The stabilities of Meisenheimer complexes. Part VI. Spiro-complexes

Abstract

The equilibrium constants KK₁(=[Spiro complex]/[Glycol ether][MeO^–]) at 25° in methanol for formation of spiro-complexes from glycol ethers and methoxide ions have the following values: 1-(2-hydroxyethoxy)-2,4-dinitronaphthalene, 3·5 × 10³| mol^–1; 1-(2-hydroxyethoxy)-2,6-dinitrobenzene, 0·22 | mol^–1; 1-(2-hydroxyethoxy)-2,4-dinitrobenzene, 1·1 × 10^–2| mol^–1. These values are orders of magnitude larger than those corresponding to the formation of the analogous 1,1-dimethoxy-complexes. Measurements of the rate constants for spiro-complex formation were made by stopped-flow spectrophotometry. The results when compared with those for similarly activated 1,1-dimethoxy-complexes suggest that spiro-complexes may not be good models for intermediates in aromatic nucleophilic substitutions.