Effect of unsaturated substituents on the hydrolysis of esters

Abstract

A study of the acid and alkaline hydrolysis of esters (R¹CO₂R²) containing unsaturated substituents in aqueous acetone confirms that where the unsaturation in R¹ is conjugated with CO₂R² in the initial state, the value of the Taft steric substituent constant, E_s, is considerably more negative than might be expected from normal steric interactions. When there is no conjugation, E_s has values consistent with steric interactions by R¹ and R². On the other hand, the Taft polar substituent constant, σ*, has fairly large positive values regardless of the presence or absence of conjugation. This may be attributed to the electron-withdrawing power of the unsaturated substituents but the property falls off as the seat of unsaturation becomes further removed from the ester group.