Cation trapping

A class of macrocyclic polyethers built on a triazine ring (192) have been proposed in 1981 by Au.291 These compounds are active as phase transfer catalysts in the conversion of C8H,7Br to C8H17OPh. These molecules have chelating arms properly arranged in order to trap cations. 

First of all the high spin density on C5 is indicative of an oxidation product. In order to be stably trapped, cations have to deprotonate. In cytosine monohydrate, this deprotonation can most easily occur at N1 or N4. Deprotonation at the amino group would give a radical species that would not fit the EPR/ENDOR data. Therefore the N1 deprotonated cation is the best model to represent the experimental data, and actually the best model from the calculations that Wetmore et al. performed [79], The disagreement Wetmore et al. report is with the C5-H isotropic hyperfine coupling. This is actually to be expected since the authors have not included the important effects of the hydrogen bonded network present in the single crystal in their calculations. 

The sodide, stable to —25°C, has been dubbed an inverse sodium hydride (see Figure 22). The strategy of using kinetically trapped cations in polyaza cages may lead to new classes of stabilized alkalides and electrides. 

For Ar-0 bond formation,the solvent is often used as the nucleophile. Thus, for example, a mixture of trifluoroacetic acid and nitromethane is sufficiently conductive, does not oxidize at potentials up to 2.4 V vs Ag/Ag+ and traps cations formed in oxidative processes to form trifluoro-acetate esters. Using this medium for electrolysis and an aqueous work-up, it is possible to perform aromatic hydroxylation reactions, often in yields of 75%.23... 

The structure of many zeolites contains cages with trapped cation templates inside. E.M. Flanigen summarized the zeolite framework structures with an SBU cage and corresponding cation template. The results are shown in Tables 3.4 and 3.5.[231... 

In the inhomogeneous coulombic field generated by the trapped cations and anions formed by irradiation, positive holes will migrate in the direction of trapped anions. When, as a result of this process, a matrix (RjH) radical cation becomes adjacent to a solute (RiiH) molecule, positive-hole transfer to the solute may occur. 

S Cascade reactions implementing the Ritter reaction Recent examples of the Ritter reaction have combined this useful synthetic tool with other reactions and rearrangements to produce complex reaction sequences. For example, Bishop has reported the combination of the Ritter reaction with the Wagner-Meerwein rearrangement, which can result in complex and sometimes unpredictable reaction sequences.17 The use of the Ritter reaction to trap cationic intermediates in the CAN-mediated dimerization of alkoxystyrenes has recently allowed the synthesis of a-aminotetralin derivatives by Nair.18... 

Fig. 1.27 An electric trap cationic groups stabilize a rotaxane structure.

Muller A, Das SK, Talismanov S, Roy S, Beckmann E, Bogge H, Schmidtmann M, Merca A, Berkle A, AUouche L, Zhou Y, Zhang L (2003) Trapping cations in specific positions in tuneable artificial cell channels new nanochemistry perspectives. Angew Chem Int Ed 42 5039-5044... 

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