Ions, concepts

The nonclassical-ion concept proved to be an intriguing one, and many tests for the... 

We wish to emphasise that the formation of esters (E) from alkenes (M) and acids (HA), the catalysis of the reactions of E by HA or MtXn, and the activation of E, such as organic chlorides, by the co-ordination of a Lewis acid, such as A1C13, are all very familiar chapters in conventional organic chemistry. It follows that the pseudo-cationic theory is nothing more than a generalisation of conventional organic-chemical ideas and a revival of some pre-Whitmore interpretations which had become occulted by the usefulness and novelty of the carbenium ion concept. 

The bromonium ion concept does rationalize the stereochemistry of bromine additions to double bonds very satisfactorily if it is recognized that olefins that can form highly stabilized carbocations need not form such a structure. As al-ready noted, nonconjugated olefins give predominantly anti addition. Cornu-gated olefins, in which the intermediate carbocation would be stabilized by Resonance- however, give a mixture of svn and anti adducts. 

There is, however, other evidence that speaks for the bromonium ion concept and against competition between AdE2 and Ad3 pathways.35 We have already noted that, in polar solvents, addition of bromine to multiple bonds is first-order in bromine when bromine is present in low concentration. Moreover, as Table 7.7 shows, increasing the number of substituents on the double bond cumulatively increases the rate of bromination of nonconjugated olefins in polar solvents irrespective of whether each new substituent is on the same or on the other olefinic carbon as the last.36 Dubois has found that the bimolecular rate constants for addition of bromine to alkyl substituted ethylenes are correlated by... 

The bromonium ion concept was quickly used by other investigators to account for stereospecific transformation of alkenes, notably by Winstein and Lucas, but... 

The clearest evidence for the validity of the molecular-ion concept is the obvious similarity between the UPS and UAS spectra of PVP and those of its corresponding model molecule 2-ethyl pyridine. These spectra are shown in Figs. 5 and 7, respectively. In particular, in Fig. 5 the UPS spectra for the series of materials pyridine(v), 2-ethyl pyridine(v), 2-ethyl pyridine(s), and PVP are presented in order to show explicitly the relative consequences of the 2-ethyl substituent and condensation effects... 

The purpose of this section has been to utilize a molecular ion concept to provide a satisfactory interpretation of the UPS and UVA data given in Figs. 5, 6, 7 and 8. In particular, the molecular ion concept affords an elementary prediction of the surprising result that the measured intermolecular relaxation energies are the same for both PVP and PS (20) even though the former is a polar material and while the latter is not (i.e., the two materials exhibit quite different low-frequency dielectric responses). 

We summarize here the features of the UPS and UVA data which lead to the molecular ion concept for these aromatic pendant group polymers. First, the spectra of the polymers PVP and PS are essentially identical to those of condensed model molecular moieties 2-vinyl pyridine and ethyl benzene, respectively. Second, the solid-state spectra are related to the gas-phase spectra of these model moieties by an essentially constant shift to higher energy (lower binding energy) of all the ionization peaks by = 1.5 0.1 eV. Third, the width in energy of the solid-state ionization peak is Air = 1.0 0.1 for both polymers... 

R.R. Pappalardo, J.M. Martmez and E. Smchez Marcos, Application of the hydrated ion concept for modeling aqueous solutions containing highly charged ions a Monte Carlo simulation of Cr3+ in water using an ab initio intermolecular potential, J. Phys. Chem., 100 (1996) 11748-11754. 

The low-temperature stability of bicyclo[2.2.1]heptane derivatives is well documented by the huge literature on liquid-phase norbornyl carbonium chemistry under such conditions, no ring expansion is observed, but instead, multiple Wagner-Meerwein rearrangements take place, preserving the bicyclo[2.2.1]heptane structure in the course of nucleophilic substitution or elimination reactions. This remarkable behavior is at the origin of the nonclassic carbonium ion concept (28). 

The radical difference between the classical and modern views is readily seen from equations (17) and (18). The basic character, as defined by the older theory, actually is determined by the true acidic dissociation constant based on the hybrid ion conception. Conversely, the acidic nature is governed by the true basic dissociation constant. 

So far we have summarized different ways to present salinity. Strictly speaking, the effect of an ion may be different from the effect of any other one, so we should take into account every ion separately. We have to use a kind of pseudo-ion concept, however, to present salinity because (1) we do not fully understand the effect of each ion, (2) it is difficult and tedious to present the effects of so many ions and their reactions, and (3) the effect of an ion could be different in different processes. 

In the epimers 369 and 370 generated identical mixtures of ions. Literary data show that until recently the same stable cations have been obtained from epimers. This is why Brown stated that for the nonclassical ion concept the solvolytic studies are far more informative than those on the generation of stable ions since only in the former epimers display different reactivity which is the most important sign of nonclassicality Recently, however, Kamschei et al. have... 

The nonclassical ion concept proved to be a popular one, and imaginative tests for the intermediacy of nonclassical ions in other bicyclic systems were employed. While the classical ion in the norbonyl system is chiral and the nonclassical ion is achiral, the situation is reversed in the bicyclo[2.2.2] system. Here, the classical ion is achiral and the nonclassical ion is chiral ... 

X 10 M. Because the [S04 ] from the Na2S04 is just over two orders of magnitude larger than this (1.5 X 10 /M),the common ion concept should tell us that the (Ba l needs to be just over two orders of magnitude smaller (less than 1 X 10 /M). 

Because of the simple 1 1 ion ratio, it is quite easy to estimate and check the answer without a calculator. The square root of the Agl value (simplified to 1 X 10 ) gives [Ag ] = [I ] 1 X 10 M. The initial [I ] from the added Nal is 1 X 10 M, which is five orders of magnitude larger. The common ion concept and 1 1 ion ratio tell us that the [Ag+] needed to initiate precipitation should be five orders of magnitude smaller than 1 X 10 M, or about 1 X 10 M. 

A principle limitation of the established Li-ion concept is that typically only one electron per transition metal atom is exchanged... 

The science of electrochemistry is concerned with electron transfer at the solution/elec-trode interface. Most of the basic principles and relationships, however, were described prior to the discovery of the electron by J. J. Thompson in 1893. In 1800, Alessandro Volta invented the first battery, then known as a voltaic pile, by alternating stacks of copper and zinc disks separated by paper soaked in acid solutions. With the discovery of a sustainable source of electrical current, the stage was set for the rapid development of the area of science now known as electrochemistry. By 1835, Michael Faraday had already defined the anode, cathode, electrode, electrolyte, and ion concepts without which any definitive description of electrochemistry is virtually impossible. 

If an appropriately positioned olefin can interact with a cationic center to make a carbo-nium ion, we might expect that the edge of a cyclopropane ring could do the same. An example of this is the ion derived from pentacyclo[4.3.0.0 .0 .0 - 0]nonane, which is known as Coates ion (shown in the margin). Even the most ardent opponents of the non-classical ion concept accept that this is a bridged, symmetrical carbonium ion. The value of fully sup-... 

Lithium ion batteries, based on a carbonaceous anode and a lithium metal oxide cathode, are high-energy power sources that are well established in the consumer electronics market. The lithium ion concept, however, can be extended to any electrode combination that assures a cyclic transfer of lithium ions across the cell. In general, a lithium ion cell can be considered as based on a lithium-rich L M Y electrode and a lithium-accepting electrode. The electrochemical process is ... 

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