Chemical substitutions cationic

Detailed investigations of the chemical reactivity of the diketiminato-stabilized phosphenium cations like 28 (Scheme 17) are to date rare and include only two reports dealing with the substitution and reduction of P-halogen-derivatives. Thus, reaction of 28 (X=Br) with sodium hydroxide in toluene was reported to proceed with displacement of the halide substituent at phosphorus and conservation of the heterocyclic ring to give a mixture of bromide and triflate salts containing a P-hydroxy-substituted cation, both of which were isolated in small yields [89], The products are remarkable as they represent one of very few examples of a stable phosphinous acid which does not rearrange to the tautomeric secondary phosphine oxide. Potassium reduction of the P-chloro-substituted derivative 34 produced the... 

Since the LFSE term is determined by Mn valence and appears to be relatively insensitive to cation ordering in the Mn02 host structures, it would seem to be the easiest energy term to manipulate through chemical substitutions. This is because the exact placement of the chemical substitutions in the Mn sublattice would presumably be less important for the LFSE term than for the terms that are more sensitive to cationic ordering (i.e., AEb and AEm/+). 

Chemical Shifts of Some Methyl Substituted and Unsubstituted Allylic Cations" Case Position Unsubstituted cation Methyl substituted cation A5 1. 

Mineral series are composed of species whose basic chemistry and three-dimensional structure are so similar that they differ in a well-documented, predictable manner, based on the substitution of comparable chemical elements. Such a series is usually defined by the end members, that is, the compounds that contain only one of the substituting cations. End members... 

Mineral series Minerals that have an identical basic chemical and structural unit in which small amounts of chemical substitution of similar elements (cations of similar size, stereochemical, and bonding character) in the same site in the crystal structure are usual and predictable. Mineral series are usually defined by the end member species, that is, those compounds that contain only one of the possible cations. Intermediate members may have specific names or be identified by the ratio of the cations (see chapter 2). 

The purpose of this chapter is not to cover the entire chemistry of the high Tc oxides but instead is to focus on one specific point the study of these materials through cationic chemical substitutions in order to illustrate how this type of chemistry can aid in the understanding of some of the crystal-chemical aspects of these new high Tc... 

For the analogous 1-methyl-substituted cation [C gCFb]"1", recent experimental investigations and quantum chemical ab initio calculations agree that the dynamics of this cation system can be adequately described by considering only one degenerate set of cations, which have the hypercoordinated puckered methylbicyclobutonium ion structure 420 without contributions from a degenerate set of (l -methylcyclopropyl)methyl cation structures 4217,166,167. 

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