Ionic compounds leaving groups

Concentration of the expansive effect of the lone pair upon the bond to a single, good leaving group may so lengthen the bond as to suggest an ionic formulation for the compound. Crystalline trimethylselenonium iodide, e.g., has been described as composed of the ions (CH3)3Se+ and I- 103) And trimethyltelluronium bromide is al l electrolyte in dime-thylformamide 104>. 

The equilibrium reaction between neutral hexacoordinate chelates and pentacoordinate siliconium halide salts is discussed in Section III.A.4 (Eq. 17). This reaction can be driven completely to the ionic side by replacement of the chloro ligand by better leaving groups triflate and bromide (Eq. (18), listed again with compound labels see Section III.A.4.iv). The products of this counterion-exchange reaction are stable siliconium salts 90(OTf)-92(OTf), 90(Br)-92(Br), which no... 

The pericyclic ring opening of halocyclopropanes that occurs on solvolysis was directly paralleled by the gas phase ionic reactivity of the same compounds. ) The ring opening of 42 was the most facile in a series (Eq. (28)). The same compound eliminated bromide from the molecule ion much more readily than related isomers. Evidently it makes little difference to the reactivity if the leaving group is Br— or Br . 

In each case, the mechanism involves generation of an aryl radical from a covalent azo compound. In acid solution, diazonium salts are ionic and their reactions are polar. When they cleave, the product is an aryl cation (see p. 856). However, in neutral or basic solution, diazonium ions are converted to covalent compounds, and these cleave to give free radicals (Ar and Z"). Note that radical reactions are presented in Chapter 14, but the coupling of an aromatic ring with an aromatic compound containing a leaving group prompted its placement here. Note the similarity to the Suzuki reaction in 13-12. 

Maartmann-Moe, K., Sanderud, K. A., Songstad, J. Reactions of benzylic compounds. Nucleophilicity, leaving group ability and carbon basicity of some ionic nucleophiles in acetonitrile. Comments on the utility of the Finkelstein reaction in synthesis. Acta Chem. Scand. 1982, 636,211-223. 

The presence of a nitrogen atom is not essential to transform natural compounds in ionic liquids. Recently, ionic liquids have been synthesized from alcohols and polyhydroxylated compounds (sugars) after transformation of the hydroxyl group on tlie primary carbon(s) in a more efficient leaving group (halogen, tosylate, triflate, and so on). 

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