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111.
Parworth CL Tucker MK Holmes BE Heard GL 《The journal of physical chemistry. A》2011,115(45):13133-13138
The 1,2-HX elimination reaction (where X = F, Cl, Br, OH) has been established as an important reaction in the degradation of compounds introduced into the upper atmosphere, including common CFC replacement compounds. By analyzing the electron densities of the transition state geometries of these reactions using QTAIM, we see that we can divide these reactions into two types. For HF and HOH elimination, the transition state is a complete ring of bonds, and neither the C-H nor the C-X bonds have been broken at the maximum of energy. There is very little accumulation of electron density on the X atom, with the majority of charge being lost by the hydrogen atom undergoing elimination, being transferred on to the two carbon atoms. In HCl and HBr elimination, a similar loss of electron density of the hydrogen atom is accompanied by significant accumulation of electron density on the X atom and a smaller change in electron density on the carbon atoms. The C-X bond is broken in the transition state geometry, with no ring critical point being present. This may explain the relative stabilities of halohydrocarbons and haloalcohols with respect to loss of H-X. 相似文献
112.
Since its introduction, click chemistry has received a considerable amount of interest. In this contribution, the term click chemistry and the reactions that fall under this term are briefly explained. The main focus of this review is on the application of click chemistry in conjunction with living radical polymerization for the synthesis of advanced macromolecular architectures. Therefore the most powerful living radical polymerization (LRP) techniques are discussed and an overview of click chemistry in the different synthetic schemes is given. A large number of examples are shown that include the synthesis of block copolymers, star-shaped polymers, surface modified particles, and polymer-protein conjugates. The enormous potential of LRP/click chemistry is probably best exemplified by the synthesis of different miktoarm star copolymers, to which a separate section is dedicated. 相似文献
113.
Zincated pyridazin-3(2H)-ones generated via bromine-magnesium exchange followed by transmetalation using ZnCl(2) or via lactam-directed ortho C4-H zincation with TMPZnCl·LiCl have been synthesized. These in situ created organometallics can be used in Negishi reactions with iodo(hetero)arenes delivering a new approach toward (hetero)arylpyridazin-3(2H)-ones. 相似文献
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Mijovilovich A Hamman S Thomas F de Groot FM Weckhuysen BM 《Physical chemistry chemical physics : PCCP》2011,13(13):5600-5604
X-ray Emission Spectroscopy (XES) crossover peaks were shown to be sensitive to the protonation state of solvent molecules in the Zn protein carbonic anhydrase and its model compounds. Here we extend such studies to galactose oxidase models i.e. Cu(ii) open d-shell systems, illustrating that XES combined with FEFF8 simulations reflect changes in the protonation state of the phenolate ligand for the copper center. 相似文献
117.
Bert Fassbender 《Journal of Graph Theory》1989,13(6):697-702
Let G be a simple non-hamiltonian graph, let C be a longest cycle in G, and let p be a positive integer. By considering a special form of connectivity, we obtain a sufficient condition on degrees for the nonexistence of (p - 1)-path-connected components in G - C. 相似文献
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We investigate the tail behavior of the sojourn-time distribution for a request of a given length in an M/G/1 Processor-Sharing
(PS) queue. An exponential asymptote is proven for general service times in two special cases: when the traffic load is sufficiently
high and when the request length is sufficiently small. Furthermore, using the branching process technique we derive exact
asymptotics of exponential type for the sojourn time in the M/M/1 queue. We obtain an equation for the asymptotic decay rate
and an exact expression for the asymptotic constant. The decay rate is studied in detail and is compared to other service
disciplines. Finally, using numerical methods, we investigate the accuracy of the exponential asymptote.
AMS 2000 Subject Classifications Primary:60K25,Secondary: 60F10,68M20,90B22 相似文献