Reactions in strongly basic solutions. Part VI. Correlation of the rates of rearrangement of weak carbon acids in aqueous dimethyl sulphoxide with an acidity function. Substituent and kinetic isotope effects
Abstract
The rates of the base-catalysed isomerisation at 30·0 °C of a series of 3- and 4-substituted allylbenzenes, 1,3,3-triphenylprop-1-yne and [3-2H]-1,3,3-triphenylprop-1-yne, have been measured in aqueous dimethyl sulphoxide containing tetramethylammonium hydroxide and give linear correlations with the acidity function, H–, for the medium. The Hammett reaction constant, ρ, for the allylbenzene rearrangement (ca. 3·5), the kinetic isotope effect for the 1,3,3-triphenylprop-1-yne rearrangement (ca. 7), the slopes of the acidity-function correlations, and other related evidence indicate rate-determining steps involving proton abstraction by the base. Estimates of the pKa values of the carbon acids under study are made.
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