Stabilization of the species

The observed equilateral triangular 3-centre, 2-electron structure is more stable than the hypothetical linear structure, and the comparative stability of the species is shown by the following gas-phase enthalpies ... 

The chemical stability of the / species has been investigated in sulfur/sodium... 

The relative stabilities of the species involved appear to be responsible for the stereochemical outcomes. Relief of ring strain must play a role in determining the course of the reaction. An explanation for the different reaction paths on using different Grignard reagents must wait further experimentation. 

The sum of this energies is a measure for the stability of the species being solvated. 

This resonance model was a completely different idea that was understood by the class and the teacher only because they enacted a simulation with concrete models. This simulation explained some other details that could not readily be represented (such as the need for stability of the species) for they were always hying to establish relationships with the actual system that they had observed. 

Hodjati, S., Petit, C., Pitchon, V. et al. (2000) Absorption/Desorption of NOx Process on Perovskites Nature and Stability of the Species formed on BaSn03, Appl. Catal. B Environ., 27, 117. 

Investigations of the equilibria obtaining in solution have provided information concerning the stoichiometry and stability of the species formed when the beryllium ion is hydrolyzed. Although the identification of the minor species can never be regarded as definitive, there is little doubt that the principal species are Be2(OH)3+ and Be3(OH)3+ in acid solutions and Be(OH)3 and Be(OH)r in strongly basic solutions. Further support for these conclusions is provided by some crystal structures. The structure of [Be3(0H)3(H20)6]... 

M = Os) has not been established. This is very remarkable because a variety of other d6 metalloporphyrin moieties show an unusual lability at their axial coordination sites (see Sect. 3). The stability of the species [Os(OEP)L2]n (n = 0 or 1) representing the osmochrome/osmichrome system has allowed a complete physical and chemical characterization of the compounds [29a-k] listed in Table 9 and their cationic derivatives [Os(OEP)L2]PF6 (78, 80). 

Calculations produce an activation energy of ca 35 kcal/mol for /1-elimination from Me2AlEt [7], Calculated geometries for structures on the elimination path (Eig. 2) clearly show the similarity with the insertion step described above. The transition state is somewhat closer to the 7c-complex, as expected from the stabilities of the species involved. 

However, a pH of 8 or 9 is more favorable to shift the overall equilibrium toward the oxidized product. Taking this remark into account, Keita and Nadjo showed recently that efficient POMs exist that meet these conditions [185]. A preliminary work is being published. The series of V-substituted derivatives selected in this work contain several POMs stable in their oxidized and reduced forms in alkahne media, thus guaranteeing the stability of the species generated during the catalytic process. The preliminary study is devoted to the electrocatalytic oxidation of NADPH, a substrate closely related to NADH, with the same importance in vivo and in vitro. 

The electrons in the n" orbital do not appreciably affect the stability of the species. Therefoie all three sptecies are more stable than the corresponding alkyl systems C3H7, CjH,-, and C,H7 . The extra electrons do increase the repulsive forces between electrons slightly, so the order of stability is C H, >... 

Often the initial electrode product will undergo subsequent chemical or electron-transfer reactions, but the stability of the species depends greatly on the reactivity of the medium in that it is produced. 

In the meantime, other Tt-delocalized systems were discovered among open-chain systems, notably the three allylic systems, Scheme 4. All of these systems showed a behavior akin to the aromatic systems they are delocalized, have uniform geometries, and are more stable than saturated analogues.90-93 Furthermore, they all possess rotational barriers with heights related to the resonance stabilization of the species. 

Draw the important resonance structures for these species. Use the curved arrow convention to show how the electrons are moved to create each new resonance structure. Discuss the relative contribution of each to the resonance hybrid and the overall resonance stabilization of the species. 

In order to obtain reliable information on speciation analysis it is necessary to evaluate the stability of the species of interest in a given matrix or sample. Also, when sample treatment is time-consuming, the knowledge of how to maintain the species integrity in the extracts to be stored is of paramount importance. 

When an electrochemical reaction is perturbed from its equilibrium state, the relative stabilities of the species in the reaction are changed. The change due to the perturbation is reflected in the measured electrode potential, which differs from the equilibrium... 

Taking the solvation into account in such models is both very difficult and necessary for the best possible understanding of these exceedingly complex phenomena. The disolvation of the amides dimer (one solvent per lithium in THF, THF + HMPA or THF + DMPU)50 seems to be indicated, while trisolvated dimers appear relatively unstable. However, a very extensive semiempirical theoretical (MNDO) study on the various cyclic and open mixed aggregates formed by LDA and LiTMP with LiCl or three different enolates, solvated by discrete molecules of THF or HMPA, showed that general conclusions are almost impossible to draw48. A complex interplay of steric effects, induced by the partners of the aggregate and the solvent, seems to be the dominant influence on the relative stabilities of the species characterized. 

Chemical reversibility. This refers to the stability of the species associated in an electron transfer step to chemical decomposition. Therefore, if in (19) species B decomposes irreversibly as it is formed from the one-electron transfer process, Ae whole process would be described as being chemically irreversible. However, if the chemical step associated with the decomposition of B was sufficiently fast in both directions on the time-scale of the... 

All these phenomena result from the great stability of the species, as pointed out by Michaelis. In determining this stability, an important factor is the protonation at nitrogen, which increases the number of resonance structures. The radical species decays rapidly in neutral and alkaline media, when the reverse of Reaction (3) takes place, followed by subsequent transformations of T+. This was confirmed by Gilbert et al., who found that on diluting the... 

Many radicals containing the S-N linkage are persistent for more than several hours at room temperature. The majority of these radicals have semioccupied orbitals to which the sulfur and nitrogen p orbitals make a dominant contribution. In cyclic species, the unpaired electron often occupies a delocalized jr-orbital, which may contribute to the stability of the species. ESR spectroscopy is an excellent technique for the characterization of S-N radicals and, in conjunction with MO calculations, provides unique information about their electronic structures. 

Anyway, it should be noted that the conformational and configurational stabilities of the species in an electrode interace may be quite different from those in free states, owing to the peculiar steric and polar factors. In a given situation, the conformation or configuration at the electrode interface may be the reverse of that in the free state. 

A deactivating agent for copper-activated sphalerite is any species that has sufficient affinity for copper(I) or (II) to compete for it with sulfide ions in the surface lattice of the mineral, thus removing it from the surface. Ligands such as cyanide or ethylenediamine, which coordinate strongly to copper, have therefore been found to be the most effective. A knowledge of the stability of the species present in a system composed of and CN ions has enabled ... 

Use MO theory to predict relative stabilities of the species in Exercise 19. Comment on the validity of these predictions. What else must be considered in addition to electron occupancy of MOs ... 

Draw and label the complete MO energy level diagrams for the following species. For each, determine the bond order, predict the stability of the species, and predict whether the species will be paramagnetic or diamagnetic, (a) He2+ (b) CN (c) HeH+. 

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