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The Reactivity of Benzoates in Mixtures of Water and Aprotic Solvents

Nucleofugalities of pentafluorobenzoate (PFB), 2, 4, 6-trifluorobenzoate (TFB), 2-nitrobenzoate, and 3, 5-dinitrobenzoate (DNB) leaving groups have been derived from the solvolysis rate constants of the corresponding X, Y-substituted Z-benzhydryl benzoates in 60 % and 80 % aqueous acetonitrile and 60 % aqueous acetone, by applying the LFER equation: log k = sf (Ef + Nf). The experimental barriers (ΔG‡ exp) for solvolyses of 13 dianisylmethyl Z-substituted benzoates in these solvents correlate very well with the ΔH‡ calc of the model epoxy ring formation (calculated earlier by the B3LYP-PCM quantum-chemical method). Using the ΔG‡ exp vs. ΔH‡ calc correlation, and taking f s based on similarity, the nucleofugality parameters for about 70 benzoates have been determined in 60 % and 80 % aqueous acetonitrile and 60 % aqueous acetone. Z-Substituents on the phenyl ring have larger impact on the solvolytic reactivity in the less polar solvent than in the more polar solvent due to the more carbocation-like transition state.

nucleofugality; reactivity; substituted benzoate; aprotic solvent

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