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 = f s (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. (doi: 10.5562/cca2179)