ALPHA-EFFECT NUCLEOPHILES AND AZIDE ION - EFFECTIVE CHARGE STUDIES OFDISPLACEMENT-REACTIONS AT ESTERS

The bimolecular reactions of azide, 2-iodosobenzoate, and acetohydroxa mate ions and methoxyamine nucleophiles with substituted phenyl acetat es possess Yukawa-Tsuno type correlations with substantial resonance i nteraction. The rate constants for hydroperoxide ion and the oxyanion of N,N-diethylhydroxylamine obey simple Hammett equations. The reactiv ities of azide, acetohydroxamate, hydroperoxide, and 2-iodosobenzoate ion nucleophiles exhibit modest a-effects when the reactivity in subst itution at 4-nitrophenyl acetate is compared with that of phenoxide io ns of similar pK(a) values. The N,N-diethylhydroxylamine oxyanion is l ess reactive than its phenoxide ion analogue due to steric requirement s, and the reactivities of the anionic nucleophiles exhibit changes in effective charge on the leaving oxygen similar to those for regular n ucleophiles of similar pK(a). Methoxyamine possesses only a small enha ncement compared with the reactivity of a normal primary amine of simi lar pK(a). Values of the Leffler parameters for the bond fission proce ss in the reactions of alpha-nuclcophiles with phenyl acetates do not exhibit any special differences apart from those due to the pK(a) of t he nucleophile. The causes of the a-effect are considered to be due to steric and solvation requirements of the reactions.