Cationic oxygen atom

Aluminum cation % Phosphorus cation Oxygen atom Lanthanum cation Calcium cation... 

The hydration of more inert ions has been studied by O labelling mass spectrometry. 0-emiched water is used, and an equilibrium between the solvent and the hydration around the central ion is first attained, after which the cation is extracted rapidly and analysed. The method essentially reveals the number of oxygen atoms that exchange slowly on the timescale of the extraction, and has been used to establish the existence of the stable [1 10304] cluster in aqueous solution. 

Figure C2.12.1. Origin of ion exchange capacity in zeolites. Since every oxygen atom contributes one negative charge to the tetrahedron incoriDorated in the framework, the silicon tetrahedron carries no net charge while the aluminium tetrahedron carries a net charge of-1 which is compensated by cations M.

The most effective Lewis-acid catalysts for the Diels-Alder reaction are hard cations. Not surprisingly, they coordinate to hard nuclei on the reacting system, typically oxygen atoms. Consequently, hard solvents are likely to affect these interactions significantly. Table 1.4 shows a selection of some solvents ranked according to their softness. Note that water is one of the hardest... 

Acyl cations are relatively weak electrophiles. This is easily understood, because their structure is of a predominantly linear carboxon-ium ion nature, with the neighboring oxygen atom delocalizing charge and limiting their carbocationic nature. 

Isopolyanions. Isopolyanions are named by indicating with numerical prefixes the number of atoms of the characteristic element. It is not necessary to give the number of oxygen atoms when the charge of the anion or the number of cations is indicated. 

N—Fe(IV)Por complexes. Oxo iron(IV) porphyrin cation radical complexes, [O—Fe(IV)Por ], are important intermediates in oxygen atom transfer reactions. Compound I of the enzymes catalase and peroxidase have this formulation, as does the active intermediate in the catalytic cycle of cytochrome P Q. Similar intermediates are invoked in the extensively investigated hydroxylations and epoxidations of hydrocarbon substrates cataly2ed by iron porphyrins in the presence of such oxidizing agents as iodosylbenzene, NaOCl, peroxides, and air. 

Fig. 2. Stmcture of the mineral 2eohte chaba2ite is depicted by packing model, left, and skeletal model, right. The sihcon and aluminum atoms He at the corners of the framework depicted by soHd lines. In this figure, and Figure 1, the soHd lines do not depict chemical bonds. Oxygen atoms He near the midpoint of the lines connecting framework corners. Cation sites are shown in three different locations referred to as sites I, II, and III.

The stmctures of STP-I and -II differ primarily in the ionic coordination of cations. In STP-II all sodium ions are octahedraHy coordinated by oxygen, whereas in STP-I some sodium ions are surrounded by only four oxygen atoms. In STP-II a distinct sheet-like arrangement occurs. The faster hydration rates are attributed to these properties. 

Compounds that have the empirical formulas MCr02 and DCr204 where M is a monovalent and D a divalent cation, are known as chromites. These are actually mixed oxides and probably are better written as M20-Cr203 and D0-Cr203, respectively. The oxides of D are largely spinels, ie, the oxygen atoms define a close-packed cubic array having the octahedral holes occupied by the Cr(III) cation and the tetrahedral holes occupied by D (54). Chromite ore is an important member of this class of oxides. 

The method described here gives higher yields of the macrocyclic tetraethers and allows the product from furan and cyclohexanone to be formed directly in 5-10% yield, whereas this product was previously obtained only by an indirect route. The added lithium perchlorate undoubtedly accelerates the reaction, since after short reaction times the product was isolated in 20% yield when the salt was present and in only 5% yield when the salt was absent. The lithium cation is presumably acting as a template which coordinates with the oxygen atoms of... 

Figure 7.7. The spinel strueture. The unit eell can be divided into octants - tetrahedrally coordinated cations A. octahedrally coordinated eations B, and oxygen atoms (large cireles) are shown in two oetants only (adapted from Smit and Wijn 1959).

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