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11.
By adopting the convention that shared double bonds in polycyclic conjugated hydrocarbons contribute with one -electron and unshared ones with two -electrons, a partition of -electrons in each ring (-electron content, EC) can be obtained by averaging over all Kekulé structures, which are assumed to have equal weights. This affords a simple measure of local aromaticity that is comparable with other such local aromaticity indices in polycyclic benzenoids. 相似文献
12.
It is shown that in several cases where planar delocalisation in organic cations would result in the formation of an anti-aromatic system, polyhedral delocalisation is the form of bonding actually preferred. This explains, for instance, why organic cations in such cases adopt cage-like structures. A full graph-theoretical analysis, similar to one previously published12 for polyhedral boranes, carboranes and metal clusters, indicates that the nido structure for (CH)5+ may readily be accounted for. Moreover, in the case of the dication (CH)62+ the fact that its energy minimum also corresponds to a nido structure is explained. In fact, no closo- or arachno-type structures appear to be possible for organic cations. A number of structural predictions concerning these species are given in the conclusion. 相似文献
13.
Christian Roussel Alexandru T. Balaban Ulf Berg Michel Chanon Roger Gallo Gerd Klatte Joseph A. Memiaghe Jacques Metzger Daniela Oniciu Johanna Pierrot-Sanders 《Tetrahedron》1983,39(24):4209-4219
The effect of the shape of a methyl group on reactivity, which cannot be accounted for by considering a methyl group as a spherical substituent with the appropriate van der Waals radius, was considered in kinetics of alkylalion of substituted pyridines and barriers to rotation and ground state conformations of an isopropyl group attached to a planar framework. The perturbation of a methyl group by an o-methyl group is accounted for by a unique conformational explanation which involves the polyhedral shape of the methyl group. 相似文献
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Condruz Mihaela Raluca Matache Gheorghe Paraschiv Alexandru Pușcașu Cristian 《Journal of Thermal Analysis and Calorimetry》2018,133(1):443-452
Journal of Thermal Analysis and Calorimetry - Two new zinc(II) coordination compounds have been synthesized by the reaction of diazine-ring containing Schiff bases di(2-pyridyl) ketone... 相似文献
16.
Gunawan Gunawan Tito Viswanathan Shawn Bourdo Alexandru S. Biris 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6):768-777
Abstract A novel, fast, and easy method for synthesizing a carbon-supported Ni2P nanocomposite (C/Ni2P) is described. The process involves a reaction between a nickel salt, phosphoric acid, and a carbon source by utilizing microwave irradiation. The carbon source for the nanocomposite is from renewable supplies, namely, tannin and lignin. The method has successfully synthesized Ni2P nanoparticles dispersed in a carbon matrix with a particle size ranging from 20 to 50 nm in diameter. During the microwave process, tannin and lignin provided a reducing environment in the microwave irradiation process. The synthesized products are characterized by several characterization methods. The method showed that phosphoric acid, which is a nontoxic compound, could be used as an alternative P source for synthesizing Ni2P. The method is fast, easy, and an economical process to synthesize the carbon-coated Ni2P nanocomposite. 相似文献
17.
Suppose that is a one-dimensional Brownian motion with negative drift . It is possible to make sense of conditioning this process to be in the state 0 at an independent exponential random time and if we kill the conditioned process at the exponential time the resulting process is Markov. If we let the rate parameter of the random time go to 0, then the limit of the killed Markov process evolves like conditioned to hit 0, after which time it behaves as killed at the last time visits 0. Equivalently, the limit process has the dynamics of the killed “bang–bang” Brownian motion that evolves like Brownian motion with positive drift when it is negative, like Brownian motion with negative drift when it is positive, and is killed according to the local time spent at 0.An extension of this result holds in great generality for a Borel right process conditioned to be in some state at an exponential random time, at which time it is killed. Our proofs involve understanding the Campbell measures associated with local times, the use of excursion theory, and the development of a suitable analogue of the “bang–bang” construction for a general Markov process.As examples, we consider the special case when the transient Borel right process is a one-dimensional diffusion. Characterizing the limiting conditioned and killed process via its infinitesimal generator leads to an investigation of the -transforms of transient one-dimensional diffusion processes that goes beyond what is known and is of independent interest. 相似文献
18.
In the present work we characterize the existence of quasistationary distributions for diffusions on allowing singular behavior at 0 and . If absorption at 0 is certain, we show that there exists a quasistationary distribution as soon as the spectrum of the generator is strictly positive. This complements results of Cattiaux et al. (2009) and Kolb and Steinsaltz (2012) for 0 being a regular boundary point and extends results by Cattiaux et al. (2009) on singular diffusions. 相似文献
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In this autobiographical sketch, I will present my contributions in two areas of chemistry: experimental organic and theoretical chemistries.
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