on quantum-chemical analysis of the linear structure of CuCl2 by Hartree-Fock (HF) and density functional theory (DFT) methods and also by time-dependent HF (TD HF) and DFT (TD DFT) techniques. Using pure DFT exchange correlation functional (B3LYP) yields the best agreement with the experimental electronic spectra of CuCl2. In this case, the odd electron is delocalized over the molecule, spin density on copper being 0.27. The ground state of the CuCl2 molecule is 2Πg with linear geometry. 相似文献